Glutathione (GSH) plays numerous critical protective roles in the erythrocyte and GSH turnover is likely an important factor in regulating susceptibility to oxidative stress and toxins. Efflux of glutathione disulfide (GSSG) from erythrocytes is an important component in the regulation of GSH levels; however, little is known of the mechanisms involved. We hypothesize that multidrug resistance associated protein 1 (MRP1) is responsible, in part, for GSSG transport from erythrocytes. To test this, we determined the levels of MRP1 protein in erythrocyte membranes from healthy adults and compared them with intracellular levels of GSH. MRP1 levels varied substantially from person to person and were inversely correlated with levels of GSH (r =-0.39, P < 0.05). In contrast, activity levels of glutamyl cysteine ligase, the rate limiting GSH biosynthetic enzyme, were unrelated to GSH levels. To directly determine the role of MRP1 in GSSG transport, in vitro studies were conducted examining the effects of MRP1 inhibitors MK571 and verapamil on GSSG efflux. Both compounds resulted in significant but not complete inhibition (20-53%) of GSSG efflux from cells. Overall, these findings support a role for MPR1 in the regulation of erythrocyte GSH levels through the transport and elimination of GSSG from cells.
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