Basolateral K+ channels in airway epithelia. I. Regulation by Ca2+ and block by charybdotoxin.
In airway epithelia, adenosine 3',5'-cyclic monophosphate (cAMP) stimulates Cl- secretion by activating apical membrane Cl- channels and basolateral membrane K+ channels. Cl- channels are regulated by cAMP-dependent phosphorylation, whereas K+ channels are regulated by the cytosolic Ca2+ concentration, [Ca2+]c. Our recent observation that cAMP increases [Ca2+]c suggested that cAMP might indirectly regulate K+ channels by increasing [Ca2+]c. To study regulation of K+ channels we measured 86Rb efflux, single K+ channels in membrane patches, and [Ca2+]c with the fluorescent indicator fura-2. Isoproterenol and Ca2+ ionophore, A23187, transiently increased [Ca2+]c and transiently stimulated 86Rb efflux. Stimulation of 86Rb efflux resulted from release of intracellular Ca2+ stores. 86Rb efflux was blocked by Ba2+ or charybdotoxin, but not by tetraethylammonium. Charybdotoxin prevented all of the 86Rb efflux that was stimulated by A23187 or by forskolin. Charybdotoxin also blocked the low-conductance inwardly rectifying K+ channel (KCLIC) in membrane patches. These results indicate that the KCLIC channel is responsible for the Ca2(+)-dependent increase in K+ permeability in airway epithelial cells. They also indicate that cAMP-induced release of intracellular Ca2+ is sufficient to activate K+ channels.
Howard Hughes Medical Institute, Department of Physiology, University of Iowa, College of Medicine, Iowa City 52242.
J D
JD
McCann
J
J
Matsuda
M
M
Garcia
G
G
Kaczorowski
M J
MJ
Welsh
D000818:Animals; D001464:Barium / Q000494:pharmacology; D001572:Benzofurans; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002478:Cells, Cultured; D018999:Charybdotoxin; D002712:Chlorides / Q000378:metabolism; D004285:Dogs; D004594:Electrophysiology / Q000379:methods; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005456:Fluorescent Dyes; D016257:Fura-2; D006706:Homeostasis; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009130:Muscle, Smooth / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D012413:Rubidium / Q000378:metabolism; D012414:Rubidium Radioisotopes; D012604:Scorpion Venoms / Q000494:pharmacology*; D014132:Trachea / Q000502:physiology*
D001572:Benzofurans; D002712:Chlorides; D005456:Fluorescent Dyes; D015221:Potassium Channels; D012414:Rubidium Radioisotopes; D012604:Scorpion Venoms; D018999:Charybdotoxin; D001464:Barium; D000001:Calcimycin; D007545:Isoproterenol; D012413:Rubidium; D002118:Calcium; D016257:Fura-2