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Bizior A, Williamson G, Harris T, Hoskisson PA, Javelle A. Prokaryotic ammonium transporters: what has three decades of research revealed? MICROBIOLOGY (READING, ENGLAND) 2023; 169:001360. [PMID: 37450375 PMCID: PMC10433425 DOI: 10.1099/mic.0.001360] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Accepted: 06/24/2023] [Indexed: 07/18/2023]
Abstract
The exchange of ammonium across cellular membranes is a fundamental process in all domains of life. In plants, bacteria and fungi, ammonium represents a vital source of nitrogen, which is scavenged from the external environment. In contrast, in animal cells ammonium is a cytotoxic metabolic waste product and must be excreted to prevent cell death. Transport of ammonium is facilitated by the ubiquitous Amt/Mep/Rh transporter superfamily. In addition to their function as transporters, Amt/Mep/Rh proteins play roles in a diverse array of biological processes and human physiopathology. Despite this clear physiological importance and medical relevance, the molecular mechanism of Amt/Mep/Rh proteins has remained elusive. Crystal structures of bacterial Amt/Rh proteins suggest electroneutral transport, whilst functional evidence supports an electrogenic mechanism. Here, focusing on bacterial members of the family, we summarize the structure of Amt/Rh proteins and what three decades of research tells us concerning the general mechanisms of ammonium translocation, in particular the possibility that the transport mechanism might differ in various members of the Amt/Mep/Rh superfamily.
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Affiliation(s)
- Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
| | - Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, UK
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2
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Chen J, Yue K, Shen L, Zheng C, Zhu Y, Han K, Kai L. Aquaporins and CO 2 diffusion across biological membrane. Front Physiol 2023; 14:1205290. [PMID: 37383148 PMCID: PMC10293838 DOI: 10.3389/fphys.2023.1205290] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 06/05/2023] [Indexed: 06/30/2023] Open
Abstract
Despite the physiological significance of effective CO2 diffusion across biological membranes, the underlying mechanism behind this process is not yet resolved. Particularly debatable is the existence of CO2-permeable aquaporins. The lipophilic characteristic of CO2 should, according to Overton's rule, result in a rapid flux across lipid bilayers. However, experimental evidence of limited membrane permeability poses a challenge to this idea of free diffusion. In this review, we summarized recent progress with regard to CO2 diffusion, and discussed the physiological effects of altered aquaporin expression, the molecular mechanisms of CO2 transport via aquaporins, and the function of sterols and other membrane proteins in CO2 permeability. In addition, we highlight the existing limits in measuring CO2 permeability and end up with perspectives on resolving such argument either by determining the atomic resolution structure of CO2 permeable aquaporins or by developing new methods for measuring permeability.
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Affiliation(s)
- Junyu Chen
- School of Life Sciences, Jiangsu Normal University, Xuzhou, China
| | - Ke Yue
- School of Life Sciences, Jiangsu Normal University, Xuzhou, China
| | - Lulu Shen
- School of Life Sciences, Jiangsu Normal University, Xuzhou, China
| | - Chuncui Zheng
- Hangzhou Institute of Test and Calibration for Quality and Technology Supervision, Hangzhou, China
| | - Yiyong Zhu
- Jiangsu Provincial Key Laboratory for Organic Solid Waste Utilization, National Engineering Research Center for Organic-Based Fertilizers, Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, Nanjing Agricultural University, Nanjing, China
| | - Kun Han
- Jiangsu Keybio Co., Ltd, Xuzhou, China
| | - Lei Kai
- School of Life Sciences, Jiangsu Normal University, Xuzhou, China
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3
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Al-Samir S, Prill M, Supuran CT, Gros G, Endeward V. CO 2 permeability of the rat erythrocyte membrane and its inhibition. J Enzyme Inhib Med Chem 2021; 36:1602-1606. [PMID: 34261373 PMCID: PMC8282279 DOI: 10.1080/14756366.2021.1952194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
We have studied the CO2 permeability of the erythrocyte membrane of the rat using a mass spectrometric method that employs 18 O-labelled CO2. The method yields, in addition, the intraerythrocytic carbonic anhydrase activity and the membrane HCO3- permeability. For normal rat erythrocytes, we find at 37 °C a CO2 permeability of 0.078 ± 0.015 cm/s, an intracellular carbonic anhydrase activity of 64,100, and a bicarbonate permeability of 2.1 × 10-3 cm/s. We studied whether the rat erythrocyte membrane possesses protein CO2 channels similar to the human red cell membrane by applying the potential CO2 channel inhibitors pCMBS, Dibac, phloretin, and DIDS. Phloretin and DIDS were able to reduce the CO2 permeability by up to 50%. Since these effects cannot be attributed to the lipid part of the membrane, we conclude that the rat erythrocyte membrane is equipped with protein CO2 channels that are responsible for at least 50% of its CO2 permeability.
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Affiliation(s)
- Samer Al-Samir
- AG Vegetative Physiologie 4220, Zentrum Physiologie, Medizinische Hochschule Hannover, Hannover, Germany
| | - Maximilian Prill
- AG Vegetative Physiologie 4220, Zentrum Physiologie, Medizinische Hochschule Hannover, Hannover, Germany
| | - Claudiu T Supuran
- Neurofarba Department, Section of Pharmaceutical and Nutritional Sciences, University of Florence, Florence, Italy
| | - Gerolf Gros
- AG Vegetative Physiologie 4220, Zentrum Physiologie, Medizinische Hochschule Hannover, Hannover, Germany
| | - Volker Endeward
- AG Vegetative Physiologie 4220, Zentrum Physiologie, Medizinische Hochschule Hannover, Hannover, Germany
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4
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Grishin D, Kasap E, Izotov A, Lisitsa A. Multifaceted ammonia transporters. ALL LIFE 2020. [DOI: 10.1080/26895293.2020.1812443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Affiliation(s)
- D.V. Grishin
- Institute of Biomedical Chemistry (IBMC), Moscow, Russia
| | - E.Y. Kasap
- Institute of Biomedical Chemistry (IBMC), Moscow, Russia
| | - A.A. Izotov
- Institute of Biomedical Chemistry (IBMC), Moscow, Russia
| | - A.V. Lisitsa
- Institute of Biomedical Chemistry (IBMC), Moscow, Russia
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5
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Single-cell O 2 exchange imaging shows that cytoplasmic diffusion is a dominant barrier to efficient gas transport in red blood cells. Proc Natl Acad Sci U S A 2020; 117:10067-10078. [PMID: 32321831 PMCID: PMC7211990 DOI: 10.1073/pnas.1916641117] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Blood is routinely tested for gas-carrying capacity (total hemoglobin), but this cannot determine the speed at which red blood cells (RBCs) exchange gases. Such information is critical for evaluating the physiological fitness of RBCs, which have very limited capillary transit times (<1 s) for turning over substantial volumes of gas. We developed a method to quantify gas exchange in individual RBCs and used it to show that restricted diffusion, imposed by hemoglobin crowding, is a major barrier to gas flows. Consequently, hematological disorders manifesting a change in cell shape or hemoglobin concentration have uncharted implications on gas exchange, which we illustrate using inherited anemias. With its single-cell resolution, the method can identify physiologically inferior subpopulations, providing a clinically useful appraisal of blood quality. Disorders of oxygen transport are commonly attributed to inadequate carrying capacity (anemia) but may also relate to inefficient gas exchange by red blood cells (RBCs), a process that is poorly characterized yet assumed to be rapid. Without direct measurements of gas exchange at the single-cell level, the barriers to O2 transport and their relationship with hematological disorders remain ill defined. We developed a method to track the flow of O2 in individual RBCs by combining ultrarapid solution switching (to manipulate gas tension) with single-cell O2 saturation fluorescence microscopy. O2 unloading from RBCs was considerably slower than previously estimated in acellular hemoglobin solutions, indicating the presence of diffusional barriers in intact cells. Rate-limiting diffusion across cytoplasm was demonstrated by osmotically induced changes to hemoglobin concentration (i.e., diffusive tortuosity) and cell size (i.e., diffusion pathlength) and by comparing wild-type cells with hemoglobin H (HbH) thalassemia (shorter pathlength and reduced tortuosity) and hereditary spherocytosis (HS; expanded pathlength). Analysis of the distribution of O2 unloading rates in HS RBCs identified a subpopulation of spherocytes with greatly impaired gas exchange. Tortuosity imposed by hemoglobin was verified by demonstrating restricted diffusivity of CO2, an acidic gas, from the dissipative spread of photolytically uncaged H+ ions across cytoplasm. Our findings indicate that cytoplasmic diffusion, determined by pathlength and tortuosity, is a major barrier to efficient gas handling by RBCs. Consequently, changes in RBC shape and hemoglobin concentration, which are common manifestations of hematological disorders, can have hitherto unrecognized and clinically significant implications on gas exchange.
