Enhanced ENaC and KCa3.1 expression by hydrocortisone increases Na+ absorption in human mammary epithelial cells.

Abstract

Immortalized human mammary epithelial cells express apical ENaC sodium channels and basolateral KCa3.1 potassium channels. Treatment of monolayers with hydrocortisone (0.5 μg/ml) for 48 hours enhanced mRNA expression for α, β and γ ENaC subunits by 7.3, 10.5 and 9.6 fold as determined by quantitative RT‐PCR. Additionally, KCa3.1 mRNA expression was enhanced by hydrocortisone by 8.1 fold, however no increase in mRNA expression was detected for the BK (Slo1) potassium channel, which had a higher basal level of expression than KCa3.1 (Slo1 CT = 23.8; KCa3.1 CT = 27.7). Hydrocortisone also increased expression of the P2Y6 receptor by 5.5 fold without significantly altering P2Y1, P2Y2 or P2Y4 receptor expression. Basolateral stimulation of hydrocortisone pretreated monolayers with UTP (10 μM) resulted in a significantly greater increase in short circuit current (Isc) compared to untreated control monolayers (peak ΔIsc + hydrocortisone = 20 ± 1 μA, control = 9.5 ± 2 μA). In addition, the duration of the Isc response was significantly lower in the absence of hydrocortisone with less oscillation. These results indicate that KCa3.1 and P2Y6 receptor expression are up‐regulated in parallel with ENaC channels in the presence of hydrocortisone resulting in enhanced electrogenic Na+ absorption following basolateral stimulation with UTP.