Effect of cytochalasin D on receptor activation and internalization. (A) Receptor internalization of 32D[WT] cells in the presence or absence of cytochalasin D, as indicated. (Bold line) 0 minutes; (dotted line) 30 minutes; (thin line) 90 minutes; (shaded histogram) 0 minutes, with initial binding in the presence of excess nonbiotinylated–G-CSF. This is representative of three independent experiments. (B) 32D[WT] cells, in the presence or absence of cytochalasin D, were stimulated with G-CSF for 10 minutes, washed extensively, and incubated in media alone for the times indicated (G-off). Nuclear extracts were prepared at the indicated times and assayed by EMSA using the m67 and β-cas probes. This is representative of three independent experiments.