Electrophysiology of collecting duct H+ secretion: effect of inhibitors

Segments of the outer medullary collecting duct were isolated from the inner stripe of the rabbit kidney (OMCDi), perfused in vitro, and impaled across their basolateral membranes with voltage-recording microelectrodes. The disulfonic stilbene 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) (10(-4) M) and the carbonic anhydrase inhibitor acetazolamide (10(-4) M) depolarized the lumen-positive transepithelial voltage (VT) toward 0 mV when added to the bath solution. Concurrently, the basolateral membrane voltage (Vbl) hyperpolarized. The hyperpolarization of Vbl, which averaged 19.3 +/- 2.9 mV (n = 11) for SITS and 22.7 +/- 3.5 mV (n = 11) for acetazolamide, was not due to an alteration in the ionic selectivity of the basolateral membrane, which was highly Cl- selective. The hyperpolarization of Vbl could best be explained by a decrease in the intracellular [Cl-], and the associated shift in the emf for Cl- (ECl) across the basolateral membrane. The decrease in intracellular [Cl-] could be attributed to inhibition of a Cl-HCO3 antiporter in the basolateral membrane. SITS appeared to inhibit this antiporter directly, whereas the effect of acetazolamide was indirect, probably secondary to a decrease in the intracellular [HCO3-]. Finally, both SITS and acetazolamide induced or unmasked an electroneutral K+-coupled transport system in the basolateral membrane.