Abstract

The present study examined how the multidrug resistance protein (MRP) 2, which is an ATP-dependent anionic conjugate transporter, also mediates transport of the chemotherapeutic cationic drug vinblastine (VBL). We show that ATP-dependent [³H]VBL (0.2 μM) uptake into membrane vesicles from Sf9 cells infected with a baculovirus encoding rabbit Mrp2 (Sf9-Mrp2) was similar to vesicles from mock-infected Sf9 cells (Sf9-mock) but could be stimulated by reduced glutathione (GSH) with a half-maximum stimulation of 1.9 ± 0.1 mM. At 5 mM GSH, initial ATP-dependent [³H]VBL uptake rates were saturable with an apparentK_m of 1.5 ± 0.3 μM. The inhibitory effect of VBL on Mrp2-mediated ATP-dependent transport of the anionic conjugate [³H]leukotriene C₄ was potentiated by increasing GSH concentrations. Membrane vesicles from Sf9-Mrp2 cells exhibited a ∼7-fold increase in initial GSH uptake rates compared with membrane vesicles from Sf9-mock cells. Uptake of [³H]GSH was osmotically sensitive, independent of ATP, and was trans-inhibited by GSH. The anionic conjugates estradiol-17β-d-glucuronide and leukotriene C₄cis-inhibited [³H]GSH uptake but only in the presence of ATP. Whereas ATP-dependent [³H]VBL uptake was stimulated by GSH, VBL did not affect [³H]GSH uptake. Our results show that GSH is required for Mrp2-mediated ATP-dependent VBL transport and that Mrp2 transports GSH independent of VBL.