AJP - Renal Journal of Applied Physiology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
 QUICK SEARCH:   [advanced]


     


Am J Physiol Renal Physiol 275: F633-F650, 1998;
0363-6127/98 $5.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Blanco, G.
Right arrow Articles by Mercer, R. W.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Blanco, G.
Right arrow Articles by Mercer, R. W.
Vol. 275, Issue 5, F633-F650, November 1998

INVITED REVIEW
Isozymes of the Na-K-ATPase: heterogeneity in structure, diversity in function

Gustavo Blanco and Robert W. Mercer

Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110

    ABSTRACT
Top
Abstract
Article
References

The Na-K-ATPase is characterized by a complex molecular heterogeneity that results from the expression and differential association of multiple isoforms of both its alpha - and beta -subunits. At present, as many as four different alpha -polypeptides (alpha 1, alpha 2, alpha 3, and alpha 4) and three distinct beta -isoforms (beta 1, beta 2, and beta 3) have been identified in mammalian cells. The stringent constraints on the structure of the Na pump isozymes during evolution and their tissue-specific and developmental pattern of expression suggests that the different Na-K-ATPases have evolved distinct properties to respond to cellular requirements. This review focuses on the functional properties, regulation, and possible physiological relevance of the Na pump isozymes. The coexistence of multiple alpha - and beta -isoforms in most cells has hindered the understanding of the roles of the individual polypeptides. The use of heterologous expression systems has helped circumvent this problem. The kinetic characteristics of different Na-K-ATPase isozymes to the activating cations (Na+ and K+), the substrate ATP, and the inhibitors Ca2+ and ouabain demonstrate that each isoform has distinct properties. In addition, intracellular messengers differentially regulate the activity of the individual Na-K-ATPase isozymes. Thus the regulation of specific Na pump isozymes gives cells the ability to precisely coordinate Na-K-ATPase activity to their physiological requirements.

ouabain; sodium pump; protein kinases

    ARTICLE
Top
Abstract
Article
References

THE DISCOVERY THAT MANY ENZYMES in the cell are expressed in multiple molecular forms has become one of the most fascinating and intriguing phenomena in biology. In 1959, Markert and Moller (134) first used the term "isozymes" to describe the separate proteins that catalyze the same biochemical reaction. Since then, researchers have looked for structural variants of enzymes to understand their physiological function. In some cases, duplication of genes or alternative posttranscriptional processing of the gene message results in isozymes with unique biological properties. The development of multiple isozymes often provides the functional versatility cells need to fulfill their physiological requirements. This review covers the present status in the continuously growing field of the isozymes of the Na-K-ATPase, emphasizing the functional properties and regulatory mechanisms of the individual Na pump polypeptides.

The Na-K-ATPase, or Na pump, is a membrane-bound protein that establishes and maintains the high internal K+ and low internal Na+ concentrations typical of most animal cells. By using the energy from the hydrolysis of one molecule of ATP, it transports three Na+ out in exchange for two K+ that are taken in. The electrochemical gradient the Na-K-ATPase generates is critical in maintaining the osmotic balance of the cell, the resting membrane potential of most tissues, and the excitable properties of muscle and nerve cells. In addition, the Na+ gradient provides the energy that fuels the Na-coupled transporters. These secondary transport systems mediate the translocation of ions (H+, Ca2+, Cl-, PO3-4, SO2-4), substrates (glucose and amino acids), and neurotransmitters across the plasma membrane (83, 84, 109, 190, 191). In the kidney, the Na-K-ATPase plays a primary role in driving the reabsorption of Na+ and water. Thus the enzyme is essential in the maintenance of body fluid and electrolyte homeostasis (83, 109).

The Na-K-ATPase or Na pump belongs to a widely distributed class of P-type ATPases that are responsible for the active transport of a variety of cations across cell membranes (127, 171). P-type ATPases are found in both prokaryotic and eukaryotic cells, and are responsible for transporting H+, Na+, Mg2+, K+, Ca2+, Cu2+, and Cd2+ (127). All these enzymes use the hydrolysis of ATP to drive the transport of cations against an electrochemical potential. The P-type designation refers to the unique characteristic of these enzymes in forming a transient, phosphorylated aspartyl residue during the catalytic cycle. Accompanying the phosphorylation-dephosphorylation process, the P-type ATPases bind, occlude, and transport ions by cycling between two different cation-dependent conformations, called E1 and E2 (167, 171, 191). The precise molecular mechanisms that couple the hydrolysis of ATP to the conformational changes and the translocation of ions remain unknown.

In addition to having a common reaction mechanism, P-type ATPases also display comparable tertiary structures, equivalent membrane topological organization, and several highly conserved protein domains (127). The region around the phosphorylated aspartate, the TGES/A (threonine, glycine glutamine, serine/alanine) motif between transmembrane domains two and three, and several regions involved in ATP binding exhibit a high degree of amino acid homology. In addition to implying a common evolutionary ancestor, the similarities in the structure and reaction mechanism of these diverse proteins often make conclusions drawn from one transporter relevant to the others (46).

The Na-K-ATPase is an oligomer composed of stoichiometric amounts of two major polypeptides, the alpha - and the beta -subunits. The primary structures and membrane organization of the Na-K-ATPase alpha - and beta -subunits are depicted in Fig. 1. The alpha -subunit is a multispanning membrane protein with a molecular mass of ~112,000 Da that is responsible for the catalytic and transport properties of the enzyme. The alpha -subunit contains the binding sites for the cations, ATP, and the inhibitor, ouabain (reviewed in Refs. 120, 147, 160, 165). The beta -subunit is a polypeptide that crosses the membrane once and, depending on the degree of glycosylation in different tissues, has a molecular weight between 40,000 and 60,000 Da. The beta -subunit is essential for the normal activity of the enzyme (31, 52, 139), and it appears to be involved in the occlusion of K+ (126) and the modulation of the K+ and Na+ affinity of the enzyme (33, 35, 62, 64, 102). In addition, in vertebrate cells, the beta -subunit may act as a chaperone, stabilizing the correct folding of the alpha -polypeptide to facilitate its delivery to the plasma membrane (reviewed in Refs. 52, 139).


View larger version (37K):
[in this window]
[in a new window]
 
Fig. 1.   Scheme of the membrane topology of the alpha - and beta -isoforms of the Na-K-ATPase. Sequences of rat alpha 1- and beta 1-isoforms are shown. Residues are colored to indicate the amino acid homology among the different alpha -isoforms (alpha 1, alpha 2, alpha 3, and alpha 4) or beta -isoforms (beta 1, beta 2, and beta 3).

A third protein, termed the gamma -subunit, has also been identified in purified preparations of the enzyme (166). The gamma -subunit is a small, hydrophobic polypeptide of 8-14 kDa that was considered to be a contaminant of purification, until it was shown that it could be covalently labeled by photoaffinity derivatives of ouabain (78, 123, 169). Other evidence that the gamma -subunit is a component of the Na-K-ATPase is that the subunit colocalizes with the alpha -subunit in nephron segments and coimmunoprecipitates with alpha beta -complexes (148). Also, the high degree of homology among gamma -subunits from several species suggests that the subunit may be important in Na-K-ATPase function.

Expression studies have shown that the gamma -subunit is not required for normal Na-K-ATPase activity (59, 91, 176). However, recently it was shown that the gamma -subunit can modify the voltage dependence of K+ activation of the alpha 1 beta 1-isozyme when expressed in Xenopus oocytes (20). In addition, it appears that the gamma -subunit can stabilize the E1 conformation of the enzyme (204) and may be required for cavitation in mouse embryos (108). Interestingly, the gamma -subunit belongs to a family of small membrane proteins involved in the passage of ions across the plasma membrane. This family of proteins, which includes phospholemman (158), channel inducing factor (CHIF; Ref. 12), and Mat-8 (mammary tumor, 8 kDa; Ref. 152), induces ion channel activity when expressed in Xenopus oocytes. Consistent with these findings, the human gamma -subunit induces cation-selective channels when expressed in Xenopus oocytes (150). The physiological significance of this activity and whether it requires the other Na-K-ATPase subunits is unknown. Although there is increasing evidence that the gamma -subunit can modify Na-K-ATPase function, the exact role of the subunit in Na-K-ATPase function awaits further experimentation.

Na Pump Isoform Diversity

As with many other essential proteins in the cell, the Na-K-ATPase is expressed as several isozymes. Indeed, there are different genes encoding distinct molecular forms of both the alpha - and beta -polypeptides (reviewed in Refs. 69, 117, 120, 121, 196, 197). Evidence for the existence of Na pump isozymes can be traced to experiments that analyzed the cardiotonic steroid sensitivity of Na-K-ATPase preparations from rodents. Marks and Seeds (135) found heterogeneous ouabain inhibition curves for the Na-K-ATPase from mouse brain. The activity could be resolved into two components of high (Ki = 10-7 M) and low (Ki = 10-4 M) affinity for the inhibitor. This was in clear contrast to the single inhibition profile for enzyme preparations from the kidney (135). The earliest structural evidence for variants of the Na pump was found in brine shrimp. In this crustacean, the alpha -subunit could be resolved into two distinct forms on SDS-polyacrylamide gels (163). The first direct demonstration of Na-K-ATPase isoforms in mammals was accomplished by Sweadner (194), who found two forms of the alpha -subunit, the already identified renal alpha -form and a brain form that was termed alpha +. This novel catalytic subunit of the enzyme had a slower migration in SDS-polyacrylamide gels and a higher sensitivity to ouabain (194). This pioneering work was followed by studies that focused on the biochemical properties of both isoforms. Thus alpha + was shown to display a higher reactivity toward N-ethylmaleimide (208), a higher sensitivity to the vitamin B derivative pyrithiamine (137), and an increased resistance to trypsin digestion compared with alpha  (209). These properties suggested distinct structural differences between the isoforms. Later, the demonstration of dissimilarities at the NH2 terminus of alpha  and alpha + (129) suggested a genetic basis for the isoform difference. The advent of molecular biological techniques resulted in the identification of at least three alpha -polypeptides in vertebrates, presently known as alpha 1, alpha 2, and alpha 3 (186, 187, 193). More recently, Shamraj and Lingrel (185) identified a fourth alpha -isoform (alpha 4) in rat testis.

The alpha -isoforms of the Na-K-ATPase have been cloned from several mammalian species. An analysis of the phylogenetic distribution of the alpha -proteins using antibodies directed to conserved and specific regions of the isoforms indicates that isoforms appear to exist in all mammals, including both placental and marsupial species (164). The identifications of Na-K-ATPase alpha -isoforms in the chicken (70) and teleost fishes (164) imply their broad presence among vertebrates (201). Moreover, the finding of alpha -isoforms in crustaceans (14) and possibly in hydra (45) and platyhelminths (159) indicates that the divergence of Na-K-ATPase genes occurred early in evolution.

Further studies have shown that the Na pump molecular diversity also extends to its beta -subunit. At present, three different Na-K-ATPase beta -isoforms have been identified. Two of the isoforms, beta 1 and beta 2, have been found in different tissues of mammals (82, 136) and birds (115), whereas beta 3 has been detected in amphibians (85), mouse (27), rat, and human (82, 136). Moreover, in the zebra fish, an Na-K-ATPase beta -subunit highly homologous to beta 3 has been isolated (7). In this species, however, a detailed characterization of other beta -isoforms has not been accomplished, making it difficult to establish a correlation with the subunits of other species.

Both the alpha - and beta -isoforms of the Na pump exhibit a tissue-specific pattern of expression. The alpha 1-isoform in association with the beta 1-subunit is found in nearly every tissue (reviewed in Refs. 69, 117, 119, 121, 196). In addition, alpha 1 beta 1 is the principal isozyme of the kidney, a tissue that has classically been used as the source of Na-K-ATPase (reviewed in Refs. 83, 84, 109, 191). The presence of other Na-K-ATPase isoforms in the kidney has been a matter of debate (2, 8, 51, 53, 71, 73, 88, 104, 140, 206). The alpha 2- and alpha 3-isoforms have been detected in renal cortex, medulla, and papilla using both reverse-transcription followed by polymerase chain reaction amplification and [3H]ouabain titration analysis (125). Measurement of mRNA and protein levels indicates that the alpha 2- and alpha 3-isoforms correspond to only 0.1% of the alpha 1 beta 1 enzyme of the kidney (125). In contrast to the broad tissue distribution of alpha 1 and beta 1, the other alpha - and beta -polypeptides are more restricted in their expression. The pattern of Na-K-ATPase isoform expression, at both the mRNA and protein level, has been studied with most detail in the rat. The alpha 4-isoform is a testis-specific isoform (185). The alpha 2-isoform predominates in adipocytes (130), muscle (99, 114), heart (215), and brain (143), and alpha 3 is abundant in nervous tissues (95, 143). In the nervous system, the expression of Na-K-ATPase isoforms reaches its greatest intricacy. Neuronal cells may express a unique isozyme or multiple isozymes consisting of the various alpha beta -heterodimer combinations (117, 119, 121, 196). Whereas neurons are the principal source of the alpha 3 polypeptide (reviewed in Refs. 117, 198), glial cells preferentially express alpha 2 (40, 43, 76). Also, the beta -isoforms are distributed in a tissue-dependent manner. The beta 2-isoform is found in skeletal muscle (114), pineal gland (189), and nervous tissues (162), whereas beta 3 is present in testis, retina, liver, and lung (11, 133). In addition, the pattern of expression of the Na-K-ATPase isoforms is subjected to developmental as well as hormonal regulation and can be altered during disease (39, 49, 50, 68, 217).

Additional Mechanisms Involved in the Production of Na-K-ATPase Isozymes

In addition to the expression of different genes for the alpha - and beta -subunits, several other mechanisms are involved in the generation of Na-K-ATPase isozymes. For example, variations in the transcriptional processing of the Na pump subunit messages occur in some cells. This is the case for a truncated form of the alpha 1-subunit, named alpha 1-T, which has been found in canine vascular smooth muscle (146). Alternative splicing of the alpha 1 mRNA results in a polypeptide of ~65,000 Da. The alpha 1-T includes the first 554 amino acids of alpha 1 and terminates with a peptide of 27 amino acids from the retained intron sequence. Although alpha 1-T lacks 40% of the COOH-terminal sequence, it retains the ATP binding and phosphorylation site. This, added to the observation that cells containing alpha 1-T show undetectable levels of the other alpha -isoforms, has led to the suggestion that the truncated isoform may function as an ATPase (4, 146). However, it remains unknown whether alpha 1-T is catalytically competent and, if so, whether it is able to support the transport of ions. Interestingly, truncated transcripts of both the alpha 1- and beta 1-isoforms have also been found in human retinal epithelium. The truncated alpha 1 sequence in this tissue encodes the first 681 amino acids of the alpha 1 polypeptide. The deletion produces a shift in the open-reading frame of the message to produce a unique COOH terminus of 44 residues, which surprisingly displays similarity to the COOH-terminal sequence of the sarcoplasmic reticulum (SR) Ca-ATPase. The truncated beta -polypeptide of retina is two amino acids shorter at the COOH terminus than the typical beta 1-isoform. In addition, the last two COOH-terminal residues differ from those of the full-length subunit (170).

Other short variants of the alpha 1 polypeptide have been found in Xenopus laevis embryos. In Xenopus, deletions at the NH2 terminus of the protein result from the alternative initiation of translation at codons encoding either Met34 or Met43. Sequential mutation of each of these residues and expression of the corresponding cRNAs in Xenopus oocytes shows that both truncated subunits are catalytically competent when coexpressed with the beta -isoform. Moreover, the alpha -subunit with Met43 at the NH2 terminus exhibits a lower affinity for K+ than the Met34 truncated or full-length polypeptides (42). These results support the hypothesis that the NH2 terminus of the alpha 1-subunit, which is rich in lysine and contains an excess of positively charged amino acids, forms a cation-selective gate (187, 210).

Another mechanism that contributes to the heterogeneity of the Na pump is the association of the alpha - and beta -isoforms into different alpha beta -heterodimers. The possibility that combinations of different heterodimers could be formed was suggested from the expression of multiple isoforms in several tissues and cells (43, 117, 162, 181, 182, 221). For example, in the pineal gland, both the alpha 1 beta 2 and alpha 3 beta 2 Na-K-ATPase isozymes are present (189). The alpha 3 beta 2-isoform combination is also found in retinal photoreceptor cells (181, 182), whereas the cells of the choroid plexus express the alpha 1 beta 1- and alpha 2 beta 1-isozymes (221). Specific cell populations within the central nervous system (117, 198), the ciliary epithelial cells of the eye (81), the sensory organ of the ear (202), and the choroid plexus (221) express several isoforms with the potential of multiple alpha  and beta  combinations. The promiscuous association between alpha - and beta -isoforms was confirmed in insect cells expressing different combinations of the rat Na-K-ATPase polypeptides. In this expression system, each alpha -isoform could properly assemble with either the beta 1- or the beta 2-subunit into catalytically active complexes (30, 33, 35, 36). Similarly, nonspecific alpha beta association was found for the Na-K-ATPase chicken isoforms exogenously expressed in mammalian cells (116). In this manner, multiple Na-K-ATPase isozymes (alpha 1 beta 1, alpha 1 beta 2, alpha 2 beta 1, alpha 2 beta 2, alpha 3 beta 1, and alpha 3 beta 2) can result from the pairing of the various alpha - and beta -polypeptides (33, 35).

The complexity of the Na-K-ATPase may also extend to the oligomeric structure of the enzyme. We have recently demonstrated that the different alpha -isoforms are able to specifically and stably associate into oligomeric complexes (32). The existence of multiple sets of oligomers raises the possibility of an even greater degree of intricacy in the molecular heterogeneity of the Na pump. However, whether the quaternary structure of the Na pump influences the functional properties of the enzyme is still unclear.

