Bumetanide is not transported by the Ntcp or by the oatp: evidence for a third organic anion transporter in rat liver cells

Horz, Jürgen A.; Honscha, Walther; Petzinger, Ernst

doi:10.1016/0005-2760(95)00239-1

Cited by 15 publications

(14 citation statements)

References 13 publications

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“…Thus, the liver needs multispecific transporter(s) of anionic compounds (18,19). cMOAT and oatp may play certain roles in organic anion transport in the liver; however, the multiplicity of drug transport has never been fully explained (20,21). Recently, organic anion/dicarboxylate exchange systems in the liver and brain have been identified (22,23), and a search of a data base revealed the existence of a liver protein that is structurally related to OAT1 but whose function has not been determined (24).…”

Section: Discussionmentioning

confidence: 99%

Expression Cloning and Characterization of a Novel Multispecific Organic Anion Transporter

Sekine

Watanabe

Hosoyamada

et al. 1997

Journal of Biological Chemistry

560

533

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Numerous drugs and endogenous compounds are efficiently excreted from the renal proximal tubule via carrier-mediated pathways. Transepithelial excretion of organic anions occurs via their accumulative transport from the blood into the proximal tubule cells across the basolateral membrane and subsequent secretion into the urine through the apical membrane. Here we report on the isolation of a novel complementary DNA from rat kidney that encodes a 551-amino acid residue protein (OAT1) with 12 putative membrane-spanning domains. When expressed in Xenopus laevis oocytes, OAT1 mediated sodium-independent para-aminohippurate (PAH) uptake (K m ‫؍‬ 14.3 ؎ 2.9 M). The uptake rate of PAH was increased by the outwardly directed dicarboxylate gradient, consisting with the idea that OAT1 is an organic anion/dicarboxylate exchanger. OAT1 displayed remarkably wide substrate selectivity, covering endogenous substrates such as cyclic nucleotides, a prostaglandin and uric acid, and a variety of drugs with different structures (e.g. antibiotics, a nonsteroidal antiinflammatory drug, diuretics, an antineoplastic drug, and a uricosuric drug). The Northern blot analysis and in situ hybridization revealed that OAT1 is exclusively expressed in the particular segment of the proximal tubule in the kidney. These data suggest that OAT1 is a multispecific organic anion transporter at the basolateral membrane of the proximal tubule. Isolation of OAT1 will facilitate elucidation of the molecular basis of drug kinetics and the development of new drugs lacking unwanted side effects.The kidney plays an essential role in the elimination of numerous organic anions including endogenous compounds, xenobiotics, and their metabolites (1-3). The proximal tubule cells actively secrete them into the urine. The first step of this secretion is the extraction of organic anion from the peritubular blood plasma by the proximal tubule cells through the basolateral membrane. This basolateral uptake of organic anions has been extensively investigated using para-aminohippuric acid (PAH) 1 as a test substrate. The most striking feature of this organic anion transport system is its extremely wide substrate selectivity, covering not only endogenous anionic substrates but also a number of clinically important drugs (1, 3). Because of its importance in renal physiology and pharmacology, cloning of the organic anion transporter has been attempted by many investigators using different approaches; however, the molecular structure of the responsible transporter has not yet determined.For the last decade it has been proposed that the basolateral uptake of organic anion is mediated by organic anion/dicarboxylate exchanger (1, 4). According to this model, outwardly directed dicarboxylate gradient is essential to express the transport activity of this exchanger. In the present study, we isolated first rat sodium dicarboxylate transporter (rNaDC-1) and then co-expressed it together with rat kidney poly(A) ϩ RNA in Xenopus oocytes to energize organic anion transport in oocyte...

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Section: Discussionmentioning

confidence: 99%

Expression Cloning and Characterization of a Novel Multispecific Organic Anion Transporter

Sekine

Watanabe

Hosoyamada

et al. 1997

Journal of Biological Chemistry

560

533

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“…[64][65][66] This carrier has not yet been cloned but was found to differ from the bile acid transporters. 54,54 It appears that the RL-Mtx-1 corresponds to the MBAT with respect to sodium-dependent bumetanide transport.…”

Section: Discussionmentioning

confidence: 99%

“…The handling of the oocytes and the uptake experiments has been described. 53,54 Computer Programs. For the assembly of the sequencing files the program DNASTAR (Lasergene, Madison, WI) was used.…”

