ENaC inhibition stimulates HCl secretion in the mouse cortical collecting duct. I. Stilbene-sensitive Cl- secretion

Inhibition of the epithelial Na+ channel (ENaC) reduces Cl- absorption in cortical collecting ducts (CCDs) from aldosterone-treated rats and mice. Since ENaC does not transport Cl-, the purpose of the present study was to explore how ENaC modulates Cl- absorption in mouse CCDs perfused in vitro. Therefore, we measured transepithelial Cl- flux and transepithelial voltage in CCDs perfused in vitro taken from mice that consumed a NaCl-replete diet alone or the diet with aldosterone administered by minipump. We observed that application of an ENaC inhibitor [benzamil (3 mu M)] to the luminal fluid unmasks conductive Cl- secretion. During ENaC blockade, this Cl- secretion fell with the application of a nonselective Cl- channel blocker [DIDS (100 mu M)] to the perfusate. While single channel recordings of intercalated cell apical membranes in split-open CCDs demonstrated a Cl- channel with properties that resemble the ClC family of Cl- channels, ClC-5 is not the primary pathway for benzamil-sensitive Cl- flux. In conclusion, first, in CCDs from aldosterone-treated mice, most Cl- absorption is benzamil sensitive, and, second, benzamil application stimulates stilbene-sensitive conductive Cl- secretion, which occurs through a ClC-5-independent pathway.