PT  - JOURNAL ARTICLE
AU  - Yumiko Urakami
AU  - Masahiro Okuda
AU  - Satohiro Masuda
AU  - Hideyuki Saito
AU  - Ken-Ichi Inui
TI  - Functional Characteristics and Membrane Localization of Rat Multispecific Organic Cation Transporters, OCT1 and OCT2, Mediating Tubular Secretion of Cationic Drugs
DP  - 1998 Nov 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 800--805
VI  - 287
IP  - 2
4099  - http://jpet.aspetjournals.org/content/287/2/800.short
4100  - http://jpet.aspetjournals.org/content/287/2/800.full
SO  - J Pharmacol Exp Ther1998 Nov 01; 287
AB  - We have isolated a kidney-specific organic cation transporter, rat OCT2, which is distinct from rat OCT1 (Okuda M, Saito H, Urakami Y, Takano M and Inui K (1996) Biochem Biophys Res Commun224:500–507). In our study, the functional characteristics and membrane localization of OCT1 and OCT2 were investigated by uptake studies using MDCK cells transfected with rat OCT1 or OCT2 cDNA (MDCK-OCT1 or MDCK-OCT2) and immunological studies. Tetraethylammonium (TEA) uptake by both MDCK-OCT1 and MDCK-OCT2 cells was markedly elevated when TEA was added to the basolateral medium, but not to the apical medium. Efflux of TEA from MDCK-OCT1 and MDCK-OCT2 cells was not changed by extracellular pH from 5.4 to 8.4, whereas TEA uptake by both transfectants was decreased by acidification of extracellular medium. Apparent Km values for TEA uptake by MDCK-OCT1 and MDCK-OCT2 cells were 38 and 45 μM, respectively. Although various hydrophilic organic cations such as 1-methyl-4-phenylpyridinium, cimetidine, quinidine, nicotine, N1-methylnicotinamide and guanidine markedly inhibited TEA uptake by both MDCK-OCT1 and MDCK-OCT2 cells, there were no significant differences in the apparent inhibition constants (Ki ) against these organic cations between both transfectants. Furthermore, immunological studies using a polyclonal antibody against OCT1 revealed that OCT1 was expressed in the basolateral membranes but not in the brush-border membranes of the rat kidney. These results suggested that both OCT1 and OCT2 are basolateral-type organic cation transporters with broad substrate specificities, mediating tubular secretion of cationic drugs. The American Society for Pharmacology and Experimental Therapeutics