3.3Calcein-AM assay
Five extracts increased calcein fluorescence in PBCEC cells, indicating that P-glycoprotein-mediated efflux of calcein-AM was inhibited. The maximal effective concentrations (ECmax) ranged from 83.0% to 347.7%. The 50% effective concentrations (EC50) of these drugs ranged from 0.11 to 0.95 μg/mL (Table 2). The well-known P glycoprotein inhibitor, verapamil, was used as positive control (Tiberghien and Loor, 1996). As expected, verapamil interacted with P-glycoprotein in PBCECs (Table 2).