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

Analysis of membrane currents recorded from hormone-deprived H441 cells showed that the membrane potential (Vm) in single cells (approximately -80 mV) was unaffected by lowering [[Na.sup.+]][sub.o] or [[Cl.sup.-]][sub.o] indicating that cellular [Na.sup.+] and [Cl.sup.-] conductances ([G.sub.Na] and [G.sub.Cl], respectively) are negligible. Although insulin (20 nM, ~24 h) and dexamethasone (0.2 [micro]M, ~24 h) both depolarized Vm by ~20 mV, the response to insulin reflected a rise in [G.sup.Cl] mediated via phosphatidylinositol 3-kinase (PI3K) whereas dexamethasone acted by inducing a serum- and glucocorticoid-regulated kinase I (SGK1)-dependent rise in [G.sup.Na]. Although insulin stimulation/P13K-P110[alpha] expression did not directly increase [G.sup.Na], these maneuvers augmented the dexamethasone-induced conductance. The glucocorticoid/SGKl-induced [G.sup.Na] in single cells discriminated poorly between [Na.sup.+] and [K.sup.+] ([P.sub.Na]/[P.sub.K] ~0.6), was insensitive to amiloride (1 mM), but was partially blocked by La[Cl.sub.3] ([La.sup.3+]; 1 mM, ~80%), pimozide (0.1 mM, ~40%), and dichlorobenzamil (15 [micro]M, ~15%). Cells growing as small groups, on the other hand, expressed an amiloride-sensitive (10 [micro]M), selective [G.sup.Na] 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 GNu, (14, 48), 2) show that these conductances are both induced by glucocorticoids/SGK1 and subject to PI3K-dependent regulation, and 3) establish that cell-cell contact is vitally important to the development of [Na.sup.+] selectivity and amiloride sensitivity. epithelial [Na.sup.+] channel; serum- and glucocorticoid regulated kinase 1; phosphatidylinositol 3-kinase; H441 cells; pulmonary [Na.sup.+] absorption