Ca2(+)-activated K+ channels in airway smooth muscle are inhibited by cytoplasmic adenosine triphosphate.
Large-conductance Ca2(+)-activated K+ channels were studied in membranes of cultured rabbit airway smooth muscle cells, using the patch-clamp technique. In cell-attached recordings, channel openings were rare and occurred only at very positive potentials. Bradykinin (10 microM), an agonist which releases Ca2+ from the sarcoplasmic reticulum, transiently increased channel activity. The metabolic blocker 2,4-dinitrophenol (20 microM), which lowers cellular adenosine triphosphate (ATP) levels, induced a sustained increase of channel activity in cell-attached patches. In excised patches, these channels had a slope conductance of 155 pS at 0 mV, were activated by depolarization and by increasing the Ca2+ concentration at the cytoplasmic side above 10(-7) mol/l. ATP, applied to the cytoplasmic side of the patches, dose-dependently decreased the channel's open-state probability. An inhibition constant (Ki) of 0.2 mmol/l was found for the ATP-induced inhibition. ATP reduced the Ca2+ sensitivity of the channel, shifting the Ca2+ activation curve to the right and additionally reducing its steepness. Our results demonstrate that cytoplasmic ATP inhibits a large-conductance Ca2(+)-activated K+ channel in airway smooth muscle. This ATP modulation of Ca2(+)-activated K+ channels might serve as an important mechanism linking energy status and the contractile state of the cells.
Groschner
K
K
University of Miami, School of Medicine, Department of Molecular and Cellular Pharmacology, FL 33101.
Silberberg
S D
SD
Gelband
C H
CH
van Breemen
C
C
D000255:Adenosine Triphosphate / Q000502:physiology*; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000502:physiology; D004553:Electric Conductivity; D009130:Muscle, Smooth / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D011817:Rabbits
D015221:Potassium Channels; D000255:Adenosine Triphosphate; D001920:Bradykinin; D002118:Calcium