Fig. (3) Functional Characterization of Uptake and Efflux Transporter Activity in SA7K cells. (A) Uptake of PAH by OAT-1 and inhibition by probenecid; (B) Uptake of amantadine by OCT2 and inhibition by doxepin; (C) Inhibition of MDR1-mediated efflux of digoxin by verapamil; (D) Inhibition of MRP2-mediated efflux of SN-38 by MK571. Substrate concentrations used were 10 µM in each experiment.