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

Rat organic anion transporter 2 (rOat2) is abundantly expressed in the live r and localized to the basolateral membrane. A previous study using the Xen opus laevis oocyte expression system has shown that rOat2 transports organi c anions such as salicylate (Sekine et al., 1998) 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 substr ates, indomethacin [IDM, Michaelis-Menten constant (K-m) of 0.37 muM] and n ucleoside derivatives such as 3'-azido-3'-deoxythymidine (AZT, K-m of 26 mu M) and 2',3'-dideoxycytidine (ddC, K-m of 3.08 mM), were also identified fo r the first time The rank order of rOat2-mediated transport of these substr ates was IDM > salicylate > prostaglandin E-2 > AZT > ddC > p-aminohippurat e (PAH). Ketoprofen, indocyanine green and glibenclamide are potent inhibit ors of the uptake of [C-14]salicylate via rOat2 (K-i of similar to 12 muM), while diclofenac, benzoate, verapamil, ibuprofen, and tolbutamide are mode rate inhibitors (K-i of similar to 150 muM). The affinity of PAH, a common substrate for the OAT family, for rOat2 is low (K-i > 1 mM) compared with t he other members of the OAT family (rOat1 and rOat3). Salicylate and IDM ar e also substrates for rOat1, but their affinity for rOat2 was higher than t hat for rOatl. The present study shows that rOat2 is a multispecific transp orter and suggests that it may be involved at least partly, in the hepatic uptake of IDM, salicyiate and nucleoside derivatives.