Structure of alpha - and beta -Isoforms

The complete amino acid sequence of the alpha -isoforms has been deduced from the cDNAs coding for the polypeptides from rat (180, 186), chicken (70), and human (121, 193). The alpha -subunits in the rat vary slightly in length; the alpha 3-isoform is the smallest with 1,014 amino acids, alpha 1 possesses 1,024, alpha 2 possesses 1,021, and alpha 4 is the largest with 1,028 residues. The amino acid sequence, site-specific labeling, and immunologic and proteolytic digestion studies have provided some insight into the possible transmembrane orientation of the alpha -subunit (9, 44, 120, 122, 151, 160, 199, 210, 213). These studies predict an NH2-terminal segment with four transmembrane spanning domains, a large cytoplasmic domain consisting of roughly one-third of the polypeptide, and a carboxy-terminal region containing six membrane spanning domains (Fig. 1). This membrane topography is also similar to the models suggested for the Ca-, H-, and H-K-ATPases (44, 46).

Across species the degree of identity for the alpha 1- and alpha 2-isoforms is ~92% and is over 96% for alpha 3. There is also a high degree of identity (approx 87%) among the alpha 1-, alpha 2-, and alpha 3-isoforms. In contrast, alpha 4 is the most divergent, sharing a 78% identity with the alpha 1-isoform. As shown in Fig. 1, the highest structural variability among the isoforms occurs at the NH2 terminus, the extracellular ouabain binding site between transmembrane segments 1 and 2, and the cytoplasmic region between amino acids 403 and 503. In contrast, the greatest similarities occur in the cytoplasmic middle region where the ATP binding and phosphorylation sites are located, the transmembrane hydrophobic regions and the COOH-terminal region (reviewed in Refs. 117, 120, 147).

The alpha -subunit undergoes translational or posttranslational modifications, some of which appear to be isoform specific. In the mature alpha 1- and alpha 2-polypeptides, the first 5 amino acids are cleaved (129). It is not known whether the alpha 3-isoform is processed in a similar fashion. A tissue-specific, posttranslational modification has been suggested for the alpha 3-isoform. An isoform-specific antibody that reacts with a region near the ATP binding site identifies alpha 3 in the brain but does not react to the same isoform from heart. This lack of reactivity has been interpreted as a blockage of the antibody epitope by a modification of the protein during synthesis (10). The nature of this modification, as well as its occurrence in other tissues and alpha -isoforms, is unknown.

The amino acid sequence of the beta -isoforms has been deduced from the rat, human, chicken, Xenopus, and mouse cDNAs (82, 115, 133, 136). In the rat, the beta 1-isoform has 304, the beta 2-isoform has 290, and the beta 3-isoform has 279 amino acids. All beta -isoforms share a common basic structure (Fig. 1). The beta -isoforms consist of a short NH2-terminal cytoplasmic region, a transmembrane spanning segment, and a large extracellular domain. The homology of the beta 1- and beta 2-isoforms across mammalian species is ~95%. This value drops to 60% when nonmammalian species are included in the comparison. The homology among different beta -isoforms is lower than that found for the catalytic subunit (Fig. 1). Compared with beta 1-, the beta 2-polypeptide exhibits 58% similarity (34% identity, 24% favored substitutions), whereas the beta 3-subunit is 68% homologous, with an identity of 39%. The similarity between beta 2 and beta 3 reaches 61%, with 49% of the residues conserved (133). Interestingly, the beta 2-subunit primary structure is more closely related to the H-K-ATPase beta -isoform than to the beta 1-isoform, suggesting that the beta 2- and H-K-ATPase beta -isoform genes diverged more recently than beta 1 and beta 2 (188). The transmembrane domain of the beta -subunit is the most highly conserved region both among isoforms and species.

All beta -isoforms are heavily glycosylated. The beta 1-isoform from mammals has three N-linked glycosylation sites. The putative N-linked glycosylation sites for the beta 2-isoform vary depending on the species. Thus the chicken subunit has four potential glycosylation sites, the rat has seven, the human has eight, and the mouse beta 2-polypeptide has nine (reviewed in Ref. 52). It is not known whether all the sites are used. Inhibition of glycosylation of the Na-K-ATPase beta 1-subunit with tunicamycin results in catalytically competent Na pumps with normal affinity for ouabain (200, 218, 219). Expression of an enzyme in which all beta -subunit N-linked glycosylation sites are mutated also renders an active enzyme with conserved K+ and ouabain affinities. However, the reduction in the ability of the nonglycosylated beta -subunit to assemble with the alpha -subunit and the higher sensitivity of the enzyme to proteolysis suggest that glycosylation may play a role in protein folding (16).

Another important feature in the structure of the beta 1-subunit is the presence of three disulfide bridges, which in the rat polypeptide occur between Cys125---Cys148, Cys158---Cys174, and Cys212---Cys275. All the cysteines, but not their relative positions within the sequences, are conserved in the beta 2- and beta 3-isoforms, suggesting similarities in the tertiary structure of the polypeptides. Treatment of the Na-K-ATPase with reducing agents results in inactivation of Na-K-ATPase, suggesting that the disulfide bonds are required for enzyme function. The removal of just one of the disulfide bonds by site-directed mutagenesis of the involved cysteines has been shown to be sufficient to abolish proper assembly of the alpha beta -subunits (16). The location and role of sulfhydryl bridges in the other Na pump beta -isoforms are unknown.

Enzymatic Properties of Na-K-ATPase Isozymes

Understanding of the enzymatic properties of the individual isozymes may help in determining the basis for the complex molecular diversity that characterizes the Na-K-ATPase. The characterization of the functional properties of the different alpha - and beta -polypeptide combinations has been a difficult task. Often more than one isoform is expressed in the same cell, complicating the analysis of the individual isoforms. Because it constitutes nearly all the Na pump in the kidney, the functional properties of the alpha 1 beta 1-isozyme have been extensively analyzed. With its high levels of Na-K-ATPase activity, the kidney has been of immense value in understanding the structure, biochemical reaction mechanism, and kinetic properties of the Na-K-ATPase. In contrast, the lack of natural sources for each of the other Na pump isozymes has made their characterization more difficult. The first attempt to evaluate the catalytic properties of the Na pump isozymes was the comparison of the substrate affinities of the enzymes from kidney and brain (208). This early work suggested that the Na-K-ATPase isozymes have distinct differences in their affinities to Na+, K+, and ATP. Later, Sweadner (195) compared the properties of Na-K-ATPases from rat axolemma and rat kidney. The renal alpha 1 beta 1-isozyme displayed a lower ATP, similar K+, and higher Na+ affinities than the neuronal enzyme composed of the alpha 2- and alpha 3-subunits. Also, differences in Na+ or K+ apparent affinities have been found between Na-K-ATPases partially purified from brine shrimp (55, 56) or different tissues of the rat (41, 72, 211). Moreover, the transport properties of rat kidney- and axolemma-derived enzyme delivered into dog erythrocytes by membrane fusion differ in their dependence on Na+ and K+ (154). In whole adipocytes from rat, it was found that the alpha 1-isozyme has a Km for Na+ that is threefold lower than that of the alpha 2-isozyme (128, 130). This difference, however, was not retained when membranes from the same source were prepared (41). Such discrepancies were also encountered for the Na+ affinity of alpha 1 and alpha 2 from entire or disrupted rat brain synaptosomes (41). Other differences in isoform enzymatic properties were found for the alpha 3 beta 2 Na-K-ATPase from the pineal gland, which exhibits a higher Na+ affinity than the renal alpha 1 beta 1 (189). On the other hand, similar Na+ and K+ kinetics were identified in cerebellar or hippocampal Na-K-ATPases at different stages of development, despite variations in the amount of isoforms expressed (13, 24, 25, 28).

Although several studies suggested differences in the enzymatic behavior of the Na pump isozymes, discrepancies in the reported kinetic parameters led to uncertainties in the functional characteristics of the isozymes. In contrast, the reactivity of the Na pump isoforms toward ouabain is less controversial. Because of their broad sensitivities to cardiotonic steroids, this is particularly evident for the rodent Na-K-ATPase isozymes. In the rat, for example, alpha 1 was reported to be 100-fold more resistant to ouabain than alpha + (alpha 2 + alpha 3) (67, 100, 135, 194, 195). On the basis of the differential sensitivities to trypsin, early experimental evidence also suggested that the alpha 3-isoform has a high affinity for ouabain (209). Working with partially purified Na-K-ATPase from rat brain stem, researchers identified three populations of Na-K-ATPase with different sensitivities to ouabain, possibly corresponding to alpha 1, alpha 2, and alpha 3 (22, 29). In rabbit, pig, dog, and human, the differences in the cardiotonic steroid affinity may not be as marked, since the alpha 1-isoform in these species is much more sensitive to ouabain (23, 88, 90, 92, 104, 131, 179).

With the introduction of molecular biology techniques to the Na pump field, a better understanding of the function of each isoform became possible. The availability of the cDNAs for the different Na pump isoforms allowed studies in heterologous expression systems. Consequently, several investigators have used mammalian cells to separately express each Na pump isoform. Thus, when expressed in cultured rodent cells, the rat alpha 2- and alpha 3-isoforms have been shown to display Ki values for ouabain of ~40 and 80 nM, respectively (89, 113). Through study of the molecular basis for the difference between primate and rodent cells in their sensitivities to the cardiac glycosides, it was shown that the rat alpha 1-isoform could confer ouabain resistance to ouabain-sensitive CV-1 cells (65, 113). Using the differences in ouabain sensitivities between rodents and other mammals, Jewell and Lingrel (105) studied the kinetic properties of the rat alpha 1-, alpha 2-, and alpha 3-subunits. By changing two residues in the extracellular loop between the first and second transmembrane segments, they converted the rat alpha 2 and alpha 3 into ouabain-resistant forms. The mutated isoforms were stably transfected into HeLa cells by their ability to support growth in 1 mM ouabain (105). Through this method, the expressed isoforms could be functionally separated from the endogenous ouabain-sensitive Na-K-ATPase. Analysis of the individual isozymes demonstrated that the alpha 1 beta 1 and alpha 2 beta 1 display similar affinities for Na+, K+, and ATP, whereas the alpha 3 beta 1-isozyme exhibits a lower affinity for Na+ compared with alpha 1 beta 1 and alpha 2 beta 1. Subsequently, the highly ouabain-sensitive Na-K-ATPase from rat brain or dog heart, ascribed to alpha 3beta 1, was also reported to have a lower apparent affinity for Na+ than the intermediate and resistant components (alpha 1 and alpha 2) from the same tissues (23, 80). To identify the structural basis for the difference in the Na+ requirements between the isoforms, a series of chimeric alpha 1/alpha 3-subunits were expressed in HeLa cells. Analysis of the Na+ affinities of each chimera did not reveal a region clearly responsible for the differences in Na+ dependence between the isoforms, indicating that multiple residues spanning the alpha -polypeptide may be cooperating in the binding and transport of the cation (106).

Expression of hybrid Na-K-ATPase molecules between alpha - and beta -isoforms from different species in Xenopus oocytes has also helped in elucidating the characteristics of the Na pump isozymes. Through this system, the alpha 1 beta 1 Na-K-ATPase has been shown to exhibit a higher activation by Rb+ than the alpha 1 beta 2- and alpha 1 beta 3-isozymes (102, 177). Utilizing heterologous expression in yeast, which lack endogenous Na-K-ATPase activity, Farley and colleagues (97, 98) successfully obtained catalytically competent Na pump molecules by expressing the alpha 1-subunit from sheep and the beta -subunit from dog. Later, they determined that the ouabain binding constant of the sheep alpha 1 and rat alpha 3 is between 5 and 10 nM (63). In addition, coexpression of the alpha 1- or alpha 3-isoforms with chimeric molecules between the Na-K- and H-K-ATPase beta -subunits indicated that the beta -polypeptide modulates the K+ and Na+ dependence of the enzyme (62, 64).

Our approach to the study of the Na-K-ATPase isozymes has included the use of the baculovirus expression system. This system employs the Autographica californica virus to express foreign genes in insect cells. By using recombinant baculoviruses coding for different alpha - and beta -isoforms we have been able to successfully obtain functional Na pump molecules in cultured Sf-9 insect cells, a cell line derived from the ovary of the fall armyworm, Spodoptera frugiperda. Sf-9 cells are able to produce high amounts of the virally directed Na-K-ATPase polypeptides. Moreover, Sf-9 cells contain very low levels of endogenous Na-K-ATPase, allowing the analysis of the expressed enzymes in an environment relatively free from contaminating Na-K-ATPase activity (36, 59). In addition, the recombinant viruses can be used independently and in combination to study assembly and activity of the various Na-K-ATPase isoforms.

The insect cells are able to correctly assemble the various alpha - and beta -isoforms into functional enzyme (30, 33, 35, 36, 59). Infecting cells with the various recombinant baculoviruses has demonstrated that all alpha -isoforms can stably assemble with either the beta 1- or the beta 2-polypeptides. This is consistent with the results of other investigators (1, 116, 177). Although all possible alpha  and beta  pairs result in active enzyme, some combinations, such as alpha 1 beta 2, exhibit lower activity, suggesting that not all associations are equally favored. Evidence for a selective interaction of certain alpha - and beta -subunits has been reported using Xenopus oocytes (178). The importance of this preferential assembly in directing isozyme expression is unknown.

By analyzing the dose-response curves toward Na+, K+, ATP, and the inhibitor ouabain, the enzymatic properties of the various Na pump isozymes were determined. Table 1 summarizes the kinetic parameters for the rat Na-K-ATPase isozymes expressed in the insect cells. As shown, the apparent affinity for Na+ varies with a rank of order alpha 2 beta 2 > alpha 2 beta 1 > alpha 1 beta 1 = alpha 3 beta 2 > alpha 3 beta 1. Also, the apparent affinity for K+ differs among the isozymes, following the sequence alpha 1 beta 1 > alpha 2 beta 1 = alpha 2 beta 2 > alpha 3 beta 1 = alpha 3 beta 2. For the activation by ATP, the enzymes composed of the alpha 2- and alpha 3-isoforms display equivalent Km values, which are approximately four times lower than that of the alpha 1 beta 1. Altogether, these results indicate that the major kinetic differences occur among Na-K-ATPases that differ in the alpha -subunit composition. These observations are in reasonably good agreement with the kinetic properties reported for the rat alpha 1-, alpha 2-, and alpha 3-isoforms expressed in HeLa cells (57, 58, 105, 154, 203). The only difference between our results and those obtained in HeLa cells is the K+ affinity of the alpha 3-isozymes, which we found to be lower than that of the alpha 1 or alpha 2. The differences in the membrane environment of mammalian and invertebrate cells, the analysis of hybrid Na pump molecules in the HeLa cells, or the alteration of the isoforms by mutation of their ouabain binding site may be responsible for the disparity in results.

                              
View this table:
[in this window]
[in a new window]
 
Table 1.   Kinetic characteristics of the rat Na-K-ATPase isozymes expressed in Sf-9 insect cells

As mentioned before, the most conspicuous kinetic difference among the isozymes corresponds to the reactivity toward ouabain, with alpha 3 beta 1 and alpha 3 beta 2 displaying a high, the alpha 2 beta 1 and alpha 2 beta 2 an intermediate, and alpha 1 beta 1 a low sensitivity to the cardiotonic steroid (36, 155). Interestingly, the rat alpha 1 beta 1 enzyme expressed in insect cells is over 2-fold more sensitive and the alpha 3 beta 1 approximately 20-fold less sensitive to ouabain than the native enzyme. This difference in sensitivity between the native and expressed Na-K-ATPase may be a result of the different lipid environments of the enzyme. Alternatively, the sensitivity to ouabain may be influenced by the gamma -subunit or by the oligomeric structure of the alpha -subunit.

At present, the enzymatic properties of Na-K-ATPases composed of the alpha 4-isoform have not been analyzed. To determine the ouabain sensitivity of the alpha 4-isoform, we performed dose-response curves for the ouabain inhibition of Na-K-ATPase activity in membrane preparations from rat testis, the only tissue known to contain this isoform. As shown in Fig. 2A, the experimental data is best fitted assuming the existence of two isozymes with different sensitivities to the cardiotonic steroid. One of the components corresponding to ~45% of the total Na-K-ATPase has a calculated Ki of 1.4 ± 0.3 × 10-4 M and very likely represents the alpha 1-isozyme. The second component represents ~55% of the total activity and exhibits a high affinity for the inhibitor, with a Ki of 1.8 ± 1.0 × 10-9 M. As previously shown (185), immunoblot analysis of the testis preparation showed that the tissue does not express the alpha 2- or alpha 3-isoforms (Fig. 2B). A complete characterization of the beta -subunits in the rat testis has not been performed. However, beta 1 and beta 3 mRNAs have been detected in the gonad (133). The possibility that alpha 1 beta 3 represents the component of high affinity for ouabain is unlikely, since the other beta -subunits do not influence the kinetics of the enzyme toward the cardiotonic steroids. Therefore, the highly ouabain-sensitive Na-K-ATPase encountered probably corresponds to alpha 4. It is unknown which beta -isoform naturally associates with alpha 4. Consequently, the highly ouabain-inhibitable ATPase activity could correspond to alpha 4 beta 1 or alpha 4 beta 3. Undoubtedly, a complete determination of the kinetic characteristics of this isoform will provide insight into its role in Na-K-ATPase function.


View larger version (18K):
[in this window]
[in a new window]
 
Fig. 2.   A: dose-response curves for the ouabain inhibition of Na-K-ATPase from rat testis membranes. Na-K-ATPase activity was determined after preincubation of the samples for 30 min at 37°C in the reaction mixture containing 120 mM NaCl, 30 mM KCl, 3 mM MgCl2, 0.2 mM EGTA, 30 mM Tris · HCl (pH 7.4), and the indicated ouabain concentrations. The reaction was started by the addition of [gamma -32P]ATP. Values are expressed as percentage of maximal activity in the absence of the inhibitor. Curves represent the best fit of the data assuming the existence of two enzyme populations with different ouabain affinities. Each value is the mean, and error bars represent the standard errors of the mean of 4 experiments performed in triplicate. B: immunoblot analysis of the Na-K-ATPase alpha -subunit expression in rat testis. Testis proteins (30 µg) were separated by SDS-PAGE (7.5% gel) and transferred to nitrocellulose. Na-K-ATPase alpha -polypeptides were detected using isoform-specific antibodies as before (32). A membrane preparation from rat brain (20 µg) is shown as control.

