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ABSTRACT: Organic anion transporter 1 (OAT1) is a p-aminohippurate/dicarboxylate exchanger that plays a primary role in the tubular secretion of endogenous and exogenous organic anions. OAT1 is located in the basolateral membrane of the proximal tubular cells and mediates the uptake of various organic anions from the peritubular fluid. In this study, we investigated the transport of antiviral nucleoside analogs via rat OAT1 (rOAT1) using a heterologous expression system in Xenopus laevis oocytes. Oocytes injected with rOAT1 cRNA showed significantly higher uptake of zidovudine (AZT) and acyclovir (ACV) than control oocytes. rOAT1-mediated uptake of AZT and ACV was probenecid-sensitive and increased by the outwardly directed gradient of glutarate. The affinity of rOAT1 for AZT and ACV was determined to be 68 and 242 microM, respectively. Five other antiviral agents that we studied (zalcitabine, didanosine, lamivudine, stavudine, and trifluridine) were also shown to be transported by rOAT1, whereas foscarnet, a phosphate analog, was not. The aforementioned nucleoside analogs lack a typical anionic group and are not very hydrophobic. This study demonstrates extension of the substrate spectrum of rOAT1 and provides a molecular basis for the pharmacokinetics of antiviral nucleoside analogs.
Journal of Pharmacology and Experimental Therapeutics 10/2000; 294(3):844-9. · 3.83 Impact Factor
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ABSTRACT: In the present study, we investigated the transport of ochratoxin A (OTA) by kidney-specific organic anion transporter 1 (OAT1). When expressed in Xenopus laevis oocytes, OAT1 mediated sodium-independent uptake of OTA (Km = 2.1 microM). Piroxicam, which has been shown to prevent the nephrotoxicity of OTA, inhibited OAT1-mediated uptake of OTA. By contrast, another protective compound, aspartame, did not. Using a cell line derived from the mouse kidney terminal proximal tubule (S3) transfected with OAT1 cDNA, we investigated the transport of OTA and also its effect on cell proliferation and cell viability. S3 cells expressing OAT1 mediated the saturable transport of OTA (Km = 0.57 microM). Cell proliferation was suppressed in S3 cells expressing OAT1 when exposed to 2 and 10 microM OTA. This suppression was rescued by the coaddition of 1 mM p-aminohippurate in the media. The present study indicates that OTA is transported by OAT1 and that the accumulation of OTA via OAT1 in proximal tubular cells is the primary event in the development of OTA nephrotoxicity.
Journal of Pharmacology and Experimental Therapeutics 07/1999; 289(3):1301-5. · 3.83 Impact Factor
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ABSTRACT: A cDNA encoding the new member of the multispecific organic anion transporter family, OAT3, was isolated by the reverse transcription-polymerase chain reaction cloning method. Degenerate primers were designed based on the sequences conserved among OAT1, OAT2, and organic cation transporter 1 (OCT1), and reverse transcription-polymerase chain reaction was performed using rat brain poly(A)+ RNA. The 536-amino acid protein sequence encoded by OAT3 showed 49, 39, and 36% identity to those of OAT1, OAT2, and OCT1, respectively. Northern blot analysis revealed that rat OAT3 mRNA is expressed in the liver, brain, kidney, and eye. When expressed in Xenopus laevis oocytes, OAT3 mediated the uptake of organic anions, such as p-aminohippurate (Km = 65 microM), ochratoxin A (Km = 0.74 microM), and estrone sulfate (Km = 2.3 microM) and a cationic compound, cimetidine. OAT3-mediated uptake of [3H]estrone sulfate was sodium-independent. para-Aminohippuric acid, estrone sulfate or ochratoxin A did not show any trans-stimulatory effect on either influx or efflux of [3H]estrone sulfate via OAT3. Organic anions such as sulfobromophthalein, probenecid, indocyanine green, bumetanide, piroxicam, furosemide, azidodeoxythymidine, 4, 4'-diisothiocyanostilbene-3,3'-disulfonic acid, and benzylpenicillin inhibited OAT3-mediated estrone sulfate uptake, while ouabain and digoxin did not. Organic cations such as tetraethylammonium, guanidine, verapamil, and quinidine did not interact with OAT3. Acidic metabolites of neurotransmitters derived from dopamine, epinephrine, norepinephrine, and serotonin inhibited the uptake of estrone sulfate via OAT3. These results suggest an important role of OAT3 in the excretion/detoxification of endogenous and exogenous organic anions, especially from the brain.
Journal of Biological Chemistry 06/1999; 274(19):13675-80. · 4.77 Impact Factor
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ABSTRACT: Carnitine is an essential component for mitochondrial beta-oxidation of fatty acid. Using the degenerate primers designed for organic anion transporters and an organic cation transporter, we isolated a novel cDNA encoding a carnitine transporter (CT1) from rat intestine. CT1 encodes a 557-amino-acid protein with 12 putative membrane-spanning domains. When expressed in Xenopus oocytes, CT1 mediated a high-affinity transport of L-carnitine (Km = 25 microM). The replacement of extracellular sodium with Li reduced CT1-mediated L-carnitine uptake to 19.8%. CT1 did not transport typical substrates for either organic anion or organic cation transporters, such as p-aminohippurate and tetraethylammonium. Octanoylcarnitine, acetylcarnitine, and gamma-butyrobetaine showed potent inhibitory effects on CT1-mediated L-carnitine uptake; betaine and d-carnitine showed moderate inhibition. CT1 mRNA was strongly expressed in the testis, colon, kidney, and liver and weakly in the skeletal muscle, placenta, small intestine, and brain. No CT1 expression was detected in the heart, spleen, or lung. The present study provides the molecular basis of carnitine transport in the body.
Biochemical and Biophysical Research Communications 11/1998; 251(2):586-91. · 2.48 Impact Factor
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ABSTRACT: In the present study, we demonstrate that NLT (novel liver-specific transport protein) is a multispecific organic anion transporter of the liver. The amino acid sequence of NLT shows 42% identity to that of the renal multispecific organic anion transporter, OAT1. When expressed in Xenopus laevis oocytes, NLT mediated uptake of organic anions, such as salicylate, acetylsalicylate, PGE2, dicarboxylates and p-aminohippurate. [14C]Salicylate uptake via NLT was saturable (Km = 88.8 +/- 23.4 microM) and sodium-independent. Expression of the mRNA of NLT was detected in the liver and kidney (liver > kidney). We propose that NLT be renamed OAT2.
FEBS Letters 06/1998; 429(2):179-82. · 3.54 Impact Factor