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Abstract
Spontaneous solute and solvent permeation through membranes is of vital importance to human life, be it gas exchange in red blood cells, metabolite excretion, drug/toxin uptake, or water homeostasis. Knowledge of the underlying molecular mechanisms is the sine qua non of every functional assignment to membrane transporters. The basis of our current solubility diffusion model was laid by Meyer and Overton. It correlates the solubility of a substance in an organic phase with its membrane permeability. Since then, a wide range of studies challenging this rule have appeared. Commonly, the discrepancies have their origin in ill-used measurement approaches, as we demonstrate on the example of membrane CO2 transport. On the basis of the insight that scanning electrochemical microscopy offered into solute concentration distributions in immediate membrane vicinity of planar membranes, we analyzed the interplay between chemical reactions and diffusion for solvent transport, weak acid permeation, and enzymatic reactions adjacent to membranes. We conclude that buffer reactions must also be considered in spectroscopic investigations of weak acid transport in vesicular suspensions. The evaluation of energetic contributions to membrane translocation of charged species demonstrates the compatibility of the resulting membrane current with the solubility diffusion model. A local partition coefficient that depends on membrane penetration depth governs spontaneous membrane translocation of both charged and uncharged molecules. It is determined not only by the solubility in an organic phase but also by other factors like cholesterol concentration and intrinsic electric membrane potentials.
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Affiliation(s)
- Christof Hannesschlaeger
- From the Institute of Biophysics , Johannes Kepler University Linz , Gruberstrasse 40 , 4020 Linz , Austria
| | - Andreas Horner
- From the Institute of Biophysics , Johannes Kepler University Linz , Gruberstrasse 40 , 4020 Linz , Austria
| | - Peter Pohl
- From the Institute of Biophysics , Johannes Kepler University Linz , Gruberstrasse 40 , 4020 Linz , Austria
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Ozu M, Galizia L, Acuña C, Amodeo G. Aquaporins: More Than Functional Monomers in a Tetrameric Arrangement. Cells 2018; 7:E209. [PMID: 30423856 PMCID: PMC6262540 DOI: 10.3390/cells7110209] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Revised: 10/27/2018] [Accepted: 11/07/2018] [Indexed: 12/11/2022] Open
Abstract
Aquaporins (AQPs) function as tetrameric structures in which each monomer has its own permeable pathway. The combination of structural biology, molecular dynamics simulations, and experimental approaches has contributed to improve our knowledge of how protein conformational changes can challenge its transport capacity, rapidly altering the membrane permeability. This review is focused on evidence that highlights the functional relationship between the monomers and the tetramer. In this sense, we address AQP permeation capacity as well as regulatory mechanisms that affect the monomer, the tetramer, or tetramers combined in complex structures. We therefore explore: (i) water permeation and recent evidence on ion permeation, including the permeation pathway controversy-each monomer versus the central pore of the tetramer-and (ii) regulatory mechanisms that cannot be attributed to independent monomers. In particular, we discuss channel gating and AQPs that sense membrane tension. For the latter we propose a possible mechanism that includes the monomer (slight changes of pore shape, the number of possible H-bonds between water molecules and pore-lining residues) and the tetramer (interactions among monomers and a positive cooperative effect).
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Affiliation(s)
- Marcelo Ozu
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EGA, Argentina.
- Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires C1428EGA CABA, Argentina.
| | - Luciano Galizia
- Instituto de investigaciones Médicas A. Lanari, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires C1427ARO, Argentina.
- Consejo Nacional de Investigaciones Científicas y Técnicas, Laboratorio de Canales Iónicos, Instituto de Investigaciones Médicas (IDIM), Universidad de Buenos Aires, Buenos Aires C1427ARO, Argentina.
| | - Cynthia Acuña
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EGA, Argentina.
- Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires C1428EGA CABA, Argentina.
| | - Gabriela Amodeo
- Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires C1428EGA, Argentina.
- Instituto de Biodiversidad y Biología Experimental y Aplicada (IBBEA), Universidad de Buenos Aires y Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires C1428EGA CABA, Argentina.
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8
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Sun A, Tang X, Nie D, Fan Y, Tang G. Positron Emission Tomography Imaging of Lesions pH Using 11C-Labeled Bicarbonate. Cancer Biother Radiopharm 2018; 33:285-294. [PMID: 30004244 DOI: 10.1089/cbr.2017.2414] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
OBJECTIVES As acid-base imbalance is involved in many pathological processes, the capability to image tissue pH alterations in the clinic could offer new ways to detect disease and respond to treatment. In this study, the authors show that tissue pH can be imaged in vivo with 11C-labeled bicarbonate (H11CO3-) buffer and positron emission tomography (PET). METHODS H11CO3- was produced by on-column NaOH adsorption. Biodistribution of H11CO3- in normal mice was determined. In addition, uptake studies and inhibition experiments of H11CO3- in the S180 fibrosarcoma-bearing mice and the inflammatory mice were investigated with PET imaging. The tumor and inflammatory interstitial pH was measured by a needle pH microelectrode. RESULTS PET imaging demonstrated the high uptake of H11CO3- in mice tumor tissues and inflammatory tissues, which showed that the average tumor or inflammatory interstitial pH was significantly lower than the surrounding tissue. Administration of sodium bicarbonate in the drinking water increased the measured tumor pH, while the uptake of H11CO3- in mice model tissues had no change. Similarly, administration with ammonium chloride (NH4Cl) decreased the pH, whereas the unchanged uptake of H11CO3- in mice model tissues was also found. However, after administration of acetazolamide, the low uptake of H11CO3- in mice model tissues was observed. CONCLUSIONS H11CO3- solution is an endogenous bicarbonate buffer tracer that can be injected into patients without toxicity. H11CO3- PET can be used clinically to image pathological processes that are associated with acid-base imbalance, such as cancer and inflammation.
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Affiliation(s)
- Aixia Sun
- 1 Department of Nuclear Medicine and Guangdong Engineering Research Center for Translational Application of Medical Radiopharmaceuticals, The First Affiliated Hospital, SunYat-Sen University , Guangzhou, China
| | - Xiaolan Tang
- 2 College of Materials and Energy, South China Agricultural University , Guangzhou, China
| | - Dahong Nie
- 1 Department of Nuclear Medicine and Guangdong Engineering Research Center for Translational Application of Medical Radiopharmaceuticals, The First Affiliated Hospital, SunYat-Sen University , Guangzhou, China
| | - Yixiang Fan
- 3 Department of Nuclear Medicine, Guangdong No. 2 Provincial People's Hospital , Guangzhou, China
| | - Ganghua Tang
- 1 Department of Nuclear Medicine and Guangdong Engineering Research Center for Translational Application of Medical Radiopharmaceuticals, The First Affiliated Hospital, SunYat-Sen University , Guangzhou, China
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9
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Arias-Hidalgo M, Al-Samir S, Gros G, Endeward V. Cholesterol is the main regulator of the carbon dioxide permeability of biological membranes. Am J Physiol Cell Physiol 2018; 315:C137-C140. [PMID: 29874108 DOI: 10.1152/ajpcell.00139.2018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
We present here a compilation of membrane CO2 permeabilities (Pco2) for various cell types from the literature. Pco2 values vary over more than two orders of magnitude. Relating Pco2 to the cholesterol content of the membranes shows that, with the exception of red blood cells, it is essentially membrane cholesterol that determines the value of Pco2. Thus, the observed strong modulation of Pco2 in the majority of membranes is caused by cholesterol rather than gas channels.
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Affiliation(s)
- Mariela Arias-Hidalgo
- Institut für Molekular und Zellphysiologie, AG Vegetative Physiologie, Medizinische Hochschule Hannover, Hannover , Germany
| | - Samer Al-Samir
- Institut für Molekular und Zellphysiologie, AG Vegetative Physiologie, Medizinische Hochschule Hannover, Hannover , Germany
| | - Gerolf Gros
- Institut für Molekular und Zellphysiologie, AG Vegetative Physiologie, Medizinische Hochschule Hannover, Hannover , Germany
| | - Volker Endeward
- Institut für Molekular und Zellphysiologie, AG Vegetative Physiologie, Medizinische Hochschule Hannover, Hannover , Germany
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10
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Flatt JF, Bruce LJ. The Molecular Basis for Altered Cation Permeability in Hereditary Stomatocytic Human Red Blood Cells. Front Physiol 2018; 9:367. [PMID: 29713289 PMCID: PMC5911802 DOI: 10.3389/fphys.2018.00367] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Accepted: 03/27/2018] [Indexed: 11/20/2022] Open
Abstract
Normal human RBCs have a very low basal permeability (leak) to cations, which is continuously corrected by the Na,K-ATPase. The leak is temperature-dependent, and this temperature dependence has been evaluated in the presence of inhibitors to exclude the activity of the Na,K-ATPase and NaK2Cl transporter. The severity of the RBC cation leak is altered in various conditions, most notably the hereditary stomatocytosis group of conditions. Pedigrees within this group have been classified into distinct phenotypes according to various factors, including the severity and temperature-dependence of the cation leak. As recent breakthroughs have provided more information regarding the molecular basis of hereditary stomatocytosis, it has become clear that these phenotypes elegantly segregate with distinct genetic backgrounds. The cryohydrocytosis phenotype, including South-east Asian Ovalocytosis, results from mutations in SLC4A1, and the very rare condition, stomatin-deficient cryohydrocytosis, is caused by mutations in SLC2A1. Mutations in RHAG cause the very leaky condition over-hydrated stomatocytosis, and mutations in ABCB6 result in familial pseudohyperkalemia. All of the above are large multi-spanning membrane proteins and the mutations may either modify the structure of these proteins, resulting in formation of a cation pore, or otherwise disrupt the membrane to allow unregulated cation movement across the membrane. More recently mutations have been found in two RBC cation channels, PIEZO1 and KCNN4, which result in dehydrated stomatocytosis. These mutations alter the activation and deactivation kinetics of these channels, leading to increased opening and allowing greater cation fluxes than in wild type.
