Abstract

Evidence for the presence of a novel transporter in primary cultures of rat striatal neurons and mouse cortical neurons similar in function to the multidrug resistance-associated protein (MRP1) is presented. Functional activity was assessed by efflux studies with the glutathione conjugate of monochlorobimane (B-SG). The glutathione transferase-catalyzed formation of B-SG in rat striatal neurons and mouse cortical neurons was inhibited by ethacrynic acid. The efflux of B-SG from rat striatal neurons and mouse cortical neurons was lower at 20°C than at 37°C and was lower in cells with reduced ATP concentrations compared with cells with constitutive ATP concentrations. In addition, the efflux of B-SG was inhibited by MK-571 in both rat striatal and mouse cortical neurons and by probenecid in rat striatal neurons, but not in mouse cortical neurons. Verapamil did not inhibit B-SG efflux in either rat striatal or mouse cortical neurons. Although functionally similar to MRP1, Western blot analysis with commercially available antibodies directed against human and mouse MRP1 failed to show MRP1-like protein in either whole-cell homogenates of rat striatal neurons or mouse cortical neurons, indicating that the described neuronal transporter differs in structure from human or mouse MRP1 or lacks epitopes in common with MRP1.