Section: Methodsmentioning

confidence: 99%

Cloning and functional characterization of the bile acid-sensitive methotrexate carrier from rat liver cells

Honscha¹,

Dötsch²,

Thomsen³

et al. 2000

Hepatology

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The antifolates methotrexate and trimetrexate are potent inhibitors of the dihydrofolate reductase, an enzyme that delivers by the metabolism of folate and its reduced forms the C1-groups for the synthesis of nucleotides and amino acids. Methotrexate, which has a comparatively moderate toxicity is one of the most important clinically used chemotherapeutics for the treatment of leukemias, such as acute lymphoblastic leukemia of children. It is also used in breast cancer, squamous tumors of the head and neck, lymphomas, and choriocarcinomas. 1,2 Uptake studies of methotrexate and the natural folic acid derivatives in different tumor and normal cells have shown that at least two different carrier systems mediate the uptake of these compounds. The 40 kd folate binding protein has a high affinity for folic acid but a low affinity for reduced folates. [3][4][5][6][7][8][9][10] The corresponding complementary DNAs (cDNAs) as well as genomic clones have been isolated from various sources, 11-19 but a detailed characterization of the transporter function is still missing.Different cDNAs and genomic clones for the reduced folate carrier, which has a high affinity for the reduced folates 5-methyltetrahydrofolate, 5-formyltetrahydrofolate, and methotrexate, but a low affinity for folate [20][21][22][23][24] have been also isolated from different immortal cell lines 25-31 but the clones were not characterized in detail.The expression and the abundance of the two carriers varied in different tumor and normal cells. From uptake studies it became evident that, first, in some cell systems both transport systems work in tandem 32 whereas two independently operating carrier systems were also described. 33,34 Second, tumor cells differ from normal cells in their transport properties. [35][36][37][38][39] Results from Chello et al. 40 showed, for example, a 30-fold higher affinity for methotrexate in the mouse leukemia cell line L1210 than in freshly isolated murine intestinal cells.Hepatocytes are exceptional with respect to folate transport. In contrast to most other cells, hepatocytes express a separate carrier system for 5-methyltetrahydrofolate, which is different from the reduced folate transporter. 41,42 We recently characterized the uptake of methotrexate into freshly isolated hepatocytes 43 and showed that this chemotherapeutic is taken up by a sodium-dependent active transport system, which is inhibited by the reduced folates, dihydrofolate, and tetrahydrofolate but not by folate itself. Moreover, substrates of two well-known organic anion transport systems in the liver, the Ntcp1 44,45 and the oatp1, 46 like the bile acids taurocholate and cholate as well as xenobiotics such as bromosulfophthalein, the loop diuretic bumetanide, and the mycotoxin ochratoxin A are potent inhibitors of the hepatocellular methotrexate carrier. Because some substrates were Abbreviations: cDNA, complementary DNA; RL-Mtx, rat liver methotrexate transporter; RACE-PCR, rapid amplification of cDNA ends polymerase chain reaction; DMEM, Dulbecco modi...

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“…Interestingly, oatp1 transports several organic anions with different chemical structures, such as bile acids, BSP, conjugated steroid hormones and ochratoxin A [9, 11–13], and has therefore been regarded as a multispecific organic anion transporter. However, oatp1 cannot totally account for the diverse organic anion transport in the liver [14–17].…”

Section: Introductionmentioning

confidence: 99%

Identification of multispecific organic anion transporter 2 expressed predominantly in the liver

et al. 1998

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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, PGE P , dicarboxylates and p-aminohippurate.[ IR C]Salicylate uptake via NLT was saturable (K m = 88.8 þ 23.4 W WM) and sodium-independent. Expression of the mRNA of NLT was detected in the liver and kidney (liverEkidney). We propose that NLT be renamed OAT2.z 1998 Federation of European Biochemical Societies.

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Bumetanide is not transported by the Ntcp or by the oatp: evidence for a third organic anion transporter in rat liver cells

Cited by 15 publications

References 13 publications

Expression Cloning and Characterization of a Novel Multispecific Organic Anion Transporter

Expression Cloning and Characterization of a Novel Multispecific Organic Anion Transporter

Cloning and functional characterization of the bile acid-sensitive methotrexate carrier from rat liver cells

Identification of multispecific organic anion transporter 2 expressed predominantly in the liver

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