Olfactory mucosa-expressed organic anion transporter, Oat6, manifests high affinity interactions with odorant organic anions

Renal proximal tubules secrete various organic anions, including drugs and p-aminohippurate (PAH). Uptake of PAH from blood into tubule cells occurs by exchange with intracellular α-ketoglutarate and is mediated by the organic anion transporter 1. PAH exit into tubule lumen is species specific and may involve ATP-independent and -dependent transporters.

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Novel properties of hepatic canalicular reduced glutathione transport revealed by radiation inactivation

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1998.274.5.g923 ◽

1998 ◽

Vol 274 (5) ◽

pp. G923-G930 ◽

Cited By ~ 2

Author(s):

Aravind V. Mittur ◽

Neil Kaplowitz ◽

Ellis S. Kempner ◽

Murad Ookhtens

Keyword(s):

Organic Anion ◽

Membrane Vesicles ◽

Organic Anion Transporter ◽

Initial Increase ◽

Radiation Inactivation ◽

High Affinity ◽

Anion Transporter ◽

Sigmoidal Kinetics ◽

Single Exponential Function ◽

Functional Size

Transport of GSH at the canalicular pole of hepatocytes occurs by a facilitative carrier and can account for ∼50% of total hepatocyte GSH efflux. A low-affinity unit with sigmoidal kinetics accounts for 90% of canalicular transport at physiological GSH concentrations. A low-capacity transporter with high affinity for GSH has also been reported. It is not known whether the same or different proteins mediate low- and high-affinity GSH transport, although they do differ in inhibitor specificity. The bile of rats with a mutation in the canalicular multispecific organic anion transporter (cMOAT or MRP-2, a 170-kDa protein) is deficient in GSH, implying that cMOAT may transport GSH. However, transport of GSH in canalicular membrane vesicles (CMV) from these mutant rats remains intact. We examined the functional size of the two kinetic components of GSH transport by radiation inactivation of GSH uptake in rat hepatic CMV. High-affinity transport of GSH was inactivated as a single exponential function of radiation dose, yielding a functional size of ∼70 kDa. In contrast, low-affinity canalicular GSH transport exhibited a complex biexponential response to irradiation, characterized by an initial increase followed by a decrease in GSH transport. Inactivation analysis yielded a ∼76-kDa size for the low-affinity transporter. The complex inactivation indicated that the low-affinity transporter is associated with a larger protein of ∼141 kDa, which masked ∼80% of the potential transport activity in CMV. Additional studies, using inactivation of leukotriene C4 transport, yielded a functional size of ∼302 kDa for cMOAT, indicating that it functions as a dimer.

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MOAT4, a novel multispecific organic-anion transporter for glucuronides and mercapturates in mouse L1210 cells and human erythrocytes

Biochemical Journal ◽

10.1042/bj3200273 ◽

1996 ◽

Vol 320 (1) ◽

pp. 273-281 ◽

Cited By ~ 20

Author(s):

Manju SAXENA ◽

Gary B HENDERSON

Keyword(s):

Transport System ◽

Organic Anion ◽

High Sensitivity ◽

Human Erythrocytes ◽

Organic Anion Transporter ◽

High Affinity ◽

L1210 Cells ◽

Anion Transporter ◽

Dependent Transport ◽

Inside Out

Glucuronides and mercapturates were examined as possible high-affinity substrates for a low-affinity ATP-dependent transport system for 2,4-dinitrophenyl S-glutathione (DNP-SG) in mouse L1210 cells. Initial inhibitor studies with inside-out vesicles revealed that the low-affinity transport of [3H]DNP-SG (Km 450 µM) exhibits a high sensitivity to N-acetyl 2,4-dinitrophenyl cysteine (NAc-DNP-Cys) (Ki 5.0 µM) and α-naphthyl β-D-glucuronide (naphthyl glucuronide) (Ki 8.5 µM). Direct transport measurements showed the presence of ATP-dependent uptake activities for NAc-DNP-[35S]Cys and naphthyl [14C] glucuronide, and Km values for half-maximal transport were comparable to the Ki values of these compounds for inhibition of [3H]DNP-SG transport. Transport of [3H]DNP-SG, NAc-DNP-[35S]Cys and naphthyl [14 C]glucuronide each showed the same sensitivity to various anions and anion conjugates. Inhibition was competitive and was most potent for bilirubin ditaurate, indoprofen, 4-biphenylacetic acid, 4-acridine 4β-D-glucuronide, N-acetyl leukotriene E4, 17β-oestradiol 3β-D-glucuronide and taurolithocholate 3-sulphate. Inside-out vesicles from human erythrocytes contain a comparable ATP-dependent transport system. These results show that NAc-DNP-Cys and naphthyl glucuronide are high-affinity substrates for a single system identified previously as a low-affinity transporter of DNP-SG. Substrate and inhibitor studies identify this system as a novel multispecific organic-anion transport system (MOAT4) that accommodates glucuronides and mercapturates and is distinct from other MOAT transporters. Human erythrocytes contain an additional ATP-dependent system for NAc-DNP-Cys (Km 33 µM) that does not transport monoglucuronides.

