Inactivation of calcium-activated chloride channels in smooth muscle by calcium/calmodulin-dependent protein kinase.
To determine the mechanisms responsible for the termination of Ca2+-activated Cl- currents (ICl(Ca)), simultaneous measurements of whole cell currents and intracellular Ca2+ concentration ([Ca2+]i) were made in equine tracheal myocytes. In nondialyzed cells, or cells dialyzed with 1 mM ATP, ICl(Ca) decayed before the [Ca2+]i decline, whereas the calcium-activated potassium current decayed at the same rate as [Ca2+]i. Substitution of AMP-PNP or ADP for ATP markedly prolonged the decay of ICl(Ca), resulting in a rate of current decay similar to that of the fall in [Ca2+]i. In the presence of ATP, dialysis of the calmodulin antagonist W7, the Ca2+/calmodulin-dependent kinase II (CaMKII) inhibitor KN93, or a CaMKII-specific peptide inhibitor the rate of ICl(Ca) decay was slowed and matched the [Ca2+]i decline, whereas H7, a nonspecific kinase inhibitor with low affinity for CaMKII, was without effect. When a sustained increase in [Ca2+]i was produced in ATP dialyzed cells, the current decayed completely, whereas in cells loaded with 5'-adenylylimidodiphosphate (AMP-PNP), KN93, or the CaMKII inhibitory peptide, ICl(Ca) did not decay. Slowly decaying currents were repeatedly evoked in ADP- or AMP-PNP-loaded cells, but dialysis of adenosine 5'-O-(3-thiotriphosphate) or okadaic acid resulted in a smaller initial ICl(Ca), and little or no current (despite a normal [Ca2+]i transient) with a second stimulation. These data indicate that CaMKII phosphorylation results in the inactivation of calcium-activated chloride channels, and that transition from the inactivated state to the closed state requires protein dephosphorylation.
Wang
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YX
Department of Animal Biology, University of Pennsylvania, Philadelphia, PA 19104-6046, USA.
Kotlikoff
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MI
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002478:Cells, Cultured; D018118:Chloride Channels / Q000378:metabolism*; D006736:Horses; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D009130:Muscle, Smooth / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D014132:Trachea
D018118:Chloride Channels; D007476:Ionophores; D010726:Phosphodiesterase Inhibitors; D002110:Caffeine; D015759:Ionomycin; D000255:Adenosine Triphosphate; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002118:Calcium