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Affiliation(s)
- Joanna F Flatt
- Bristol Institute for Transfusion Sciences, NHS Blood and Transplant, Bristol, United Kingdom
| | - Lesley J Bruce
- Bristol Institute for Transfusion Sciences, NHS Blood and Transplant, Bristol, United Kingdom
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11
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CO₂ Permeability of Biological Membranes and Role of CO₂ Channels. MEMBRANES 2017; 7:membranes7040061. [PMID: 29064458 PMCID: PMC5746820 DOI: 10.3390/membranes7040061] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/17/2017] [Revised: 10/13/2017] [Accepted: 10/18/2017] [Indexed: 01/09/2023]
Abstract
We summarize here, mainly for mammalian systems, the present knowledge of (a) the membrane CO₂ permeabilities in various tissues; (b) the physiological significance of the value of the CO₂ permeability;
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12
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Abstract
Acid-base homeostasis is critical to maintenance of normal health. Renal ammonia excretion is the quantitatively predominant component of renal net acid excretion, both under basal conditions and in response to acid-base disturbances. Although titratable acid excretion also contributes to renal net acid excretion, the quantitative contribution of titratable acid excretion is less than that of ammonia under basal conditions and is only a minor component of the adaptive response to acid-base disturbances. In contrast to other urinary solutes, ammonia is produced in the kidney and then is selectively transported either into the urine or the renal vein. The proportion of ammonia that the kidney produces that is excreted in the urine varies dramatically in response to physiological stimuli, and only urinary ammonia excretion contributes to acid-base homeostasis. As a result, selective and regulated renal ammonia transport by renal epithelial cells is central to acid-base homeostasis. Both molecular forms of ammonia, NH3 and NH4+, are transported by specific proteins, and regulation of these transport processes determines the eventual fate of the ammonia produced. In this review, we discuss these issues, and then discuss in detail the specific proteins involved in renal epithelial cell ammonia transport.
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Affiliation(s)
- I David Weiner
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Renal Transplantation, University of Florida College of Medicine, Gainesville, Florida; and Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville, Florida
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13
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Durant AC, Chasiotis H, Misyura L, Donini A. Aedes aegypti Rhesus glycoproteins contribute to ammonia excretion by larval anal papillae. ACTA ACUST UNITED AC 2016; 220:588-596. [PMID: 27885043 DOI: 10.1242/jeb.151084] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Accepted: 11/21/2016] [Indexed: 02/06/2023]
Abstract
In larval Aedes aegypti, transcripts of the Rhesus-like glycoproteins AeRh50-1 and AeRh50-2 have been detected in the anal papillae, sites of ammonia (NH3/NH4+) excretion; however, these putative ammonia transporters have not been previously localized or functionally characterized. In this study, we show that the AeRh50s co-immunolocalize with apical V-type H+-ATPase as well as with basal Na+/K+-ATPase in the epithelium of anal papillae. The double-stranded RNA-mediated knockdown of AeRh50-1 and AeRh50-2 resulted in a significant reduction in AeRh50 protein abundance in the anal papillae, and this was coupled to decreased ammonia excretion. The knockdown of AeRh50-1 resulted in decreased hemolymph [NH4+] and pH whereas knockdown of AeRh50-2 had no effect on these parameters. We conclude that the AeRh50s are important contributors to ammonia excretion at the anal papillae of larval A. aegypti, which may be the basis for their ability to inhabit areas with high ammonia levels.
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Affiliation(s)
- Andrea C Durant
- Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3
| | - Helen Chasiotis
- Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3
| | - Lidiya Misyura
- Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3
| | - Andrew Donini
- Department of Biology, York University, 4700 Keele Street, Toronto, Ontario, Canada M3J 1P3
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14
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Pérez-Escuredo J, Van Hée VF, Sboarina M, Falces J, Payen VL, Pellerin L, Sonveaux P. Monocarboxylate transporters in the brain and in cancer. BIOCHIMICA ET BIOPHYSICA ACTA 2016; 1863:2481-97. [PMID: 26993058 PMCID: PMC4990061 DOI: 10.1016/j.bbamcr.2016.03.013] [Citation(s) in RCA: 267] [Impact Index Per Article: 33.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 03/01/2016] [Accepted: 03/12/2016] [Indexed: 12/20/2022]
Abstract
Monocarboxylate transporters (MCTs) constitute a family of 14 members among which MCT1-4 facilitate the passive transport of monocarboxylates such as lactate, pyruvate and ketone bodies together with protons across cell membranes. Their anchorage and activity at the plasma membrane requires interaction with chaperon protein such as basigin/CD147 and embigin/gp70. MCT1-4 are expressed in different tissues where they play important roles in physiological and pathological processes. This review focuses on the brain and on cancer. In the brain, MCTs control the delivery of lactate, produced by astrocytes, to neurons, where it is used as an oxidative fuel. Consequently, MCT dysfunctions are associated with pathologies of the central nervous system encompassing neurodegeneration and cognitive defects, epilepsy and metabolic disorders. In tumors, MCTs control the exchange of lactate and other monocarboxylates between glycolytic and oxidative cancer cells, between stromal and cancer cells and between glycolytic cells and endothelial cells. Lactate is not only a metabolic waste for glycolytic cells and a metabolic fuel for oxidative cells, but it also behaves as a signaling agent that promotes angiogenesis and as an immunosuppressive metabolite. Because MCTs gate the activities of lactate, drugs targeting these transporters have been developed that could constitute new anticancer treatments. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.
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Affiliation(s)
- Jhudit Pérez-Escuredo
- Pole of Pharmacology, Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain (UCL), Avenue Emmanuel Mounier 52 box B1.53.09, 1200 Brussels, Belgium
| | - Vincent F Van Hée
- Pole of Pharmacology, Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain (UCL), Avenue Emmanuel Mounier 52 box B1.53.09, 1200 Brussels, Belgium
| | - Martina Sboarina
- Pole of Pharmacology, Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain (UCL), Avenue Emmanuel Mounier 52 box B1.53.09, 1200 Brussels, Belgium
| | - Jorge Falces
- Pole of Pharmacology, Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain (UCL), Avenue Emmanuel Mounier 52 box B1.53.09, 1200 Brussels, Belgium
| | - Valéry L Payen
- Pole of Pharmacology, Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain (UCL), Avenue Emmanuel Mounier 52 box B1.53.09, 1200 Brussels, Belgium
| | - Luc Pellerin
- Laboratory of Neuroenergetics, Department of Physiology, University of Lausanne, Rue du Bugnon 7, 1005 Lausanne, Switzerland.
| | - Pierre Sonveaux
- Pole of Pharmacology, Institut de Recherche Expérimentale et Clinique (IREC), Université catholique de Louvain (UCL), Avenue Emmanuel Mounier 52 box B1.53.09, 1200 Brussels, Belgium.
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15
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Al-Samir S, Goossens D, Cartron JP, Nielsen S, Scherbarth F, Steinlechner S, Gros G, Endeward V. Maximal Oxygen Consumption Is Reduced in Aquaporin-1 Knockout Mice. Front Physiol 2016; 7:347. [PMID: 27559317 PMCID: PMC4978734 DOI: 10.3389/fphys.2016.00347] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Accepted: 07/29/2016] [Indexed: 12/01/2022] Open
Abstract
We have measured maximal oxygen consumption (V˙O2,max) of mice lacking one or two of the established mouse red-cell CO2 channels AQP1, AQP9, and Rhag. We intended to study whether these proteins, by acting as channels for O2, determine O2 exchange in the lung and in the periphery. We found that V˙O2,max as determined by the Helox technique is reduced by ~16%, when AQP1 is knocked out, but not when AQP9 or Rhag are lacking. This figure holds for animals respiring normoxic as well as hypoxic gas mixtures. To see whether the reduction of V˙O2,max is due to impaired O2 uptake in the lung, we measured carotid arterial O2 saturation (SO2) by pulse oximetry. Neither under normoxic (inspiratory O2 21%) nor under hypoxic conditions (11% O2) is there a difference in SO2 between AQP1null and WT mice, suggesting that AQP1 is not critical for O2 uptake in the lung. The fact that the % reduction of V˙O2,max is identical in normoxia and hypoxia indicates moreover that the limitation of V˙O2,max is not due to an O2 diffusion problem, neither in the lung nor in the periphery. Instead, it appears likely that AQP1null animals exhibit a reduced V˙O2,max due to the reduced wall thickness and muscle mass of the left ventricles of their hearts, as reported previously. We conclude that very likely the properties of the hearts of AQP1 knockout mice cause a reduced maximal cardiac output and thus cause a reduced V˙O2,max, which constitutes a new phenotype of these mice.
