title: Regulation of A-type potassium channels in murine colonic myocytes by phosphatase activity.
abstract: A rapidly inactivating K(+) current (A-type current) participates in the regulation of colonic muscle excitability. We found 19-pS K(+) channels in cell-attached patches of murine colonic myocytes that activated and inactivated with kinetics similar to the A-type current. The A-type current in colonic myocytes is regulated by Ca(2+)/calmodulin-dependent protein kinase II. Therefore, we studied regulation of the 19-pS K(+) channels by Ca(2+)-dependent phosphorylation/dephosphorylation. The rates of inactivation of ensemble-averaged currents resulting from 19-pS K(+) channels were increased by the calmodulin antagonist W-7. Inhibitors of calcineurin, cyclosporin A and FK-506, slowed the inactivation of the 19-pS K(+) channels. Okadaic acid, an inhibitor of the calcineurin/inhibitor-1/protein phosphatase 1 cascade, also slowed inactivation of the 19-pS K(+) channels. Polymerase chain reaction detected transcripts encoding calcineurin A in isolated colonic smooth muscle cells, and immunohistochemical studies demonstrated specific expression of calcineurin A-like immunoreactivity in colonic muscle tissues and in colonic myocytes. These data, when considered with previous findings, suggest that Ca(2+)-dependent phosphorylation/dephosphorylation regulates the A-type current in murine colonic smooth muscle cells.
authors.affiliation: Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557, USA.
authors.forename: G C
authors.initials: GC
authors.lastname: Amberg
authors.forename: S D
authors.initials: SD
authors.lastname: Koh
authors.forename: B A
authors.initials: BA
authors.lastname: Perrino
authors.forename: W J
authors.initials: WJ
authors.lastname: Hatton
authors.forename: K M
authors.initials: KM
authors.lastname: Sanders
mesh_terms: D000818:Animals; D019703:Calcineurin / Q000737:chemistry / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D003106:Colon / Q000166:cytology* / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007166:Immunosuppressive Agents / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism*; D054645:Protein Phosphatase 1; D013449:Sulfonamides / Q000494:pharmacology; D016559:Tacrolimus / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D024642:Potassium Channels, Voltage-Gated; D013449:Sulfonamides; D019319:Okadaic Acid; C017967:W 7; D016572:Cyclosporine; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019703:Calcineurin; D054645:Protein Phosphatase 1; D002118:Calcium; D016559:Tacrolimus