Calcium-dependent regulation of airway epithelial chloride channels.
To determine how cell calcium ([Ca2+]c) regulates apical Cl- channels, we measured the rate of 125-Iodide (125I-) efflux to assay Cl- channel activity in intact cells and examined cell-free membrane patches from cultured canine tracheal epithelial cells. The Ca2+ elevating agonist bradykinin and the calcium ionophore A23187 increased 125I- efflux. This response did not require prostaglandin production. Under several conditions, changes in [Ca2+]c were temporally dissociated from changes in channel activation: a transient increase in [Ca2+]c caused a prolonged stimulation of 125I- efflux. Neither Cl- channel activation nor open-channel probability was affected by varying internal [Ca2+] in excised membrane patches. Adenosine 3',5'-cyclic monophosphate (cAMP)- and Ca2(+)-dependent channel activation may be independent: cAMP-stimulated 125I- efflux did not require an increase in [Ca2+]c, Ca2(+)-stimulated efflux did not require an increase in cAMP, and simultaneous addition of A23187 and isoproterenol produced additive effects on 125I- efflux. The data suggest that an increase in [Ca2+]c activates Cl- channels, however, the effect of Ca2+ appears to be indirect, not involving a ligand-type interaction with the channel.
Howard Hughes Medical Institute, Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242.
J P
JP
Clancy
J D
JD
McCann
M
M
Li
M J
MJ
Welsh
D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D018118:Chloride Channels; D002712:Chlorides / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology; D004285:Dogs; D004848:Epithelium / Q000502:physiology; D007213:Indomethacin / Q000494:pharmacology; D007454:Iodides / Q000378:metabolism; D007473:Ion Channels / Q000502:physiology*; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008565:Membrane Proteins / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology; D009579:Nitrobenzoates / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D013806:Theophylline / Q000494:pharmacology; D014132:Trachea / Q000502:physiology*; D014634:Valinomycin / Q000494:pharmacology
D018118:Chloride Channels; D002712:Chlorides; D007454:Iodides; D007473:Ion Channels; D008565:Membrane Proteins; D009579:Nitrobenzoates; D002034:Bumetanide; D014634:Valinomycin; D000001:Calcimycin; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D013806:Theophylline; D000242:Cyclic AMP; D007545:Isoproterenol; D011188:Potassium; D002118:Calcium; D007213:Indomethacin