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Affiliation(s)
- Samer Al-Samir
- Vegetative Physiologie 4220, Abt. Molekular-und Zellphysiologie, Medizinische Hochschule Hannover Hannover, Germany
| | - Dominique Goossens
- Institut National de la Transfusion Sanguine-Institut National de la Santé et de la Recherche Médicale UMR_S1134 Paris, France
| | - Jean-Pierre Cartron
- Institut National de la Transfusion Sanguine-Institut National de la Santé et de la Recherche Médicale UMR_S1134 Paris, France
| | - Søren Nielsen
- Biomedicine, Department Health Science and Technology, Aalborg University Aalborg, Denmark
| | - Frank Scherbarth
- Institut für Zoologie, Tierärztliche Hochschule Hannover Hannover, Germany
| | | | - Gerolf Gros
- Vegetative Physiologie 4220, Abt. Molekular-und Zellphysiologie, Medizinische Hochschule Hannover Hannover, Germany
| | - Volker Endeward
- Vegetative Physiologie 4220, Abt. Molekular-und Zellphysiologie, Medizinische Hochschule Hannover Hannover, Germany
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16
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Nawata CM, Walsh PJ, Wood CM. Nitrogen metabolism, acid-base regulation, and molecular responses to ammonia and acid infusions in the spiny dogfish shark (Squalus acanthias). J Comp Physiol B 2015; 185:511-25. [PMID: 25794843 DOI: 10.1007/s00360-015-0898-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2014] [Revised: 01/18/2015] [Accepted: 03/10/2015] [Indexed: 11/25/2022]
Abstract
Although they are ureotelic, marine elasmobranchs express Rh glycoproteins, putative ammonia channels. To address questions raised by a recent study on high environmental ammonia (HEA) exposure, dogfish were intravascularly infused for 24 h at 3 ml kg(-1) h(-1) with isosmotic NaCl (500 mmol l(-1), control), NH4HCO3 (500 mmol l(-1)), NH4Cl (500 mmol l(-1)), or HCl (as 125 mmol l(-1) HCl + 375 mmol l(-1) NaCl). While NaCl had no effect on arterial acid-base status, NH4HCO3 caused mild alkalosis, NH4Cl caused strong acidosis, and HCl caused lesser acidosis, all predominantly metabolic in nature. Total plasma ammonia (T(Amm)) and excretion rates of ammonia (J(Amm)) and urea-N (J(Urea-N)) were unaffected by NaCl or HCl. However, despite equal loading rates, plasma T(Amm) increased to a greater extent with NH4Cl, while J(Amm) increased to a greater extent with NH4HCO3 due to much greater increases in blood-to-water PNH3 gradients. As with HEA, both treatments caused large (90%) elevations of J(Urea-N), indicating that urea-N synthesis by the ornithine-urea cycle (OUC) is driven primarily by ammonia rather than HCO3(-). Branchial mRNA expressions of Rhbg and Rhp2 were unaffected by NH4HCO3 or NH4Cl, but v-type H(+)-ATPase was down-regulated by both treatments, and Rhbg and Na(+)/H(+) exchanger NHE2 were up-regulated by HCl. In the kidney, Rhbg was unresponsive to all treatments, but Rhp2 was up-regulated by HCl, and the urea transporter UT was up-regulated by HCl and NH4Cl. These responses are discussed in the context of current ideas about branchial, renal, and OUC function in this nitrogen-limited predator.
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Affiliation(s)
- C Michele Nawata
- Bamfield Marine Sciences Centre, 100 Pachena Road, Bamfield, BC, V0R 1B0, Canada,
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17
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Tsiavaliaris G, Itel F, Hedfalk K, Al‐Samir S, Meier W, Gros G, Endeward V. Low CO
2
permeability of cholesterol‐containing liposomes detected by stopped‐flow fluorescence spectroscopy. FASEB J 2015; 29:1780-93. [DOI: 10.1096/fj.14-263988] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 12/19/2014] [Indexed: 01/21/2023]
Affiliation(s)
- Georgios Tsiavaliaris
- Institut für Biophysikalische Chemie, Medizinische Hochschule HannoverHannoverGermany
| | - Fabian Itel
- Departement ChemieUniversität BaselBaselSwitzerland
| | - Kristina Hedfalk
- Department Chemistry & Molecular BiologyUniversity of GothenburgGöteborgSweden
| | - Samer Al‐Samir
- Institut für Molekular‐ und Zellphysiologie, AG Vegetative Physiologie, Medizinische Hochschule HannoverHannoverGermany
| | | | - Gerolf Gros
- Institut für Molekular‐ und Zellphysiologie, AG Vegetative Physiologie, Medizinische Hochschule HannoverHannoverGermany
| | - Volker Endeward
- Institut für Molekular‐ und Zellphysiologie, AG Vegetative Physiologie, Medizinische Hochschule HannoverHannoverGermany
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18
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Weiner ID, Verlander JW. Ammonia transport in the kidney by Rhesus glycoproteins. Am J Physiol Renal Physiol 2014; 306:F1107-20. [PMID: 24647713 PMCID: PMC4024734 DOI: 10.1152/ajprenal.00013.2014] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Accepted: 03/14/2014] [Indexed: 12/26/2022] Open
Abstract
Renal ammonia metabolism is a fundamental element of acid-base homeostasis, comprising a major component of both basal and physiologically altered renal net acid excretion. Over the past several years, a fundamental change in our understanding of the mechanisms of renal epithelial cell ammonia transport has occurred, replacing the previous model which was based upon diffusion equilibrium for NH3 and trapping of NH4(+) with a new model in which specific and regulated transport of both NH3 and NH4(+) across renal epithelial cell membranes via specific membrane proteins is required for normal ammonia metabolism. A major advance has been the recognition that members of a recently recognized transporter family, the Rhesus glycoprotein family, mediate critical roles in renal and extrarenal ammonia transport. The erythroid-specific Rhesus glycoprotein, Rh A Glycoprotein (Rhag), was the first Rhesus glycoprotein recognized as an ammonia-specific transporter. Subsequently, the nonerythroid Rh glycoproteins, Rh B Glycoprotein (Rhbg) and Rh C Glycoprotein (Rhcg), were cloned and identified as ammonia transporters. They are expressed in specific cell populations and membrane domains in distal renal epithelial cells, where they facilitate ammonia secretion. In this review, we discuss the distribution of Rhbg and Rhcg in the kidney, the regulation of their expression and activity in physiological disturbances, the effects of genetic deletion on renal ammonia metabolism, and the molecular mechanisms of Rh glycoprotein-mediated ammonia transport.
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Affiliation(s)
- I David Weiner
- Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville Florida; and Division of Nephrology, Hypertension, and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Jill W Verlander
- Nephrology and Hypertension Section, North Florida/South Georgia Veterans Health System, Gainesville Florida; and
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19
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Nakhoul NL, Lee Hamm L. The challenge of determining the role of Rh glycoproteins in transport of NH3and NH4+. ACTA ACUST UNITED AC 2014. [DOI: 10.1002/wmts.105] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Nazih L. Nakhoul
- Department of Physiology; Tulane University Medical School; New Orleans LA USA
- Department of Medicine, Section of Nephrology; Tulane University Medical School; New Orleans LA USA
| | - L. Lee Hamm
- Department of Medicine, Section of Nephrology; Tulane University Medical School; New Orleans LA USA
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20
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Endeward V, Al-Samir S, Itel F, Gros G. How does carbon dioxide permeate cell membranes? A discussion of concepts, results and methods. Front Physiol 2014; 4:382. [PMID: 24409149 PMCID: PMC3884148 DOI: 10.3389/fphys.2013.00382] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Accepted: 12/05/2013] [Indexed: 12/13/2022] Open
Abstract
We review briefly how the thinking about the permeation of gases, especially CO2, across cell and artificial lipid membranes has evolved during the last 100 years. We then describe how the recent finding of a drastic effect of cholesterol on CO2 permeability of both biological and artificial membranes fundamentally alters the long-standing idea that CO2—as well as other gases—permeates all membranes with great ease. This requires revision of the widely accepted paradigm that membranes never offer a serious diffusion resistance to CO2 or other gases. Earlier observations of “CO2-impermeable membranes” can now be explained by the high cholesterol content of some membranes. Thus, cholesterol is a membrane component that nature can use to adapt membrane CO2 permeability to the functional needs of the cell. Since cholesterol serves many other cellular functions, it cannot be reduced indefinitely. We show, however, that cells that possess a high metabolic rate and/or a high rate of O2 and CO2 exchange, do require very high CO2 permeabilities that may not be achievable merely by reduction of membrane cholesterol. The article then discusses the alternative possibility of raising the CO2 permeability of a membrane by incorporating protein CO2 channels. The highly controversial issue of gas and CO2 channels is systematically and critically reviewed. It is concluded that a majority of the results considered to be reliable, is in favor of the concept of existence and functional relevance of protein gas channels. The effect of intracellular carbonic anhydrase, which has recently been proposed as an alternative mechanism to a membrane CO2 channel, is analysed quantitatively and the idea considered untenable. After a brief review of the knowledge on permeation of O2 and NO through membranes, we present a summary of the 18O method used to measure the CO2 permeability of membranes and discuss quantitatively critical questions that may be addressed to this method.
