The localization of lectin binding sites on photoreceptor outer segments and pigment epithelium of dystrophic retinas.

Carbohydrate-containing macromolecules on pigment epithelium (PE) and photoreceptor outer segment (OS) membranes of 14 to 16-day-old Royal College of Surgeons (RCS) rats and their genetic control (RCS-rdy+) have been localized with peroxidase-conjugated lectins from wheat germ agglutinin (WGA), Ricinus communis (RCA), Lens culinaris (LCA), and concanavalin A (Con A). All lectins stain the plasma membranes of photoreceptor inner segments and intact OSs of normal (RCS-rdy+) and dystrophic (RCS) retinas. In the normal retinas, all lectins stain also the plasma membranes of shed OSs, and WGA stains some intradisc membranes. In contrast, WGA, RCA, and Con A do not label the OS debris membranes in dystrophic retinas, but LCA labels some of them. In both normal and dystophic retinas, WGA uniformly labels both proximal and distal membrane surfaces of PE mcirovilli, whereas RCA labels primarily the distal regions. Con A labels both normal and dystrophic PE microvilli sparsely, and LCA stains the PE microvilli in RCS-rdy+ retinas more intensely than those in the RCS retinas. The major differences between the lectin labeling in normal and dystrophic retinas are the presence of LCA staining on OS debris and the absence of any other lectin staining on these membranes. Other differences are the sparse LCA staining on dystrophic PE microvillous membranes vs. the normal and the presence of WGA staining on OS intradisc membranes of normal retinas. These differences may reflect changes in the accessibility or composition of certain cell surface sugars on OS membranes and PE microvilli which may be related to the diminished rate of phagocytosis in RCS retinas.