As shown in Table 1, the beta -isoform composition does not influence the kinetic properties of the Na-K-ATPase isozymes as much as the alpha -polypeptides do. However, the beta -subunit is able to influence the Na+ requirement of the enzyme. Thus, for the alpha 2- and alpha 3-isoforms, the apparent affinity for Na+ increases when associated with beta 2. A modulatory effect of the beta -isoform on the catalytic properties of the alpha -subunit has also been shown using Xenopus oocytes. Hybrid alpha 1 beta 1- and alpha 1 beta 2-isozymes consisting of a Torpedo alpha - and a rat beta -subunit, have different affinities for Rb+ (102, 103, 177). Moreover, comparison of results from transfected HeLa cells (57, 105) with native enzyme from pineal gland (189) suggests an effect of the beta -isoform on the Na+ dependence of the rat alpha 3-isoform. At present, the role the beta -subunit plays in the reaction cycle of the Na-K-ATPase is uncertain. Characterization of the kinetics of hybrid Na-K-ATPases composed of the alpha 1- or alpha 3-isoforms and chimeric beta -subunits containing the NH2 terminus of beta 1 and the COOH terminus of the H-K beta -subunit suggests that the beta -subunit influences the interaction of the enzyme with Na+ and reduces the ability of Na+ in forming the phosphoenzyme complex from ATP (64). It also appears that the beta -subunit can influence the K+ affinity of the Na-K-ATPase (62). With use of the Xenopus oocytes as an expression system, the alpha 1 beta 2 enzyme exhibits a lower affinity for K+ than alpha 1 beta 1 (102, 103, 177). Similarly, this trend was maintained in Sf-9 cells where the alpha 2- and alpha 3-isoforms in combination with beta 2 exhibit a slightly lower affinity for K+ than the beta 1 counterparts (33, 35). In addition, the beta -subunit has been shown to be actively involved in forming or stabilizing the K+-occluding complex of the enzyme (126). Because in insect cells the beta -isoforms are mainly expressed in their core-glycosylated forms (36, 59), the difference in Na+ affinity between isozymes containing beta 1 or beta 2 most likely depends on the dissimilar amino acid structure of the beta -isoforms rather than the sugar composition. Additional evidence of the importance of the beta -subunit in modulating the activity of the Na-K-ATPase has been suggested from the kinetic analysis of the human alpha 1 beta 3 Na-K-ATPase expressed in insect cells. The beta 3-isoform slightly influences the Na+, K+, and ouabain affinities of the enzyme (214).

A physiological role for the difference between Na-K-ATPases composed of beta 1 and beta 2 is difficult to infer. Although beta 2 confers alpha 2 and alpha 3 with a similar apparent affinity for Na+ as the alpha 1 beta 1 enzyme, alpha 2 beta 2 and alpha 3 beta 2 still retain the particular K+, ATP, and ouabain reactivities of their counterpart beta 1-containing isozymes. The importance of the beta 2-polypeptide in Na-K-ATPase function may be related to other properties intrinsic to this subunit. For example, an unexpected functional property of the beta 2-isoform is that, in addition to its role as a constituent of the Na pump, it serves as a cell adhesion molecule that mediates Ca2+ independent neuron-astrocyte interactions (82, 177). In addition, beta 2 has been shown to be involved in neuronal migration and neurite outgrowth (5, 82, 153). Coinciding with its role in cell-cell interaction, the decrease in beta 2 mRNA levels in human kidney, lung, and liver carcinomas suggests that this subunit may be involved in tumorigenesis (3). Although the link between cell recognition and ion transport is unknown, it is conceivable that beta 2 might modulate Na pump function to provide the ionic environment required in such specific cellular processes. The importance of the beta 2 has recently been demonstrated in mice carrying a targeted deletion of the gene for this isoform (132). The beta 2-deficient animals exhibit motor incoordination at 15 days of age, develop tremors and paralysis of extremities, and subsequently die at 17-18 days after birth. The observation that at different areas of the nervous system there is swelling and vacuolization of astrocyte processes suggested the requirement of beta 2 in maintaining ionic homeostasis. However, the cause of death in these rodents is unclear, since beta 2 is not necessary for the long-term survival of cultured telencephalic grafts obtained from the transgenic mice (101).

Physiological Relevance of Na Pump Isozymes

It seems plausible that the existence of Na-K-ATPase isozymes is based, at least in part, on their specific kinetic characteristics (30, 33, 35, 57, 105, 107). The subtle differences in their affinities for cations and ATP may be essential in adapting cellular Na-K-ATPase activity to specific physiological requirements. Because of its ubiquitous expression, the alpha 1 beta 1-isozyme may function as the housekeeping Na-K-ATPase in the cell, whereas the other isozymes may mediate tissue-specific roles. For example, in neurons where all the isozymes are present, while the alpha 1- and alpha 2-isoforms are maintaining the basal ionic gradients, alpha 3, because of its low affinity for the cations, will be operating very slowly. With depolarization and the repeated firing of action potentials, the Na+ and K+ gradients are dissipated. Under these conditions, while the alpha 1- and alpha 2-isoforms are working at saturation, the alpha 3-isoform will be activated. In this manner, alpha 3 functions as a spare pump to help restore the resting membrane potential. Also, the high affinity for ATP endows alpha 3 with the ability to utilize the low nucleotide concentrations occurring near the cell membrane after intense neuronal activity. Moreover, the higher Na+ affinity of the alpha 2-isoform gives it a steady working capability, since Na+ will be rate limiting only at very low concentrations. This is important in glial cells, where after neuronal activity, alpha 2 can efficiently clear the high extracellular K+ to prevent further depolarization. In addition, as discussed below, multiple Na-K-ATPase isozymes with different apparent affinities for Na+ may be physiologically important in secondary control of intracellular Ca2+ levels. These variations in cytoplasmic Ca2+ are important in the regulation of contraction, secretion, and excitability (37).

A differential function for the Na-K-ATPase isozymes is suggested by the stringent regulation of the expression of the alpha - and beta -polypeptides under various physiological conditions. During development, a change in the relative amount of Na pump isoforms occurs in several tissues (157). A remarkable example of regulation of Na-K-ATPase isoform expression is found in the developing rat heart. In this tissue, between the second and third week of life, there is a switch from the alpha 3-isoform to alpha 2-isoform, which becomes the predominant isoform of the adult myocardium (124). Interestingly, this event coincides with important changes in the electrophysiological properties of the myocardium (121, 124). The Na pump isozymes may also be differentially regulated by hormones (reviewed in Ref. 68). Hormones can elicit their action by modulating the expression of a particular isoform or by directly affecting the activity of an individual Na-K-ATPase (68). For example, in rat skeletal muscle, insulin is able to produce a rapid translocation of preexisting alpha 2 Na-K-ATPase from intracellular stores to the plasma membrane (99). This results in the recruitment of additional functional Na pumps to the cell surface and increased Na-K-ATPase activity. In addition, the normal expression of Na-K-ATPase isoforms can be altered by pathological conditions. For instance, in several cardiac diseases, the Na-K-ATPase isoform composition of the heart is modified. These changes may reflect the cellular attempt to reestablish the altered homeostasis associated with the disease. Consequently, it seems conceivable that the preferential regulation or modification of a specific isoform may be important in finely adjusting cellular ionic homeostasis.

The difference among rodent Na-K-ATPase isozymes in ouabain affinity is intriguing, although its physiological relevance remains unknown. It is possible that differences in ouabain binding may have a role in the regulation of Na-K-ATPase activity. Only rodents are known to have Na-K-ATPases that vastly differ in their ouabain affinities. In other species, the alpha 1 beta 1-isozyme is much more sensitive to the cardiotonic steroids, making the isoform differences in ouabain sensitivity less conspicuous. A detailed study of the ouabain binding constants for species other than rodents has not been accomplished. Nevertheless, more than one ouabain affinity site has been reported in non-rodent species (66, 67, 88, 90, 104, 131). In humans, both single as well as complex ouabain binding have been found in the heart (66, 67, 184), which is known to express the alpha 1-, alpha 2-, and alpha 3-isoforms of the Na pump (216). In the heart, the existence of multiple isoforms is undoubtedly important in mediating the action of the cardiotonic steroids. It is clear that cardiotonic steroids act through their ability to inhibit the Na-K-ATPase. This inhibition results in a transient increase in intracellular Na+, which induces through the Na/Ca exchange system an increase in intracellular Ca2+. The rise in internal Ca2+ is taken up by the SR via an SR Ca-ATPase. Because of the elevated Ca2+ content in the SR, more Ca2+ can be released when the cardiocyte is stimulated, leading to an augmented force of contraction and an increased cardiac output (37, 48, 118, 141, 145, 205). The relevance of the cardiotonic glycosides as Na-K-ATPase modulators is supported by the finding of endogenous, digitalis-like compounds in mammals (reviewed in Refs. 37, 38, 60, 61, 111, 168). An isomer of ouabain has been found to be produced in the bovine hypothalamus (93, 94, 220), and ouabain itself is present in the adrenal glands of several species including humans (37, 38, 86, 87). Thus endogenous ouabain may regulate cardiovascular tonicity by inhibiting a discrete number of Na-K-ATPase pumps to modulate cellular excitability and heart and vascular muscle contractility.

Studying the effect of Ca2+ on the activity of the different rat Na-K-ATPase isozymes expressed in Sf-9 cells, we found that the cation differentially affects the function of each isoform (34). As has been shown before, the alpha 1 beta 1-isozyme is quite resistant to Ca2+ (15). In contrast, the alpha 2 beta 1- and alpha 3 beta 1-isozymes display Ki values 10- and 100-fold lower than that of the alpha 1 beta 1, respectively (Table 1). Similarly, in rat axolemma, myometrium, and skeletal muscle, the Na-K-ATPase activity that has a high sensitivity to ouabain is inhibited by physiological concentrations of Ca2+ (142, 207). This suggests that in excitable cells after depolarization, when the intracellular Ca2+ concentration rises to 5-10 µM, the alpha 1 beta 1-isozyme remains active, while the alpha 2 beta 1- and alpha 3 beta 1-isozymes are functioning at approximately one-half of their maximal capability. This may be particularly relevant in the heart, where the rise in intracellular Ca2+ elicited by the cardiotonic steroids may be enhanced by further inhibition of the ouabain-sensitive alpha 2- and alpha 3-isoforms in a positive feedback mechanism. The differential affinity to Ca2+ also ensures that only a fraction of the total enzyme is inhibited, the same fraction that is sensitive to the cardiotonic steroids. Interestingly, in contrast to the alpha 1-isoform, alpha 2-isoform in astrocytes and alpha 3-isoform in neurons and myocytes exhibit a reticular distribution on the plasma membrane which parallels the underlying endoplasmic reticulum or SR (110). This distribution is identical to that of the Na/Ca exchanger. Thus, while alpha 1 is regulating bulk cytosolic Na+, alpha 2 and alpha 3 may adjust Na+ concentrations in the restricted cytosolic space between the plasma membrane and reticulum to indirectly control Ca2+ (110).

Regulation of Na-K-ATPase Isozymes

Regulation of the Na-K-ATPase activity occurs by different cellular mechanisms and can be achieved by modulation of the number of enzyme molecules present at the plasma membrane or by influencing the activity of the Na-K-ATPase already at the cell surface. For example, the amount of the enzyme at the plasma membrane can be modified by changes in the rate of synthesis or degradation of the individual Na pump polypeptides as well as by mobilization of Na pump molecules from the endosomal pools to the cell surface (reviewed in Refs. 68, 138). Alternatively, the activity of the Na pump at the cell surface can be directly regulated (26, 68, 138, 149), providing a rapid adjustment in Na pump function. Several effectors have been implicated in this acute response; the primary one is the intracellular Na+ concentration, which at steady state is rate limiting. Also, as mentioned before, endogenous ouabain and intracellular Ca2+ are potential short-term modulators of Na pump activity (34, 37, 212).

Recent evidence suggests that intracellular messengers can also affect Na-K-ATPase activity. Depending on the tissue, activation of protein kinases can induce an increase or decrease in Na pump activity (26, 54, 68, 138, 149, 172). Agents that increase cellular cAMP, as well as exogenous derivatives of cAMP, lead to Na-K-ATPase inhibition in the medullary thick ascending limb of the loop of Henle and the cortical collecting duct (18, 26, 96, 149, 172, 174) and to Na-K-ATPase stimulation in the proximal convoluted tubules (47, 74). This response seems to be mediated, at least in part, by protein kinase A (PKA)-directed phosphorylation of Ser943 of the Na pump alpha -subunit (77). Phosphorylation of the Na pump alpha -subunit is reversible, as demonstrated by the decrease in Na-K-ATPase activity after activation of a dopamine- and cAMP- regulated phosphoprotein (DARPP-32), an endogenous inhibitor of protein phosphatase 1 (PP1) (6). This suggests that a phosphorylation/dephosphorylation event may dynamically regulate the activity of the Na pump. Moreover, in the proximal nephron and in cultured canine kidney cells, the Na-K-ATPase is inhibited by phorbol esters or diacylglycerol analogs, in a process that involves protein kinase C (PKC) activation (79, 172, 183) and, possibly, the phosphorylation of the Na pump alpha -subunit at Ser16 (17). In addition, several other mechanisms have been postulated concerning the way by which protein kinases exert their effects on the Na pump. For example, in amphibian nephron cells, PKC produces Na-K-ATPase inhibition by increasing cell endocytosis and internalization of Na pump molecules (21), and in isolated nephron segments, PKA may stimulate phospholipase A2 (PLA2) and the production of arachidonic acid and its metabolites (173). Moreover, in the kidney another kinase, protein kinase G (PKG), and the production of cGMP appear to mediate the loss of salt and water produced by acetylcholine, bradykinin, and atrial natriuretic peptide (144, 175). In contrast, in the duck salt gland cGMP stimulates ouabain-sensitive p-nitrophenylphosphatase hydrolysis by the Na pump (192).

Although the effect of intracellular messengers on the function of the alpha 1 beta 1-isozyme has been well documented (26, 68, 138), the regulation of the other Na-K-ATPase isozymes by protein kinases is poorly understood. We studied the effect of different protein kinases on the rat Na-K-ATPase isoforms expressed in Sf-9 cells. Similar to mammalian cells, insect cells glycosylate, phosphorylate, acylate, and perform most other posttranslational modifications dictated by the primary amino acid sequence. In addition, they display a complex signal transduction machinery comparable to that of their mammalian counterparts (156). As shown in Fig. 3, activation of PKA, PKC, and PKG, using dibutyryl-cAMP, phorbol 12-myristate 13 acetate (PMA), or dibutyryl-cGMP, respectively, is able to differentially modify the function of the Na-K-ATPase isozymes. Specificity of the response is demonstrated by the reversibility of the effect by the respective protein kinase competitive inhibitors. As shown, PKC activation leads to inhibition of all isozymes, PKA activation stimulates the activity of the Na-K-ATPase alpha 3 beta 1 and decreases that of the alpha 1 beta 1- and alpha 2 beta 1-isozymes. Finally, activation of PKG diminishes the activity of the alpha 1 beta 1- and alpha 3 beta 1-isozymes, without altering that of alpha 2 beta 1. The regulation of the activity of the Na pump isozymes elicited by PKA and PKC does not depend on changes in the rate of synthesis or degradation of the Na-K-ATPase polypeptides, but is rather a result of changes in the molecular activity of the Na-K-ATPases (34).


View larger version (43K):
[in this window]
[in a new window]
 


View larger version (30K):
[in this window]
[in a new window]
 


View larger version (26K):
[in this window]
[in a new window]
 
Fig. 3.   Effect of protein kinase activation on the rat alpha 1 beta 1, alpha 2 beta 1, and alpha 3 beta 1 Na-K-ATPase isozymes expressed in Sf-9 insect cells. A: effect of stimulation of protein kinase C (PKC) with phorbol 12-myristate 13-acetate (PMA). Sf-9 cells coinfected with alpha 1 beta 1-, alpha 2 beta 1-, or alpha 3 beta 1-isoforms were treated 40 h after infection with PMA alone (1 µM for 1 h) or with addition of either staurosporine (200 nM) or 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7; 50 µM). Protein phosphatase 2A (PP2A) effect was investigated on cell homogenates after 1 h at 25°C in the absence or presence of 2 units of PP2A/mg total protein. B: effect of stimulation of PKA with dibutyryl-cAMP. Cells coinfected with the corresponding isoforms were treated 40 h after infection with dibutyryl-cAMP alone (2 mM for 1 h) or with addition of 50 µM of 8-bromoadenosine cyclic monophosphothioate, Rp isomer (Br-cAMPS). C: effect of stimulation of PKG with dibutyryl-cGMP. Insect cells expressing the indicated isozymes were treated 40 h after infection with dibutyryl-cGMP alone (1 mM for 1 h) or with the addition of 1 µM of KT-5823. In all cases, cells were then processed for Na-K-ATPase activity. Each value is the mean, and error bars represent the standard errors of the mean of 3-7 experiments performed in triplicate on samples obtained from different infections. * Significantly different from the respective controls are indicated, P < 0.01.

