Expression of MRP1 and the resistance to sodium arsenite in Jurkat cells. (A) Crude membranes (100 μg protein) were prepared and separated by 7.5% SDS-PAGE and transferred to a PVDF membrane. The transferred proteins were reacted with an antibody against MRP1 as described in “Patients, materials, and methods.” KB/MRP membrane vesicles (10 μg) were used as a positive control. (B) Jurkat and S1T cells were incubated with the indicated concentrations of drugs for 72 hours, and cell viability was determined by the MTT assay. The points represent the means of triplicate determinations, and the bars show SD.