PURPOSE - To examine the biochemical characteristics of rod and cone arrestin with respect to their ability to quench the activity of light-activated rhodopsin in transgenic mice.
METHODS - The mouse rod opsin promoter was used to drive expression of mouse cone arrestin in rod photoreceptor cells of rod arrestin knockout (arr1-/-) mice. Suction electrode recordings from single rods were performed to investigate cone arrestin's ability to quench the catalytic activity of light-activated rhodopsin. In addition, the ability of cone arrestin to prevent light-induced retinal damage caused by prolonged activation of the phototransduction cascade was assessed.
RESULTS - Two independent lines of transgenic mice were obtained that expressed cone arrestin in rod photoreceptors, and each was bred into the arr1-/- background. Flash responses measured by suction electrode recordings showed that cone arrestin reduced signaling from photolyzed rhodopsin but was unable to quench its activity completely. Consistent with this observation, expression of mouse cone arrestin conferred dose-dependent protection against photoreceptor cell death caused by low light exposure to arr1-/- retinas, but did not appear to be as effective as rod arrestin.
CONCLUSIONS - Cone arrestin can partially substitute for rod arrestin in arr1-/- rods, offering a degree of protection from light-induced damage and increasing the extent of rhodopsin deactivation in response to flashes of light. Although earlier work has shown that rod arrestin can bind and deactivate cone pigments efficiently, the results suggest that cone arrestin binds light-activated, phosphorylated rhodopsin less efficiently than does rod arrestin in vivo. These results suggest that the structural requirements for high-affinity binding are fundamentally distinct for rod and cone arrestins.