Fig. 2. Effect of thapsigargin on the endocytosis of ricin. MDCK II cells were preincubated with or without the indicated concentrations of thapsigargin for 30 minutes at 37°C before TAG- and biotin-labeled ricin (30 ng/ml) was added to the medium. The incubation was continued for either 20 minutes or 2 hours before the cells were washed with 0.1 M lactose and then lysed. The amount of TAG- and biotin-labeled ricin in the lysates was measured using streptavidin beads and Origen Analyzer. Deviations between duplicates are represented by error bars.