Cholera Toxin Enhances ENaC‐Mediated Sodium Absorption Across Cultured Human Mammary Epithelial Cells

Abstract

Mechanisms that control ion transport across human mammary gland and contribute to the unique low sodium concentration in human milk have not been fully described. When grown on permeable supports, MCF10A cells, an epithelial cell line derived from human mammary gland, exhibited amiloride‐sensitive ion transport, suggesting activity of the epithelial Na+ channel, ENaC. When cultured in the presence of cholera toxin, MCF10A cells exhibited significantly greater amiloride sensitive short circuit current (Isc) at all time points tested (2 h to 7 d). Maximal amiloride‐sensitive Isc was observed with 1 d exposure to cholera toxin (4.76 ± 0.73 μA cm−2) when compared to vehicle‐treated monolayers (1.19 ± 0.27 μA cm−2). Effects of cholera toxin on Isc were neither mimicked by forskolin nor inhibited by H‐89 (10 μM), a protein kinase A (PKA) inhibitor. RT‐PCR analyses showed that cholera toxin increased the copy number for mRNA coding for each of the three ENaC subunits by 2 to 4 fold. Taken together, these results suggest that human mammary epithelial cells express ENaC, a mechanism that can remove Na+ from milk. Furthermore, the results suggest a novel mechanism to regulate ENaC expression that involves cholera toxin, but that is independent of cAMP and PKA. [NIH (P20‐RR017686) and KS Ag Exp Stn support]