title: Stimulation of protein phosphorylations in frog rod outer segments by protein kinase activators. Suppression of light-induced changes in membrane current and cGMP by protein kinase C activators.
abstract: Addition of protein kinase C activators to electropermeabilized frog rod photoreceptors enhances the phosphorylation of proteins with molecular masses of 54, 24, 19, 17, 12, and 11 kDa. The latter two correspond to components I and II, which are also phosphorylated by cyclic nucleotide-dependent protein kinase. Stimulation of phosphorylation by the protein kinase C activator oleoylacetylglycerol (OAG) is half-maximal at 7.7 microM OAG and is reduced by the protein kinase C inhibitor H-7. In contrast with earlier observations, no effects of calcium, calmodulin, or insulin on protein phosphorylations are observed. We find evidence for only three protein kinases in rod outer segments: a protein kinase C-like activity, cAMP-dependent protein kinase, and rhodopsin kinase. With the exception of components I and II, the substrate proteins for each kinase are distinct. Treatment of intact rods with OAG decreases the amplitude of the photoresponse and dark levels of cGMP up to 40%, as well as depressing the light-stimulated decrease in cGMP levels. These effects are observed between 0.1 and 1 microM OAG. The data suggest that OAG-sensitive reactions may modulate pathways that support the light response.
authors.affiliation: Neuroscience Training Program, University of Wisconsin, Madison 53706.
authors.forename: B M
authors.initials: BM
authors.lastname: Binder
authors.forename: E
authors.initials: E
authors.lastname: Brewer
authors.forename: M D
authors.initials: MD
authors.lastname: Bownds
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D004075:Diglycerides / Q000494:pharmacology*; D004789:Enzyme Activation; D005989:Glycerides / Q000494:pharmacology*; D007700:Kinetics; D008027:Light; D008564:Membrane Potentials; D008970:Molecular Weight; D019301:Oleic Acid; D009829:Oleic Acids / Q000494:pharmacology; D010750:Phosphoproteins / Q000302:isolation & purification; D010766:Phosphorylation; D010786:Photoreceptor Cells / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D011892:Rana catesbeiana; D012374:Rod Cell Outer Segment / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D004075:Diglycerides; D005989:Glycerides; D009829:Oleic Acids; D010750:Phosphoproteins; D011506:Proteins; D015124:8-Bromo Cyclic Adenosine Monophosphate; D019301:Oleic Acid; C016276:8-bromocyclic GMP; C038237:1-oleoyl-2-acetylglycerol; D011494:Protein Kinases; D011493:Protein Kinase C; D006152:Cyclic GMP; D013755:Tetradecanoylphorbol Acetate