title: Galactose-specific receptors on liver cells. I. Hepatocyte and liver macrophage receptors differ in their membrane anchorage.
abstract: Colloidal gold particles coated with asialoglycoproteins are bound by hepatocytes as well as by liver macrophages. Binding by both cell types is inhibited by N-acetylgalactosamine and related saccharides and is dependent on the presence of Ca2+. We have now performed an electron microscopic study on receptor anchorage in the plasma membranes. Cells with prebound ligand were treated with 20 mM EDTA at 4 degrees C, washed free of chelator and tested for residual galactose-specific receptor activity. Whereas hepatocytes preserve binding activity (73% of untreated control), liver macrophages lose galactose-specific receptor activity (12% of untreated control). Liver macrophages regain binding activity after a 2 min incubation at 37 degrees C allowing for receptor recycling. If the macrophages were fixed with low glutaraldehyde concentration prior to EDTA treatment they fully retained their receptor activity (74% of control). Ligands were also removed from both cell types by incubation with 80 mM N-acetylgalactosamine. After washing the cells free of the competing monosaccharide, both the hepatocytes as well as the macrophages show full binding activity (120% and 85% of untreated controls). Therefore, membrane anchorage sites of the macrophage receptors are not identical to ligand-binding sites. These results suggest a Ca2+-Mg2+-dependent receptor anchorage on the macrophage plasma membrane. As shown in the accompanying paper (Roos, P.H., Hartmann, H.J., Schlepper-Schäfer, J., Kolb, H. and Kolb-Bachofen, V. (1985) Biochim. Biophys. Acta 847, 115-121), EDTA-induced dissociation from the membrane can be used for isolation of the galactose-specific receptors of liver macrophages.
mesh_terms: D000116:Acetylgalactosamine / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure; D004492:Edetic Acid / Q000494:pharmacology; D006046:Gold / Q000378:metabolism; D007785:Lactose / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008854:Microscopy, Electron; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000378:metabolism
chemical_list: D011956:Receptors, Cell Surface; C039707:galactose receptor; D012710:Serum Albumin, Bovine; D006046:Gold; D004492:Edetic Acid; D007785:Lactose; D000116:Acetylgalactosamine; D002118:Calcium