title: Regulation of M-like K+ current, IKx, by Ca(2+)-dependent phosphorylation in rod photoreceptors.
abstract: An M-like K+ current (IKx) helps set the rod photoreceptor resting potential and accelerates the response to dim light. Recorded with ruptured-patch whole cell techniques, the amplitude of IKx diminished, and activation occurred at increasingly negative potentials as a function of time. In contrast, IKx was stable during nystatin perforated-patch recording. Stability during ruptured-patch recording could be induced by raising the intracellular Ca2+ concentration ([Ca2+]i) or by including caffeine or D-myo-inositol 1,4,5-trisphosphate in the pipette. This Ca(2+)-induced stability of IKx was blocked by inhibitors of Ca2+/calmodulin-dependent protein kinases, such as W-7, KN-62, chelerythrine, or H-7. Okadaic acid, an inhibitor of protein phosphatases, maintained IKx stability even at low [Ca2+]i. The requirement for phosphorylation was demonstrated by depleting MgATP or by providing 5'-adenylylimidophosphate, a nonhydrolyzable analog of ATP, either of which blocked the Ca(2+)-induced stability of IKx. These observations show that phosphorylation regulates IKx and that a stimulus controlling this action is [Ca2+]i. Should [Ca2+]i change during light adaptation, changes in IKx might alter the resting potential and temporal response properties of rod photoreceptors.
authors.affiliation: Neuroscience Research Group, University of Calgary, Faculty of Medicine, Alberta, Canada.
authors.forename: D E
authors.initials: DE
authors.lastname: Kurennyi
authors.forename: S
authors.initials: S
authors.lastname: Barnes
mesh_terms: D000557:Ambystoma; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D007700:Kinetics; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008954:Models, Biological; D019319:Okadaic Acid / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D015221:Potassium Channels / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects / Q000502:physiology*
chemical_list: D004791:Enzyme Inhibitors; D015221:Potassium Channels; D019319:Okadaic Acid; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D002118:Calcium