NH3 Is Involved in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif"><mml:msubsup><mml:mi>NH</mml:mi><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mo>+</mml:mo></mml:msubsup></mml:math> Transport Induced by the Functional Expression of the Human Rh C Glycoprotein

Bakouh, Naziha; Benjelloun, Fatine; Hulin, Philippe; Brouillard, Franck; Edelman, Aleksander; Chérif-Zahar, Baya; Planelles, Gabrielle

doi:10.1074/jbc.m308528200

Cited by 109 publications

(170 citation statements)

References 33 publications

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“…Similar studies in RhCG-expressing oocytes have concluded that RhCG could mediate electrogenic transport that is consistent with NH 3 and NH 4 + enhanced influx [14]. The discrepancies between these studies might be explained by the different methodologies used and by the existence of an ammonium-activated endogenous transport pathway in oocytes [18,19] that could hamper more precise analysis of an exogenous ammonium transporter.…”

Section: Introductionmentioning

confidence: 79%

“…A recent study also identified RhBG and RhCG as having a cell specific, axially heterogeneous and polarized expression in the gastrointestinal tract [13]. As is the case for RhAG, ammonium transport activity of RhCG was first shown by complementation studies in yeast [5] and then confirmed by functional studies in Xenopus oocytes [14]. RhBG-mediated ammonium transport was also recently demonstrated in the Xenopus oocyte expression system [15,16].…”

Section: Introductionmentioning

confidence: 90%

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Human Rhesus B and Rhesus C glycoproteins: properties of facilitated ammonium transport in recombinant kidney cells

Zidi-Yahiaoui

Mouro-Chanteloup

d'Ambrosio

et al. 2005

Biochemical Journal

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The mammalian Rh (Rhesus) protein family belongs to the Amt/ Mep (ammonia transporter/methylammonium permease)/Rh superfamily of ammonium transporters. Whereas RhCE, RhD and RhAG are erythroid specific, RhBG and RhCG are expressed in key organs associated with ammonium transport and metabolism. We have investigated the ammonium transport function of human RhBG and RhCG by comparing intracellular pH variation in wild-type and transfected HEK-293 (human embryonic kidney) cells and MDCK (Madin-Darby canine kidney) cells in the presence of ammonium (NH 4 + /NH 3 ) gradients. Stopped-flow spectrofluorimetry analysis, using BCECF [2 ,7 -bis-(2-carboxyethyl)-5(6)-carboxyfluorescein] as a pH-sensitive probe, revealed that all cells submitted to inwardly or outwardly directed ammonium gradients exhibited rapid alkalinization or acidification phases respectively, which account for ammonium movements in transfected and native cells. However, as compared with wildtype cells known to have high NH 3 lipid permeability, RhBGand RhCG-expressing cells exhibited ammonium transport characterized by: (i) a five to six times greater kinetic rateconstant; (ii) a weak temperature-dependence; and (iii) reversible inhibition by mercuric chloride (IC 50: 52 µM). Similarly, when subjected to a methylammonium gradient, RhBG-and RhCGexpressing cells exhibited kinetic rate constants greater than those of native cells. However, these constants were five times higher for RhBG as compared with RhCG, suggesting a difference in substrate accessibility. These results, indicating that RhBG and RhCG facilitate rapid and low-energy-dependent bi-directional ammonium movement across the plasma membrane, favour the hypothesis that these Rh glycoproteins, together with their erythroid homologue RhAG [Ripoche, Bertrand, Gane, Birkenmeier, Colin and Cartron (2005) Proc. Natl. Acad. Sci. U.S.A. 101, 17222-17227] constitute a family of NH 3 channels in mammalian cells.

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Section: Introductionmentioning

confidence: 79%

Section: Introductionmentioning

confidence: 90%

Human Rhesus B and Rhesus C glycoproteins: properties of facilitated ammonium transport in recombinant kidney cells

Zidi-Yahiaoui

Mouro-Chanteloup

d'Ambrosio

et al. 2005

Biochemical Journal

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“…In the absence of heterologously expressed ammonia channels, this response to ammonia influx is seen only above about 1 mM external NH 4 + at pH 7.5 [5,23]. The significant currents seen in RhBG [32] and RhCG oocytes [2] at even lower concentrations may, therefore, be the consequence of RhBG/RhCG-enhanced NH 3 permeability rather than proof of NH 4 + transport. All the studies with heterologously expressed Rh proteins appear compatible with their functioning as NH 3 channels.…”

Section: Rh-mediated Ammonia Transport In Animal Cellsmentioning

confidence: 88%

“…Functional studies with RhAG, RhBG, and RhCG have been carried out by expression in oocytes [2,23,32,47], and in ammonium transport deficient S. cerevisiae [27,48]. They have been interpreted in terms of NH 4 + transport [27,32], influx of both NH 3 and NH 4 + ([2] and NH 4 + /H + exchange [23,47,48].…”

