Immunocytochemical localization of rhodopsin-like immunoreactivity in the outer segments of the rods and single cones of chick retina.

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Abstract
Photoreceptor cells in chick retina consist of a rod and five types of cones. Immunocytochemical techniques have pinpointed rhodopsin-like immunoreactivity in the outer segments of some single cones as well as in rods. The antibody used in our study was raised against bovine rhodopsin purified by SDS-polyacrylamide gel electrophoresis. No rhodopsin-like immunoreactivity was found in the principal and accessory cone. Epon-embedded, semi-thin sections also were treated with potassium hydroxide to remove epoxy resin and then subjected to immunoreaction with the antibody. With this method the same results were obtained repeatedly, and the possibility of staining failure in double cones and some single cones due to insufficient permeability was avoided. Electron microscopy revealed that the oil droplets of stained single cones are slightly smaller and are located in a more vitreal position than those of unstained single cones. The stained single cones are presumed to be types II and III single cones. In the inner segment, especially in the Golgi region and the rER, no staining was seen. Only slight staining was found in the connecting cilium and in the small vesicular or granular structure between the oil droplet and the plasma membrane facing the heavily stained outer segment. This suggests that opsin is incorporated into the plasma membrane in the distal portion of the inner segment.