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Affiliation(s)
- Volker Endeward
- Zentrum Physiologie, Vegetative Physiologie 4220, Medizinische Hochschule Hannover Hannover, Germany
| | - Samer Al-Samir
- Zentrum Physiologie, Vegetative Physiologie 4220, Medizinische Hochschule Hannover Hannover, Germany
| | - Fabian Itel
- Departement Chemie, Universität Basel Basel, Switzerland
| | - Gerolf Gros
- Zentrum Physiologie, Vegetative Physiologie 4220, Medizinische Hochschule Hannover Hannover, Germany
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21
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Clanton TL, Hogan MC, Gladden LB. Regulation of cellular gas exchange, oxygen sensing, and metabolic control. Compr Physiol 2013; 3:1135-90. [PMID: 23897683 DOI: 10.1002/cphy.c120030] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Cells must continuously monitor and couple their metabolic requirements for ATP utilization with their ability to take up O2 for mitochondrial respiration. When O2 uptake and delivery move out of homeostasis, cells have elaborate and diverse sensing and response systems to compensate. In this review, we explore the biophysics of O2 and gas diffusion in the cell, how intracellular O2 is regulated, how intracellular O2 levels are sensed and how sensing systems impact mitochondrial respiration and shifts in metabolic pathways. Particular attention is paid to how O2 affects the redox state of the cell, as well as the NO, H2S, and CO concentrations. We also explore how these agents can affect various aspects of gas exchange and activate acute signaling pathways that promote survival. Two kinds of challenges to gas exchange are also discussed in detail: when insufficient O2 is available for respiration (hypoxia) and when metabolic requirements test the limits of gas exchange (exercising skeletal muscle). This review also focuses on responses to acute hypoxia in the context of the original "unifying theory of hypoxia tolerance" as expressed by Hochachka and colleagues. It includes discourse on the regulation of mitochondrial electron transport, metabolic suppression, shifts in metabolic pathways, and recruitment of cell survival pathways preventing collapse of membrane potential and nuclear apoptosis. Regarding exercise, the issues discussed relate to the O2 sensitivity of metabolic rate, O2 kinetics in exercise, and influences of available O2 on glycolysis and lactate production.
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Affiliation(s)
- T L Clanton
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, USA.
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22
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Characteristics of mammalian Rh glycoproteins (SLC42 transporters) and their role in acid-base transport. Mol Aspects Med 2013; 34:629-37. [PMID: 23506896 DOI: 10.1016/j.mam.2012.05.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2012] [Accepted: 04/16/2012] [Indexed: 01/06/2023]
Abstract
The mammalian Rh glycoproteins belong to the solute transporter family SLC42 and include RhAG, present in red blood cells, and two non-erythroid members RhBG and RhCG that are expressed in various tissues, including kidney, liver, skin and the GI tract. The Rh proteins in the red blood cell form an "Rh complex" made up of one D-subunit, one CE-subunit and two RhAG subunits. The Rh complex has a well-known antigenic effect but also contributes to the stability of the red cell membrane. RhBG and RhCG are related to the NH4(+) transporters of the yeast and bacteria but their exact function is yet to be determined. This review describes the expression and molecular properties of these membrane proteins and their potential role as NH3/NH4(+) and CO2 transporters. The likelihood that these proteins transport gases such as CO2 or NH3 is novel and significant. The review also describes the physiological importance of these proteins and their relevance to human disease.
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23
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Geyer RR, Musa-Aziz R, Qin X, Boron WF. Relative CO(2)/NH(3) selectivities of mammalian aquaporins 0-9. Am J Physiol Cell Physiol 2013; 304:C985-94. [PMID: 23485707 DOI: 10.1152/ajpcell.00033.2013] [Citation(s) in RCA: 71] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Previous work showed that aquaporin 1 (AQP1), AQP4-M23, and AQP5 each has a characteristic CO(2)/NH(3) and CO(2)/H(2)O permeability ratio. The goal of the present study is to characterize AQPs 0-9, which traffic to the plasma membrane when heterologously expressed in Xenopus oocytes. We use video microscopy to compute osmotic water permeability (P(f)) and microelectrodes to record transient changes in surface pH (ΔpH(S)) caused by CO(2) or NH(3) influx. Subtracting respective values for day-matched, H(2)O-injected control oocytes yields the channel-specific values P(f)* and ΔpH(S)*. We find that P(f)* is significantly >0 for all AQPs tested except AQP6. (ΔpH(S)*)(CO(2)) is significantly >0 for AQP0, AQP1, AQP4-M23, AQP5, AQP6, and AQP9. (ΔpH(S)*)(NH(3)) is >0 for AQP1, AQP3, AQP6, AQP7, AQP8, and AQP9. The ratio (ΔpH(S)*)(CO(2))/P(f)* falls in the sequence AQP6 (∞) > AQP5 > AQP4-M23 > AQP0 ≅ AQP1 ≅ AQP9 > others (0). The ratio (ΔpH(S)*)(NH(3))/P(f)* falls in the sequence AQP6 (∞) > AQP3 ≅ AQP7 ≅ AQP8 ≅ AQP9 > AQP1 > others (0). Finally, the ratio (ΔpH(S)*)(CO(2))/(-ΔpH(S)*)(NH(3)) falls in the sequence AQP0 (∞) ≅ AQP4-M23 ≅ AQP5 > AQP6 > AQP1 > AQP9 > AQP3 (0) ≅ AQP7 ≅ AQP8. The ratio (ΔpH(S)*)(CO(2))/(-ΔpH(S)*)(NH(3)) is indeterminate for both AQP2 and AQP4-M1. In summary, we find that mammalian AQPs exhibit a diverse range of selectivities for CO(2) vs. NH(3) vs. H(2)O. As a consequence, by expressing specific combinations of AQPs, cells could exert considerable control over the movements of each of these three substances.
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Affiliation(s)
- R Ryan Geyer
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA.
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24
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Uehlein N, Otto B, Eilingsfeld A, Itel F, Meier W, Kaldenhoff R. Gas-tight triblock-copolymer membranes are converted to CO₂ permeable by insertion of plant aquaporins. Sci Rep 2012; 2:538. [PMID: 22844579 PMCID: PMC3406340 DOI: 10.1038/srep00538] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2012] [Accepted: 07/09/2012] [Indexed: 11/15/2022] Open
Abstract
We demonstrate that membranes consisting of certain triblock-copolymers were tight for CO2. Using a novel approach, we provide evidence for aquaporin facilitated CO2 diffusion. Plant aquaporins obtained from heterologous expression were inserted into triblock copolymer membranes. These were employed to separate a chamber with a solution maintaining high CO2 concentrations from one with depleted CO2 concentrations. CO2 diffusion was detected by measuring the pH change resulting from membrane CO2 diffusion from one chamber to the other. An up to 21 fold increase in diffusion rate was determined. Besides the supply of this proof of principle, we could provide additional arguments in favour of protein facilitated CO2 diffusion to the vivid on-going debate about the principles of membrane gas diffusion in living cells.
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Affiliation(s)
- Norbert Uehlein
- Department of Biology, Applied Plant Sciences, Technische Universität Darmstadt, Schnittspahnstrasse 10, D-64287 Darmstadt, Germany.
