Polymorphous endocytotic organelles in the receptor-mediated endocytosis of gold-labelled alpha 2-macroglobulin complexes by human fibroblasts.
The receptor-mediated endocytosis of gold-labelled alpha 2-macroglobulin complexes with trypsin or methylamine (alpha 2M-T-Au or alpha 2M-MA-Au) was studied by electron microscopy in human skin fibroblasts. The gold label was found in coated structures and very small tubules as well as in tubulovesicular structures and in multivesicular bodies/lysosomes. Thick sections (200 nm), but especially serial thin sections, clearly showed the polymorphic character of the cellular structures involved in endocytosis. Numerous intercommunications were particularly obvious between the tubulovesicular structures, the larger vesicles and the multivesicular bodies (MVB). Continuities between MVBs and endoplasmic reticulum and interconnections between MVBs were also observed. The specificity of the staining reaction was confirmed by indirect labelling of intracellular alpha 2M by polyclonal and by monoclonal antibodies on ultracryosections. These findings are discussed in relation to observations made on epithelial cells with other ligands.
B
B
Van der Schueren
D
D
Gasser
P
P
Marynen
F
F
Van Leuven
G
G
David
J J
JJ
Cassiman
H
H
Van den Berghe
D004705:Endocytosis; D004847:Epithelial Cells; D005347:Fibroblasts / Q000502:physiology; D006048:Gold Colloid, Radioactive; D006801:Humans; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008854:Microscopy, Electron; D011869:Radioligand Assay; D011971:Receptors, Immunologic / Q000502:physiology*; D014357:Trypsin / Q000502:physiology; D000511:alpha-Macroglobulins / Q000502:physiology*
D006048:Gold Colloid, Radioactive; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011971:Receptors, Immunologic; C028939:alpha-2-macroglobulin-trypsin complex; D000511:alpha-Macroglobulins; D014357:Trypsin