Nongenomic regulation of ENaC by aldosterone

Aldosterone is involved in salt and water homeostasis. The main effect is t hought to involve genomic mechanisms. However, the existence of plasma memb rane steroid receptors has been postulated. We used whole cell patch clamp to test the hypothesis that epithelial sodium channels (ENaC) expressed by renal collecting duct principal cells can be regulated nongenomically by al dosterone. In freshly isolated principal cells from rabbit, aldosterone (10 0 nM) rapidly (<2 min) increased ENaC sodium current specifically. The aldo sterone-activated current was completely inhibited by amiloride. Aldosteron e also activated ENaC in cells treated with the mineralocorticoid receptor blocker spiranolactone. Nongenomic activation was inhibited by inclusion of S-adenosyl-L-homocysteine in the pipette solution, which inhibits methylat ion reactions. Also, the nongenomic activation required 2 mM ATP supplement ation in the pipette solution. Aldosterone did not activate any ENaC curren t in whole cell clamped rat collecting duct principal cells. These function al studies are consistent with aldosterone membrane binding studies, sugges ting the presence of a plasma membrane steroid receptor that affects cellul ar processes by mechanisms unrelated to altered gene expression.