Fig. 1. Effect of mßCD, mßCD/chol and a 1:1 mixture of mßCD and mßCD/chol (which does not change the cellular cholesterol content) on ricin endocytosis in the absence and presence of TPA to stimulate macropinocytosis. A431 cells were washed twice in Hepes medium, serum-starved for 4 hours and incubated with or without 5 mM mßCD, mßCD/chol or a 1:1 mixture of mßCD and mßCD/chol for 30 minutes at 37°C prior to addition of 1 µM TPA. After 10 minutes ¹²⁵I-labeled ricin was added to the cells, and the amounts of endocytosed ricin were measured after 15 minutes, as described in Materials and Methods. The error bars show deviations (s.d.) between three independent experiments.