title: Identification and functional characterization of a new human kidney-specific H+/organic cation antiporter, kidney-specific multidrug and toxin extrusion 2.
abstract: A cDNA coding a new H+/organic cation antiporter, human kidney-specific multidrug and toxin extrusion 2 (hMATE2-K), has been isolated from the human kidney. The hMATE2-K cDNA had an open reading frame that encodes a 566-amino acid protein, which shows 94, 82, 52, and 52% identity with the hMATE2, hMATE2-B, hMATE1, and rat MATE1, respectively. Reverse transcriptase-PCR revealed that hMATE2-K mRNA but not hMATE2 was expressed predominantly in the kidney, and hMATE2-B was ubiquitously found in all tissues examined except the kidney. The immunohistochemical analyses revealed that the hMATE2-K as well as the hMATE1 was localized at the brush border membranes of the proximal tubules. HEK293 cells that were transiently transfected with the hMATE2-K cDNA but not hMATE2-B exhibited the H+ gradient-dependent antiport of tetraethylammonium (TEA). Transfection of hMATE2-B had no affect on the hMATE2-K-mediated transport of TEA. hMATE2-K also transported cimetidine, 1-methyl-4-phenylpyridinium (MPP), procainamide, metformin, and N1-methylnicotinamide. Kinetic analyses demonstrated that the Michaelis-Menten constants for the hMATE2-K-mediated transport of TEA, MPP, cimetidine, metformin, and procainamide were 0.83 mM, 93.5 microM, 0.37 mM, 1.05 mM, and 4.10 mM, respectively. Ammonium chloride-induced intracellular acidification significantly stimulated the hMATE2-K-dependent transport of organic cations such as TEA, MPP, procainamide, metformin, N1-methylnicotinamide, creatinine, guanidine, quinidine, quinine, thiamine, and verapamil. These results indicate that hMATE2-K is a new human kidney-specific H+/organic cation antiporter that is responsible for the tubular secretion of cationic drugs across the brush border membranes.
authors.affiliation: Department of Pharmacy, Kyoto University Hospital, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: Satohiro
authors.initials: S
authors.lastname: Masuda
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Terada
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yonezawa
authors.forename: Yuko
authors.initials: Y
authors.lastname: Tanihara
authors.forename: Koshiro
authors.initials: K
authors.lastname: Kishimoto
authors.forename: Toshiya
authors.initials: T
authors.lastname: Katsura
authors.forename: Osamu
authors.initials: O
authors.lastname: Ogawa
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Inui
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D017920:Antiporters / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002412:Cations / Q000378:metabolism*; D002460:Cell Line; D017124:Conserved Sequence; D006801:Humans; D007150:Immunohistochemistry; D007668:Kidney / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016366:Open Reading Frames; D011522:Protons; D017386:Sequence Homology, Amino Acid; D019789:Tetraethylammonium / Q000378:metabolism / Q000494:pharmacology; D014118:Toxins, Biological / Q000378:metabolism*; D014162:Transfection
chemical_list: D017920:Antiporters; D002412:Cations; D011522:Protons; D014118:Toxins, Biological; D019789:Tetraethylammonium