The mechanisms by which protein kinases regulate the Na-K-ATPase isozymes are not well characterized. Direct phosphorylation of the Na pump alpha -subunit by PKA and PKC was originally demonstrated in vitro for the purified enzyme from kidney (6). Although it has been more difficult to demonstrate, phosphorylation of the endogenous Na pump has also been shown in intact cells (reviewed in Refs. 26, 68, 149). In the insect cells, we found a PKA- and PKC-dependent phosphorylation of alpha 1-, as well as the alpha 2- and alpha 3-isoforms. Figure 4 shows that competitive inhibitors of PKC and PKA partially prevent the phosphorylation of the Na pump alpha -isoforms by treatment with PMA and dibutyryl-cAMP respectively. This implies that PKC and PKA are able to specifically phosphorylate the alpha 1-, alpha 2-, and alpha 3-polypeptides. However, it has not been ruled out that the PKA- and PKC-dependent phosphorylation involves another downstream messenger that may induce the phosphorylation or inhibit the dephosphorylation of the enzyme. In any case, phosphorylation appears to be at least one of the mechanisms by which PKA and PKC affect Na-K-ATPase isozyme activity. In agreement with these results, Beguin et al. (19) have shown that PKC is able to phosphorylate the rat alpha 2-isoform, although less efficiently than the alpha 1-isoform. Also, it appears that rat alpha 3-isoform is phosphorylated by PKC, whereas the same isoform from other species is not. In the alpha 1-isoform, phosphorylation by PKC was originally mapped to Ser16 (17). Recently, Ser23 has also been identified as a potential site for phosphorylation (75). Furthermore, Pedemonte et al. (161) have shown that an alpha 1 deletion mutant, which lacks the first 31 amino acids, fails to respond to PKC. The region containing the NH2 terminus of the alpha -subunit exhibits the most sequence divergence, both among species and isoforms. For example, Ser16 is present only in the alpha 1-isoform, whereas Ser23 is present in the alpha 1-subunit of the rat and Torpedo californica as well as in the rat alpha 3-isoform. Phosphorylation of the alpha 2-isoform suggests that additional residues may also be involved. The similar decrease in activity found after PKC stimulation for alpha 2 beta 1 and alpha 3 beta 1 indicates that phosphorylation of other serine residues might be occurring within the same protein domain in these isozymes. In contrast, phosphorylation of the alpha 1-isoform by PKA takes place at Ser943 (77) in a highly conserved cytoplasmic region between transmembrane segments 8 and 9. Thus the same residue might be involved in the phosphorylation of alpha 1 and alpha 3 by this protein kinase. Interestingly, if Ser943 is involved in the effect of PKA on all isoforms, then the incorporation of Pi must somehow alter alpha 3 beta 1 in a different manner, to increase Na-K-ATPase activity in this isozyme.


View larger version (31K):
[in this window]
[in a new window]
 
Fig. 4.   Phosphorylation of the Na-K-ATPase alpha 1-, alpha 2-, and alpha 3-isoforms by PKA and PKC. Sf-9 were grown in 6-well plates and infected with baculovirus containing the different rat Na-K-ATPase isozymes. Forty hours after infection, cells were starved for 1 h in phosphate-free medium and labeled for 1 h with [32P]orthophosphate (0.3 mCi/well). Then, for PKC phosphorylation (A), cells were treated either with or without H7 (200 nM) for 30 min and PMA (1 µM) for an additional hour. For PKA phosphorylation (B), cells were treated with or without 8-bromoadenosine cyclic monophosphothioate, Rp isomer (8-BrcAMPS, 50 µM) for 30 min and dibutyryl-cAMP (DBcAMP, 2 mM) for another hour. Cells expressing only the beta -subunit and treated with PMA or dibutyryl-cAMP are shown as a control. In all cases, cells were lysed and samples were subjected to immunoprecipitation using monoclonal antibodies as described (32). Precipitated proteins were separated by SDS-PAGE (7.5%), gels were dried, and radioactivity was quantified using a PhosphorImager SI scanner and the ImageQuanNT software (Molecular Dynamics, Sunnyvale, CA). A representative experiment is shown, and bars represent the intensity of labeling as a percentage of the phosphorylation obtained in absence of protein kinase inhibitors.

A physiological explanation for these isozyme-specific effects is difficult to infer; nevertheless, the observation provides additional evidence for a role for the Na pump isozymes. For example, the Na-K-ATPase alpha 3 beta 1-isozyme has the distinct kinetic characteristics of a low affinity for Na+ and K+ and a high affinity for ATP (Table 1). The specific activation of alpha 3 beta 1, concomitant with the inhibition of the other two Na pump isozymes, could lead to subtle variations in the Na+ and K+ ionic gradients and hence to changes in the membrane potential and cellular excitability. This could be particularly important in neuronal cells, where alpha 3 is predominantly expressed.

It is clear that the activity of the Na-K-ATPase is under the control of a variety of intracellular messengers that are able to modulate the function of the particular isozymes in a specific fashion. Because the Na-K-ATPase isozymes have kinetic properties that are unique, isozyme-specific regulation may be important in adapting Na pump function to the requirements of each cell.

Conclusions

Since the Na-K-ATPase isoforms were identified in 1979 (194), our knowledge regarding their expression, function and regulation has significantly broadened. The structural heterogeneity that characterizes the enzyme does not represent simple redundancy, but rather it is an evolutionary refinement that contributes to the diversity in Na pump function. It is therefore not surprising that stringent regulatory mechanisms have developed to adjust their expression and activity to serve the requirements of each cell under various physiological and pathological conditions. Future studies to clarify the mechanisms important in Na-K-ATPase isoform regulation and to precisely link isozyme function to physiological processes will provide a better understanding of the role of the Na-K-ATPase isozymes in cellular functions.

    FOOTNOTES

Address for reprint requests: G. Blanco, Dept. of Cell Biology and Physiology, Washington Univ. School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110.

    REFERENCES
Top
Abstract
Article
References

1.   Ackermann, U., and K. Geering. beta 1 and beta 3 subunits can associate with presynthesized alpha  subunits of Xenopus oocytes Na,K-ATPase. J. Cell Biol. 267: 12911-12915, 1992.

2.   Ahn, K., K. M. Madsen, C. C. Tisher, and B. C. Kone. Differential expression and cellular distribution of mRNAs encoding alpha - and beta -isoforms of Na,K-ATPase in rat kidney. Am. J. Physiol. 265 (Renal Fluid Electrolyte Physiol. 34): F792-F801, 1993[Abstract/Free Full Text].

3.   Akopyanz, N. S., N. E. Broude, E. P. Bekman, E. O. Marzen, and E. D. Sverdlov. Tissue-specific expression of Na,K-ATPase beta -subunit. Does beta 2 expression correlate with tumorigenesis? FEBS Lett. 289: 8-10, 1991[Medline].

4.   Allen, J. C., T. A. Pressley, T. Odebunmi, and R. M. Medford. Tissue specific membrane association of alpha 1T, a truncated form of the alpha 1 subunit of the Na pump. FEBS Lett. 337: 285-288, 1994[Medline].

5.   Antonicek, H., E. Persohn, and M. Schachner. Biochemical and functional characterization of a novel neuron-glia adhesion molecule that is involved in neuronal migration. J. Cell Biol. 104: 1587-1595, 1987[Abstract/Free Full Text].

6.   Aperia, A., J. Fryckstedt, L. Svensson, H. C. Hemmings, Jr., A. C. Nairn, and P. Greengard. Phosphorylated Mr 32,000 dopamine- and cAMP-regulated phosphoprotein inhibits Na+,K+-ATPase activity in renal tubule cells. Proc. Natl. Acad. Sci. USA 88: 2798-2801, 1991[Abstract/Free Full Text].

7.   Appel, C., S. Gloor, G. Schmalzing, M. Schachner, and R. R. Bernhardt. Expression of a Na,K-ATPase beta 3 subunit during development of the zebrafish central nervous system. J. Neurosci. Res. 46: 551-564, 1996[Medline].

8.   Arystarkhova, E. A., O. E. Lakhtinaa, and N. N. Modyanov. Immunodetection of Na,K-ATPase alpha -isoforms in renal and nerve tissues. FEBS Lett. 250: 545-548, 1989[Medline].

9.   Arystarkhova, E., D. L. Gibbons, and K. J. Sweadner. Topology of the Na,K-ATPase. Evidence for externalization of a labile transmembrane structure during heating. J. Biol. Chem. 270: 8785-8796, 1995[Abstract/Free Full Text].

10.   Arystarkhova, E., and K. J. Sweadner. Isoform-specific monoclonal antibodies to Na,K-ATPase alpha  subunits. Evidence for a tissue-specific post-translational modification of the alpha  subunit. J. Biol. Chem. 271: 23407-23417, 1996[Abstract/Free Full Text].

11.   Arystarkhova, E., and K. J. Sweadner. Tissue-specific expression of the Na,K-ATPase beta 3 subunit. The presence of beta 3 in lung and liver addresses the problem of the missing subunit. J. Biol. Chem. 272: 22405-22408, 1997[Abstract/Free Full Text].

12.   Attali, B., H. Latter, N. Rachamim, and H. Garty. A corticosteroid-induced gene expressing an "IsK-like" K+ channel activity in Xenopus oocytes. Proc. Natl. Acad. Sci. USA 92: 6092-6096, 1995[Abstract/Free Full Text].

13.   Atterwill, C. K., and P. Collins. Studies on the ontogenesis of the different isoenzymes of Na+, K+-ATPase in rat brain in vivo and in vitro in relation to their regulation and cellular localisation. Biochem. Pharmacol. 36: 2679-2683, 1987[Medline].

14.   Baxter-Lowe, L. A., J. Z. Guo, E. E. Bergstrom, and L. E. Hokin. Molecular cloning of the Na,K-ATPase alpha  subunit in developing brine shrimp and sequence comparison with higher organisms. FEBS Lett. 257: 181-187, 1989[Medline].

15.   Beauge, L., and M. A. Campos. Calcium inhibition of the ATPase and phosphatase activities of (Na+ + K+)-ATPase. Biochim. Biophys. Acta 729: 137-149, 1983[Medline].

16.   Beggah, A. T., P. Jaunin, and K. Geering. Role of glycosylation and disulfide bond formation in the beta  subunit in the folding and functional expression of Na,K-ATPase. J. Biol. Chem. 272: 10318-10326, 1997[Abstract/Free Full Text].

17.   Beguin, P., A. T. Beggah, A. V. Chibalin, P. Burgener-Kairuz, F. Jaisser, P. M. Mathews, B. C. Rossier, S. Cotecchia, and K. Geering. Phosphorylation of the Na,K-ATPase alpha  subunit by protein kinase A and C in vitro and in intact cells. Identification of a novel motif for PKC-mediated phosphorylation. J. Biol. Chem. 269: 24437-24445, 1994[Abstract/Free Full Text].

18.   Beguin, P., A. Beggah, S. Cotecchia, and K. Geering. Adrenergic, dopaminergic, and muscarinic receptor stimulation leads to PKA phosphorylation of Na-K-ATPase. Am. J. Physiol. 270 (Cell Physiol. 39): C131-C137, 1996[Abstract/Free Full Text].

19.   Beguin, P., M. C. Peitsch, and K. Geering. alpha 1 but not alpha 2 or alpha 3 isoforms of Na,K-ATPase are efficiently phosphorylated in a novel protein kinase C motif. Biochemistry 35: 14098-14108, 1996[Medline].

20.   Beguin, P., X. Wang, D. Firsov, A. Puoti, D. Claeys, J. D. Horisberger, and K. Geering. The gamma  subunit is a specific component of the Na,K-ATPase and modulates its transport function. EMBO J. 16: 4250-4260, 1997[Medline].

21.   Beron, J., I. Forster, P. Beguin, K. Geering, and F Verrey. Phorbol 12-myristate 13-acetate down-regulates Na,K-ATPase independent of its protein kinase C site: decrease in basolateral cell surface area. Mol. Biol. Cell 8: 387-398, 1997[Abstract].

22.   Berrebi-Bertrand, I., J. M. Maixent, G. Christe, and L. G. Lelievre. Two active Na+/K+-ATPases of high affinity for ouabain in adult rat brain membranes. Biochim. Biophys. Acta 1021: 148-156, 1990[Medline].

23.   Berrebi-Bertrand, I., and J. M. Maixent. Immunodetection and enzymatic characterization of the alpha 3 isoform of Na,K-ATPase in dog heart. FEBS Lett. 348: 55-60, 1994[Medline].

24.   Bertoni, J. M., and G. J. Siegel. Development of (Na+-K+)-ATPase in rat cerebrum: correlation with Na+-dependent phosphorylation and K+-paranitrophenylphosphatase. J. Neurochem. 31: 1501-1511, 1978[Medline].

25.   Bertoni, J. M., and G. J. Siegel. Development of (Na+-K+)-ATPase in rat hindbrain: increments in parallel with Na+-dependent phosphorylation and K+-p-nitrophenylphosphatase. J. Neurochem. 32: 573-580, 1979[Medline].

26.   Bertorello, A. M., and A. I. Katz. Short-term regulation of renal Na-K-ATPase activity: physiological relevance and cellular mechanisms. Am. J. Physiol. 265 (Renal Fluid Electrolyte Physiol. 34): F743-F755, 1993[Abstract/Free Full Text].

27.   Besirli, C. G., T. W. Gong, and M. I. Lomax. Novel beta 3 isoform of the Na,K-ATPase beta  subunit from mouse retina. Biochim. Biophys. Acta 1350: 21-26, 1997[Medline].

28.   Blanco, G., and L. Beauge. Pools of (Na+,K+)-ATPase isoforms in unborn and adult rats can be detected by their sensitivity to strophanthidin, but have similar reactivity to Na+, K+ and ATP. Prog. Clin. Biol. Res. 268: 271-278, 1988.

29.   Blanco, G., G. Berberian, and L. Beauge. Detection of a highly ouabain sensitive isoform of rat brainstem Na,K-ATPase. Biochim. Biophys. Acta 1027: 1-7, 1990[Medline].

30.   Blanco, G., Z. J. Xie, and R. W. Mercer. Functional expression of the alpha 2 and alpha 3 isoforms of the Na,K-ATPase in baculovirus-infected insect cells. Proc. Natl. Acad. Sci. USA 90: 1824-1828, 1993[Abstract/Free Full Text].

31.   Blanco, G., A. W. DeTomaso, J. Koster, Z. J. Xie, and R. W. Mercer. The alpha -subunit of the Na,K-ATPase has catalytic activity independent of the beta -subunit. J. Biol. Chem. 269: 23420-23425, 1994[Abstract/Free Full Text].

32.   Blanco, G., J. C. Koster, and R. W. Mercer. The alpha  subunit of the Na,K-ATPase specifically and stably associates into oligomers. Proc. Natl. Acad. Sci. USA 91: 8542-8546, 1994[Abstract/Free Full Text].

33.   Blanco, G., J. C. Koster, G. Sanchez, and R. W. Mercer. Kinetic properties of the alpha 2beta 1 and alpha 2beta 2 isozymes of the Na,K-ATPase. Biochemistry 34: 319-325, 1995[Medline].

34.   Blanco, G., and R. W. Mercer. Regulation of the alpha 2beta 1 and alpha 3beta 1 isozymes of the Na,K-ATPase by Ca2+, PKA, and PKC. Ann. NY Acad. Sci. 834: 572-575, 1997[Medline].

35.   Blanco, G., G. Sanchez, and R. W. Mercer. Comparison of the enzymatic properties of the Na,K-ATPase alpha 3beta 1 and alpha 3beta 2 isozymes. Biochemistry 34: 9897-9903, 1995[Medline].

36.   Blanco, G., Z. J. Xie, and R. W. Mercer. Functional expression of Na,K-ATPase alpha  and beta  isoforms. In: The Sodium Pump: Structure, Mechanism, Hormonal Control and Its Role in Disease, edited by E. Bamberg, and W. Schoner. Darmstadt, Germany: Steinkopff, 1994, p. 82-85.

37.   Blaustein, M. P. Physiological effects of endogenous ouabain: control of intracellular Ca2+ stores and cell responsiveness. Am. J. Physiol. 264 (Cell Physiol. 33): C1367-C1387, 1993[Abstract/Free Full Text].

38.   Blaustein, M. P. Endogenous ouabain: physiological activity and pathophysiological implications. Clin. Investig. 72: 706-707, 1994[Medline].

39.   Book, C. B., R. P. Wilson, and Y. C. Ng. Cardiac hypertrophy in the ferret increases expression of the Na,K-ATPase alpha 1- but not alpha 3-isoform. Am. J. Physiol. 266 (Heart Circ. Physiol. 35): H1221-H1227, 1994[Abstract/Free Full Text].

40.   Brines, M. L., and R. J. Robbins. Cell-type specific expression of Na+, K+-ATPase catalytic subunits in cultured neurons and glia: evidence for polarized distribution in neurons. Brain Res. 631: 1-11, 1993[Medline].

41.   Brodsky, J. L., and G. Guidotti. Sodium affinity of brain Na+-K+-ATPase is dependent on isozyme and environment of the pump. Am. J. Physiol. 258 (Cell Physiol. 27): C803-C811, 1990[Abstract/Free Full Text].

42.   Burgener-Kairuz, P., J. D. Horisberger, K. Geering, and B. C. Rossier. Functional expression of N-terminal truncated alpha  subunits of Na,K-ATPase in Xenopus laevis oocytes. FEBS Lett. 290: 83-86, 1991[Medline].

43.   Cameron, R., L. Klein, A. W. Shyjan, P. Rakic, and R. Levenson. Neurons and astroglia express distinct subsets of Na,K-ATPase alpha  and beta  subunits. Mol. Brain Res. 21: 333-343, 1994[Medline].

44.   Canfield, V. A., and R. Levenson. Transmembrane organization of the Na,K-ATPase determined by epitope addition. Biochemistry 32: 13782-13786, 1993[Medline].

45.   Canfield, V. A., K. Y. Xu, T. D'Aquila, A. W. Shyjan, and R. Levenson. Molecular cloning and characterization of Na,K-ATPase from Hydra vulgaris: implications for enzyme evolution and ouabain sensitivity. New Biol. 4: 339-348, 1992[Medline].

46.   Carafoli, E. P-Type ATPases. J. Bioenerg. Biomembr. 24: 245-247, 1992[Medline].

47.   Carranza, M. L., E. Feraille, and H. Favre. Protein kinase C-dependent phosphorylation of Na-K-ATPase alpha -subunit in rat kidney cortical tubules. Am. J. Physiol. 271 (Cell Physiol. 40): C136-C143, 1996[Abstract/Free Full Text].

48.   Charlemagne, D. Molecular and cellular level of action of digitalis. Herz 18: 79-85, 1993[Medline].

49.   Charlemagne, D., J. Orlowski, P. Oliviero, F. Rannou, C. Sainte Beuve, B. Swynghedauw, and L. K. Lane. Alteration of Na,K-ATPase subunit mRNA and protein levels in hypertrophied rat heart. J. Biol. Chem. 269: 1541-1547, 1994[Abstract/Free Full Text].

50.   Charlemagne, D., and B. Swynghedauw. Myocardial phenotypic changes in Na, K-ATPase in left ventricular hypertrophy: pharmacological consequences. Eur. Heart J. 16: 20-23, 1995.

51.   Cheval, L., C. Barlet-Bas, and A. Doucet. Characterization of molecular isoforms of Na,K-ATPase subunits along the rat nephron by polymerase chain reaction. In: The Sodium Pump, edited by E. Bamberg, and W. Schoner. Darmstadt, Germany: Steinko, 1994, p. 704-709.

