Mannose-sensitive HRP endocytosis by the retinal pigment epithelium.
Mannose-sensitive endocytosis by rat retinal pigment epithelium (RPE) explants was characterized using the mannose-rich glycoprotein horseradish peroxidase (HRP). The number of HRP-containing endosomes in the RPE was morphologically quantitated by light microscopy while the amount of HRP ingested was biochemically quantitated by enzyme assay. HRP internalized via a mannose-sensitive receptor was differentiated from fluid-phase uptake in competitive inhibition studies using D-mannose. Morphological results showed that most HRP-containing endosomes formed within the first 15 min of incubation and showed little increase in number during 4 hr of continued incubation with HRP. In contrast, the biochemical assay showed a steady increase in the amount of HRP in RPE endosomes measured over time. The addition of 10 mM D-mannose to the incubation medium was associated with a significant decrease in both the number of HRP-containing endosomes and the amount of HRP ingested by RPE explants. Values indicate that half of the total uptake of HRP is mediated by a mannose-sensitive receptor while the balance is ingested via non-specific fluid-phase endocytosis.
Heth
C A
CA
Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, MI 48201.
Bernstein
M H
MH
D000818:Animals; D004705:Endocytosis; D006651:Histocytochemistry; D006735:Horseradish Peroxidase / Q000493:pharmacokinetics*; D008358:Mannose / Q000494:pharmacology*; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D010857:Pigment Epithelium of Eye / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D011919:Rats, Inbred Strains
D006735:Horseradish Peroxidase; D008358:Mannose