CYTOCHEMICAL DEMONSTRATION OF LECTIN BINDING SITES IN ROD PHOTORECEPTOR CELLS AND INTERPHOTORECEPTOR MATRIX OF RAT RETINAS BY LABELING FROZEN THIN-SECTIONS WITH VARIOUS LECTINS

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We examined lectin binding sites in rod photoreceptor (RP) cells and inter- photoreceptor matrix (IPM) of Wistar rat retinas in situ using frozen thin-sections reacted with various labeled lectins. Neuraminidase digestion was employed to study the glycosyl residues next to the terminal sialic acid. Lectins used in this study are as follows: concanavalin A (Con A), wheat germ agglutinin (WGA), Maclura pomifera agglutinin (MPA), peanut agglutinin (PNA) and Dolichos biflorus agglutinin (DBA) . We also used isolated rod outer segments to study MPA-binding sites of the plasma membrane of the rod outer segment (ROS).
In fluorescence micrographs of Con A- or WGA-fluorescence isothiocyanate (FITC) reacted retina, an intense staining was observed in the ROS and a meshwork-like staining was observed in the rod inner segment (RIS) and the outer nuclear layer. Electron microscopic observations of frozen thin-sections labeled with Con A- or WGA-ferritin revealed that these ligands were bound to disk membranes of the ROS, membranous structures of the RIS, entire plasma membranes of the RP cells, and the IPM. In MPA-FITC reacted retina, an intense staining in the ROS and the RIS showed a linear pattern. MPA-ferritin particles were bound to plasma membranes of the ROS and RIS, and to the IPM. In electron micrographs of isolated rod outer segments labeled with MPA-ferritin, MPA-bindings to the plasma membrane were greatly reduced, which suggest MPA was mainly bound to the IPM. No PNA- or DBA-labeling was observed in either RP cells or IPM. Following neuraminidase digestion, WGA-labeling was reduced and PNA-labeling appeared complementarily in the plasma membrane of the ROS and RIS, and the IPM.