Ca2+ induces an increase in cGMP-phosphodiesterase activity in squid retinal photoreceptors.
In invertebrate photoreceptors, light elicits the opening of cationic channels to produce a depolarizing receptor potential. One hypothesis is that cGMP is the agent that gates the channels. It has been previously proposed that the light-induced rise in intracellular Ca2+ down-regulates phosphodiesterase activity, thereby eliciting an increase in intracellular cGMP concentration. cGMP-phosphodiesterase activity from squid photoreceptors was monitored both by a continuous fluorescence assay using 2'-o-(N-methylanthraniloyl)-cGMP and by hydrolysis of [3H]cGMP. The activity of cGMP-phosphodiesterase was found to be increased by Ca2+ in the physiological range of concentrations. These findings suggest that the previously known light-induced increase in Ca2+ in invertebrate photoreceptors cannot directly account for light-elicited down-regulation of cGMP-phosphodiesterase.
Brown
J E
JE
Department of Ophthalmology and Visual Sciences, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Kelman
E S
ES
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D006152:Cyclic GMP / Q000378:metabolism; D049832:Decapodiformes; D015536:Down-Regulation; D004789:Enzyme Activation; D008027:Light; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism*; D012160:Retina / Q000378:metabolism
D015106:3',5'-Cyclic-GMP Phosphodiesterases; D006152:Cyclic GMP; D002118:Calcium