THE BOVINE ROD OUTER SEGMENT GUANYLATE-CYCLASE, ROS-GC, IS PRESENT INBOTH OUTER SEGMENT AND SYNAPTIC LAYERS OF THE RETINA

Cyclic-GMP, which plays a pivotal role in visual transduction in the v ertebrate retina, is synthesized by guanylate cyclase. The purpose of this study was to localize a rod outer segment-derived particulate gua nylate cyclase (ROS-GC) to the retina of several species that have dif ferent populations of rods and cones. A rabbit antibody was raised aga inst a synthetic peptide, corresponding to the sequence A107-L125 of b ovine ROS-GC. Western blot analysis showed a single immunoreactive ban d at about 115 kDa with bovine rod outer segments but not with human r od outer segments. Light microscopic immunocytochemistry of tissue sec tions revealed immunoreactivity in the outer segment layer and in the outer and inner plexiform layers. The rod-rich rat retina showed unifo rm immunolabeling of outer segments; the cone-containing cat retina sh owed heavily labeled cone outer segments and lighter labeling of rod o uter segments; the cone-rich chicken retina showed a uniformly and int ensely labeled outer segment layer. Preincubation of the primary antib ody with the peptide completely blocked antibody binding. Electron mic roscopic immunocytochemistry of the eat retina confirmed the presence of guanylate cyclase in photoreceptor outer segments and demonstrated its association with disk and plasma membranes. These data support a c oncept in which guanylate cyclase is much more concentrated in the out er segments of cones than rods. The immunolabeling of the plexiform la yers suggests that the particulate guanylate cyclase is not unique to the photoreceptor outer segments, and may also play a role in transduc tion processes of retinal synapses.