Abstract
A novel member of the organic anion transporter (OAT) family, Oat5 (Slc22a19), has been reported to transport a naturally occurring mycotoxin, ochratoxin A (OTA). However, neither its endogenous substrate and driving force nor physiological functions have been determined. Herein, we report the functional characterization of rat Oat5 (rOat5), as well as its intrarenal distribution and membrane localization. When expressed in Xenopus laevis oocytes, rOat5 mediated the transport of sulfate conjugates of steroids such as estrone-3-sulfate (E1S; Km = 18.9 ± 3.9 μM) and dehydroepiandrosterone sulfate (Km = 2.3 ± 0.2 μM) in a sodium-independent manner, in addition to OTA. The rOat5-mediated E1S transport was strongly inhibited by four-carbon (C4) dicarboxylate succinate and longer dicarboxylates (C7–C9). The uptake of [3H]E1S via rOat5 was significantly trans-stimulated by succinate, and the efflux of [14C]succinate was significantly trans-stimulated by E1S. A similar trans-stimulatory effect of preloaded succinate on E1S uptake was also detected in cells stably expressing rOat5 (S2 rOat5). rOat5 interacted with chemically heterogenous anionic compounds. The rOat5-mediated E1S transport was inhibited by several sulfate conjugates, such as 4-methylumbelliferyl sulfate and β-estradiol sulfate, but not by glucuronide conjugates. An immunohistochemical study showed that rOat5 was localized at the apical membrane of renal proximal tubules in the corticomedullary region. rOat5 mRNA was expressed in the late segments (S2 and S3) of proximal tubules. These results indicate that rOat5 is renal organic anion/dicarboxylates exchanger and, under physiological conditions, may function as an apical reabsorptive pathway for organic anions in proximal tubules driven by an outward gradient of dicarboxylates.
Footnotes
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This work was supported in part by grants from the Japanese Ministry of Education, Culture, Sports, Science and Technology (grants-in-aid for Scientific Research and High-Tech Research Center), the Science Research Promotion Fund of the Japan Private School Promotion Foundation, Research on Health Sciences Focusing on Drug Innovation from the Japan Health Sciences Foundation, grants-in-aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS), grants-in-aid from the Salt Science Research Foundation (no. 0524), and Health and Labor Sciences Research Grants for Research on Advanced Medical Technology: Toxicogenomics Project. P.J. is a research fellow supported by the Labor Sciences Research Grants for Research on Advanced Medical Technology: Toxicogenomics Project.
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Part of this work was presented at the 36th Annual Meeting and Scientific Exposition of the American Society of Nephrology, San Diego, CA, October 2003.
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N.A. and P.J. contributed equally to this work.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.105.088583.
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ABBREVIATIONS: OAT/Oat, organic anion transporter; PAH, para-aminohippuric acid; rOat5, rat Oat5; BBMV, brush-border membrane vesicle; NPT/Npt, sodium-dependent inorganic phosphate transporter; MRP/Mrp, multidrug resistance-associated protein; OATP/oatp, organic anion-transporting polypeptide(s); MAL, medullarly thick ascending limb; OATV1, voltage-driven organic anion transporter; EST, expressed sequence tag; E1S, estrone-3-sulfate; DHEAS, dehydroepiandrosterone sulfate; OTA, ochratoxin A; NaDC, Na+-dependent dicarboxylate transporter; HEK, human embryonic kidney; PCR, polymerase chain reaction; S1, S2, S3, the first, second, and third segments of proximal tubule, respectively; hOAT, human OAT; D-PBS, Dulbecco's modified phosphate-buffered saline; RT, reverse transcription; CCD, cortical collecting duct.
- Received April 25, 2005.
- Accepted August 1, 2005.
- The American Society for Pharmacology and Experimental Therapeutics
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