Immunogold localization of chondroitin 6-sulfate in the interphotoreceptor matrix of normal and RCS rats.

Localization of chondroitin 6-sulfate (6S) in the interphotoreceptor matrix (IPM) of both normal and RCS rats with inherited retinal dystrophy has been carried out using light and electron microscopic immunogold cytochemistry. In the normal rat, 6S antibody labeling was found in highest concentration at the apical surface of the retinal pigment epithelium (RPE) and between adjacent photoreceptors near their basal inner segment-outer segment junction. In the apical zone, label was localized in the IPM and toward the distal portions of the RPE apical processes. In the basal zone, label was found in the IPM and near the outer plasma membranes of inner and outer segments. Interstitial labeling, between the shafts of outer segments, occurred at much lower concentration than in the apical and basal zones. In all zones, the extent of labeling appeared to be space-dependent; it was most abundant where extracellular spaces were large, and little was present where adjacent cell membranes were contiguous. In the dystrophic rat, apical zone labeling of the RPE apical processes was minimal; instead, the relatively small amount of label that was present was localized primarily in the IPM and within encapsulated spaces of membranous whorls of debris. Label was most concentrated in the basal zone, primarily associated with the IPM within abundant interphotoreceptor spaces, and near the plasma membranes of disorganized inner and outer segments. In isolated eyecups and neural retinas, some labeling persisted after extensive buffer rinses which suggests that chondroitin 6-sulfate is a somewhat insoluble component of the IPM in the rat retina.