Abstract P272: Mechanisms By Which Aldosterone And Insulin Stimulate Endothelial Cell Sodium Currents.

Abstract

Aldosterone and insulin are known to increase the activity of the epithelial Na + channel (ENaC) in tubular epithelial cells through multiple mechanisms involving both transcriptional and post-transcriptional events. Such studies have implicated a key role for serum and glucocorticoid-stimulated kinase 1 (SGK-1) in determining ENaC activity. Comparatively less information is available regarding such regulation of the endothelial cell (EC) Na+ channel (EnNaC). The importance of such knowledge relates to prior studies having shown that EnNaC contributes to cardiovascular stiffening in states of hyperaldosteronism and hyperinsulinemia/insulin resistance. We hypothesized that aldosterone and insulin converge on SGK-1 to increase EnNaC activity. To determine how EnNaC is affected by insulin and aldosterone pulmonary ECs were isolated from wild-type mice and global SGK-1 deficient mice and held under conditions of short-term tissue culture. ECs were subsequently exposed to aldosterone (10 nM), insulin (100 nM) or DMSO control for 24 hr and whole cell EnNaC currents measured by patch clamp. Both chronic aldosterone and insulin increased Na + currents in ECs from wild-type mice, while in cells from SGK-1-/- mice the response to aldosterone was significantly blunted. However, insulin continued to increase EnNaC activity in SGK-1-/- mice. Acute insulin treatment (10 mins) showed a concentration-dependent (10 – 100 nM) increase in EC Na + currents in both SGK+/+ and SGK-/- mice which was prevented by PI3 kinase inhibition with LY294002 (30 uM). Thus, in ECs aldosterone-mediated activation of EnNaC is dependent on SGK-1 while insulin exerts a stimulatory effect via PI3 kinase, even in the absence of SGK-1.