The effect of glutathione on the ATPase activity of MRP1 in its natural membranes

The transport mechanism by which the multidrug resistance protein 1 (MRP1) effluxes cytotoxic agents out of cells is still not completely understood. However, the cellular antioxidant glutathione (GSH) has been shown to have an important role in MRP1-mediated drug transport. In this study we show th at GSH stimulates the ATPase activity of MRP1 in a natural plasma membrane environment. This stimulation was dose-dependent up to 5 mM. The MRP1 subst rates vincristine and daunorubicin do not induce MRP1 ATPase activity. In a ddition, the effect of GSH on the MRP1 ATPase activity is not increased by daunorubicin or by vincristine, In contrast, a GSH conjugate of daunorubici n (WP811) does induce the ATPase activity of MRP1. In the presence of GSH t he effect of WP811 was not significantly increased. Finally, (iso)flavonoid -induced MRP1 ATPase activity is not synergistically increased by the prese nce of GSH. In conclusion, we show that GSH has no apparent influence on th e ATPase reaction induced by several MRP1 substrates and/or modulators. The subclasses of molecules had different effects on the MRP1 ATPase activity, which supports the existence of different drug binding sites. (C) 2000 Fed eration of European Biochemical Societies.