52.   Chow, D. C., and J. G. Forte. Functional significance of the beta  subunit for heterodimeric P-type ATPases. J. Exp. Biol. 198: 1-17, 1995[Abstract].

53.   Clapp, W. L., P. Bowman, G. S. Shaw, P. Patel, and B. C. Kone. Segmental localization of mRNAs encoding Na+-K+-ATPase alpha  and beta  subunit isoforms in rat kidney using RT-PCR. Kidney Int. 46: 627-638, 1994[Medline].

54.   Cornelius, F., and N. Logvinenko. Functional regulation of reconstituted Na,K-ATPase by protein kinase A phosphorylation. FEBS Lett. 380: 277-280, 1996[Medline].

55.   Cortas, N., M. Arnaout, J. Salon, and I. S. Edelman. Isoforms of Na,K-ATPase in Artemia salina. II. Tissue distribution and kinetic characterization. J. Membr. Biol. 108: 187-195, 1989[Medline].

56.   Cortas, N., and I. S. Edelman. Isolation of two isoforms of Na,K-ATPase from Artemia salina: kinetic characterization. Prog. Clin. Biol. Res. 268: 287-292, 1988.

57.   Daly, S. E., L. K. Lane, and R. Blostein. Functional consequences of amino-terminal diversity of the catalytic subunit of the Na,K-ATPase. J. Biol. Chem. 269: 23944-23948, 1994[Abstract/Free Full Text].

58.   Daly, S. E., L. K. Lane, and R. Blostein. Structure/function analysis of the amino-terminal region of the alpha 1 and alpha 2 subunits of Na,K-ATPase. J. Biol. Chem. 271: 23683-23689, 1996[Abstract/Free Full Text].

59.   DeTomaso, A. W., Z. J. Xie, G. Liu, and R. W. Mercer. Expression, targeting, and assembly of functional Na,K-ATPase polypeptides in baculovirus-infected insect cells. J. Biol. Chem. 268: 1470-1478, 1993[Abstract/Free Full Text].

60.   Doris, P. A. Regulation of Na,K-ATPase by endogenous ouabain-like materials. Proc. Soc. Exp. Biol. Med. 205: 202-212, 1994[Medline].

61.   Doris, P. A. Endogenous inhibitors of the Na,K pump. Miner. Electrolyte Metab. 22: 303-310, 1996[Medline].

62.   Eakle, K. A., M. A. Kabalin, S. G. Wang, and R. A. Farley. The influence of beta  subunit structure on the stability of Na+/K+-ATPase complexes and interaction with K+. J. Biol. Chem. 269: 6550-6557, 1994[Abstract/Free Full Text].

63.   Eakle, K. A., K. S. Kim, M. A. Kabalin, and R. A. Farley. High-affinity ouabain binding by yeast cells expressing Na+,K+-ATPase alpha  subunits and the gastric H+, K+-ATPase beta  subunit. Proc. Natl. Acad. Sci. USA 89: 2834-2838, 1992[Abstract/Free Full Text].

64.   Eakle, K. A., R. M. Lyu, and R. A. Farley. The influence of beta  subunit structure on the interaction of Na+/K+-ATPase complexes with Na+. A chimeric beta  subunit reduces the Na+ dependence of phosphoenzyme formation from ATP. J. Biol. Chem. 270: 13937-13947, 1995[Abstract/Free Full Text].

65.   Emanuel, J. R., J. Schulz, X. M. Zhou, R. B. Kent, D. Housman, L. Cantley, and R. Levenson. Expression of an ouabain-resistant Na,K-ATPase in CV-1 cells after transfection with a cDNA encoding the rat Na,K-ATPase alpha 1 subunit. J. Biol. Chem. 263: 7726-7733, 1988[Abstract/Free Full Text].

66.   Erdmann, E., K. Werdan, and L. Brown. Evidence for two kinetically and functionally different types of cardiac glycoside receptors in the heart. Eur. Heart J. 5: 297-302, 1984.

67.   Erdmann, E., K. Werdan, and L. Brown. Multiplicity of cardiac glycoside receptors in the heart. Trends Pharmacol. Sci. 6: 293-295, 1985.

68.   Ewart, H. S., and A. Klip. Hormonal regulation of the Na+-K+-ATPase: mechanisms underlying rapid and sustained changes in pump activity. Am. J. Physiol. 269 (Cell Physiol. 38): C295-C311, 1995[Abstract/Free Full Text].

69.   Fambrough, D. M. The sodium pump becomes a family. Trends Neurosci. 11: 325-328, 1988[Medline].

70.   Fambrough, D. M., and E. K. Bayne. Multiple forms of (Na+ + K+)-ATPase in the chicken. Selective detection of the major nerve, skeletal muscle, and kidney form by a monoclonal antibody. J. Biol. Chem. 258: 3926-3935, 1983[Abstract/Free Full Text].

71.   Farman, N., I. Corthesy-Theulaz, J. P. Bonvalet, and B. C. Rossier. Localization of alpha -isoforms of Na,K-ATPase in rat kidney by in-situ hybridization. Am. J. Physiol. 260 (Cell Physiol. 29): C468-C474, 1991[Abstract/Free Full Text].

72.   Feige, G., T. Leutert, and A. De Pover. Na,K-ATPase isozymes in rat tissues: differential sensitivities to sodium, vanadate and dihydroouabain. Prog. Clin. Biol. Res. 268: 377-384, 1988.

73.   Feraille, E., C. Barlet-Bas, L. Cheval, M. Rousselot, M. L. Carranza, D. Dreher, E. Arystarkhova, A. Doucet, and H. Favre. Presence of two isoforms of Na, K-ATPase with different pharmacological and immunological properties in the rat kidney. Pflügers Arch. 430: 205-212, 1995[Medline].

74.   Feraille, E., M. L. Carranza, B. Buffin-Meyer, M. Rousselot, A. Doucet, and H. Favre. Protein kinase C-dependent stimulation of Na,K-ATPase in rat proximal convoluted tubule. Am. J. Physiol. 268 (Cell Physiol. 37): C1277-C1283, 1995[Abstract/Free Full Text].

75.   Feschenko, M. S., and K. J. Sweadner. Structural basis for species-specific differences in the phosphorylation of Na,K-ATPase by protein kinase C. J. Biol. Chem. 270: 14072-14077, 1995[Abstract/Free Full Text].

76.   Fink, D., P. E. Knapp, and M. Mata. Differential expression of Na,K-ATPase isoforms in oligodendrocytes and astrocytes. Dev. Neurosci. 18: 319-326, 1996[Medline].

77.   Fisone, G., S. X. Cheng, A. C. Nairn, A. J. Czernik, H. C. Hemmings, Jr., J. O. Hoog, A. M. Bertorello, R. Kaiser, T. Bergman, and H. Jornvall. Identification of the phosphorylation site for cAMP-dependent protein kinase on Na+,K+-ATPase and effects of site-directed mutagenesis. J. Biol. Chem. 269: 9368-9373, 1994[Abstract/Free Full Text].

78.   Forbush, B., III, J. H. Kaplan, and J. F. Hoffman. Characterization of a new photoaffinity derivative of ouabain: labeling of the large polypeptide and of a proteolipid component of the Na,K-ATPase. Biochemistry 17: 3667-3676, 1978[Medline].

79.   Garg, L. C., P. K. Saha, and D. Mohuczy-Dominiak. Cholinergic inhibition of Na-K-ATPase via activation of protein kinase C in Madin-Darby canine kidney cells. J. Am. Soc. Nephrol. 4: 195-205, 1993[Abstract].

80.   Gerbi, A., M. Debray, J. M. Maixent, C. Chanez, and J. M. Bourre. Heterogeneous Na+ sensitivity of Na+,K+-ATPase isoenzymes in whole brain membranes. J. Neurochem. 60: 246-252, 1993[Medline].

81.   Ghosh, S., A. C. Freitag, P. Martin-Vasallo, and M. Coca-Prados. Cellular distribution and differential gene expression of the three alpha subunit isoforms of the Na,K-ATPase in the ocular ciliary epithelium. J. Biol. Chem. 265: 2935-2940, 1990[Abstract/Free Full Text].

82.   Gloor, S., H. Antonicek, K. J. Sweadner, S. Pagliusi, R. Frank, M. Moos, and M. Schachner. The adhesion molecule on glia (AMOG) is a homologue of the beta  subunit of the Na,K-ATPase. J. Cell Biol. 110: 165-174, 1990[Abstract/Free Full Text].

83.  Glynn, I. M. The Na,K-transporting adenosine triphosphatase. In: The Enzymes of Biological Membranes (2nd ed.), edited by A. Martonosi. New York: Plenum, vol. 3, p. 35-114.

84.   Glynn, I. M. All hands to the sodium pump. J. Physiol. (Lond.) 462: 1-30, 1993[Free Full Text].

85.   Good, P. J., K. Richter, and I. B. Dawid. A nervous system-specific isotype of the beta  subunit of Na+,K+-ATPase expressed during early development of Xenopus laevis. Proc. Natl. Acad. Sci. USA 87: 9088-9092, 1990[Abstract/Free Full Text].

86.   Hamlyn, J. M., B. P. Hamilton, and P. Manunta. Endogenous ouabain, sodium balance and blood pressure: a review and a hypothesis. J. Hypertens. 14: 151-167, 1996[Medline].

87.   Hamlyn, J. M., D. W. Harris, and J. H. Ludens. Digitalis-like activity in human plasma. Purification, affinity, and mechanism. J. Biol. Chem. 264: 7395-7404, 1989[Abstract/Free Full Text].

88.   Hansen, O. Heterogeneity of Na,K-ATPase from kidney. Acta Physiol. Scand. Suppl. 607: 229-234, 1992[Medline].

89.   Hara, Y., O. Urayama, K. Kawakami, H. Nojima, H. Nagamune, T. Kojima, T. Ohta, K. Nagano, and M. Nakao. The third type of alpha  subunit of Na,K-ATPase. Prog. Clin. Biol. Res. 268: 73-78, 1988.

90.   Harashima, H., Y. Sugiyama, Y. Sawada, K. Shigenobu, Y. Kasuya, T. Iga, and M. Hanano. Kinetic analysis of the positive inotropic action (PIA) of ouabain in isolated perfused rabbit heart. Slow onset of PIA and slow binding to Na, K adenosine triphosphatase. J. Pharmacobio-Dyn. 11: 533-540, 1988[Medline].

91.   Hardwicke, P. M., and J. W. Freytag. A proteolipid associated with Na,K-ATPase is not essential for ATPase activity. Biochem. Biophys. Res. Commun. 102: 250-257, 1981[Medline].

92.   Hauger, R., H. M. D. Luu, F. K. Goodwin, and S. M. Paul. Characterization of [3H]ouabain binding sites in human brain, platelet and erythrocyte. J. Neurochem. 44: 1704-1708, 1985[Medline].

93.   Haupert, G. T., Jr. Characteristics of the Na,K-ATPase inhibitor from hypothalamus. Prog. Biochem. Pharmacol. 23: 10-21, 1988[Medline].

94.   Haupert, G. T., Jr. Physiological inhibitors of Na,K-ATPase: concept and status. Prog. Clin. Biol. Res. 268: 297-320, 1988.

95.   Hieber, V., G. J. Siegel, D. J. Fink, M. W. Beaty, and M. Mata. Differential distribution of (Na,K)-ATPase alpha isoforms in the central nervous system. Cell. Mol. Neurobiol. 11: 253-262, 1991[Medline].

96.   Horiuchi, A., K. Takeyasu, M. M. Mouradian, P. A. Jose, and R. A. Felder. D1A dopamine receptor stimulation inhibits Na+/K+-ATPase activity through protein kinase A. Mol. Pharmacol. 43: 281-285, 1993[Abstract].

97.   Horowitz, B., K. A. Eakle, G. Scheiner-Bobis, G. R. Randolph, C. Y. Chen, R. A. Hitzeman, and R. A. Farley. Synthesis and assembly of functional mammalian Na,K-ATPase in yeast. J. Biol. Chem. 265: 4189-4192, 1990[Abstract/Free Full Text].

98.   Horowitz, B., and R. A. Farley. Development of a heterologous gene expression system for the Na,K-ATPase subunits in the yeast Saccharomyces cerevisiae. Prog. Clin. Biol. Res. 268: 85-90, 1988.

99.   Hundal, H. S., A. Marette, Y. Mitsumoto, T. Ramlal, R. Blostein, and A. Klip. Insulin induces translocation of the alpha 2 and beta 1 subunits of the Na,K-ATPase from intracellular compartments to the plasma membrane in mammalian skeletal muscle. J. Biol. Chem. 267: 5040-5043, 1992[Abstract/Free Full Text].

100.   Inoue, N., H. Matsui, H. Tsukui, and H. Hatanaka. The appearance of a highly digitalis-sensitive isoform of Na+,K+-ATPase during maturation in vitro of primary cultured rat cerebral neurons. J. Biochem. (Tokyo) 104: 349-354, 1988[Abstract/Free Full Text].

101.   Isenmann, S., M. Molthagen, S. Brandner, U. Bartsch, G. Kuhne, J. P. Magyar, U. Sure, M. Schachner, and A. Aguzzi. The AMOG/beta 2 subunit of Na,K-ATPase is not necessary for long-term survival of telencephalic grafts. Glia 15: 377-388, 1995[Medline].

102.   Jaisser, F., J. D. Horisberger, and B. C. Rossier. The beta  subunit modulates potassium activation of the Na-K pump. Ann. NY Acad. Sci. 671: 113-119, 1992[Medline].

103.   Jaisser, F., P. Jaunin, K. Geering, B. C. Rossier, and J. D. Horisberger. Modulation of the Na,K-pump function by beta  subunit isoforms. J. Gen. Physiol. 103: 605-623, 1994[Abstract/Free Full Text].

104.   Jensen, J. Heterogeneity of pig kidney Na,K-ATPase as indicated by ADP- and ouabain-binding stoichiometry. Biochim. Biophys. Acta 1110: 81-87, 1992[Medline].

105.   Jewell, E. A., and J. B. Lingrel. Comparison of the substrate dependence properties of the rat Na,K-ATPase alpha 1, alpha 2, and alpha 3 isoforms expressed in HeLa cells. J. Biol. Chem. 266: 16925-16930, 1991[Abstract/Free Full Text].

106.   Jewell, E. A., and J. B. Lingrel. Chimeric rat Na,K-ATPase alpha 1/alpha 3 isoforms. Analysis of the structural basis for differences in Na+ requirements in the alpha 1 and alpha 3 isoforms. Ann. NY Acad. Sci. 671: 120-132, 1992[Medline].

107.   Jewell, E. A., O. I. Shamraj, and J. B. Lingrel. Isoforms of the alpha  subunit of Na,K-ATPase and their significance. Acta Physiol. Scand. Suppl. 607: 161-169, 1992[Medline].

108.   Jones, D. H., T. C. Davies, and G. M. Kidder. Embryonic expression of the putative gamma  subunit of the sodium pump is required for acquisition of fluid transport capacity during mouse blastocyst development. J. Cell Biol. 139: 1545-1552, 1997[Abstract/Free Full Text].

109.   Jørgensen, P. L. Structure and molecular mechanisms of the Na,K-pump. In: Monovalent Cations in Biological Systems. Boca Raton, FL: CRC, 1990, p. 117-154.

110.   Juhaszova, M., and M. P. Blaustein. Na+ pump low and high ouabain affinity alpha subunit isoforms are differently distributed in cells. Proc. Natl. Acad. Sci. USA 94: 1800-1805, 1997[Abstract/Free Full Text].

111.   Kelly, R. A., and T. W. Smith. Endogenous cardiac glycosides. Adv. Pharmacol. 25: 263-288, 1994.

112.   Kent, R. B., J. R. Emanuel, Y. Ben Neriah, R. Levenson, and D. E. Housman. Ouabain resistance conferred by expression of the cDNA for a murine Na+, K+-ATPase alpha  subunit. Science 237: 901-903, 1987[Abstract/Free Full Text].

113.   Kolansky, D. M., M. L. Brines, M. Gilmore-Hebert, and E. J. Benz, Jr. The A2 isoform of rat Na+,K+-adenosine triphosphatase is active and exhibits high ouabain affinity when expressed in transfected fibroblasts. FEBS Lett. 303: 147-153, 1992[Medline].

114.   Lavoie, L., R. Levenson, P. Martin-Vasallo, and A. Klip. The molar ratios of alpha  and beta  subunits of the Na+-K+-ATPase differ in distinct subcellular membranes from rat skeletal muscle. Biochemistry 36: 7726-7732, 1997[Medline].

115.   Lemas, M. V., and D. M. Fambrough. Sequence analysis of DNA encoding an avian Na+,K+-ATPase beta 2-subunit. Biochim. Biophys. Acta 1149: 339-342, 1993[Medline].

116.   Lemas, M. V., H. Y. Yu, K. Takeyasu, B. Kone, and D. M. Fambrough. Assembly of Na,K-ATPase alpha  subunit isoforms with Na,K-ATPase beta  subunit isoforms and H,K-ATPase beta  subunit. J. Biol. Chem. 269: 18651-18655, 1994[Abstract/Free Full Text].

117.   Levenson, R. Isoforms of the Na,K-ATPase: family members in search of function. Rev. Physiol. Biochem. Pharmacol. 123: 1-45, 1994[Medline].

118.   Levi, A. J., M. R. Boyett, and C. O. Lee. The cellular actions of digitalis glycosides on the heart. Prog. Biophys. Mol. Biol. 62: 1-54, 1994[Medline].

119.   Lingrel, J. B. Na,K-ATPase: isoform structure, function, and expression. J. Bioenerg. Biomembr. 24: 263-270, 1992[Medline].

120.   Lingrel, J. B., and T. Kuntzweiler. Na+,K+-ATPase. J. Biol. Chem. 269: 19659-19662, 1994[Free Full Text].

121.   Lingrel, J. B., J. Orlowsky, M. M. Shull, and E. M. Price. Molecular genetics of Na,K-ATPase. Prog. Nucleic Acid Res. Mol. Biol. 38: 37-89, 1990[Medline].

