Cytochemical characterization of sialoglycoconjugates on rat photoreceptor cell surface.

Terminal saccharide sequences in rat photoreceptor cell surface glycoconjugates were characterized. Lectin cytochemistry and electron microscopy were used for preembedding cytochemical localization of surface carbohydrates. Neuraminidase digestion was employed for the exposure of penultimate saccharides in sialoglycoconjugates. Isolated rat retinas were incubated with ferritin-labeled wheat germ agglutinin (WGA), peanut agglutinin (PNA), and soybean agglutinin (SBA) prior to and after neuraminidase digestion. PNA and SBA did not label untreated photoreceptors. WGA densely labeled the photoreceptor surface and interphotoreceptor matrix (IPM) components. Following neuraminidase treatment, PNA, but not SBA, labeled the photoreceptor surface and the IPM. WGA labeling of the IPM was abolished, and the labeling of the photoreceptor surface was reduced. Based on the lectin specificity, it was concluded that photoreceptor surface glycoconjugates in the rat retina contain a terminal trisaccharide: sialic acid-D-galactose-(beta 1----3)-N-acetyl-D-galactosamine.