Modulation of Sodium Transport in Alveolar Epithelial Cells by Estradiol and Progesterone

The effects of estradiol (E2) and progesterone (P) on alveolar epithelial Na(+) transport were studied in isolated alveolar epithelial cells from 18- to 19-d GA rat fetuses, grown to confluence in serum-free media supplemented with E2 (0–1 μM) and P (0–2.8 μM). Short-circuit currents (I(SC)) were measured, showing an increase by E2 and P in a dose-dependent manner. The Na,K-ATPase subunits -α(1) and -β(1) were detected by Western blotting, but total expression was not significantly altered. Furthermore, all three epithelial Na(+) channel (ENaC) subunits -α, -β, and -γ were detected, with trends toward a higher expression in the presence of E2 and P. Real-time PCR revealed an increase of α- and β-ENaC expression but no alteration of γ-ENaC. In addition, the mRNA expression of cystic fibrosis transmembrane conductance regulator (CFTR) and Na,K-ATPase-β(1) subunit were elevated in the presence of E2 and P. Single-channel patch clamp analysis demonstrated putative highly selective and nonselective cation channels in the analyzed cells, with a higher percentage of responsive patches under the influence of E2 and P. We conclude that E2 and P increased Na(+) transport in alveolar epithelial cells by enhancing the expression and activity of ENaC and Na,K-ATPase.