FIG. 2.

Binding of AC toxin to sheep RBC shows a steep calcium concentration dependence. Sheep RBC were washed three times in buffer A and resuspended at 10⁷/ml in the same buffer. Calcium was added to achieve the indicated free calcium concentrations. AC toxin (10 μg/ml) was added and incubated for 30 min at 37°C. Cells were washed and incubated with polyclonal antibody as described in Materials and Methods. Data are expressed as mean fluorescence obtained from flow cytometry. Each point represents mean ± standard deviation from three similar experiments.