Fig. 8. GABA_B receptors are internalized by non-coated endocytosis. Cells preincubated at 4°C for 30 minutes and labeled with anti-GABA_B receptor antibody (dilution 1:100) for 30 minutes (a) are fixed after a 20-minute chase at 25°C in the absence (b) or in the presence of non-coated-pit endocytosis inhibitors filipin (c) and nystatin (d). (e) Measurement of the internalization representatively shown in b-d. Constitutive receptor internalization is partially inhibited by filipin (0.1 µg/ml) and nystatin (2 µg/ml) (47% and 38%, respectively); P<0.01, Student's t-test). Data were normalized to cells before internalization at 25°C (shown in a). Bar, 20 µm.