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25
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Benga G. The first discovered water channel protein, later called aquaporin 1: molecular characteristics, functions and medical implications. Mol Aspects Med 2012; 33:518-34. [PMID: 22705445 DOI: 10.1016/j.mam.2012.06.001] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Accepted: 06/07/2012] [Indexed: 02/08/2023]
Abstract
After a decade of work on the water permeability of red blood cells (RBC) Benga group in Cluj-Napoca, Romania, discovered in 1985 the first water channel protein in the RBC membrane. The discovery was reported in publications in 1986 and reviewed in subsequent years. The same protein was purified by chance by Agre group in Baltimore, USA, in 1988, who called in 1991 the protein CHIP28 (CHannel forming Integral membrane Protein of 28 kDa), suggesting that it may play a role in linkage of the membrane skeleton to the lipid bilayer. In 1992 the Agre group identified CHIP28's water transport property. One year later CHIP28 was named aquaporin 1, abbreviated as AQP1. In this review the molecular structure-function relationships of AQP1 are presented. In the natural or model membranes AQP1 is in the form of a homotetramer, however, each monomer has an independent water channel (pore). The three-dimensional structure of AQP1 is described, with a detailed description of the channel (pore), the molecular mechanisms of permeation through the channel of water molecules and exclusion of protons. The permeability of the pore to gases (CO(2), NH(3), NO, O(2)) and ions is also mentioned. I have also reviewed the functional roles and medical implications of AQP1 expressed in various organs and cells (microvascular endothelial cells, kidney, central nervous system, eye, lacrimal and salivary glands, respiratory apparatus, gastrointestinal tract, hepatobiliary compartments, female and male reproductive system, inner ear, skin). The role of AQP1 in cell migration and angiogenesis in relation with cancer, the genetics of AQP1 and mutations in human subjects are also mentioned. The role of AQP1 in red blood cells is discussed based on our comparative studies of water permeability in over 30 species.
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Affiliation(s)
- Gheorghe Benga
- First Laboratory of Genetic Explorations, Cluj County Clinical Emergency Hospital, Cluj-Napoca, Romania.
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26
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Perry SF, Braun MH, Noland M, Dawdy J, Walsh PJ. Do zebrafish Rh proteins act as dual ammonia-CO2 channels? ACTA ACUST UNITED AC 2010; 313:618-21. [DOI: 10.1002/jez.631] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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27
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Huang CH, Ye M. The Rh protein family: gene evolution, membrane biology, and disease association. Cell Mol Life Sci 2010; 67:1203-18. [PMID: 19953292 PMCID: PMC11115862 DOI: 10.1007/s00018-009-0217-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2009] [Revised: 11/10/2009] [Accepted: 11/12/2009] [Indexed: 11/25/2022]
Abstract
The Rh (Rhesus) genes encode a family of conserved proteins that share a structural fold of 12 transmembrane helices with members of the major facilitator superfamily. Interest in this family has arisen from the discovery of Rh factor's involvement in hemolytic disease in the fetus and newborn, and of its homologs widely expressed in epithelial tissues. The Rh factor and Rh-associated glycoprotein (RhAG), with epithelial cousins RhBG and RhCG, form four subgroups conferring upon vertebrates a genealogical commonality. The past decade has heralded significant advances in understanding the phylogenetics, allelic diversity, crystal structure, and biological function of Rh proteins. This review describes recent progress on this family and the molecular insights gleaned from its gene evolution, membrane biology, and disease association. The focus is on its long evolutionary history and surprising structural conservation from prokaryotes to humans, pointing to the importance of its functional role, related to but distinct from ammonium transport proteins.
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Affiliation(s)
- Cheng-Han Huang
- Laboratory of Biochemistry and Molecular Genetics, Lindsley F. Kimball Research Institute, New York Blood Center, New York, NY 10065, USA.
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28
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Wu SC, Horng JL, Liu ST, Hwang PP, Wen ZH, Lin CS, Lin LY. Ammonium-dependent sodium uptake in mitochondrion-rich cells of medaka (Oryzias latipes) larvae. Am J Physiol Cell Physiol 2010; 298:C237-50. [DOI: 10.1152/ajpcell.00373.2009] [Citation(s) in RCA: 131] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
In this study, a scanning ion-selective electrode technique (SIET) was applied to measure H+, Na+, and NH4+ gradients and apparent fluxes at specific cells on the skin of medaka larvae. Na+ uptake and NH3/NH4+ excretion were detected at most mitochondrion-rich cells (MRCs). H+ probing at MRCs revealed two group of MRCs, i.e., acid-secreting and base-secreting MRCs. Treatment with EIPA (100 μM) blocked 35% of the NH3/NH4+ secretion and 54% of the Na+ uptake, suggesting that the Na+/H+ exchanger (NHE) is involved in Na+ and NH3/NH4+ transport. Low-Na+ water (<0.001 mM) or high-NH4+ (5 mM) acclimation simultaneously increased Na+ uptake and NH3/NH4+ excretion but decreased or even reversed the H+ gradient at the skin and MRCs. The correlation between NH4+ production and H+ consumption at the skin surface suggests that MRCs excrete nonionic NH3 (base) by an acid-trapping mechanism. Raising the external NH4+ significantly blocked NH3/NH4+ excretion and Na+ uptake. In contrast, raising the acidity of the water (pH 7 to pH 6) enhanced NH3/NH4+ excretion and Na+ uptake by MRCs. In situ hybridization and real-time PCR showed that the mRNAs of the Na+/H+ exchanger ( slc9a3) and Rhesus glycoproteins ( Rhcg1 and Rhbg) were colocalized in MRCs of medaka, and their expressions were induced by low-Na+ acclimation. This study suggests a novel Na+/NH4+ exchange pathway in apical membranes of MRCs, in which a coupled NHE and Rh glycoprotein is involved and the Rh glycoprotein may drive the NHE by generating H+ gradients across apical membranes of MRCs.
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Affiliation(s)
- Shu-Chen Wu
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan, Republic of China
| | - Jiun-Lin Horng
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan, Republic of China; and
| | - Sian-Tai Liu
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan, Republic of China
| | - Pung-Pung Hwang
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan, Republic of China; and
| | - Zhi-Hong Wen
- Department of Marine Biotechnology and Resources, College of Marine Science and Division of Marine Biotechnology, Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung, Taiwan, Republic of China
| | - Chan-Shing Lin
- Department of Marine Biotechnology and Resources, College of Marine Science and Division of Marine Biotechnology, Asia-Pacific Ocean Research Center, National Sun Yat-sen University, Kaohsiung, Taiwan, Republic of China
| | - Li-Yih Lin
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan, Republic of China
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29
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Nakada T, Westhoff CM, Yamaguchi Y, Hyodo S, Li X, Muro T, Kato A, Nakamura N, Hirose S. Rhesus glycoprotein p2 (Rhp2) is a novel member of the Rh family of ammonia transporters highly expressed in shark kidney. J Biol Chem 2009; 285:2653-64. [PMID: 19926789 DOI: 10.1074/jbc.m109.052068] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Rhesus (Rh) glycoproteins are a family of membrane proteins capable of transporting ammonia. We isolated the full-length cDNA of a novel Rh glycoprotein, Rhp2, from a kidney cDNA library from the banded hound shark, Triakis scyllium. Molecular cloning and characterization indicated that Rhp2 consists of 476 amino acid residues and has 12 putative transmembrane spans, consistent with the structure of other family members. The shark Rhp2 gene was found to consist of only one coding exon. Northern blotting and in situ hybridization revealed that Rhp2 mRNA is exclusively expressed in the renal tubules of the sinus zone but not in the bundle zone and renal corpuscles. Immunohistochemical staining with a specific antiserum showed that Rhp2 is localized in the basolateral membranes of renal tubule cells. Double fluorescence labeling with phalloidin or labeling of the Na(+)/K(+)-ATPase further narrowed the location to the second and fourth loops in the sinus zone. Vacuolar type H(+)-ATPase was localized in apical membranes of the Rhp2-expressing tubule cells. Quantitative real-time PCR analysis and Western blotting showed that expression of Rhp2 was increased in response to elevation of environmental salinity. Functional analysis using the Xenopus oocyte expression system showed that Rhp2 has transport activity for methylammonium, an analog of ammonia. This transport activity was inhibited by NH(4)Cl but not trimethylamine-N-oxide and urea. These results suggested that Rhp2 is involved in ammonia reabsorption in the kidney of the elasmobranch group of cartilaginous fish comprising the sharks and rays.
