[Organic anion carriers].

Recent studies using molecular biological techniques elucidated various organic anion carriers at the sinusoidal and the canalicular liver plasma membrane. Two sinusoidal membrane carrier have been cloned; Na+/taurocholate cotransporting polypeptide (Ntcp, 51 kDa), which mediates secondary active transport of bile acids, and Cl- -dependent organic anion-transporting protein (oatp, 74 kDa), which transports organic anions and bile acids. The existance of at least two canalicular membrane carriers for bile acids and organic anions have been identified. Both carriers transport substrates by the ATP-dependent primary active transport. As a bile acid carrier, a 110 kDa protein has been purified. Recently, the multidrug resistance protein (MRP), a member of the ATP binding cassette (ABC) transporter superfamily, is reported to closely relate to an ATP-dependent canalicular organic anion carrier.