Epidermal growth factor regulates the transition from basal sodium absorption to anion secretion in cultured endometrial epithelial cells

The objective of this study was to investigate acute and long-term effects of epidermal growth factor (EGF) and transforming growth factor α (TGFα) on basal ion transport activity of glandular endometrial epithelial cells in primary culture. The effects of EGF on insulin-dependent regulation of Na⁺ transport across this epithelium was also investigated. Addition of 1.6 nM EGF or 2 nM TGFα to the basolateral, but not the apical, solution inhibited both basal and insulin-stimulated Na⁺ transport with a maximum response within 45-60 min. This effect was mimicked by the calcium ionophore ionomycin. Incubation with EGF for 4 days inhibited insulin-stimulated Na absorption in a concentration-dependent fashion with an IC₅₀ value of 0.3 nM. Experiments using amphotericin B-permeabilized monolayers demonstrated that EGF inhibited Na transport by decreasing apical membrane Na conductance without affecting insulin-dependent stimulation of the Na⁺-K⁺ ATPase. Addition of EGF or TGFα for 24 h resulted in increased basal Cl^- secretion in addition to inhibition of Na absorption. The EGF-induced increase in Cl^- secretion was inhibited in part by indomethacin, suggesting that long-term regulation by EGF involves stimulation of arachidonic acid synthesis and prostaglandin release. The EGF-induced increase in indomethacin-insensitive Cl^- secretion was prevented by the protein synthesis inhibitor cyclohexamide, and by the DNA transcription inhibitor actinomycin D indicating that EGF-stimulated anion secretion required DNA transcription and protein synthesis. The results of these studies demonstrated that the basal transport properties of endometrial epithelial cells are differentially regulated by EGF, TGFα, and insulin.