Functional characteristics and membrane localization of rat multispecific organic cation transporters, OCT1 and OCT2, mediating tubular secretion of cationic drugs

Yumiko Urakami, Masahiro Okuda, Satohiro Masuda, Hideyuki Saito, Ken Ichi Inui

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Abstract

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 Commun 224:500-507). 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 K(m) 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 (K(i)) 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.

Original languageEnglish
Pages (from-to)800-805
Number of pages6
JournalJournal of Pharmacology and Experimental Therapeutics
Volume287
Issue number2
Publication statusPublished - Dec 1 1998
Externally publishedYes

Fingerprint

Tetraethylammonium
Madin Darby Canine Kidney Cells
Cations
Membranes
Pharmaceutical Preparations
1-Methyl-4-phenylpyridinium
Kidney
Quinidine
Cimetidine
Guanidine
Microvilli
Substrate Specificity
Nicotine
Complementary DNA
Antibodies

All Science Journal Classification (ASJC) codes

  • Molecular Medicine
  • Pharmacology

Cite this

Functional characteristics and membrane localization of rat multispecific organic cation transporters, OCT1 and OCT2, mediating tubular secretion of cationic drugs. / Urakami, Yumiko; Okuda, Masahiro; Masuda, Satohiro; Saito, Hideyuki; Inui, Ken Ichi.

In: Journal of Pharmacology and Experimental Therapeutics, Vol. 287, No. 2, 01.12.1998, p. 800-805.

Research output: Contribution to journalArticle

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abstract = "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 Commun 224:500-507). 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 K(m) 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 (K(i)) 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.",
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