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 [³H]methotrexate (MTX) was stimulated by infection of cDNAs for hMRP3 and rMRP3. The mean (± SE) K_m values for the uptake of 17 estradiol 17-D-glucuronide ([³H]E₂17 G) by hMRP3 and rMRP3 were 42.9 ± 4.3 M and 33.4 ± 2.2 M, respectively. Although the K_i values of glucuronides on the uptake of E₂17G 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 E₂17G 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.