Early aldosterone effect in distal colon by transcriptional regulation of ENaC subunits

Abstract

Aldosterone-induced sodium absorption is mediated by the epithelial Na+ channel (ENaC). It is thought that the “early effect” is not based on genomic regulation of ENaC expression, because ENaC subunit transcription was reported to start later than Na+ transport. We investigated electrogenic Na+ absorption ( J Na) and, in identical tissues, mRNA expression of ENaC subunits in early (EDC) and late (LDC) distal colon of the rat. In both segments, 8-h in vitro incubation with 3 nM aldosterone enhanced expression of β- and γ-ENaC mRNA and induced J Na. J Na was 10 times higher in LDC than in EDC. α-ENaC mRNA was unchanged in EDC, whereas it decreased in LDC. In LDC, β- and γ-ENaC mRNA was induced 1 h after aldosterone addition, whereas J Na became apparent >1 h later. Downregulation of α-ENaC mRNA did not take part in acute regulation because it started after a lag time of 3 h. Time correlation of β- and γ-ENaC induction and J Na stimulation suggests that the early aldosterone effect on Na+ absorption in distal colon is caused by transcriptional upregulation of β- and γ-ENaC expression.