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 17β estradiol 17β-D-glucuronide ([³H]E₂17 βG) by hMRP3 and rMRP3 were 42.9 ± 4.3 μM and 33.4 ± 2.2 μM, respectively. Although the K_i values of glucuronides on the uptake of E₂17βG 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 E₂17βG 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.