The successful lowering of the intracellular concentration of multidrug resistance (MDR)-type
drugs by P-glycoprotein (Pgp) relies on its ability to overcome the passive influx rate of each
MDR-type drug. Thus, the aim of the present work was to study the effect of passive
transbilayer drug movement on the multidrug resistance and its modulation. Fluorescence
quenching studies indicated that whereas the Pgp substrate rhodamine 123 traverses an
artificial lipid membrane with a lifetime of 3 min, the transbilayer movement rate of the MDR …