title: Endocytosis and degradation of interstitial retinol-binding protein: differential capabilities of cells that border the interphotoreceptor matrix.
abstract: Between the pigment epithelium and the outer limiting membrane of the retina is an extracellular compartment filled with the interphotoreceptor matrix (IPM). A prominent component of the IPM is a glycoprotein known as interstitial retinol-binding protein (IRBP). Using in vitro techniques, we compared the ability of the cells that border this compartment to internalize colloidal gold (CG) coated with either IRBP or ovalbumin, a glycoprotein not found in the IPM. Neither IRBP-CG nor ovalbumin-CG was internalized by the Muller's cells. Both rod and cone photoreceptors take up IRBP-CG, which is observed in small vesicles and multivesicular bodies. Neither photoreceptor type takes up ovalbumin-CG. Acid phosphatase cytochemistry indicates that acid phosphatase reaction product in the multivesicular bodies co-localizes with IRBP-CG, which suggests that this molecule is degraded by rod and cone photoreceptors and is not recycled. The pigment epithelium internalizes IRBP-CG and ovalbumin-CG, both of which remain in small cytoplasmic vesicles near the apical plasma membrane. There is no indication that vesicles that contain either IRBP-CG or ovalbumin-CG fuse with the lysosomal system in the pigment epithelial cells during the incubation.
mesh_terms: D000818:Animals; D002417:Cattle; D004705:Endocytosis; D005109:Extracellular Matrix / Q000378:metabolism; D008854:Microscopy, Electron; D010047:Ovalbumin / Q000378:metabolism; D010857:Pigment Epithelium of Eye / Q000378:metabolism*; D012160:Retina / Q000378:metabolism*; D012177:Retinol-Binding Proteins / Q000378:metabolism*; D054839:Retinol-Binding Proteins, Plasma
chemical_list: D012177:Retinol-Binding Proteins; D054839:Retinol-Binding Proteins, Plasma; D010047:Ovalbumin