Glycerol Transport in Human Red Cells

Carlsen, Anders Helles; Wieth, Jens Otto

doi:10.1111/j.1748-1716.1976.tb10290.x

Cited by 62 publications

(48 citation statements)

References 13 publications

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“…Second, the pK for glycerol transport could be shifted due to a competitive interaction between H ϩ and glycerol at the sites. Such competition has been described in intact human red blood cells (9) where glycerol transport is mediated by AQP3 (10). In these cells pK for P Gl was about 6.0 at external glycerol concentrations of 1 mM and 5.5 at external glycerol concentrations of 2 M. In addition, the Hill coefficients were estimated to be larger than 2 (9).…”

Section: Mechanisms and Coupling Of Water And Glycerol Fluxes-mentioning

confidence: 64%

“…Some AQPs can transport other solutes as well, AQP3 for example, supports significant fluxes of glycerol (2-7). It has long been known that glycerol transport across the plasma membrane of the red blood cell is mediated by a pore and that the transport mechanism is inhibited at low pH (8,9). Recently it was established that AQP3 is involved in glycerol transport in the red blood cell (10).…”

Section: Aquaporins (Aqps)mentioning

confidence: 99%

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Transport of Water and Glycerol in Aquaporin 3 Is Gated by H+

Zeuthen¹,

Klærke²

1999

Journal of Biological Chemistry

190

123

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Aquaporins (AQPs) were expressed in Xenopus laevis oocytes in order to study the effects of external pH and solute structure on permeabilities. For AQP3 the osmotic water permeability, L p , was abolished at acid pH values with a pK of 6.4 and a Hill coefficient of 3. The L p values of AQP0, AQP1, AQP2, AQP4, and AQP5 were independent of pH. For AQP3 the glycerol permeability P Gl , obtained from [ 14 C]glycerol uptake, was abolished at acid pH values with a pK of 6.1 and a Hill coefficient of 6. Consequently, AQP3 acts as a glycerol and water channel at physiological pH, but predominantly as a glycerol channel at pH values around 6.1. The pH effects were reversible. The interactions between fluxes of water and straight chain polyols were inferred from reflection coefficients (). For AQP3, water and glycerol interacted by competing for titratable site(s): Gl was 0.15 at neutral pH but doubled at pH 6.4. The values were smaller for polyols in which the -OH groups were free to form hydrogen bonds. The activation energy for the transport processes was around 5 kcal mol ؊1 . We suggest that water and polyols permeate AQP3 by forming successive hydrogen bonds with titratable sites. Aquaporins (AQPs)1 are a class of membrane proteins that allows osmotic water transport probably via an aqueous pore (1). Some AQPs can transport other solutes as well, AQP3 for example, supports significant fluxes of glycerol (2-7). It has long been known that glycerol transport across the plasma membrane of the red blood cell is mediated by a pore and that the transport mechanism is inhibited at low pH (8, 9). Recently it was established that AQP3 is involved in glycerol transport in the red blood cell (10). This raises the questions of whether glycerol transport in AQP3 is gated by H ϩ and whether water transport through AQP3 and other AQPs is also sensitive to H ϩ .We have previously applied a fast and high resolution optical method to determine the transport properties of AQPs expressed in Xenopus oocytes (6). Here we combine this method with tracer measurements in order to study the effects of H ϩ , temperature, and solute structure on transport of water, glycerol, and other straight chain polyols. The study is performed predominantly in AQP3, but also in AQP0, AQP1, AQP2, AQP4, and AQP5.At present, transport models are restricted to the use of macrophysical concepts such as pore diameter and pore length. This is mainly due to the lack of knowledge about the structure of the putative pore and the nature of the chemical interactions with the permeating molecules (11, 12). Our data for AQP3 suggest a model where the permeation of water and polyols are determined by the formation of hydrogen bonds between the pore and the permeating molecule. From a physiological point of view, it is interesting that both the glycerol and the water transport through the AQP3 exhibited a strong, immediate, and reversible pH dependence. Such short term and direct gating of transport is a novel feature of aquaporins. MATERIALS AND METHODSDetails of the pre...

