Transport activity of human MRP3 expressed in Sf9 cells: Comparative studies with rat MRP3

Purpose. Multidrug resistance-associated protein 3 (MRP3) was initially cloned as a hepatic transporter induced under cholestatic/hyperbilirubinemic conditions. In the present study, transport property of human MRP3 (hMRP3) was compared with that of rat MRP3 (rMRP3). Methods. Adenosine 5' triphosphate (ATP)-dependent uptake of several organic anions into the membrane vesicles isolated from the Sf9 cells expressing hMRP3 and rMRP3 was measured by rapid filtration technique. Results. ATP-dependent uptake of glucuronide conjugates, glutathione conjugates, and [H-3]methotrexate (MTX) was stimulated by infection of cDNAs for hMRP3 and rMRP3. The mean (+/- SE) K-m values for the uptake of 17beta estradiol 17beta-D-glucuronide ([H-3]E(2)17 betaG) by hMRP3 and rMRP3 were 42.9 +/- 4.3 muM and 33.4 +/- 2.2 mum, respectively. Although the K-i values of glucuronides on the uptake of E(2)17betaG were similar in humans and rats, hMRP3 exhibited higher K-i values toward MTX. In addition. although glycocholate and taurolithocholate 3-sulfate (TLC-S) were transported by both hMRP3 and rMRP3, taurocholate was only transported to a significant degree by rMRP3. Moreover, the inhibitory effect of taurocholate and glycocholate on the transport of E(2)17betaG was much more potent in rMRP3 compared to hMRP3. Conclusion. Collectively, the substrate specificity of hMRP3 resembles that of rMRP3 although differences were observed, particularly in bile acid transport.