Fig. 8.

Inhibitory effect of TPGS, PEG_2K-VE, PEG_2K-VE₂, PEG_5K-VE or PEG_5K-VE₂ on verapamil-stimulated P-gp ATPase activity. Test samples containing verapamil (50µM) and PEG-derivatized Vitamin E conjugates (final concentrations at 10 and 100 µM, respectively) or Na₃VO₄ (a selective inhibitor of P-gp) were incubated with P-gp membrane for 5 min at 37 °C. The reaction was initiated by the addition of MgATP followed by another 40 minutes’ incubation at 37°C. ATP detection reagent was then added luminescence was examined. *p < 0.05 and **p < 0.001 (vs TPGS of equivalent concentration). Values are reported as the means ± SD for triplicate samples.