Functional characterization of rat organic anion transporter 2 in LLC-PK1 cells

Rat organic anion transporter 2 (rOat2) is abundantly expressed in the liver and localized to the basolateral membrane. A previous study using the Xenopus laevis oocyte expression system has shown that rOat2 transports organic anions such as salicylate () and, in the present study, rOat2 was characterized using a mammalian expression system. In addition to the substrates previously shown to be transported by rOat2, three substrates, indomethacin [IDM, Michaelis-Menten constant (K(m)) of 0.37 microM] and nucleoside derivatives such as 3'-azido-3'-deoxythymidine (AZT, K(m) of 26 microM) and 2',3'-dideoxycytidine (ddC, K(m) of 3.08 mM), were also identified for the first time The rank order of rOat2-mediated transport of these substrates was IDM > salicylate > prostaglandin E(2) > AZT > ddC > p-aminohippurate (PAH). Ketoprofen, indocyanine green and glibenclamide are potent inhibitors of the uptake of [(14)C]salicylate via rOat2 (K(i) of approximately 12 microM), while diclofenac, benzoate, verapamil, ibuprofen, and tolbutamide are moderate inhibitors (K(i) of approximately 150 microM). The affinity of PAH, a common substrate for the OAT family, for rOat2 is low (K(i) > 1 mM) compared with the other members of the OAT family (rOat1 and rOat3). Salicylate and IDM are also substrates for rOat1, but their affinity for rOat2 was higher than that for rOat1. The present study shows that rOat2 is a multispecific transporter and suggests that it may be involved at least partly, in the hepatic uptake of IDM, salicylate and nucleoside derivatives.