title: Redistribution of cell surface transferrin receptors prior to their concentration in coated pits as revealed by immunoferritin labels.
abstract: Immunocytochemistry has been used to study distribution of cell surface transferrin receptors in erythroid, leukemic (K562) cells. The cells were fixed and labelled with monoclonal (OKT-9) anti-transferrin receptor antibodies; the antibody-labelled receptors were then detected by either immunofluorescein- or immunoferritin-antimouse-antibody conjugates. Typically, the immunoferritin labels were distributed diffusely at the non-coated regions of the cell surface as well as concentrated in the clathrin-coated pits. To examine further this pattern of distribution, cells were labelled at 0 degrees C and then warmed to 37 degrees C for zero to 30 min prior to fixation. The majority of the immunoferritin labels were initially dispersed in small groups at the non-coated regions of the cell surface (mean = 6 immunoferritin labels/cluster), but larger groups were common subsequent to incubation at 37 degrees C (mean = 13 immunoferritin labels/cluster). However, the size of immunoferritin labels in the coated pits was unchanged (mean = 12 immunoferritin labels/pit). Immunoferritin labels were typical in coated and uncoated vesicles 1 min after warming to 37 degrees C, but common in endosomes, multivesicular bodies and lysosomes by 30 min. It appears that single cell-surface receptors form large aggregates prior to their concentration in coated pits. Coated vesicles, uncoated vesicles, and endosomal vacuoles may together form the non-lysosomal compartment where the internalized receptors might be dissociated from the ligands (antibodies).
authors.forename: T P
authors.initials: TP
authors.lastname: Cheng
mesh_terms: D000911:Antibodies, Monoclonal; D002460:Cell Line; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism* / Q000648:ultrastructure; D011992:Endosomes / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006801:Humans; D007938:Leukemia; D004915:Leukemia, Erythroblastic, Acute; D008854:Microscopy, Electron; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011990:Receptors, Transferrin; D013601:T-Lymphocytes / Q000378:metabolism / Q000648:ultrastructure; D014168:Transferrin / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D011956:Receptors, Cell Surface; D011990:Receptors, Transferrin; D014168:Transferrin