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Affiliation(s)
- Tsutomu Nakada
- Department of Biological Sciences, Tokyo Institute of Technology, Yokohama 226-8501, Japan
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30
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Wright PA, Wood CM. A new paradigm for ammonia excretion in aquatic animals: role of Rhesus(Rh) glycoproteins. J Exp Biol 2009; 212:2303-12. [DOI: 10.1242/jeb.023085] [Citation(s) in RCA: 283] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
SUMMARY
Ammonia excretion at the gills of fish has been studied for 80 years, but the mechanism(s) involved remain controversial. The relatively recent discovery of the ammonia-transporting function of the Rhesus (Rh) proteins, a family related to the Mep/Amt family of methyl ammonia and ammonia transporters in bacteria, yeast and plants, and the occurrence of these genes and glycosylated proteins in fish gills has opened a new paradigm. We provide background on the evolution and function of the Rh proteins, and review recent studies employing molecular physiology which demonstrate their important contribution to branchial ammonia efflux. Rhag occurs in red blood cells,whereas several isoforms of both Rhbg and Rhcg occur in many tissues. In the branchial epithelium, Rhcg appears to be localized in apical membranes and Rhbg in basolateral membranes. Their gene expression is upregulated during exposure to high environmental ammonia or internal ammonia infusion, and may be sensitive to synergistic stimulation by ammonia and cortisol. Rhcg in particular appears to be coupled to H+ excretion and Na+uptake mechanisms. We propose a new model for ammonia excretion in freshwater fish and its variable linkage to Na+ uptake and acid excretion. In this model, Rhag facilitates NH3 flux out of the erythrocyte, Rhbg moves it across the basolateral membrane of the branchial ionocyte, and an apical “Na+/NH +4 exchange complex” consisting of several membrane transporters (Rhcg, V-type H+-ATPase, Na+/H+ exchanger NHE-2 and/or NHE-3, Na+ channel) working together as a metabolon provides an acid trapping mechanism for apical excretion. Intracellular carbonic anhydrase(CA-2) and basolateral Na+/HCO –3cotransporter (NBC-1) and Na+/K+-ATPase play indirect roles. These mechanisms are normally superimposed on a substantial outward movement of NH3 by simple diffusion, which is probably dependent on acid trapping in boundary layer water by H+ ions created by the catalysed or non-catalysed hydration of expired metabolic CO2. Profitable areas for future investigation of Rh proteins in fish are highlighted: their involvement in the mechanism of ammonia excretion across the gills in seawater fish, their possible importance in ammonia excretion across the skin, their potential dual role as CO2 transporters,their responses to feeding, and their roles in early life stages prior to the full development of gills.
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Affiliation(s)
- Patricia A. Wright
- Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1,Canada
| | - Chris M. Wood
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1,Canada
- Division of Marine Biology and Fisheries, Rosenstiel School of Marine Atmospheric Science, University of Miami, Miami, FL 33149, USA
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Weihrauch D, Wilkie MP, Walsh PJ. Ammonia and urea transporters in gills of fish and aquatic crustaceans. J Exp Biol 2009; 212:1716-30. [PMID: 19448081 DOI: 10.1242/jeb.024851] [Citation(s) in RCA: 184] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The diversity of mechanisms of ammonia and urea excretion by the gills and other epithelia of aquatic organisms, especially fish and crustaceans, has been studied for decades. Although the decades-old dogma of ;aquatic species excrete ammonia' still explains nitrogenous waste excretion for many species, it is clear that there are many mechanistic variations on this theme. Even within species that are ammonoteles, the process is not purely ;passive', often relying on the energizing effects of proton and sodium-potassium ATPases. Within the ammonoteles, Rh (Rhesus) proteins are beginning to emerge as vital ammonia conduits. Many fishes are also known to be capable of substantial synthesis and excretion of urea as a nitrogenous waste. In such species, members of the UT family of urea transporters have been identified as important players in urea transport across the gills. This review attempts to draw together recent information to update the mechanisms of ammonia and urea transport by the gills of aquatic species. Furthermore, we point out several potentially fruitful avenues for further research.
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Affiliation(s)
- Dirk Weihrauch
- Department of Biological Sciences, University of Manitoba, 190 Dysart Road, Winnipeg, MB, R3T 2N2 Canada
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Endeward V, Gros G. Extra- and intracellular unstirred layer effects in measurements of CO2 diffusion across membranes--a novel approach applied to the mass spectrometric 18O technique for red blood cells. J Physiol 2009; 587:1153-67. [PMID: 19139045 DOI: 10.1113/jphysiol.2008.165027] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
We have developed an experimental approach that allows us to quantify unstirred layers around cells suspended in stirred solutions. This technique is applicable to all types of transport measurements and was applied here to the (18)O technique used to measure CO(2) permeability of red cells (PCO2). We measure PCO2 in well-stirred red cell (RBC) suspensions of various viscosities adjusted by adding different amounts of 60 kDa dextran. Plotting 1/PCO2 vs. viscosity nu gives a linear relation, which can be extrapolated to nu=0. Theoretical hydrodynamics predicts that extracellular unstirred layers vanish at zero viscosity when stirring is maintained, and thus this extrapolation gives us an estimate of the PCO2 free from extracellular unstirred layer artifacts. The extrapolated value is found to be 0.16 cm s(-1) instead of the experimental value in saline of 0.12 cm s(-1) (+30%). This effect corresponds to an unstirred layer thickness of 0.5 microm. In addition, we present a theoretical approach modelling the actual geometrical and physico-chemical conditions of (18)O exchange in our experiments. It confirms the role of an extracellular unstirred layer in the determination of PCO2. Also, it allows us to quantify the contribution of the so-called intracellular unstirred layer, which results from the fact that in these transport measurements--as in all such measurements in general--the intracellular space is not stirred. The apparent thickness of this intracellular unstirred layer is about 1/4-1/3 of the maximal intracellular diffusion distance, and correction for it results in a true PCO2 of the RBC membrane of 0.20 cm s(-1). Thus, the order of magnitude of this is PCO2 unaltered compared to our previous reports. Discussion of the available evidence in the light of these results confirms that CO(2) channels exist in red cell and other membranes, and that PCO2 of red cell membranes in the absence of these channels is quite low.
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Affiliation(s)
- Volker Endeward
- Zentrum Physiologie, Medizinische Hochschule Hannover, 30625 Hannover, Germany.
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33
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Nawata CM, Wood CM. The effects of CO2 and external buffering on ammonia excretion and Rhesus glycoprotein mRNA expression in rainbow trout. ACTA ACUST UNITED AC 2008; 211:3226-36. [PMID: 18840656 DOI: 10.1242/jeb.020396] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Rhesus (Rh) proteins were recently characterized as ammonia gas (NH(3)) channels. Studies indicate, however, that Rh proteins also facilitate CO2 transport in a green alga and in human erythrocytes. Previously, we reported that Rh mRNA expression in various rainbow trout tissues responded to high environmental ammonia. To determine whether or not Rh proteins may also be involved in CO2 transport in rainbow trout, we examined the effects of a 12 h exposure to external hypercapnia (1% CO2 in air) on Rh mRNA expression in the gill, skin and erythrocytes. External hypercapnic conditions lowered the water pH and facilitated ammonia excretion; therefore, we also studied the effects of hypercapnia and normocapnia in the presence of 10 mmol l(-1) Hepes-buffered water. Hepes treatment prevented water acidification, but resulted in elevated plasma ammonia levels and reduced ammonia excretion rates. Hypercapnia exposure without buffering did not elicit changes in Rh mRNA expression in the gill or skin. However, Rhcg2 mRNA expression was downregulated in the gills and upregulated in the skin of both normocapnia- and hypercapnia-exposed fish in Hepes-buffered water. mRNA expression of a newly cloned Rhbg2 cDNA was downregulated in the skin of fish exposed to buffered water, and Rhag mRNA expression in erythrocytes was decreased with exposure to normocapnia in buffered water but not with hypercapnia exposure in either buffered or unbuffered water. With the aid of Hepes buffering, we were able to observe the effects of both CO2 and ammonia on Rh mRNA expression. Overall, we conclude that high CO2 did not directly elicit changes in Rh mRNA transcription levels in the gill and skin, and that the changes observed probably reflect responses to high plasma ammonia, mirroring those in trout exposed to high environmental ammonia. Therefore a dual function for gill and skin Rh proteins in CO2 and ammonia transport is not evident from these results. Rhag expression, however, responded differentially to high CO2 and high ammonia, suggesting a possible dual role in the erythrocytes.
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Affiliation(s)
- C Michele Nawata
- Department of Biology, McMaster University, Hamilton, Ontario, Canada.
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Yoshihara C, Inoue K, Schichnes D, Ruzin S, Inwood W, Kustu S. An Rh1-GFP fusion protein is in the cytoplasmic membrane of a white mutant strain of Chlamydomonas reinhardtii. MOLECULAR PLANT 2008; 1:1007-20. [PMID: 19825599 PMCID: PMC2902906 DOI: 10.1093/mp/ssn074] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2008] [Accepted: 10/14/2008] [Indexed: 05/21/2023]
Abstract
The major Rhesus (Rh) protein of the green alga Chlamydomonas reinhardtii, Rh1, is homologous to Rh proteins of humans. It is an integral membrane protein involved in transport of carbon dioxide. To localize a fusion of intact Rh1 to the green fluorescent protein (GFP), we used as host a white (lts1) mutant strain of C. reinhardtii, which is blocked at the first step of carotenoid biosynthesis. The lts1 mutant strain accumulated normal amounts of Rh1 heterotrophically in the dark and Rh1-GFP was at the periphery of the cell co-localized with the cytoplasmic membrane dye FM4-64. Although Rh1 carries a potential chloroplast targeting sequence at its N-terminus, Rh1-GFP was clearly not associated with the chloroplast envelope membrane. Moreover, the N-terminal half of the protein was not imported into chloroplasts in vitro and N-terminal regions of Rh1 did not direct import of the small subunit of ribulose bisphosphate carboxylase (SSU). Despite caveats to this interpretation, which we discuss, current evidence indicates that Rh1 is a cytoplasmic membrane protein and that Rh1-GFP is among the first cytoplasmic membrane protein fusions to be obtained in C. reinhardtii. Although lts1 (white) mutant strains cannot be used to localize proteins within sub-compartments of the chloroplast because they lack thylakoid membranes, they should nonetheless be valuable for localizing many GFP fusions in Chlamydomonas.
