title: Functional and immunochemical characterization of a novel organic anion transporter Oat8 (Slc22a9) in rat renal collecting duct.
abstract: In this study, we demonstrate that a putative membrane unknown solute transporter 1 of the rat kidney (UST1r; Slc22a9) is a multispecific transporter of organic anions (OAs). When expressed in Xenopus oocytes, UST1r mediated uptake of ochratoxin A (OTA; K(m) = 1.0 microM) and sulfate conjugates of steroids, such as estrone-3-sulfate (ES; K(m) = 3.1 microM) and dehydroepiandrosterone sulfate (DHEAS; K(m) = 2.1 microM) in a sodium-independent manner. We herein propose that UST1r be renamed OA transporter 8 (rOat8). rOat8 interacted with chemically heterogenous anionic compounds, such as nonsteroidal anti-inflammatory drugs, diuretics, probenecid, taurocholate, and methotrexate, but not with the organic cation tetraethylammonium. The rOat8-mediated ES transport was: a) cis-inhibited by 4-methylumbelliferyl sulfate and beta-estradiol sulfate, but not by glucuronide conjugates of these compounds, b) cis-inhibited by four- and five- carbon (C4/C5) dicarboxylates (succinate and glutarate (GA)), and c) trans-stimulated by GA, whereas the efflux of GA was significantly trans-stimulated by ES. By RT-PCR, rOat8 mRNA was expressed in proximal convoluted tubules and cortical and outer medullary collecting ducts, whereas in immunochemical studies, Oat8 was identified as the ñ58 kDa protein that in the collecting duct colocalized with the V-ATPase in plasma membranes and intracellular vesicles in various subtypes of intercalated cells. Molecular identification of Oat8 in these cells indicates a possible novel role of OAT family in the renal secretion/reabsorption of OA and acids and bases via affecting the V-ATPase-dependent functions.
authors.affiliation: Department of Pharmacology and Toxicology, Kyorin University School of Medicine, Tokyo, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Yokoyama
authors.forename: Naohiko
authors.initials: N
authors.lastname: Anzai
authors.forename: Marija
authors.initials: M
authors.lastname: Ljubojevic
authors.forename: Naoko
authors.initials: N
authors.lastname: Ohtsu
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sakata
authors.forename: Hiroki
authors.initials: H
authors.lastname: Miyazaki
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nonoguchi
authors.forename: Rafiqul
authors.initials: R
authors.lastname: Islam
authors.forename: Maristella
authors.initials: M
authors.lastname: Onozato
authors.forename: Akihiro
authors.initials: A
authors.lastname: Tojo
authors.forename: Kimio
authors.initials: K
authors.lastname: Tomita
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Kanai
authors.forename: Takashi
authors.initials: T
authors.lastname: Igarashi
authors.forename: Ivan
authors.initials: I
authors.lastname: Sabolic
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Endou
mesh_terms: D000818:Animals; D001692:Biological Transport; D005260:Female; D007150:Immunohistochemistry; D007685:Kidney Tubules, Collecting / Q000276:immunology* / Q000378:metabolism*; D008297:Male; D009865:Oocytes; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism*; D029362:Organic Anion Transporters, Sodium-Independent / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D014982:Xenopus laevis
chemical_list: D027361:Organic Anion Transporters; D029362:Organic Anion Transporters, Sodium-Independent; C111542:Slc22a25 protein, rat