THE EFFECT OF RECOVERIN-LIKE CALCIUM-BINDING PROTEINS ON THE PHOTORESPONSE OF RETINAL RODS

The rod photoresponse is triggered by an enzyme cascade that stimulates cGMP hydrolysis. The resulting fall in cGMP leads to a decrease in Ca2+, which promotes photoresponse recovery by activating guanylate cyclase, causing cGMP resynthesis. In vitro biochemical studies suggest that Ca2+ activation of guanylate cyclase is mediated by recoverin, a 26 kd Ca2+-binding protein. To evaluate this, exogenous bovine recoverin and two other homologous Ca2+-binding proteins from chicken and Gecko retina were dialyzed into functionally intact Gecko rods using whole-cell recording. All three proteins prolonged the rising phase of the photoresponse without affecting the kinetics of response recovery. These results suggest that recoverin-like proteins affect termination of the transduction cascade, rather than mediate Ca2+-sensitive activation of guanylate cyclase.