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Section: Mechanisms and Coupling Of Water And Glycerol Fluxes-mentioning

confidence: 64%

Section: Aquaporins (Aqps)mentioning

confidence: 99%

Transport of Water and Glycerol in Aquaporin 3 Is Gated by H+

Zeuthen¹,

Klærke²

1999

Journal of Biological Chemistry

190

123

View full text Add to dashboard Cite

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“…Urea transporter B, a urea transporter expressed in erythrocytes and testes, has been shown to be the main route for urea to pass through erythrocyte membranes (18). Glycerol permeability of erythrocytes has long been recognized and can be pharmacologically inhibited by phloretin and mercury (16,19). Nevertheless, the existence of glycerol channels in mouse erythrocytes has been controversial.…”

Section: Discussionmentioning

confidence: 99%

Aquaporin 9 is the major pathway for glycerol uptake by mouse erythrocytes, with implications for malarial virulence

Liu

Promeneur

Rojek

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Human and rodent erythrocytes are known to be highly permeable to glycerol. Aquaglyceroporin aquaporin (AQP)3 is the major glycerol channel in human and rat erythrocytes. However, AQP3 expression has not been observed in mouse erythrocytes. Here we report the presence of an aquaglyceroporin, AQP9, in mouse erythrocytes. AQP9 levels rise as reticulocytes mature into erythrocytes and as neonatal pups develop into adult mice. Mice bearing targeted disruption of both alleles encoding AQP9 have erythrocytes that appear morphologically normal. Compared with WT cells, erythrocytes from AQP9-null mice are defective in rapid glycerol transport across the cell membrane when measured by osmotic lysis, [ 14 C]glycerol uptake, or stopped-flow light scattering. In contrast, the water and urea permeabilities are intact. Although the physiological role of glycerol in the normal function of erythrocytes is not clear, plasma glycerol is an important substrate for lipid biosynthesis of intraerythrocytic malarial parasites. AQP9-null mice at the age of 4 months infected with Plasmodium berghei survive longer during the initial phase of infection compared with WT mice. We conclude that AQP9 is the major glycerol channel in mouse erythrocytes and suggest that this transport pathway may contribute to the virulence of intraerythrocytic stages of malarial infection.Plasmodium berghei ͉ aquaglyceroporin A quaglyceroporins are transmembrane proteins belonging to the aquaporin (AQP) water channel family (1). Aquaglyceroporins are the only known glycerol channels in mammalian cells. Among 13 identified mammalian aquaporins, AQP3, AQP7, AQP9, and AQP10 represent the aquaglyceroporin subfamily on the basis of their amino acid sequences and solute permeabilities (1). Aquaglyceroporins are also permeable to urea and water when expressed in Xenopus laevis oocytes (1).The first defined water channel, AQP1, was discovered in human erythrocytes (2). The high expression and water permeability of AQP1 in erythrocytes led to the hypothesis that AQP1 is important in adaptation to dramatic osmolarity changes in the circulation (2). In addition to high water permeability, human and rodent erythrocytes are known to be highly permeable to urea and glycerol (3). AQP3 has been identified as the main channel for glycerol transport in human and rat erythrocytes (4). AQP3 has not been detected in mouse erythrocytes, and the glycerol permeability of mouse erythrocytes from AQP3 knockout mice has been shown to not be affected by gene deletion (5). We revisited this question and detected AQP9 expression in mouse erythrocytes. By using AQP9-null mice, we provide evidence that AQP9 is the major pathway for glycerol transport in mouse erythrocytes.The physiological role of aquaglyceroporins in erythrocytes is still not clear. However, recent studies indicate that aquaglyceroporins AQP7 and AQP9 participate in metabolism. Under fasting conditions, up-regulated AQP7 expression in adipocytes facilitates the release of glycerol, which can then be transported through the ...