122.   Lingrel, J. B., J. Van Huysse, W. O'Brien, E. Jewell-Motz, and P. Schultheis. Na,K-ATPase: structure-function studies. Renal Physiol. Biochem. 17: 198-200, 1994[Medline].

123.   Lowndes, J. M., M. Hokin-Neaverson, and A. E. Ruoho. Photoaffinity labeling of (Na+K+)-ATPase with [125I]iodoazidocymarin. J. Biol. Chem. 259: 10533-10538, 1984[Abstract/Free Full Text].

124.   Lucchesi, P. A., and K. J. Sweadner. Postnatal changes in Na,K-ATPase isoform expression in rat cardiac ventricle. Conservation of biphasic ouabain affinity. J. Biol. Chem. 266: 9327-9331, 1991[Abstract/Free Full Text].

125.   Lucking, K., J. M. Nielsen, P. A. Pedersen, and P. L. Jorgensen. Na-K-ATPase isoform (alpha 3, alpha 2, alpha 1) abundance in rat kidney estimated by competitive RT-PCR and ouabain binding. Am. J. Physiol. 271 (Renal Fluid Electrolyte Physiol. 40): F253-F260, 1996[Abstract/Free Full Text].

126.   Lutsenko, S., and J. H. Kaplan. An essential role for the extracellular domain of the Na,K-ATPase beta-subunit in cation occlusion. Biochemistry 32: 6737-6743, 1993[Medline].

127.   Lutsenko, S., and J. H. Kaplan. Organization of P-type ATPases: significance of structural diversity. Biochemistry 34: 15607-15613, 1995[Medline].

128.   Lytton, J. Insulin affects the sodium affinity of the rat adipocyte (Na+,K+)-ATPase. J. Biol. Chem. 260: 10075-10080, 1985[Abstract/Free Full Text].

129.   Lytton, J. The catalytic subunits of the (Na+,K+)-ATPase alpha  and alpha (+) isozymes are the products of different genes. Biochem. Biophys. Res. Commun. 132: 764-769, 1985[Medline].

130.   Lytton, J., J. C. Lin, and G. Guidotti. Identification of two molecular forms of (Na+,K+)-ATPase in rat adipocytes. Relation to insulin stimulation of the enzyme. J. Biol. Chem. 260: 1177-1184, 1985[Abstract/Free Full Text].

131.   Madsen, K. L., J. B. Meddings, and R. N. Fedorak. Basolateral membrane lipid dynamics alter Na-K ATPase activity in rabbit small intestine. Can. J. Pharmacol. 70: 1483-1490, 1992.

132.   Magyar, J. P., U. Bartsch, Z. Q. Wang, N. Howells, A. Aguzzi, E. F. Wagner, and M. Schachner. Degeneration of neural cells in the central nervous system of mice deficient in the gene for the adhesion molecule on glia, the beta 2 subunit of murine Na,K-ATPase. J. Cell Biol. 127: 835-845, 1994[Abstract/Free Full Text].

133.   Malik, N., V. A. Canfield, M. C. Beckers, P. Gros, and R. Levenson. Identification of the mammalian Na,K-ATPase beta 3 subunit. J. Biol. Chem. 271: 22754-22758, 1996[Abstract/Free Full Text].

134.   Markert, C. L., and F. Moller. Multiple forms of enzymes: tissue, ontogenetic and species-specific patterns. Proc. Natl. Acad. Sci. USA 45: 753-763, 1959[Free Full Text].

135.   Marks, M. J., and N. W. Seeds. A heterogeneous ouabain-ATPase interaction in mouse brain. Life Sci. 23: 2735-2744, 1978[Medline].

136.   Martin-Vasallo, P., W. Dackowski, J. R. Emanuel, and R. Levenson. Identification of a putative isoform of the Na,K-ATPase beta subunit. Primary structure and tissue-specific expression. J. Biol. Chem. 264: 4613-4618, 1989[Abstract/Free Full Text].

137.   Matsuda, T., H. Iwata, and J. R. Cooper. Specific inactivation of alpha (+) molecular form of (Na+ + K+)-ATPase by pyrithiamin. J. Biol. Chem. 259: 3858-3863, 1984[Abstract/Free Full Text].

138.   McDonough, A. A., and R. A. Farley. Regulation of Na,K-ATPase activity. Curr. Opin. Nephrol. Hypertens. 2: 725-734, 1993[Medline].

139.   McDonough, A. A., K. Geering, and R. A. Farley. The sodium pump needs its beta subunit. FASEB J. 4: 1598-1605, 1990[Abstract].

140.   McDonough, A. A., C. E. Magyar, and Y. Komatsu. Expression of Na-K-ATPase alpha - and beta -subunits along rat nephron: isoform specificity and response to hypokalemia. Am. J. Physiol. 267 (Cell Physiol. 36): C901-C908, 1994[Abstract/Free Full Text].

141.   McDonough, A. A., J. Wang, and R. A. Farley. Significance of sodium pump isoforms in digitalis therapy. J. Mol. Cell. Cardiol. 27: 1001-1009, 1995[Medline].

142.   McGeoch, J. E. The alpha-2 isomer of the sodium pump is inhibited by calcium at physiological levels. Biochem. Biophys. Res. Commun. 173: 99-105, 1990[Medline].

143.   McGrail, K. M., J. M. Phillips, and K. J. Sweadner. Immunofluorescent localization of three Na,K-ATPase isozymes in the rat central nervous system: both neurons and glia can express more than one Na,K-ATPase. J. Neurosci. 11: 381-391, 1991[Abstract].

144.   McKee, M., C. Scavone, and J. A. Nathanson. Nitric oxide, cGMP, and hormone regulation of active sodium transport. Proc. Natl. Acad. Sci. USA 91: 12056-12060, 1994[Abstract/Free Full Text].

145.   Medford, R. M. Digitalis and the Na+,K+-ATPase. Heart Dis. Stroke 2: 250-255, 1993[Medline].

146.   Medford, R. M., R. Hyman, M. Ahmad, J. C. Allen, T. A. Pressley, P. D. Allen, and B. Nadal-Ginard. Vascular smooth muscle expresses a truncated Na+, K+-ATPase alpha 1 subunit isoform. J. Biol. Chem. 266: 18308-18312, 1991[Abstract/Free Full Text].

147.   Mercer, R. W. Structure of the Na,K-ATPase. Int. Rev. Cytol. 137: 139-168, 1993.

148.   Mercer, R. W., D. Biemesderfer, D. P. Bliss, J. H. Collins, and B. Forbush. Molecular cloning and immunological characterization of the gamma -polypeptide, a small protein associated with the Na,K-ATPase. J. Cell Biol. 121: 579-586, 1993[Abstract/Free Full Text].

149.   Middleton, J. P. Direct regulation of the Na,K pump by signal transduction mechanisms. Miner. Electrolyte Metab. 22: 293-302, 1996[Medline].

150.   Minor, N. T., Q. Sha, C. G. Nichols, and R. W. Mercer. The gamma subunit of the Na,K-ATPase induces cation channel activity. Proc. Natl. Acad. Sci. USA 95: 6521-6525, 1998[Abstract/Free Full Text].

151.   Mohraz, M., E. Ackermann, and K. J. Sweadner. Immunoelectron microscopy of epitopes on Na,K-ATPase catalytic subunit. Implication for the transmembrane organization of the C-terminal domain. J. Biol. Chem. 266: 2929-2936, 1994.

152.   Morrison, B. W., J. R. Moorman, G. C. Kowdley, Y. M. Kobayashi, L. R. Jones, and P. Leder. Mat-8, a novel phospholemman-like protein expressed in human breast tumors, induces a chloride conductance in Xenopus oocytes. J. Biol. Chem. 270: 2176-2182, 1995[Abstract/Free Full Text].

153.   Muller-Husmann, G., S. Gloor, and M. Schachner. Functional characterization of beta  isoforms of murine Na,K-ATPase. The adhesion molecule on glia (AMOG/beta 2), but not beta 1, promotes neurite outgrowth. J. Biol. Chem. 268: 26260-26267, 1993[Abstract/Free Full Text].

154.   Munzer, J. S., S. E. Daly, E. A. Jewell-Motz, J. B. Lingrel, and R. Blostein. Tissue- and isoform-specific kinetic behavior of the Na,K-ATPase. J. Biol. Chem. 269: 16668-16676, 1994[Abstract/Free Full Text].

155.   O'Brien, W. J., J. B. Lingrel, and E. T. Wallick. Ouabain binding kinetics of the rat alpha two and alpha three isoforms of the sodium-potassium adenosine triphosphate. Arch. Biochem. Biophys. 310: 32-39, 1994[Medline].

156.   O'Reilly, D. R., L. K. Miller, and V. A. Luckow. Baculovirus Expression Vectors. A Laboratory Manual. New York: Freeman, 1992.

157.   Orlowski, J., and J. B. Lingrel. Tissue-specific and developmental regulation of rat Na,K-ATPase catalytic alpha  isoform and beta  subunit mRNAs. J. Biol. Chem. 263: 10436-10442, 1988[Abstract/Free Full Text].

158.   Palmer, C. J., B. T. Scott, and L. R. Jones. Purification and complete sequence determination of the major plasma membrane substrate for cAMP-dependent protein kinase and protein kinase C in myocardium. J. Biol. Chem. 266: 11126-11130, 1991[Abstract/Free Full Text].

159.   Pardon, R. S., and F. Noel. Heterogeneity of ouabain binding sites in Schistosoma mansoni. First evidence for the presence of two (Na+ + K+)-ATPase isoforms in Platyhelminths. Biochem. Pharmacol. 47: 331-336, 1994[Medline].

160.   Pedemonte, C. H., and J. H. Kaplan. Chemical modification as an approach to elucidation of sodium pump structure-function relations. Am. J. Physiol. 258 (Cell Physiol. 27): C1-C23, 1990[Abstract/Free Full Text].

161.   Pedemonte, C. H., T. A. Pressley, M. F. Lokhandwala, and A. R. Cinelli. Regulation of Na,K-ATPase transport activity by protein kinase C. J. Membr. Biol. 155: 219-227, 1997[Medline].

162.   Peng, L., P. Martin-Vasallo, and K. J. Sweadner. Isoforms of Na,K-ATPase alpha  and beta  subunits in the rat cerebellum and in granule cell cultures. J. Neurosci. 17: 3488-3502, 1997[Abstract/Free Full Text].

163.   Peterson, G. L., R. D. Ewing, and F. P. Conte. Membrane differentiation and de nova synthesis of the (Na+ + K+)-activated adenosine triphosphatase during development of Artemia salina nauplii. Dev. Biol. 67: 90-98, 1978[Medline].

164.   Pressley, T. A. Phylogenetic conservation of isoform-specific regions within alpha -subunit of Na+-K+-ATPase. Am. J. Physiol. 262 (Cell Physiol. 31): C743-C751, 1992[Abstract/Free Full Text].

165.   Pressley, T. A. Structure and function of the Na,K pump: ten years of molecular biology. Miner. Electrolyte Metab. 22: 264-271, 1996[Medline].

166.   Reeves, A. S., J. H. Collins, and A. Schwartz. Isolation and characterization of (Na,K)-ATPase proteolipid. Biochem. Biophys. Res. Commun. 95: 1591-1598, 1980[Medline].

167.   Repke, K. R., and R. Schon. Role of protein conformation changes and transphosphorylations in the function of Na+/K+-transporting adenosine triphosphatase: an attempt at an integration into the Na+/K+ pump mechanism. Biol. Rev. Camb. Philos. Soc. 67: 31-78, 1992[Medline].

168.   Repke, K. R., K. J. Sweadner, J. Weiland, R. Megges, and R. Schon. In search of ideal inotropic steroids: recent progress. Prog. Drug Res. 47: 9-52, 1996[Medline].

169.   Rogers, T. B., and M. Lazdunski. Photoaffinity labeling of the digitalis receptor in the (sodium + potassium)-activated adenosinetriphosphatase. Biochemistry 18: 135-140, 1979[Medline].

170.   Ruiz, A., S. P. Bhat, and D. Bok. Characterization and quantification of full-length and truncated Na,K-ATPase alpha 1 and beta 1 RNA transcripts expressed in human retinal pigment epithelium. Gene 155: 179-184, 1995[Medline].

171.   Sachs, G., and K. Munson. Mammalian phosphorylating ion-motive ATPases. Curr. Opin. Cell Biol. 3: 685-694, 1991[Medline].

172.   Satoh, T., H. T. Cohen, and A. I. Katz. Different mechanisms of renal Na-K-ATPase regulation by protein kinases in proximal and distal nephron. Am. J. Physiol. 265 (Renal Fluid Electrolyte Physiol. 34): F399-F405, 1993[Abstract/Free Full Text].

173.   Satoh, T., H. T. Cohen, and A. I. Katz. Intracellular signaling in the regulation of renal Na-K-ATPase. II. Role of eicosanoids. J. Clin. Invest. 91: 409-415, 1993.

174.   Satoh, T., M. Ominato, and A. I. Katz. Different mechanisms of renal Na-K-ATPase regulation by dopamine in the proximal and distal nephron. Hypertens. Res. 18: S137-S140, 1995.

175.   Scavone, C., C. Scanlon, M. McKee, and J. A. Nathanson. Atrial natriuretic peptide modulates sodium and potassium-activated adenosine triphosphatase through a mechanism involving cyclic GMP and cyclic GMP-dependent protein kinase. J. Pharmacol. Exp. Ther. 272: 1036-1043, 1995[Abstract/Free Full Text].

176.   Scheiner-Bobis, G., and R. A. Farley. Subunit requirements for expression of functional sodium pumps in yeast cells. Biochim. Biophys. Acta 1193: 226-234, 1994[Medline].

177.   Schmalzing, G., S. Kroner, M. Schachner, and S. Gloor. The adhesion molecule on glia (AMOG/beta 2) and alpha 1 subunits assemble to functional sodium pumps in Xenopus oocytes. J. Biol. Chem. 267: 20212-20216, 1992[Abstract/Free Full Text].

178.   Schmalzing, G., K. Ruhl, and S. M. Gloor. Isoform-specific interactions of Na,K-ATPase subunits are mediated via extracellular domains and carbohydrates. Proc. Natl. Acad. Sci. USA 94: 1136-1141, 1997[Abstract/Free Full Text].

179.   Schmidt, T. A., S. Hasselbach, J. S. Larsen, H. Bundgaard, M. Juhler, and K. Kjeldsen. Reduction of cerebral cortical [3H]ouabain binding site (Na,K-ATPase) density in dementia as evaluated in fresh human cerebral cortical biopsies. Brain Res. Cogn. Brain Res. 4: 281-287, 1996[Medline].

180.   Schneider, J. W., R. W. Mercer, M. Caplan, J. R. Emanuel, K. J. Sweadner, E. J. Benz, Jr., and R. Levenson. Molecular cloning of rat brain Na,K-ATPase alpha  subunit cDNA. Proc. Natl. Acad. Sci. USA 82: 6357-6361, 1985[Abstract/Free Full Text].

181.   Schneider, B. G., and E. Kraig. Na+, K+-ATPase of the photoreceptor: selective expression of alpha 3 and beta 2 isoforms. Exp. Eye Res. 51: 553-564, 1990[Medline].

182.   Schneider, B. G., A. W. Shyjan, and R. Levenson. Co-localization and polarized distribution of Na,K-ATPase alpha 3 and beta 2 subunits in photoreceptor cells. J. Histochem. Cytochem. 39: 507-517, 1991[Abstract].

183.   Shahedi, M., K. Laborde, L. Bussieres, M. Dechaux, and C. Sachs. Protein kinase C activation causes inhibition of Na/K-ATPase activity in Madin-Darby canine kidney epithelial (MDCK) cells. Pflügers Arch. 420: 269-274, 1992[Medline].

184.   Shamraj, O. I., I. L. Grupp, G. Grupp, D. Melvin, N. Gradoux, W. Kremers, J. B. Lingrel, and A. De Pover. Characterisation of Na,K-ATPase, its isoforms, and the inotropic response to ouabain in isolated failing human hearts. Cardiovasc. Res. 27: 2229-2237, 1993[Abstract/Free Full Text].

185.   Shamraj, O. I., and J. B. Lingrel. A putative fourth Na+,K+-ATPase alpha  subunit gene is expressed in testis. Proc. Natl. Acad. Sci. USA 91: 12952-12956, 1994[Abstract/Free Full Text].

186.   Shull, G. E., J. Greeb, and J. B. Lingrel. Molecular cloning of three distinct forms of the Na+,K+-ATPase alpha  subunit from rat brain. Biochemistry 25: 8125-8132, 1986[Medline].

187.   Shull, G. E., A. Schwartz, and J. B. Lingrel. Amino-acid sequence of the catalytic subunit of the (Na+ + K+)ATPase deduced from a complementary DNA. Nature 316: 691-695, 1985[Medline].

188.   Shyjan, A. W., V. A. Canfield, and R. Levenson. Evolution of the Na,K- and H,K-ATPase beta  subunit gene family: structure of the murine Na,K-ATPase beta 2 subunit gene. Genomics 11: 435-442, 1991[Medline].

189.   Shyjan, A. W., V. Cena, D. C. Klein, and R. Levenson. Differential expression and enzymatic properties of the Na+,K+-ATPase alpha 3 isoenzyme in rat pineal glands. Proc. Natl. Acad. Sci. USA 87: 1178-1182, 1990[Abstract/Free Full Text].

190.   Skou, J. C. The energy coupled exchange of Na+ for K+ across the cell membrane. The Na+, K(+)-pump. FEBS Lett. 268: 314-324, 1990[Medline].

191.   Skou, J. C., and M. Esmann. The Na,K-ATPase. J. Bioenerg. Biomembr. 24: 249-261, 1992[Medline].

192.   Stewart, D. J., and A. K. Sen. Role of cyclic GMP in cholinergic activation of Na-K pump in duck salt gland. Am. J. Physiol. 240 (Cell Physiol. 9): C207-C214, 1981[Abstract/Free Full Text].

