title: A glucocorticoid-induced Na+ conductance in human airway epithelial cells identified by perforated patch recording.
abstract: The perforated patch recording technique was used to investigate the effects of dexamethasone (0.2 microm, 24-30 h), a synthetic glucocorticoid, on membrane conductance in the human airway epithelial cell line H441. Under zero current clamp conditions this hormone induced amiloride-sensitive depolarization of the membrane potential (V(m)). Lowering external Na(+) to 10 mm by replacing Na(+) with N-methyl-d-glucammonium (NMDG(+)) also hyperpolarized the dexamethasome-treated cells, whilst replacing Na(+) with Li(+) caused a small depolarization. Although V(m) was insensitive to amiloride in control cells, NMDG(+) substitution caused a small hyperpolarization and so an amiloride-insensitive cation conductance is present. Replacing Na(+) with Li(+) had no effect on V(m) in such cells. Voltage clamp studies of dexamethasone-treated cells showed that the amiloride-sensitive component of the membrane current reversed at a potential close to the Na(+) equilibrium potential (E(Na)), and replacing Na(+) with K(+) caused a leftward shift in reversal potential (V(Rev)) that correlated with the corresponding shift in E(Na). Lowering [Na(+)](o) to 10 mm, the concentration in the pipette solution, by substitution with NMDG(+) shifted V(Rev) to 0 mV, whilst replacing Na(+) with Li(+) caused a rightward shift. Exposing dexamethasone-treated cells to a cocktail of cAMP-activating compounds (20 min) caused a approximately 2-fold increase in amiloride-sensitive conductance that was associated with no discernible change in ionic selectivity and an 18 mV depolarization. Dexamethasone thus induces the expression of a selective Na(+) conductance with a substantial permeability to Li(+) that is subject to acute regulation via cAMP. These data thus suggest that selective Na(+) channels underlie cAMP-regulated Na(+) transport in airway epithelia.
authors.affiliation: Lung Membrane Transport Group, Division of Maternal and Child Health Sciences, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK.
authors.forename: M T
authors.initials: MT
authors.lastname: Clunes
authors.forename: A G
authors.initials: AG
authors.lastname: Butt
authors.forename: S M
authors.initials: SM
authors.lastname: Wilson
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D002460:Cell Line; D000242:Cyclic AMP / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004594:Electrophysiology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D008094:Lithium / Q000378:metabolism / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000187:drug effects*
chemical_list: D004232:Diuretics; D005938:Glucocorticoids; D015222:Sodium Channels; D000584:Amiloride; D003907:Dexamethasone; D008094:Lithium; D000242:Cyclic AMP