Molucular analysis of tissue distribution and structure-function relationship of transporters responsible for the regulation of drug transport

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Tissue distribution and structure-function relationship of membrane transporters responsible for absorption and excretion of drugs have been studied, and then following results were obtained.1.Structure-function relationship of H^+-coupled peptide transportersWhen stable transfectans expressing rat peptide transporters PEPT1 and PEPT2 were treated with DEPC, a histidine-modifying agent, glycylsarcosine uptake by both transfectants were decreased. Interactions of dipeptides and beta-lactam antibiotics were analyzed, and then it became clear that alpha-amino moiety of beta-lactam antibiotics should interact with histidine residues, and may participate in substrate recognition.2.Tissue distribution and functional characteristics of renal organic ion transporters.(1)Organic anion transporter, OAT-K1 : Expression of mRNA along nephron segments was analyzed by RT-PCR.OAT-K1 mRNAs were mainly expressed in proximal straight tubules of superficial and juxtamedullary nephrons. Western blot analysis revealed that OAT-K1 is expressed only in brush-border membranes of renal tubules. Methotrexate transport by the transfectants stably expressing OAT-K1 was significantly inhibited in the presence of nonsteroidal anti-inflammatory drugs (NSAID).(2)Organic cation transporter, OCT2 : Because tetraethylammonium transport by OCT2 was H^+-gradient independent and was affected by membrane potential, OCT2 is deduced to be basolateral-type organic cation transporter. By constructing stable transfectants expressing OCT1 or OCT2, transport characteristics were further analyzed, and then it became clear that both OCT1 and OCT2 are basolateral-type organic cation transporters with broad substrate specificity and have similar substate recognition in each other.