Initial steps in receptor-mediated endocytosis

摘要: We have examined the shape and distribution of clathrin-coated pits in Swiss 3T3 cells at 4 or 37 degrees C using electron microscopy with serial sections immunofluorescence light microscopy. Both groups were fixed glutaraldehyde preserved further a membrane contrast enhancement technique consisting sequential osmium-ferrocyanide, thiocarbohydrazide osmium-ferrocyanide treatment situ. Concanavalin A-horseradish peroxidase (conA-HRP) was used to identify these structures participating endocytosis. Two hundred twenty-two analysed; 126 from C, 96 after 3 min warm-up C. All coated labeled conA-HRP had demonstrable connections plasma membrane. These morphologically classified into three categories: (a) flat pits; (b) curved (c) narrow-neck At 27% narrow neck whereas only 1% such connections. Receptosomes (endosomes) found incubation indicating that active endocytosis occurring but not Immunofluorescence anti-clathrin antibody quantitate number incubated prior fixation. No difference detected. There 426 +/- 122 per cell 441 106 results support hypothesis formation connected pit surface is an early step mechanism receptor-mediated