Figure 5.

Selective effects of filipin and chlorpromazine on the activity of cholera and diphtheria toxins. CaCo-2 and A431 cells were incubated in the absence or presence of 1 μg/ml filipin or 25 μg/ml chlorpromazine for 1 h at 37°C. Then the cells were exposed to either 0.03 nM CT or 100 ng/ml DT for an additional 2 h at 37°C and assayed for CT stimulation of cAMP accumulation or DT inhibition of protein synthesis as described in Materials and Methods. The results represent the mean ± SEM of two experiments, each done in triplicate. Absolute inhibition of protein synthesis in DT-treated cells was between 30–50%.