Fig. 2. (A) Rate of internalization of CT in non-induced () and induced () BHK cells with inducible expression of antisense CHC, which inhibits clathrin-dependent endocytosis. The cells were washed, and TAG- and biotin-labeled CT (9 ng/ml) in 0.2 ml of Hepes-buffered MEM medium was added to each well containing approximately 35,000 cells. The cells were incubated at 37°C for 2-20 minutes, and bound and endocytosed CT were quantified as described in Materials and Methods, and is presented here as percent of total cell-associated toxin (mean ± s.d., n=6). The amount of total cell-associated CT after 2 and 20 minutes of endocytosis was 0.058 and 0.47 ng/35,000 cells, respectively. (B) Endocytosis of ¹²⁵I-labeled transferrin in BHK cells with (open bar) and without (filled bar) induction of antisense CHC. Endocytosed transferrin was quantified after 5 minutes of internalization as described in Materials and Methods. The results are mean ± s.d. (n=6).