Figure 2.

Effect of QT and dimers QT₂C₂ (1) and QT₂C₂Me₂ (8) on P-gp-mediated ATPase activity in crude membranes from Sf9 cells overexpressing human P-gp. (A) P-gp-mediated ATP hydrolysis was stimulated by QT with a peak at 50 to 100 μM. Verapamil (Ver., 30 μM) served as a positive control. (B) Stimulation of P-gp mediated ATP hydrolysis by QT₂C₂ (1) (white bars) and QT₂C₂Me₂ (8) (gray bars). Verapamil (Ver., 30 μM) served as a positive control. Sf9 crude membrane vesicles (10 μg) were incubated with verapamil or various concentrations of QT or dimer for 20 min at 37 °C. ATPase activity was determined by quantifying the amount of inorganic phosphate release spectrophotometrically. Each data point represents the mean of two independent experiments performed in duplicate ± SEM.