Fig. 4. GABA_B-receptor internalization is mediated by clathrin-coated vesicles. In cells whose phagocytic activity is blocked by trifluoperazine, 20-minute treatment with 150 mM sucrose (b) or cytosol acidification (c) inhibits receptor internalization, which can be seen by receptor accumulation on the cell membrane and receptor reduction inside the cytoplasm. Controls (a) are cells incubated with the anti-GABA_B receptor antibody in the absence of inhibitors; the antibody is localized in endosomes and phagosomes. Incubation temperature, 25°C. Bar, 20 µm.