cDNA cloning, functional characterization, and tissue distribution of an alternatively spliced variant of organic cation transporter hOCT2 predominantly expressed in the human kidney.
A cDNA coding a novel organic cation transporter, hOCT2-A, was isolated from human kidney. The hOCT2-A cDNA is an alternatively spliced variant of hOCT2 with an insertion of 1169 bp. The open reading frame encodes a 483-amino acid protein that has 81% amino acid identity with hOCT2. From hydropathy analysis, hOCT2-A is predicted to have nine transmembrane domains. hOCT2-A mRNA is expressed mainly in kidney and weakly in brain, liver, colon, skeletal muscle, bone marrow, spinal cord, testis, and placenta. When expressed in HEK293 cells, hOCT2-A stimulated the uptake of tetraethylammonium (TEA) in an electrogenic manner. The transport of TEA by hOCT2-A-transfected cells was saturable with the apparent Km value of 63 microM. hOCT2-A stimulated the uptake of TEA, 1-methyl-4-phenylpyridinium, and cimetidine as well as did hOCT2. The uptake of guanidine and choline by hOCT2-transfected cells also increased markedly but not that by hOCT2-A-transfected cells. The uptake of TEA mediated by hOCT2-A but not by hOCT2 was inhibited significantly by organic cations such as procainamide, N-acetylprocainamide, and levofloxacin, indicating that hOCT2-A differs from hOCT2 in its affinity for several compounds. These findings suggested that hOCT2-A contributes to the renal clearance of endogenous and exogenous organic cations.
Urakami
Yumiko
Y
Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan.
Akazawa
Maiko
M
Saito
Hideyuki
H
Okuda
Masahiro
M
Inui
Ken-Ichi
K
D017398:Alternative Splicing; D000595:Amino Acid Sequence / Q000235:genetics; D001483:Base Sequence / Q000235:genetics; D002412:Cations / Q000493:pharmacokinetics / Q000494:pharmacology; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics*; D014644:Genetic Variation; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008969:Molecular Sequence Data; D027701:Organic Cation Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000075102:Organic Cation Transporter 2; D019789:Tetraethylammonium / Q000378:metabolism; D014018:Tissue Distribution; D014162:Transfection
D002412:Cations; D018076:DNA, Complementary; D027701:Organic Cation Transport Proteins; D000075102:Organic Cation Transporter 2; C491013:SLC22A2 protein, human; D019789:Tetraethylammonium