Calcium-dependent regulation of cyclic GMP phosphodiesterase by a protein from frog retinal rods.
In vertebrate photoreceptors, light reduces cyclic GMP concentration and closes cGMP-activated channels to induce a hyperpolarizing response. As Ca2+ can permeate the channels and the Na(+)-Ca2+ exchanger continuously extrudes Ca2+, closure of the channel results in a reduction of the inter-rod Ca2+ concentration. This is believed to be one of the mechanisms of light-adaptation produced by activation of guanylate cyclase. Effects of Ca2+ on the cGMP phosphodiesterase (PDE) have been reported, but their physiological significance has remained unclear. We have perfused the inside-out preparation of a frog rod outer segment (I/O ROS, originally termed truncated ROS, and find that Ca2+ in a physiological range regulates the light-activation of PDE. Therefore, PDE regulation by Ca2+ must be involved in light-adaptation in rods. The effect is mediated by a newly found protein which binds to disk membranes at high Ca2+ concentrations and prolongs PDE activation.
Kawamura
S
S
Department of Physiology, Keio University School of Medicine, Tokyo, Japan.
Murakami
M
M
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D004789:Enzyme Activation; D066298:In Vitro Techniques; D008027:Light; D008970:Molecular Weight; D009419:Nerve Tissue Proteins / Q000502:physiology*; D011898:Ranidae; D012374:Rod Cell Outer Segment / Q000201:enzymology*
D009419:Nerve Tissue Proteins; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D002118:Calcium