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Am J Physiol Renal Physiol 287: F932-F939, 2004. First published August 3, 2004; doi:10.1152/ajprenal.00131.2004
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Involvement of cytosolic Cl– in osmoregulation of {alpha}-ENaC gene expression

Naomi Niisato,1 Douglas C. Eaton,2 and Yoshinori Marunaka1,3

Departments of 1Molecular Cell Physiology and 3Respiratory Molecular Medicine, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan; and 2Center for Cell and Molecular Signaling and Department of Physiology, Emory University School of Medicine, Atlanta, Georgia 30322

Submitted 12 April 2004 ; accepted in final form 23 June 2004

Hypotonicity stimulates transepithelial Na+ reabsorption in renal A6 cells, but the mechanism for this stimulation is not fully understood. In the present study, we found that hypotonicity stimulated Na+ reabsorption through increases in mRNA expression of the {alpha}-subunit of the epithelial Na+ channel ({alpha}-ENaC). Hypotonicity decreases cytosolic Cl– concentration; therefore, we hypothesized that hypotonicity-induced decreases in cytosolic Cl– concentration could act as a signal to regulate Na+ reabsorption through changes in {alpha}-ENaC mRNA expression. Treatment with the flavone apigenin, which activates the Na+-K+-2Cl– cotransporter and increases cytosolic Cl– concentration, markedly suppressed the hypotonicity-induced increase in {alpha}-ENaC mRNA expression. On the other hand, blockade of the Na+-K+-2Cl– cotransporter decreases cytosolic Cl– concentration and increased {alpha}-ENaC mRNA expression and Na+ reabsorption. Blocking Cl– channels with 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) inhibited the hypotonicity-induced decrease in cytosolic Cl– concentration and suppressed the hypotonicity-induced increase in {alpha}-ENaC mRNA expression. Coapplication of NPPB and apigenin synergistically suppressed {alpha}-ENaC mRNA expression. Thus, in every case, changes in cytosolic Cl– concentration were associated with changes in {alpha}-ENaC mRNA expression and changes in Na+ reabsorption: decreases in cytosolic Cl– concentration increased {alpha}-ENaC mRNA and increased Na+ reabsorption, whereas increases in cytosolic Cl– concentration decreased {alpha}-ENaC mRNA and decreased Na+ reabsorption. These findings support the hypothesis that changes in cytosolic Cl– concentration are an important and novel signal in hypotonicity-induced regulation of {alpha}-ENaC expression and Na+ reabsorption.

epithelial sodium channel; sodium transport; epithelial sodium channel regulation; hypotonicity; sodium-potassium-2 chloride cotransporter; chloride channels


Address for reprint requests and other correspondence: Y. Marunaka, Dept. of Molecular Cell Physiology, Kyoto Prefectural Univ. of Medicine, Kyoto 602-8566, Japan (E-mail: marunaka{at}koto.kpu-m.ac.jp)




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