Mannose-specific binding sites in synoviocytes of rat synovial membrane: an ultrastructural-cytochemical study.
Mannose-specific binding sites in the two types of synoviocytes (A and S) from the synovial membrane of normal rat knee joints were studied by an ultrastructural-cytochemical method using horseradish peroxidase (HRP) as a ligand. The A cells showed mannose-specific binding sites for HRP which were localized in coated pits and coated vesicles (110 nm) as well as in smooth-walled vesicles, vacuoles, and tubules. No mannose-specific binding sites for HRP were detected in the S cells. Together with previous observations on absorption of intraarticularly injected HRP in type A and type S synoviocytes, the present results strongly support the interpretation that the A cells internalize HRP by receptor-mediated endocytosis and that the S cells internalize HRP by fluid-phase endocytosis only. The present results agree with the suggestion that mannose-specific binding sites consist of two pools, the one concerned with internalization of ligand and the other with intracellular targeting of internalized ligand.
D000818:Animals; D005690:Galactose / Q000494:pharmacology; D006651:Histocytochemistry; D006735:Horseradish Peroxidase; D037181:Lectins, C-Type; D008297:Male; D008358:Mannose / Q000378:metabolism / Q000494:pharmacology; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000032:analysis*; D013583:Synovial Membrane / Q000032:analysis / Q000166:cytology*
D037181:Lectins, C-Type; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; D006735:Horseradish Peroxidase; D008358:Mannose; D005690:Galactose