Localization of lectin receptors on bovine photoreceptor cells using dextran-gold markers

Using a newly developed dextran-gold particle preparation combined with both pre- and post-embedding labeling techniques, three lectins were investigated for their surface and intracellular binding patterns in bovine retinal photoreceptor cells. Concanavalin A staining revealed heavy labeling of both the inner and outer segment plasma membranes (preembedded labeling), and intense labeling of the outer segment with lower levels in the inner segment (postembedded labeling). Rods and cones had similar patterns. Ricinus communis agglutinin-120 revealed only sparse to moderate labeling of the rod inner and outer segments (preembedded labeling). Much heavier labeling was apparent on the cone outer and inner segments. Direct labeling of thin sections revealed generally sparse labeling of inner and outer segments, but there was a noticeably greater intensity of binding in the basal region of rod outer segments. Wheat germ agglutinin revealed heavy labeling of rod and cone outer segments, with much reduced binding in the corresponding inner segments (preembedded labeling). A similar pattern was visible in directly labeled thin sectioned tissue, with the additional appearance of heavy binding to the proximal region of the connecting cilium. This latter binding is suggestive of a specialized connecting cilium region, possibly involved in regulation of rhodopsin transport to or prevention of backflow from the outer segment.