Feedback Inhibition of the epithelial Na+ channel (ENaC): in vitro vs. in vivo

Abstract

The mechanism of feedback inhibition of ENaC was investigated in vitro in ENaC‐expressing oocytes and correlated to an in vivo protocol in rats. Two‐electrode voltage clamp (TEVC) and patch clamp was used to measure amiloride‐sensitive currents (INa) in oocytes and split‐open cortical collecting ducts from rats, respectively. Biotin labeling was used to examine cell surface expression of ENaC in both oocytes and rats. 1–1.5 hour incubation in high Na+ of ENaC‐expressing oocytes caused a 74% decrease in INa, but little change in cell‐surface γ ENaC. An overnight incubation in high Na+ caused a 92% decrease in INa and a 73% decrease in cell‐surface γ ENaC. There was no change in cell‐surface expression of β ENaC during either high Na+ incubation. Rats on a low‐Na+ diet with an aldosterone pump had a 70% decrease in INa when resalted with decreases in cell‐surface β and γ ENaC of 60% and 71%, respectively. Resalting with amiloride blocked feedback inhibition but did not significantly change INa compared to resalted rats but increased cell‐surface β and γ ENaC by 123% and 419%, respectively. In oocytes, feedback inhibition causes changes in ENaC activity prior to changes in cell‐surface γ ENaC and no changes in cell‐surface β ENaC. In rats, feedback inhibition during resalting regulates cell‐surface β and γ ENaC exprssion without effecting INa. NIH RO1‐ DK59659 (LGP) and T32‐GM07739 (ABP).