Cyclic nucleotides in rod- and cone-dominant retinas.

Rod-and cone-dominant retinas differ in their relative content of cyclic AMP and cyclic GMP. Cyclic GMP is concentrated in retinas dominated by rods and is responsive to light; cyclic AMP is enriched in those having a majority of cones. Light reduces by about 50% the content of cyclic AMP in cone-dominant retinas, but the levels of cyclic GMP are affected only minimally. Microdissection of rod-dominant retinas shows that most of the cyclic GMP is localized in photoreceptor cells whereas cyclic AMP is evenly distributed throughout the retina. In contrast, our studies of cyclic nucleotides and the morphological changes that occur in cone visual cells of the ground squirrel retina, during hibernation and iodoacetate-induced cone degeneration, suggest that cyclic AMP is localized in cone visual cells. By analogy with the rod system, cyclic AMP may modulate the intracellular metabolism of cones.