193.   Sverdlov, E. D., G. S. Monastyrskaya, N. E. Broude, A. Ushkaryov Yu, R. L. Allikmets, A. M. Melkov, V. Smirnov Yu, I. V. Malyshev, I. E. Dulobova, and K. E. Petrukhin. The family of human Na+,K+-ATPase genes. No less than five genes and/or pseudogenes related to the alpha  subunit. FEBS Lett. 217: 275-278, 1987[Medline].

194.   Sweadner, K. J. Two molecular forms of (Na+ + K+)-stimulated ATPase in brain. Separation, and difference in affinity for strophanthidin. J. Biol. Chem. 254: 6060-6067, 1979[Abstract/Free Full Text].

195.   Sweadner, K. J. Enzymatic properties of separated isozymes of the Na,K-ATPase. Substrate affinities, kinetic cooperativity, and ion transport stoichiometry. J. Biol. Chem. 260: 11508-11513, 1985[Abstract/Free Full Text].

196.   Sweadner, K. J. Isozymes of the Na+/K+-ATPase. Biochim. Biophys. Acta 988: 185-220, 1989[Medline].

197.   Sweadner, K. J. Overview: subunit diversity in the Na,K-ATPase. Soc. Gen. Physiol. Ser. 46: 63-76, 1991[Medline].

198.   Sweadner, K. J. Overlapping and diverse distribution of Na-K ATPase isozymes in neurons and glia. Can. J. Physiol. Pharmacol. 70: S255-S259, 1992.

199.   Sweadner, K. J., and E. Arystarkhova. Constraints on models for the folding of the Na,K-ATPase. Ann. NY Acad. Sci. 671: 217-227, 1992[Medline].

200.   Takeda, K., S. Noguchi, S. Atsuko, and M. Kawamura. Functional activity of oligosaccharide-deficient Na,K-ATPase expressed in Xenopus oocytes. FEBS Lett. 238: 201-204, 1988[Medline].

201.   Takeyasu, K., V. Lemas, and D. M. Fambrough. Stability of Na+-K+-ATPase alpha  subunit isoforms in evolution. Am. J. Physiol. 259 (Cell Physiol. 28): C619-C630, 1990[Abstract/Free Full Text].

202.   Ten Cate, W. J., L. M. Curtis, and K. E. Rarey. Na,K-ATPase alpha  and beta  subunit isoform distribution in the rat cochlear and vestibular tissues. Hear. Res. 75: 151-160, 1994[Medline].

203.   Therien, A. G., N. B. Nestor, W. J. Ball, and R. Blostein. Tissue-specific versus isoform-specific differences in cation activation kinetics of the Na,K-ATPase. J. Biol. Chem. 271: 7104-7112, 1996[Abstract/Free Full Text].

204.   Therien, G., R. Goldshleger, S. J. D. Karlish, and R. Blostein. Tissue-specific distribution and modulatory role of the gamma  subunit of the Na,K-ATPase J. Biol. Chem. 272: 32628-32634, 1997[Abstract/Free Full Text].

205.   Thomas, R., P. Gray, and J. Andrews. Digitalis: its mode of action, receptor, and structure-activity relationships. Adv. Drug Delivery Res. 19: 313-550, 1990.

206.   Tumlin, J. A., C. A. Hoban, R. M. Medford, and J. M. Sands. Expression of Na-K-ATPase alpha  and beta  subunit mRNA and protein isoforms in the rat nephron. Am. J. Physiol. 266 (Renal Fluid Electrolyte Physiol. 35): F240-F245, 1994[Abstract/Free Full Text].

207.   Turi, A., J. Somogyi, and N. Mullner. The effect of micromolar Ca2+ on the activities of the different Na+/K+-ATPase isozymes in the rat myometrium. Biochem. Biophys. Res. Commun. 174: 969-974, 1991[Medline].

208.   Urayama, O., and M. Nakao. Organ specificity of rat sodium- and potassium-activated adenosine triphosphatase. J. Biochem. (Tokyo) 86: 1371-1381, 1979[Abstract/Free Full Text].

209.   Urayama, O., and K. J. Sweadner. Ouabain sensitivity of the alpha 3 isozyme of rat Na,K-ATPase. Biochem. Biophys. Res. Commun. 156: 796-800, 1988[Medline].

210.   Vasilets, L. A., and W. Schwarz. Structure-function relationships of cation binding in the Na+/K+-ATPase. Biochim. Biophys. Acta 1154: 201-222, 1993[Medline].

211.   Wilson, W. E. A comparison of Na-K-ATPases obtained from brains of adult and fetal rats. Int. J. Biochem. 12: 379-385, 1980[Medline].

212.   Yingst, D. R. Modulation of the Na,K-ATPase by Ca and intracellular proteins. Annu. Rev. Physiol. 50: 291-303, 1988[Medline].

213.   Yoon, K. L., and G. Guidotti. Studies on the membrane topology of the Na,K-ATPase. J. Biol. Chem. 269: 28249-28258, 1994[Abstract/Free Full Text].

214.   Yu, C. L., Z. J. Xie, A. Askari, and N. N. Modyanov. Enzymatic properties of human Na,K-ATPase alpha 1beta 3 isozyme. Arch. Biochem. Biophys. 345: 143-149, 1997[Medline].

215.   Zahler, R., M. Brines, M. Kashgarian, E. J. Benz, Jr., and M. Gilmore-Hebert. The cardiac conduction system in the rat expresses the alpha 2 and alpha 3 isoforms of the Na+,K+-ATPase. Proc. Natl. Acad. Sci. USA 89: 99-103, 1992[Abstract/Free Full Text].

216.   Zahler, R., M. Gilmore-Hebert, J. C. Baldwin, K. Franco, and E. J. Benz, Jr. Expression of alpha  isoforms of the Na,K-ATPase in human heart. Biochim. Biophys. Acta 1149: 189-194, 1993[Medline].

217.   Zahler, R., M. Gilmore-Hebert, W. Sun, and E. J. Benz. Na, K-ATPase isoform gene expression in normal and hypertrophied dog heart. Basic Res. Cardiol. 91: 256-266, 1996[Medline].

218.   Zamofing, D., B. C. Rossier, and K. Geering. Effects of tunicamycin on the cellular expression and structural arrangement of Na K-ATPase. Prog. Clin. Biol. Res. 268: 163-168, 1988.

219.   Zamofing, D., B. C. Rossier, and K. Geering. Inhibition of N-glycosylation affects transepithelial Na+ but not Na+-K+-ATPase transport. Am. J. Physiol. 256 (Cell Physiol. 25): C958-C966, 1989[Abstract/Free Full Text].

220.   Zhao, N., L. C. Lo, N. Berova, K. Nakanishi, A. A. Tymiak, J. H. Ludens, and G. T. Haupert, Jr. Na,K-ATPase inhibitors from bovine hypothalamus and human plasma are different from ouabain: nanogram scale CD structural analysis. Biochemistry 34: 9893-9896, 1995[Medline].

221.   Zlokovic, B. V., J. B. Mackic, L. Wang, J. G. McComb, and A. McDonough. Differential expression of Na,K-ATPase alpha  and beta  subunit isoforms at the blood-brain barrier and the choroid plexus. J. Biol. Chem. 268: 8019-8025, 1993[Abstract/Free Full Text].


Am J Physiol Renal Physiol 275(5):F633-F650
0002-9513/98 $5.00 Copyright © 1998 the American Physiological Society



This article has been cited by other articles:


Home page
Am. J. Physiol. Endocrinol. Metab.Home page
D. Galuska, O. Kotova, R. Barres, D. Chibalina, B. Benziane, and A. V. Chibalin
Altered expression and insulin-induced trafficking of Na+-K+-ATPase in rat skeletal muscle: effects of high-fat diet and exercise
Am J Physiol Endocrinol Metab, July 1, 2009; 297(1): E38 - E49.
[Abstract] [Full Text] [PDF]


Home page
PhysiologyHome page
T. Krupinski and G. J. Beitel
Unexpected Roles of the Na-K-ATPase and Other Ion Transporters in Cell Junctions and Tubulogenesis
Physiology, June 1, 2009; 24(3): 192 - 201.
[Abstract] [Full Text] [PDF]


Home page
HypertensionHome page
M. P. Blaustein, J. Zhang, L. Chen, H. Song, H. Raina, S. P. Kinsey, M. Izuka, T. Iwamoto, M. I. Kotlikoff, J. B. Lingrel, et al.
The Pump, the Exchanger, and Endogenous Ouabain: Signaling Mechanisms That Link Salt Retention to Hypertension
Hypertension, February 1, 2009; 53(2): 291 - 298.
[Full Text] [PDF]


Home page
Am. J. Physiol. Renal Physiol.Home page
C. Cao, K. Payne, W. Lee-Kwon, Z. Zhang, S. W. Lim, J. Hamlyn, M. P. Blaustein, H. M. Kwon, and T. L. Pallone
Chronic ouabain treatment induces vasa recta endothelial dysfunction in the rat
Am J Physiol Renal Physiol, January 1, 2009; 296(1): F98 - F106.
[Abstract] [Full Text] [PDF]


Home page
Exp PhysiolHome page
K. T. Murphy, I. Medved, M. J. Brown, D. Cameron-Smith, and M. J. McKenna
Antioxidant treatment with N-acetylcysteine regulates mammalian skeletal muscle Na+-K+-ATPase {alpha} gene expression during repeated contractions
Exp Physiol, December 1, 2008; 93(12): 1239 - 1248.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Renal Physiol.Home page
R. J. Clifford and J. H. Kaplan
{beta}-Subunit overexpression alters the stoicheometry of assembled Na-K-ATPase subunits in MDCK cells
Am J Physiol Renal Physiol, November 1, 2008; 295(5): F1314 - F1323.
[Abstract] [Full Text] [PDF]


Home page
J. Physiol.Home page
J. A. Armitage, S. Gupta, C. Wood, R. I. Jensen, A.-M. Samuelsson, W. Fuller, M. J. Shattock, L. Poston, and P. D. Taylor
Maternal dietary supplementation with saturated, but not monounsaturated or polyunsaturated fatty acids, leads to tissue-specific inhibition of offspring Na+,K+-ATPase
J. Physiol., October 15, 2008; 586(20): 5013 - 5022.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
S. P. Soltoff and L. Hedden
Regulation of ERK1/2 by ouabain and Na-K-ATPase-dependent energy utilization and AMPK activation in parotid acinar cells
Am J Physiol Cell Physiol, September 1, 2008; 295(3): C590 - C599.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Endocrinol. Metab.Home page
H. J. Green, T. A. Duhamel, R. D. Stewart, A. R. Tupling, and J. Ouyang
Dissociation between changes in muscle Na+-K+-ATPase isoform abundance and activity with consecutive days of exercise and recovery
Am J Physiol Endocrinol Metab, April 1, 2008; 294(4): E761 - E767.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
C. K. Tipsmark
Identification of FXYD protein genes in a teleost: tissue-specific expression and response to salinity change
Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2008; 294(4): R1367 - R1378.
[Abstract] [Full Text] [PDF]


Home page
J. Physiol.Home page
N. Nordsborg, J. Ovesen, M. Thomassen, M. Zangenberg, C. Jons, F. M. Iaia, J. J. Nielsen, and J. Bangsbo
Effect of dexamethasone on skeletal muscle Na+,K+ pump subunit specific expression and K+ homeostasis during exercise in humans
J. Physiol., March 1, 2008; 586(5): 1447 - 1459.
[Abstract] [Full Text] [PDF]


Home page
J. Physiol.Home page
K. S. Richards, K. Bommert, G. Szabo, and R. Miles
Differential expression of Na+/K+-ATPase {alpha}-subunits in mouse hippocampal interneurones and pyramidal cells
J. Physiol., December 1, 2007; 585(2): 491 - 505.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
L. Liu, X. Zhao, S. V. Pierre, and A. Askari
Association of PI3K-Akt signaling pathway with digitalis-induced hypertrophy of cardiac myocytes
Am J Physiol Cell Physiol, November 1, 2007; 293(5): C1489 - C1497.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
S. N. Orlov and A. A. Mongin
Salt-sensing mechanisms in blood pressure regulation and hypertension
Am J Physiol Heart Circ Physiol, October 1, 2007; 293(4): H2039 - H2053.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
T. Feldmann, V. Glukmann, E. Medvenev, U. Shpolansky, D. Galili, D. Lichtstein, and H. Rosen
Role of endosomal Na+-K+-ATPase and cardiac steroids in the regulation of endocytosis
Am J Physiol Cell Physiol, September 1, 2007; 293(3): C885 - C896.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Endocrinol. Metab.Home page
H. J. Green, T. A. Duhamel, G. P. Holloway, J. W. Moule, J. Ouyang, D. Ranney, and A. R. Tupling
Muscle Na+-K+-ATPase response during 16 h of heavy intermittent cycle exercise
Am J Physiol Endocrinol Metab, August 1, 2007; 293(2): E523 - E530.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
W. Schoner and G. Scheiner-Bobis
Endogenous and exogenous cardiac glycosides: their roles in hypertension, salt metabolism, and cell growth
Am J Physiol Cell Physiol, August 1, 2007; 293(2): C509 - C536.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
T. J. Pritchard, M. Parvatiyar, D. P. Bullard, R. M. Lynch, J. N. Lorenz, and R. J. Paul
Transgenic mice expressing Na+-K+-ATPase in smooth muscle decreases blood pressure
Am J Physiol Heart Circ Physiol, August 1, 2007; 293(2): H1172 - H1182.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
H. J. Green, T. A. Duhamel, K. P. Foley, J. Ouyang, I. C. Smith, and R. D. Stewart
Glucose supplements increase human muscle in vitro Na+-K+-ATPase activity during prolonged exercise
Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2007; 293(1): R354 - R362.
[Abstract] [Full Text] [PDF]


Home page
Clin. Chem.Home page
K. Ihenetu, H. M. Qazzaz, F. Crespo, R. Fernandez-Botran, and R. Valdes Jr
Digoxin-Like Immunoreactive Factors Induce Apoptosis in Human Acute T-Cell Lymphoblastic Leukemia
Clin. Chem., July 1, 2007; 53(7): 1315 - 1322.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Renal Physiol.Home page
A. Edwards and T. L. Pallone
Modification of cytosolic calcium signaling by subplasmalemmal microdomains
Am J Physiol Renal Physiol, June 1, 2007; 292(6): F1827 - F1845.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Renal Physiol.Home page
M. D. Laughery, R. J. Clifford, Y. Chi, and J. H. Kaplan
Selective basolateral localization of overexpressed Na-K-ATPase beta1- and beta2- subunits is disrupted by butryate treatment of MDCK cells
Am J Physiol Renal Physiol, June 1, 2007; 292(6): F1718 - F1725.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
K. L. Lansbery, L. C. Burcea, M. L. Mendenhall, and R. W. Mercer
Cytoplasmic targeting signals mediate delivery of phospholemman to the plasma membrane
Am J Physiol Cell Physiol, May 1, 2006; 290(5): C1275 - C1286.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
J. Li, L. I. Sinoway, and Y.-C. Ng
Aging augments interstitial K+ concentrations in active muscle of rats
J Appl Physiol, April 1, 2006; 100(4): 1158 - 1163.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
M. P. Blaustein, J. Zhang, L. Chen, and B. P. Hamilton
How does salt retention raise blood pressure?
Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2006; 290(3): R514 - R523.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
F. J. Haddy, P. M. Vanhoutte, and M. Feletou
Role of potassium in regulating blood flow and blood pressure
Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2006; 290(3): R546 - R552.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
D. Plourde and S. P. Soltoff
Ouabain potentiates the activation of ERK1/2 by carbachol in parotid gland epithelial cells; inhibition of ERK1/2 reduces Na+-K+-ATPase activity
Am J Physiol Cell Physiol, March 1, 2006; 290(3): C702 - C710.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Renal Physiol.Home page
K. Geering
FXYD proteins: new regulators of Na-K-ATPase
Am J Physiol Renal Physiol, February 1, 2006; 290(2): F241 - F250.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
K. T. Murphy, A. C. Petersen, C. Goodman, X. Gong, J. A. Leppik, A. P. Garnham, D. Cameron-Smith, R. J. Snow, and M. J. McKenna
Prolonged submaximal exercise induces isoform-specific Na+-K+-ATPase mRNA and protein responses in human skeletal muscle
Am J Physiol Regulatory Integrative Comp Physiol, February 1, 2006; 290(2): R414 - R424.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
S. D. E. Sandiford, H. J. Green, and J. Ouyang
Mechanisms underlying increases in rat soleus Na+-K+-ATPase activity by induced contractions
J Appl Physiol, December 1, 2005; 99(6): 2222 - 2232.
[Abstract] [Full Text] [PDF]


Home page
J. Physiol.Home page
J. Zhang, M. Y. Lee, M. Cavalli, L. Chen, R. Berra-Romani, C. W. Balke, G. Bianchi, P. Ferrari, J. M. Hamlyn, T. Iwamoto, et al.
Sodium pump {alpha}2 subunits control myogenic tone and blood pressure in mice
J. Physiol., November 15, 2005; 569(1): 243 - 256.
[Abstract] [Full Text] [PDF]


Home page
J. Physiol.Home page
G. Ebensperger, R. Ebensperger, E. A Herrera, R. A Riquelme, E. M Sanhueza, F. Lesage, J. J Marengo, R. I Tejo, A. J Llanos, and R. V Reyes
Fetal brain hypometabolism during prolonged hypoxaemia in the llama
J. Physiol., September 15, 2005; 567(3): 963 - 975.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
D. J. Barr, H. J. Green, D. S. Lounsbury, J. W. E. Rush, and J. Ouyang
Na+-K+-ATPase properties in rat heart and skeletal muscle 3 mo after coronary artery ligation
J Appl Physiol, August 1, 2005; 99(2): 656 - 664.
[Abstract] [Full Text] [PDF]


Home page
J. Physiol.Home page
H. Lin, S. Ozaki, N. Fujishiro, K. Takeda, I. Imanaga, G. D Prestwich, and M. Inoue
Subunit composition and role of Na+,K+-ATPases in adrenal chromaffin cells
J. Physiol., April 1, 2005; 564(1): 161 - 172.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
L. Liu, J. Abramowitz, A. Askari, and J. C. Allen
Role of caveolae in ouabain-induced proliferation of cultured vascular smooth muscle cells of the synthetic phenotype
Am J Physiol Heart Circ Physiol, November 1, 2004; 287(5): H2173 - H2182.
[Abstract] [Full Text] [PDF]


