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Abstract
The interphotoreceptor matrix (IPM) is a mixture of acidic mucosubstances, which can be demonstrated histochemically with cationic dyes, such as Alcian blue, and metal precipitates, such as colloidal iron. In the normal rat retina, staining of the IPM with these reagents is found predominantly at the apical surface of the retinal pigment epithelium (RPE) and, to a lesser extent, at the junction of the photoreceptor inner and outer segments (basal IS/OS zone). The authors have attempted to characterize the IPM in these two regions using histochemical staining of wax-embedded sections. Prior to staining, the following chemical treatments or enzymatic digestions were performed: neuraminidase (NA), with or without prior deacetylation, mild acid hydrolysis (MAH), testicular hyaluronidase (TH), Streptomyces hyaluronidase (SH), and chondroitinase AC (ChAC). NA alone, deacetylation/NA, and MAH all result in great reduction or total loss of stainable IPM at the RPE apical surface, and only slight or no reduction of stainable IPM in the basal IS/OS zone. Since these procedures remove sialoglycoconjugates, the findings suggest that the IPM concentrated at the apical surface of the RPE is composed in large part of sialoglycoconjugates, that little sialoglycoconjugate is present in the basal zone, and that the sialoglycoconjugates are of a neuraminidase-labile group. SH produces little or no reduction of stainable IPM in either the apical RPE or basal IS/OS zones. TH and ChAC also cause little or no reduction of stainable IPM at the RPE apical surface, but produce a great reduction of stainable IPM in the basal IS/OS zone, leaving a small amount of residual basal material. Since SH digests only hyaluronic acid, and TH and ChAC both digest hyaluronic acid and chondroitin SO4 A and C, the findings suggest that little or no hyaluronic acid is present in either the apical RPE or basal IS/OS zones, and the IPM at the RPE apical surface contains little or no chondroitin SO4 A and C, whereas the stainable IPM in the basal IS/OS zone is composed, at least in large part, of chondroitin SO4 A and C. Predominant basal localization of chondroitin SO4 is further suggested by the staining of this region with Alcian blue at low pH. Sequential digestion with TH/MAH or ChAC/NA produces a complete removal of all stainable IPM, including the TH-insensitive residual basal material. This residual material at the basal IS/OS zone, therefore, appears to be sialoglycoconjugate.(ABSTRACT TRUNCATED AT 400 WORDS)