The regulation of selective and nonselective Na+ conductances in H441 human airway epithelial cells.

Analysis of membrane currents recorded from hormone-deprived H44 I cells showed that the membrane potential (Vm) in single cells (approximately -80 mV) was unaffected by lowering [Na+ ] or [Cl- ]0, indicating that cellular N+ and C1 conductances (GNa and Gc1, respectively) are negligible. Although insulin (20 nM, -24 h) and dexamethasone (0.2 μM, -24 h) both depolarized Vm by --20 mV, the response to insulin reflected a rise in Gc1 mediated via phosphatidylinositol 3-kinase (P13K) whereas dexamethasone acted by inducing a serum and glucocorticoid-regulated kinase 1 (SGKI) dependent rise in GNa. Although insulin stimulationfPl3K-Pl lOct expression did not directly increase GNa, these maneuvers augmented the dexamethasone-induced conductance. The glucocorticoid/SGKl-induced GNa in single cells discriminated poorly between Na+ and K+ (PNaIPK --0.6), was insensitive to amiloride (1 mM), but was partially blocked by LaCI3 (La3+ 1 mM, -80%), pimozide(0.I mM, --40%), and dichlorobenzamil (15 riM, -.15%). Cells growing as small groups, on the other hand, expressed an amiloride-sensitive (10μM), selective GNNa that displayed the same pattern of hormonal regulation as the nonselective conductance in single cells. These data therefore 1) confirm that H441 cells can express selective or nonselective GNa (14, 48), 2) show that these conductances are both induced by glucocorticoids/SGKI and subject to P13K-dependent regulation, and 3) establish that cell-cell contact is vitally important to the development of Na+ selectivity and amiloride sensitivity. [ABSTRACT FROM AUTHOR]