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“…It is well documented that glycerol permeability of human red blood cells is decreased in the presence of copper (11,21,25), but the mechanisms of the copper action have been unknown. In red blood cells AQP3 is co-expressed with AQP1, which is not glycerol permeable.…”

Section: Discussionmentioning

confidence: 99%

Copper Inhibits the Water and Glycerol Permeability of Aquaporin-3

Zelenina

Tritto

Bondar

et al. 2004

Journal of Biological Chemistry

123

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Aquaporin-3 (AQP3) is an aquaglyceroporin expressed in erythrocytes and several other tissues. Erythrocytes are, together with kidney and liver, the main targets for copper toxicity. Here we report that both water and glycerol permeability of human AQP3 is inhibited by copper. Inhibition is fast, dose-dependent, and reversible. If copper is dissolved in carbonic acid-bicarbonate buffer, the natural buffer system in our body, doses in the range of those observed in Wilson disease and in copper poisoning caused significant inhibition. AQP7, another aquaglyceroporin, was insensitive to copper. Copper is an essential trace element in the human body. It is present in the blood and is incorporated in several vital proteins, such as Cu,Zn-SOD, dopamine ␤-hydroxylase, ceruloplasmin, cytochrome c oxidase, etc. (recently reviewed in Ref. 1). Blood levels of copper are increased in several pathological conditions, such as Wilson disease, Indian childhood cirrhosis, juvenile rheumatoid arthritis, thalassemia, and sickle cell anemia (1-5).Aquaporin-3 (AQP3) 1 is an aquaglyceroporin expressed in several mammalian tissues including erythrocytes (6 -12). It is well established that erythrocytes are permeable for glycerol, but the molecular mechanism for this effect is still obscure. It is also well established that glycerol permeability of erythrocytes is extremely sensitive to copper. We have recently shown that AQP3 water permeability is sensitive to nickel (13). Here we report that copper is a potent inhibitor of AQP3 permeability for glycerol and water. We expressed AQP3 in a human cell line and tested the effect of copper on glycerol and water permeability of the transfected cells. Three extracellular amino acid residues were found to be responsible for the copper sensitivity. We modeled the situation when AQP3 is co-expressed with another AQP, not permeable for glycerol, and found that only glycerol but not water permeability will be inhibited by copper in such cells. The results of this study provide a better understanding of processes that occur in severe copper metabolism defects and copper poisoning. MATERIALS AND METHODScDNA Constructs-The constructs for expression of human AQP3 (wild type and mutants) and the long form of AQP4 have been described previously (13). cDNA fragments encoding full-length AQP3 and AQP4 were obtained by amplification from the human lung QUICK-Clone cDNA library (Clontech). cDNA encoding mouse AQP7 was a kind gift from J. M. Carbrey and P. Agre (Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD). The cDNA fragments were subcloned in-frame into the pEGFP-N2 vector for AQP3 tagged with green fluorescent protein (GFP) at the COOH terminus into pIRES2-EGFP vector (Clontech) for AQP3 and GFP expressed in the same cell as separate proteins and into the pEGFP-C2 vector for AQP4 and AQP7 tagged with GFP at NH 2 termini. The point mutations in extracellular loops of human AQP3 were generated by PCR-based mutagenesis using wild-type cDNA as a template and c...

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Glycerol Transport in Human Red Cells

Cited by 62 publications

References 13 publications

Transport of Water and Glycerol in Aquaporin 3 Is Gated by H+

Transport of Water and Glycerol in Aquaporin 3 Is Gated by H+

Aquaporin 9 is the major pathway for glycerol uptake by mouse erythrocytes, with implications for malarial virulence

Copper Inhibits the Water and Glycerol Permeability of Aquaporin-3

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