Recoverin Regulates Light-dependent Phosphodiesterase Activity in Retinal Rods

The Ca(2+)-binding protein recoverin may regulate visual transduction in retinal rods and cones, but its functional role and mechanism of action remain controversial. We compared the photoresponses of rods from control mice and from mice in which the recoverin gene was knocked out. Our analysis indicates that Ca(2+)-recoverin prolongs the dark-adapted flash response and increases the rod's sensitivity to dim steady light. Knockout rods had faster Ca(2+) dynamics, indicating that recoverin is a significant Ca(2+) buffer in the outer segment, but incorporation of exogenous buffer did not restore wild-type behavior. We infer that Ca(2+)-recoverin potentiates light-triggered phosphodiesterase activity, probably by effectively prolonging the catalytic activity of photoexcited rhodopsin.