Quercetin and NPPB-induced diminution of aldosterone action on Na + absorption and ENaC expression in renal epithelium

Abstract

In renal epithelial A6 cells, aldosterone applied for 24 h increased the transepithelial Cl − secretion over 30-fold due to activation of the Na +/K +/2Cl − cotransporter and stimulated the transepithelial Na + absorption, activity of epithelial Na + channel (ENaC), and α-ENaC mRNA expression. The stimulatory action of aldosterone on the transepithelial Na + absorption, ENaC activity, and α-ENaC mRNA expression was diminished by 24 h-pretreatment with quercetin (an activator of Na +/K +/2Cl − cotransporter participating in Cl − entry into the cytosolic space) or 5-nitro 2-(3-phenylpropylamino)benzoate (NPPB) (a blocker of Cl − channel participating in Cl − release from the cytosolic space), while 24 h-pretreatment with bumetanide (a blocker of Na +/K +/2Cl − cotransporter) enhanced the stimulatory action of aldosterone on transepithelial Na + absorption. On the other hand, under the basal (aldosterone-unstimulated) condition, quercetin, NPPB or bumetanide had no effect on transepithelial Na + absorption, activity of ENaC or α-ENaC mRNA expression. These observations suggest that although aldosterone shows overall its stimulatory action on ENaC (transepithelial Na + transport), aldosterone has an inhibitory action on ENaC (transepithelial Na + transport) via activation of the Na +/K +/2Cl − cotransporter, and that modification of activity of Cl − transporter/channel participating in the transepithelial Cl − secretion influences the aldosterone-stimulated ENaC (transepithelial Na + transport).