Formation of receptosomes from plasma membrane coated pits during endocytosis: analysis by serial sections with improved membrane labeling and preservation techniques.

摘要: Abstract The early events in the entry of ligands into cultured fibroblasts through plasma membrane clathrin-coated pits were examined by using serial sections and electron microscopy. Swiss 3T3 cells labeled at 4 degrees C with concanavalin A-horseradish peroxidase warmed to 37 for 1 or 2 min label organelles participating endocytosis. Cells fixed glutaraldehyde further preserved a contrast-enhancement technique that utilized sequential osmium/ferrocyanide, thiocarbohydrazide, osmium/ferrocyanide treatment situ. This provides exceptional preservation enhanced contrast membranous structures. Serial taken both parallel perpendicular substratum microscopy, 263 structures containing horseradish evaluated their connection membrane. All these coated found be connected either directly via necks approximately equal 170 A width up 7,000 length. These often surrounded dense filamentous network. results strongly suggest isolated vesicles do not form during endocytosis process cells.