title: Depolarization-induced calcium channel facilitation in rod photoreceptors is independent of G proteins and phosphorylation.
abstract: Depolarization-induced facilitation of L-type Ca channels in rod photoreceptors was investigated with nystatin-perforated and ruptured whole cell patch-clamp techniques in cells isolated from tiger salamander retina. Induction of facilitation was voltage dependent with a half-maximal effect seen at prepulse potentials near +31 mV. Reversal of facilitation was time dependent with fast (tau approximately 20 ms) and slow (tau approximately 1 s) components at -60 mV. Incubation of cells with pertussis toxin or intracellular administration of guanosine 5'-O-(3-thiotriphosphate) or guanosine 5'-O-(2-thiodiphosphate) had no effect on the degree to which facilitation could be evoked, implying the absence of a significant role for G proteins. Application of the phosphatase inhibitor okadaic acid or inclusion of ATP, to boost levels of phosphorylation, or inclusion of 5'adenylylimidophosphate or inhibitors of protein kinase in the pipette, to reduce levels of phosphorylation, had no effect on the development of facilitation, suggesting that phosphorylation has little or no role in this phenomenon. These results show that the L-type Ca channels in rod photoreceptors, which appear to be composed of alpha(1F)-like subunits, undergo voltage-dependent facilitation in a manner that differs from some other L-type Ca channels which undergo facilitation via phosphorylation or through G-protein-mediated inhibition.
authors.affiliation: Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Kourennyi
authors.forename: S
authors.initials: S
authors.lastname: Barnes
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000557:Ambystoma; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D019319:Okadaic Acid / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation; D017948:Retinal Rod Photoreceptor Cells / Q000737:chemistry / Q000502:physiology*; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
chemical_list: D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D010446:Peptide Fragments; C518603:protein kinase inhibitor peptide (5-24); D019319:Okadaic Acid; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D020866:omega-Conotoxin GVIA; D019204:GTP-Binding Proteins