ENaC inhibition stimulates HCl secretion in the mouse cortical collecting duct. II. Bafilomycin-sensitive H+ secretion.

Epithelial Na⁺ channel (ENaC) blockade stimulates stilbene-sensitive conductive Cl^- secretion in the mouse cortical collecting duct (CCD). This study's purpose was to determine the co-ion that accompanies benzamil- and DIDS-sensitive Cl^- flux. Thus transepithelial voltage, V_T, as well as total CO₂ (tCO₂) and Cl^- flux were measured in CCDs from aldosterone-treated mice consuming a NaCl-replete diet. We reasoned that if stilbene inhibitors (DIDS) reduce conductive anion secretion they should reduce the lumen-negative V_T. However, during ENaC blockade (benzamil, 3μM), DIDS (100μM) application to the perfusate reduced net H⁺ secretion, which increased the lumennegative V_T. Conversely, ENaC blockade alone stimulated H⁺ secretion, which reduced the lumen-negative V_T. Application of an ENaC inhibitor to the perfusate reduced the lumen-negative V_T, increased intercalated cell intracellular pH, and reduced net tCO₂ secretion. However, benzamil did not change tCO₂ flux during apical H⁺- ATPase blockade (bafilomycin, 5 nM). The increment in H⁺ secretion observed with benzamil application contributes to the fall in V_T observed with application of this diuretic. As such, ENaC blockade reduces the lumen-negative V_T by inhibiting conductive Na⁺ absorption and by stimulating H⁺ secretion by type A intercalated cells. In conclusion, 1) in CCDs from aldosterone-treated mice, benzamil application stimulates HCl secretion mediated by the apical H⁺- ATPase and a yet to be identified conductive Cl^- transport pathway; 2) benzamil-induced HCl secretion is reversed with the application of stilbene inhibitors or H⁺-ATPase inhibitors to the perfusate; and 3) benzamil reduces V_T not only by inhibiting conductive Na⁺ absorption, but also by stimulating H⁺ secretion. [ABSTRACT FROM AUTHOR]