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Am J Physiol Renal Physiol 277: F567-F574, 1999;
0363-6127/99 $5.00
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Vol. 277, Issue 4, F567-F574, October 1999

Mechanisms of HCOminus 3 secretion in the rabbit connecting segment

Shuichi Tsuruoka and George J. Schwartz

Department of Pediatrics, University of Rochester School of Medicine, Rochester, New York 14642

The connecting tubule (CNT) contains alpha -(H+-secreting) and beta -(HCO-3-secreting) intercalated cells and is therefore likely to contribute to acid-base homeostasis. To characterize the mechanisms of HCO-3 transport in the rabbit CNT, in which there is little definitive data presently available, we microdissected the segments from the superficial cortical labyrinth, perfused them in vitro, measured net HCO-3 transport (JHCO-3) by microcalorimetry, and examined the effects of several experimental maneuvers. Mean ± SE basal JHCO-3 was -3.4 ± 0.1 pmol · min-1 · mm-1 (net HCO-3 secretion), and transepithelial voltage was -13 ± 1 mV (n = 47). Net HCO-3 secretion was markedly inhibited by removal of luminal Cl- or application of basolateral H+-ATPase inhibitors (bafilomycin or concanamycin), maneuvers that inhibit beta -intercalated cell function. Net HCO-3 secretion was not affected by inhibitors of alpha -intercalated cell function (basolateral Cl- removal, basolateral DIDS, or luminal H+-ATPase inhibitors). Net HCO-3 secretion was stimulated by isoproterenol and inhibited by acetazolamide. These data indicate that 1) CNTs secrete HCO-3 via an apical DIDS-insensitive Cl-/HCO-3 exchanger, mediated by a basolateral bafilomycin- and concanamycin-sensitive H+-ATPase; 2) inhibition of cytosolic carbonic anhydrase decreases HCO-3 secretion; and 3) stimulation of beta -adrenergic receptors increases HCO-3 secretion. The failure to influence net HCO-3 transport by inhibiting alpha -intercalated cell apical H+-ATPases or basolateral Cl-/HCO-3 exchange suggests that the CNT has fewer functioning alpha -intercalated cells than the cortical collecting duct. These are the first studies to examine the rate and mechanisms of HCO-3 secretion by the rabbit CNT; this is clearly an important segment in mediating acid-base homeostasis.

intercalated cell; distal nephron; collecting duct; hydrogen-adenosine 5'-triphosphatase; carbonic anhydrase; chloride/bicarbonate exchange; isoproterenol; microperfusion in vitro; bafilomycin; concanamycin; acetazolamide; 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid; Sch-28080


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