Molecular Bases of the Difference between Rod- and Cone-mediated Vision.

Abstract

In the vertebrate retina, there are two types of visual photoreceptor cells, rods and cones. Both rods and cones convert light signals to neural signals, and the resultant light responses in rods and cones are different in two aspects, light sensitivity and duration of a light response. Light sensitivity is higher in rods than in cones. Thus, rods mediate night vision, and cones mediate daylight vision. Duration of a cone light response is much shorter than that of a rod, so that the time-resolution of daylight vision is higher than that of scotopic vision. Fortunately, we succeeded in purification of rods and cones form carp (Cyprinus carpio) retina, which enables us to investigate biochemically the molecular bases of these differences in the light response between rods and cones. Our studies showed that the signal amplification in the signal transduction cascade is higher in rods than in cones, and that the reactions to terminate a photoresponse are much faster in cones than in rods. These results well explain the lower light sensitivity and shorter duration of a light response in cones than in rods.