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Molecular cloning of canalicular multispecific organic anion transporter defective in EHBR

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1997.272.1.g16 ◽

1997 ◽

Vol 272 (1) ◽

pp. G16-G22 ◽

Cited By ~ 24

Author(s):

K. Ito ◽

H. Suzuki ◽

T. Hirohashi ◽

K. Kume ◽

T. Shimizu ◽

...

Keyword(s):

Amino Acid ◽

Stop Codon ◽

Organic Anion ◽

Amino Acid Level ◽

Premature Stop Codon ◽

Autosomal Recessive Inheritance ◽

Organic Anions ◽

Organic Anion Transporter ◽

Sprague Dawley ◽

Anion Transporter

Several organic anions are excreted into the bile via a canalicular multispecific organic anion transporter (cMOAT), which is hereditarily defective in mutant rats, such as the Eisai hyperbilirubinemic rat (EHBR) and TR- rat. In the present study, we cloned cMOAT from the Sprague-Dawley rat liver cDNA library based on the homology with human multidrug resistance-associated protein (hMRP). cMOAT was encoded by 4,623-base pair (bp) cDNA with a homology of 53.0 and 46.3% with hMRP at the cDNA and deduced amino acid level, respectively. The deduced amino acid sequence was the same as that cloned in Wistar rats (C. C. Paulusma, P. J. Bosma, G. J. Zaman, C. T. Bakker, M. Otter, G. L. Sceffer, P. Borst, and R. P. Oude Elferink. Science Wash. DC 271: 1126, 1996) except for four amino acid substitutions. By screening the library, three kinds of cDNA species for cMOAT with the same open reading frame and different 3'-untranslated region lengths (0.2, 1.5, and 3.5 kbp) were isolated. The Northern blot analysis of poly(A)+ RNA from the liver revealed that the expression of plural bands (approximately 5, 6, and 8 kb) was defective in EHBR, and this may be due to the presence of these cDNA species. Expression of cMOAT was observed almost exclusively in the liver and to a lesser extent in the duodenum, kidney, and jejunum. Reverse transcription-polymerase chain reaction (RT-PCR) and subsequent sequence analysis of EHBR liver, kidney, duodenum, and jejunum revealed that 1-bp replacement from G to A at nucleotide 2564 resulted in the introduction of the premature stop codon in all tissues examined. This mutation was different from that observed in TR (C. C. Paulusma, P. J. Bosma, G. J. Zaman, C. T. Bakker, M. Otter, G. L. Sceffer, P. Borst, and R. P. Oude Elferink. Science Wash. DC 271: 1126, 1996). Because EHBR and TR- are allelic mutants and both strains exhibit an autosomal recessive inheritance in the biliary excretion of organic anions it was concluded that the impaired expression of this particular protein is related to the pathogenesis of hyperbilirubinemia in the mutant animals.

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Molecular physiology of renal organic anion transporters

AJP Renal Physiology ◽

10.1152/ajprenal.00439.2004 ◽

2006 ◽

Vol 290 (2) ◽

pp. F251-F261 ◽

Cited By ~ 156

Author(s):

Takashi Sekine ◽

Hiroki Miyazaki ◽

Hitoshi Endou

Keyword(s):

Organic Anion ◽

Organic Anions ◽

Organic Anion Transporter ◽

Transepithelial Transport ◽

Gene Localization ◽

Organic Anion Transporters ◽

Molecular Physiology ◽

Anion Transporters ◽

Anion Transporter ◽

Molecular Information

Recent advances in molecular biology have identified three organic anion transporter families: the organic anion transporter (OAT) family encoded by SLC22A, the organic anion transporting peptide (OATP) family encoded by SLC21A ( SLCO), and the multidrug resistance-associated protein (MRP) family encoded by ABCC. These families play critical roles in the transepithelial transport of organic anions in the kidneys as well as in other tissues such as the liver and brain. Among these families, the OAT family plays the central role in renal organic anion transport. Knowledge of these three families at the molecular level, such as substrate selectivity, tissue distribution, and gene localization, is rapidly increasing. In this review, we will give an overview of molecular information on renal organic anion transporters and describe recent topics such as the regulatory mechanisms and molecular physiology of urate transport. We will also discuss the physiological roles of each organic anion transporter in the light of the transepithelial transport of organic anions in the kidneys.

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