Figure 2.

Inhibition of toxin activity and activation in CaCo-2 cells by filipin but not CADs. (A) CaCo-2 cells were treated with increasing concentrations of filipin (•), chlorpromazine (○), or imipramine (▪) for 1 h at 37°C. The cells were then incubated an additional 2 h at 37°C with 0.03 nM CT and assayed for cAMP accumulation as described in Materials and Methods. (B) CaCo-2 cells were incubated for 1 h at 37°C in the absence (UNTREATED) or presence of the indicated effector (1 μg/ml BFA and filipin; 10 μg/ml chlorpromazine and imipramine). The cells then were incubated with ¹²⁵I-CT for 1 h at 4°C in media containing the effector, washed and either harvested or incubated an additional 1 h at 37°C in fresh medium with effectors. All cells were then analyzed for the formation of CT-A₁ peptide as described in Materials and Methods.