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

摘要

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 ben-zamil- and DIDS-sensitive Cl~- flux. Thus transepithelial voltage, V_T, as well as total CO_2 (tCO_2) 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, 3 muM), DIDS (100 muM) application to the perfusate reduced net H~+ secretion, which increased the lumen-negative 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 tCO_2 secretion. However, benzamil did not change tCO_2 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 HC1 secretion mediated by the apical H~+-ATPase and a yet to be identified conductive Cl~- transport pathway; 2) benzamil-induced HC1 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.