Section: Rh-mediated Ammonia Transport In Animal Cellsmentioning

confidence: 99%

Amt/MEP/Rh proteins conduct ammonia

Winkler

2005

Pflugers Arch - Eur J Physiol

110

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The structure determination of the ammonium transport protein AmtB from Escherichia coli strongly indicates that the members of the ubiquitous ammonium transporter/methylamine permease/Rhesus (Amt/ MEP/Rh) protein family are ammonia-conducting channels rather than ammonium ion transporters. The most conserved part of these proteins, apart from the common overall structure with 11 transmembrane helices, is the pore lined by hydrophobic side chains except for two highly conserved histidine residues. A highaffinity ion-binding site specific for ammonium is present at the extracellular pore entry of the Amt/MEP proteins. It is proposed to play an important role in enhancing net transport at very low external ammonium concentrations and to provide discrimination against water. The site is not conserved in the animal Rhesus proteins which are implicated in ammonium homeostasis and saturate at millimolar ammonium concentrations. Many aspects of the biological function of these ammonia channels are still poorly understood and further studies in cellular systems are needed. Likewise, studies with purified, reconstituted Amt/MEP/Rh proteins will be needed to resolve open mechanistic questions and gain a more quantitative understanding of the conduction mechanism in general and for different subfamily representatives.

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“…RhAG expression is restricted to the erythrocyte membrane, whereas RhBG and RhCG are expressed in various tissues in the mammalian systems, including liver, kidney and gastrointestinal tract (Handlogten et al, 2005;Liu et al, 2000;Liu et al, 2001;. Studies in mammalian and plant systems reveal that at least some of those Rh genes encode proteins that mediate NH 3 /NH 4 + movement (Khademi et al, 2004;Zheng et al, 2004;Mayer et al, 2006), but the form of ammonia (NH 3 gas or NH 4 + ion) being transported, and whether the transport is active or passive, are still under much debate (Bakouh et al, 2004;Khademi et al, 2004;Nakhoul et al, 2005). A fulllength cDNA of Rh-like protein (Rh-CM) has been identified recently from the gills of the aquatic crab Carcinus maenas, which has a similar predicted transmembrane structure as the mammalian Rh proteins (Weihrauch et al, 2004).…”

Section: Introductionmentioning

confidence: 99%

Rhesus glycoprotein gene expression in the mangrove killifishKryptolebias marmoratusexposed to elevated environmental ammonia levels and air

Hung

Tsui

Wilson³

et al. 2007

Journal of Experimental Biology

116

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SUMMARY The mechanism(s) of ammonia excretion in the presence of elevated external ammonia are not well understood in fish. Recent studies in other organisms have revealed a new class of ammonia transporters, Rhesus glycoprotein genes(Rh genes), which may also play a role in ammonia excretion in fish. The first objective of this study was to clone and characterize Rhgenes in a fish species with a relatively high tolerance to environmental ammonia, the mangrove killifish Kryptolebias marmoratus (formerly Rivulus marmoratus). We obtained full-length cDNAs of three Rh genes in K. marmoratus: RhBG (1736 bp), RhCG1 (1920 bp) and RhCG2 (2021 bp), which are highly homologous with other known Rh gene sequences. Hydropathy analysis revealed that all three Rh genes encode membrane proteins with 10–12 predicted transmembrane domains. RhBG, RhCG1 and RhCG2 are highly expressed in gill tissue, with RhBG also present in skin of K. marmoratus. Exposure to elevated environmental ammonia (2 mmol l–1 NH4HCO3) for 5 days resulted in a modest (+37%) increase in whole-body ammonia levels, whereas gill RhCG2 and skin RhCG1 mRNA levels were upregulated by 5.8- and 7.7-fold, respectively. RhBG mRNA levels were also increased in various tissues, with 3- to 7-fold increases in the liver and skeletal muscle. In a separate group of killifish exposed to air for 24 h, RhCG1 and RhCG2 mRNA levels were elevated by 4- to 6-fold in the skin. Thus, the multifold induction of Rh mRNA levels in excretory tissues (gills and skin) and internal tissues in response to conditions that perturb normal ammonia excretion suggests that RhBG, RhCG1 and RhCG2 may be involved in facilitating ammonia transport in this species. Furthermore, the findings support earlier studies demonstrating that the skin is an important site of ammonia excretion in K. marmoratus.

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NH3 Is Involved in the NH4+ Transport Induced by the Functional Expression of the Human Rh C Glycoprotein

Cited by 109 publications

References 33 publications

Human Rhesus B and Rhesus C glycoproteins: properties of facilitated ammonium transport in recombinant kidney cells

Human Rhesus B and Rhesus C glycoproteins: properties of facilitated ammonium transport in recombinant kidney cells

Amt/MEP/Rh proteins conduct ammonia

Rhesus glycoprotein gene expression in the mangrove killifishKryptolebias marmoratusexposed to elevated environmental ammonia levels and air

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