The regulation of selective and nonselective Na+ conductances in H441 human airway epithelial cells.
Analysis of membrane currents recorded from hormone-deprived H441 cells showed that the membrane potential (V(m)) in single cells (approximately -80 mV) was unaffected by lowering [Na+]o or [Cl(-)]o, indicating that cellular Na+ and Cl(-) conductances (GNa and GCl, respectively) are negligible. Although insulin (20 nM, approximately 24 h) and dexamethasone (0.2 microM, approximately 24 h) both depolarized Vm by approximately 20 mV, the response to insulin reflected a rise in GCl mediated via phosphatidylinositol 3-kinase (PI3K) whereas dexamethasone acted by inducing a serum- and glucocorticoid-regulated kinase 1 (SGK1)-dependent rise in GNa. Although insulin stimulation/PI3K-P110 alpha expression did not directly increase GNa, these maneuvers augmented the dexamethasone-induced conductance. The glucocorticoid/SGK1-induced GNa in single cells discriminated poorly between Na+ and K+ (PNa/PK approximately 0.6), was insensitive to amiloride (1 mM), but was partially blocked by LaCl3 (La3+; 1 mM, approximately 80%), pimozide (0.1 mM, approximately 40%), and dichlorobenzamil (15 microM, approximately 15%). Cells growing as small groups, on the other hand, expressed an amiloride-sensitive (10 microM), selective GNa 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/SGK1 and subject to PI3K-dependent regulation, and 3) establish that cell-cell contact is vitally important to the development of Na+ selectivity and amiloride sensitivity.
Brown
Sean G
SG
Lung Membrane Transport Group, Division of Maternal and Child Health Sciences, Ninewells Hospital and Medical School, Univ. of Dundee, Dundee DD1 9SY, Scotland, United Kingdom.
Gallacher
Michael
M
Olver
Richard E
RE
Wilson
Stuart M
SM
D000584:Amiloride / Q000494:pharmacology; D002450:Cell Communication / Q000502:physiology*; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000502:physiology; D053492:Elafin / Q000235:genetics / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000502:physiology; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D007811:Lanthanum / Q000493:pharmacokinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D016296:Mutagenesis; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology* / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000494:pharmacology; D015222:Sodium Channels / Q000502:physiology*; D014162:Transfection; D000099184:Serum-Glucocorticoid Regulated Kinases
D000584:Amiloride; D002712:Chlorides; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D053492:Elafin; D053503:Epithelial Sodium Channels; D007004:Hypoglycemic Agents; D017874:Immediate-Early Proteins; D007328:Insulin; D007811:Lanthanum; D017346:Protein Serine-Threonine Kinases; D012964:Sodium; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D000099184:Serum-Glucocorticoid Regulated Kinases; C505032:CFTR protein, human; C506806:PI3 protein, human