Home page
Physiol. Rev.Home page
M. Cereijido, R. G. Contreras, and L. Shoshani
Cell Adhesion, Polarity, and Epithelia in the Dawn of Metazoans
Physiol Rev, October 1, 2004; 84(4): 1229 - 1262.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
H. J. Green, D. J. Barr, J. R. Fowles, S. D. Sandiford, and J. Ouyang
Malleability of human skeletal muscle Na+-K+-ATPase pump with short-term training
J Appl Physiol, July 1, 2004; 97(1): 143 - 148.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
N. B. Pestov, T. V. Korneenko, R. Radkov, H. Zhao, M. I. Shakhparonov, and N. N. Modyanov
Identification of the {beta}-subunit for nongastric H-K-ATPase in rat anterior prostate
Am J Physiol Cell Physiol, June 1, 2004; 286(6): C1229 - C1237.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
J. Palacios, E. T. Marusic, N. C. Lopez, M. Gonzalez, and L. Michea
Estradiol-induced expression of Na+-K+-ATPase catalytic isoforms in rat arteries: gender differences in activity mediated by nitric oxide donors
Am J Physiol Heart Circ Physiol, May 1, 2004; 286(5): H1793 - H1800.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
Y. Shao and F. Ismail-Beigi
Control of Na+-K+-ATPase {beta}1-subunit expression: role of 3'-untranslated region
Am J Physiol Cell Physiol, March 1, 2004; 286(3): C580 - C585.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
J. R. Fowles, H. J. Green, and J. Ouyang
Na+-K+-ATPase in rat skeletal muscle: content, isoform, and activity characteristics
J Appl Physiol, January 1, 2004; 96(1): 316 - 326.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
Y.-C. Ng, M. Nagarajan, K. N. Jew, L. C. Mace, and R. L. Moore
Exercise training differentially modifies age-associated alteration in expression of Na+-K+-ATPase subunit isoforms in rat skeletal muscles
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 2003; 285(4): R733 - R740.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Lung Cell. Mol. Physiol.Home page
J. Lei, S. Nowbar, C. N. Mariash, and D. H. Ingbar
Thyroid hormone stimulates Na-K-ATPase activity and its plasma membrane insertion in rat alveolar epithelial cells
Am J Physiol Lung Cell Mol Physiol, September 1, 2003; 285(3): L762 - L772.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
J. Yu, Y. F. Wang, and J. W. Zhang
Structure of slowly adapting pulmonary stretch receptors in the lung periphery
J Appl Physiol, July 1, 2003; 95(1): 385 - 393.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
B. Helwig, K. M. Schreurs, J. Hansen, K. S. Hageman, M. G. Zbreski, R. M. McAllister, K. E. Mitchell, and T. I. Musch
Training-induced changes in skeletal muscle Na+-K+ pump number and isoform expression in rats with chronic heart failure
J Appl Physiol, June 1, 2003; 94(6): 2225 - 2236.
[Abstract] [Full Text] [PDF]


Home page
IOVSHome page
S. Rauz, E. A. Walker, S. V. Hughes, M. Coca-Prados, M. Hewison, P. I. Murray, and P. M. Stewart
Serum- and Glucocorticoid-Regulated Kinase Isoform-1 and Epithelial Sodium Channel Subunits in Human Ocular Ciliary Epithelium
Invest. Ophthalmol. Vis. Sci., April 1, 2003; 44(4): 1643 - 1651.
[Abstract] [Full Text] [PDF]


Home page
J. Neurosci.Home page
M. J. Palladino, J. E. Bower, R. Kreber, and B. Ganetzky
Neural Dysfunction and Neurodegeneration in Drosophila Na+/K+ ATPase Alpha Subunit Mutants
J. Neurosci., February 15, 2003; 23(4): 1276 - 1286.
[Abstract] [Full Text] [PDF]


Home page
J. Biol. Chem.Home page
A. E. Moseley, S. P. Lieske, R. K. Wetzel, P. F. James, S. He, D. A. Shelly, R. J. Paul, G. P. Boivin, D. P. Witte, J. M. Ramirez, et al.
The Na,K-ATPase alpha 2 Isoform Is Expressed in Neurons, and Its Absence Disrupts Neuronal Activity in Newborn Mice
J. Biol. Chem., February 7, 2003; 278(7): 5317 - 5324.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
V. A. Golovina, H. Song, P. F. James, J. B. Lingrel, and M. P. Blaustein
Na+ pump alpha 2-subunit expression modulates Ca2+ signaling
Am J Physiol Cell Physiol, February 1, 2003; 284(2): C475 - C486.
[Abstract] [Full Text] [PDF]


Home page
J. Neurosci.Home page
D. Z. Ellis, J. Rabe, and K. J. Sweadner
Global Loss of Na,K-ATPase and Its Nitric Oxide-Mediated Regulation in a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis
J. Neurosci., January 1, 2003; 23(1): 43 - 51.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
J. R. Fowles, H. J. Green, J. D. Schertzer, and A. R. Tupling
Reduced activity of muscle Na+-K+-ATPase after prolonged running in rats
J Appl Physiol, November 1, 2002; 93(5): 1703 - 1708.
[Abstract] [Full Text] [PDF]


Home page
J. Appl. Physiol.Home page
J. I. Sznajder, P. Factor, and D. H. Ingbar
Lung Edema Clearance: 20 Years of Progress: Invited Review: Lung edema clearance: role of Na+-K+-ATPase
J Appl Physiol, November 1, 2002; 93(5): 1860 - 1866.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Renal Physiol.Home page
S. V. Pierre, M.-J. Duran, D. L. Carr, and T. A. Pressley
Structure/function analysis of Na+-K+-ATPase central isoform-specific region: involvement in PKC regulation
Am J Physiol Renal Physiol, November 1, 2002; 283(5): F1066 - F1074.
[Abstract] [Full Text] [PDF]


Home page
J. Pharmacol. Exp. Ther.Home page
W. Kang and M. Weiss
Digoxin Uptake, Receptor Heterogeneity, and Inotropic Response in the Isolated Rat Heart: A Comprehensive Kinetic Model
J. Pharmacol. Exp. Ther., August 1, 2002; 302(2): 577 - 583.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
K. A. Dora, N. T. Ings, and C. J. Garland
KCa channel blockers reveal hyperpolarization and relaxation to K+ in rat isolated mesenteric artery
Am J Physiol Heart Circ Physiol, August 1, 2002; 283(2): H606 - H614.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Renal Physiol.Home page
A. A. McDonough, C. B. Thompson, and J. H. Youn
Skeletal muscle regulates extracellular potassium
Am J Physiol Renal Physiol, June 1, 2002; 282(6): F967 - F974.
[Abstract] [Full Text] [PDF]


Home page
Cereb CortexHome page
N. Cholet, L. Pellerin, P. J. Magistretti, and E. Hamel
Similar Perisynaptic Glial Localization for the Na+,K+-ATPase {alpha}2 Subunit and the Glutamate Transporters GLAST and GLT-1 in the Rat Somatosensory Cortex
Cereb Cortex, May 1, 2002; 12(5): 515 - 525.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
G. Sweeney, W. Niu, V. A. Canfield, R. Levenson, and A. Klip
Insulin increases plasma membrane content and reduces phosphorylation of Na+-K+ pump alpha 1-subunit in HEK-293 cells
Am J Physiol Cell Physiol, December 1, 2001; 281(6): C1797 - C1803.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
E. Songu-Mize, N. Sevieux, X. Liu, and M. Jacobs
Effect of short-term cyclic stretch on sodium pump activity in aortic smooth muscle cells
Am J Physiol Heart Circ Physiol, November 1, 2001; 281(5): H2072 - H2078.
[Abstract] [Full Text] [PDF]


Home page
Physiol. Rev.Home page
H. G. Glitsch
Electrophysiology of the Sodium-Potassium-ATPase in Cardiac Cells
Physiol Rev, October 1, 2001; 81(4): 1791 - 1826.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
J. Muller-Ehmsen, P. Juvvadi, C. B. Thompson, L. Tumyan, M. Croyle, J. B. Lingrel, R. H. G. Schwinger, A. A. McDonough, and R. A. Farley
Ouabain and substrate affinities of human Na+-K+-ATPase alpha 1beta 1, alpha 2beta 1, and alpha 3beta 1 when expressed separately in yeast cells
Am J Physiol Cell Physiol, October 1, 2001; 281(4): C1355 - C1364.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
I. Lavelin, N. Meiri, O. Genina, R. Alexiev, and M. Pines
Na+-K+-ATPase gene expression in the avian eggshell gland: distinct regulation in different cell types
Am J Physiol Regulatory Integrative Comp Physiol, October 1, 2001; 281(4): R1169 - R1176.
[Abstract] [Full Text] [PDF]


Home page
J. Pharmacol. Exp. Ther.Home page
J.-Q. Kong, J. Meng, P. S. Biser, W. W. Fleming, and D. A. Taylor
Cellular Depolarization of Neurons in the Locus Ceruleus Region of the Guinea Pig Associated with the Development of Tolerance to Opioids
J. Pharmacol. Exp. Ther., September 1, 2001; 298(3): 909 - 916.
[Abstract] [Full Text]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
S. He, D. A. Shelly, A. E. Moseley, P. F. James, J. H. James, R. J. Paul, and J. B. Lingrel
The {alpha}1- and {alpha}2-isoforms of Na-K-ATPase play different roles in skeletal muscle contractility
Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2001; 281(3): R917 - R925.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Renal Physiol.Home page
R. K. Wetzel and K. J. Sweadner
Immunocytochemical localization of Na-K-ATPase alpha - and gamma -subunits in rat kidney
Am J Physiol Renal Physiol, September 1, 2001; 281(3): F531 - F545.
[Abstract] [Full Text] [PDF]


Home page
J. Nutr.Home page
B. P. Bode
Recent Molecular Advances in Mammalian Glutamine Transport
J. Nutr., September 1, 2001; 131(9): 2475S - 2485.
[Abstract] [Full Text] [PDF]


Home page
Physiol. GenomicsHome page
D. H. JONES, M. C. GOLDING, K. J. BARR, G.-H. FONG, and G. M. KIDDER
The mouse Na+-K+-ATPase {gamma}-subunit gene (Fxyd2) encodes three developmentally regulated transcripts
Physiol Genomics, August 28, 2001; 6(3): 129 - 135.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
J. A. Wong, A. R. Gosmanov, E. G. Schneider, and D. B. Thomason
Insulin-independent, MAPK-dependent stimulation of NKCC activity in skeletal muscle
Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2001; 281(2): R561 - R571.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
N. Sevieux, J. Alam, and E. Songu-Mize
Effect of cyclic stretch on {alpha}-subunit mRNA expression of Na+-K+-ATPase in aortic smooth muscle cells
Am J Physiol Cell Physiol, June 1, 2001; 280(6): C1555 - C1560.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
K. A. Dora and C. J. Garland
Properties of smooth muscle hyperpolarization and relaxation to K+ in the rat isolated mesenteric artery
Am J Physiol Heart Circ Physiol, June 1, 2001; 280(6): H2424 - H2429.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
A. Aydemir-Koksoy and J. C. Allen
Regulation of Na+ pump expression by vascular smooth muscle cells
Am J Physiol Heart Circ Physiol, April 1, 2001; 280(4): H1869 - H1874.
[Abstract] [Full Text] [PDF]


Home page
IOVSHome page
R. K. Wetzel and K. J. Sweadner
Immunocytochemical Localization of NaK-ATPase Isoforms in the Rat and Mouse Ocular Ciliary Epithelium
Invest. Ophthalmol. Vis. Sci., March 1, 2001; 42(3): 763 - 769.
[Abstract] [Full Text]


Home page
DiabetesHome page
S. Shen, A. Alt, E. Wertheimer, M. Gartsbein, T. Kuroki, M. Ohba, L. Braiman, S. R. Sampson, and T. Tennenbaum
PKC{delta} Activation: A Divergence Point in the Signaling of Insulin and IGF-1--Induced Proliferation of Skin Keratinocytes
Diabetes, February 1, 2001; 50(2): 255 - 264.
[Abstract] [Full Text]


Home page
Am. J. Physiol. Cell Physiol.Home page
D. R. Yingst, J. Davis, and R. Schiebinger
Effects of extracellular calcium and potassium on the sodium pump of rat adrenal glomerulosa cells
Am J Physiol Cell Physiol, January 1, 2001; 280(1): C119 - C125.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
A. G. Therien and R. Blostein
Mechanisms of sodium pump regulation
Am J Physiol Cell Physiol, September 1, 2000; 279(3): C541 - C566.
[Abstract] [Full Text] [PDF]


Home page
J. Histochem. Cytochem.Home page
G. Blanco, G. Sánchez, R. J. Melton, W. G. Tourtellotte, and R. W. Mercer
The {alpha}4 Isoform of the Na,K-ATPase Is Expressed in the Germ Cells of the Testes
J. Histochem. Cytochem., August 1, 2000; 48(8): 1023 - 1032.
[Abstract] [Full Text]


Home page
Am. J. Physiol. Heart Circ. Physiol.Home page
A. Arnon, J. M. Hamlyn, and M. P. Blaustein
Ouabain augments Ca2+ transients in arterial smooth muscle without raising cytosolic Na+
Am J Physiol Heart Circ Physiol, August 1, 2000; 279(2): H679 - H691.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
C. P. Cutler, S. Brezillon, S. Bekir, I. L. Sanders, N. Hazon, and G. Cramb
Expression of a duplicate Na,K-ATPase beta 1-isoform in the European eel (Anguilla anguilla)
Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2000; 279(1): R222 - R229.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
M. Johansson, T. Jansson, and T. L. Powell
Na+-K+-ATPase is distributed to microvillous and basal membrane of the syncytiotrophoblast in human placenta
Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2000; 279(1): R287 - R294.
[Abstract] [Full Text] [PDF]


Home page
Clin. Chem.Home page
A. M. Rose, H. M. Qazzaz, N. Zolotarjova, B. J. Mellett, A. W. Martin, and R. Valdes Jr
Sodium Pump Isoforms in Xenotransplantation: Importance of Biochemical Compatibility
Clin. Chem., February 1, 2000; 46(2): 234 - 241.
[Abstract] [Full Text] [PDF]


Home page
J. Biol. Chem.Home page
G. Crambert, U. Hasler, A. T. Beggah, C. Yu, N. N. Modyanov, J.-D. Horisberger, L. Lelievre, and K. Geering
Transport and Pharmacological Properties of Nine Different Human Na,K-ATPase Isozymes
J. Biol. Chem., January 21, 2000; 275(3): 1976 - 1986.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
A. Arnon, J. M. Hamlyn, and M. P. Blaustein
Na+ entry via store-operated channels modulates Ca2+ signaling in arterial myocytes
Am J Physiol Cell Physiol, January 1, 2000; 278(1): C163 - C173.
[Abstract] [Full Text] [PDF]


Home page
J. Biol. Chem.Home page
E. Arystarkhova, R. K. Wetzel, N. K. Asinovski, and K. J. Sweadner
The gamma Subunit Modulates Na+ and K+ Affinity of the Renal Na,K-ATPase
J. Biol. Chem., November 19, 1999; 274(47): 33183 - 33185.
[Abstract] [Full Text] [PDF]


Home page
J. Neurosci.Home page
R. K. Wetzel, E. Arystarkhova, and K. J. Sweadner
Cellular and Subcellular Specification of Na,K-ATPase alpha and beta Isoforms in the Postnatal Development of Mouse Retina
J. Neurosci., November 15, 1999; 19(22): 9878 - 9889.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
A. G. Therien and R. Blostein
K+/Na+ antagonism at cytoplasmic sites of Na+-K+-ATPase: a tissue-specific mechanism of sodium pump regulation
Am J Physiol Cell Physiol, November 1, 1999; 277(5): C891 - C898.
[Abstract] [Full Text] [PDF]


Home page
Proc. Natl. Acad. Sci. USAHome page
B. Sun, P. Xu, and P. M. Salvaterra
Dynamic visualization of nervous system in live Drosophila
PNAS, August 31, 1999; 96(18): 10438 - 10443.
[Abstract] [Full Text] [PDF]


Home page
J. Biol. Chem.Home page
A. L. Woo, P. F. James, and J. B Lingrel
Sperm Motility Is Dependent on a Unique Isoform of the Na,K-ATPase
J. Biol. Chem., June 30, 2000; 275(27): 20693 - 20699.
[Abstract] [Full Text] [PDF]


Home page
J. Biol. Chem.Home page
L. Segall, S. E. Daly, and R. Blostein
Mechanistic Basis for Kinetic Differences between the Rat alpha 1, alpha 2, and alpha 3 Isoforms of the Na,K-ATPase
J. Biol. Chem., August 17, 2001; 276(34): 31535 - 31541.
[Abstract] [Full Text] [PDF]


Home page
Proc. Natl. Acad. Sci. USAHome page
W. Wang, D. J. Seward, L. Li, J. L. Boyer, and N. Ballatori
Expression cloning of two genes that together mediate organic solute and steroid transport in the liver of a marine vertebrate
PNAS, July 31, 2001; 98(16): 9431 - 9436.
[Abstract] [Full Text] [PDF]


Home page
Genome ResHome page
F. C. Serluca, A. Sidow, J. D. Mably, and M. C. Fishman
Partitioning of Tissue Expression Accompanies Multiple Duplications of the Na+/K+ ATPase alpha Subunit Gene
Genome Res., October 1, 2001; 11(10): 1625 - 1631.
[Abstract] [Full Text] [PDF]


Home page
Am. J. Physiol. Cell Physiol.Home page
N. B. Pestov, T. V. Korneenko, G. Adams, M. Tillekeratne, M. I. Shakhparonov, and N. N. Modyanov
Nongastric H-K-ATPase in rodent prostate: lobe-specific expression and apical localization
Am J Physiol Cell Physiol, April 1, 2002; 282(4): C907 - C916.
[Abstract] [Full Text] [PDF]


This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Blanco, G.
Right arrow Articles by Mercer, R. W.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Blanco, G.
Right arrow Articles by Mercer, R. W.


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online