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Affiliation(s)
- Corinne Yoshihara
- Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA
| | - Kentaro Inoue
- Department of Plant Sciences, 131 Asmundson Hall, University of California, One Shields Avenue, Davis, CA 95616, USA
| | - Denise Schichnes
- CNR Biological Imaging Facility, 381 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA
| | - Steven Ruzin
- CNR Biological Imaging Facility, 381 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA
| | - William Inwood
- Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA
| | - Sydney Kustu
- Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720-3102, USA
- To whom correspondence should be addressed. E-mail , fax (510) 642-4995, tel. (510) 643-9308
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Lupo D, Li XD, Durand A, Tomizaki T, Cherif-Zahar B, Matassi G, Merrick M, Winkler FK. The 1.3-A resolution structure of Nitrosomonas europaea Rh50 and mechanistic implications for NH3 transport by Rhesus family proteins. Proc Natl Acad Sci U S A 2007; 104:19303-8. [PMID: 18032606 PMCID: PMC2148285 DOI: 10.1073/pnas.0706563104] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Indexed: 12/19/2022] Open
Abstract
The Rhesus (Rh) proteins are a family of integral membrane proteins found throughout the animal kingdom that also occur in a number of lower eukaryotes. The significance of Rh proteins derives from their presence in the human red blood cell membrane, where they constitute the second most important group of antigens used in transfusion medicine after the ABO group. Rh proteins are related to the ammonium transport (Amt) protein family and there is considerable evidence that, like Amt proteins, they function as ammonia channels. We have now solved the structure of a rare bacterial homologue (from Nitrosomonas europaea) of human Rh50 proteins at a resolution of 1.3 A. The protein is a trimer, and analysis of its subunit interface strongly argues that all Rh proteins are likely to be homotrimers and that the human erythrocyte proteins RhAG and RhCE/D are unlikely to form heterooligomers as previously proposed. When compared with structures of bacterial Amt proteins, NeRh50 shows several distinctive features of the substrate conduction pathway that support the concept that Rh proteins have much lower ammonium affinities than Amt proteins and might potentially function bidirectionally.
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Affiliation(s)
- Domenico Lupo
- *Biomolecular Research, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
| | - Xiao-Dan Li
- *Biomolecular Research, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
| | - Anne Durand
- Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, United Kingdom
| | - Takashi Tomizaki
- Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
| | - Baya Cherif-Zahar
- Université Paris Descartes, Institut National de la Santé et de la Recherche Médicale U845, Faculté de Medecine René Descartes, F-75015 Paris, France; and
| | - Giorgio Matassi
- Institut Jacques Monod Centre National de la Recherche Scientifique-Unite Mixte de Recherche 7592, Université Paris 6 et Université Paris 7, 2 Place Jussieu, 75251 Paris Cedex 05, France
| | - Mike Merrick
- Department of Molecular Microbiology, John Innes Centre, Norwich NR4 7UH, United Kingdom
| | - Fritz K. Winkler
- *Biomolecular Research, Paul Scherrer Institut, CH-5232 Villigen, Switzerland
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36
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Abstract
Amt/MEP/Rh proteins are a family of integral membrane proteins implicated in the transport of NH3, CH(2)NH2, and CO2. Whereas Amt/MEP proteins are agreed to transport ammonia (NH3/NH4+), the primary substrate for Rh proteins has been controversial. Initial studies suggested that Rh proteins also transport ammonia, but more recent evidence suggests that they transport CO2. Here we report the first structure of an Rh family member, the Rh protein from the chemolithoautotrophic ammonia-oxidizing bacterium Nitrosomonas europaea. This Rh protein exhibits a number of similarities to its Amt cousins, including a trimeric oligomeric state, a central pore with an unusual twin-His site in the middle, and a Phe residue that blocks the channel for small-molecule transport. However, there are some significant differences, the most notable being the presence of an additional cytoplasmic C-terminal alpha-helix, an increased number of internal proline residues along the transmembrane helices, and a specific set of residues that appear to link the C-terminal helix to Phe blockage. This latter linkage suggests a mechanism in which binding of a partner protein to the C terminus could regulate channel opening. Another difference is the absence of the extracellular pi-cation binding site conserved in Amt/Mep structures. Instead, CO2 pressurization experiments identify a CO2 binding site near the intracellular exit of the channel whose residues are highly conserved in all Rh proteins, except those belonging to the Rh30 subfamily. The implications of these findings on the functional role of the human Rh antigens are discussed.
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37
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Fong RN, Kim KS, Yoshihara C, Inwood WB, Kustu S. The W148L substitution in the Escherichia coli ammonium channel AmtB increases flux and indicates that the substrate is an ion. Proc Natl Acad Sci U S A 2007; 104:18706-11. [PMID: 17998534 PMCID: PMC2141841 DOI: 10.1073/pnas.0709267104] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2007] [Indexed: 11/18/2022] Open
Abstract
The Amt/Mep ammonium channels are trimers in which each monomer contains a long, narrow, hydrophobic pore. Whether the substrate conducted by these pores is NH(3) or NH(4)(+) remains controversial. Substitution of leucine for the highly conserved tryptophan 148 residue at the external opening to Escherichia coli AmtB pores allowed us to address this issue. A strain carrying AmtB(W148L) accumulates much larger amounts of both [(14)C]methylammonium and [(14)C]methylglutamine in a washed cell assay than a strain carrying wild-type AmtB. Accumulation of methylammonium occurs within seconds and appears to reflect channel conductance, whereas accumulation of methylglutamine, which depends on the ATP-dependent activity of glutamine synthetase, increases for many minutes. Concentration of methylammonium was most easily studied in strains that lack glutamine synthetase. It is eliminated by the protonophore carbonyl cyanide m-chlorophenyl hydrazone and is approximately 10-fold higher in the strain carrying AmtB(W148L) than wild-type AmtB. The results indicate that AmtB allows accumulation of CH(3)NH(3)(+) ion in response to the electrical potential across the membrane and that the rate of flux through AmtB(W148L) is approximately 10 times faster than through wild-type AmtB. We infer that both mutant and wild-type proteins also carry NH(4)(+). Contrary to our previous views, we assess that E. coli AmtB does not differ from plant Amt proteins in this regard; both carry ions. We address the role of W148 in decreasing the activity and increasing the selectivity of AmtB and the implications of our findings with respect to the function of Rh proteins, the only known homologues of Amt/Mep proteins.
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Affiliation(s)
- Rebecca N. Fong
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
| | - Kwang-Seo Kim
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
| | - Corinne Yoshihara
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
| | - William B. Inwood
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
| | - Sydney Kustu
- Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720-3102
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Endeward V, Cartron JP, Ripoche P, Gros G. RhAG protein of the Rhesus complex is a CO2channel in the human red cell membrane. FASEB J 2007; 22:64-73. [PMID: 17712059 DOI: 10.1096/fj.07-9097com] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
We have determined CO2 permeabilities, P(CO2), of red cells of normal human blood and of blood deficient in various blood group proteins by a previously described mass spectrometric technique. While P(CO2) of normal red cells is approximately 0.15 cm/s, we find in red blood cells (RBCs) lacking the Rh protein complex (Rh(null)) a significantly reduced P(CO2) of 0.07 cm/s +/-0.02 cm/s (P<0.02). This value is similar to the value we have reported previously for RBCs lacking aquaporin-1 protein (AQP-1(null)), suggesting that each of the Rh and AQP-1 proteins is responsible for approximately 1/2 of the normal CO2 permeability of the RBC membrane. Four other blood group deficiencies tested lack diverse membrane proteins but exhibit normal CO2 permeability. The CO2 pathway constituted by Rh proteins was inhibitable at pH(e)= 7.4 by NH4Cl with an I50 of approximately 10 mM corresponding to an I50 for NH3 of approximately 0.3 mM. The pathway independent of Rh proteins, presumably that constituted by AQP-1, was not inhibitable by NH4Cl/NH3. However, both pathways were strongly inhibited by DIDS, which accounts for the marked inhibitory effect of DIDS on normal P(CO2), while in contrast another AE1 inhibitor, DiBAC, does not inhibit P(CO2), although it markedly reduces P(HCO3-). We conclude that Rh protein, presumably the Rh-associated glycoprotein RhAG, possesses a gas channel that allows passage of CO2 in addition to NH3.
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Affiliation(s)
- Volker Endeward
- Abt. Vegetative Physiologie Medizinische Hochschule Hannover, 30623-Hannover, Germany
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39
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Nawata CM, Hung CCY, Tsui TKN, Wilson JM, Wright PA, Wood CM. Ammonia excretion in rainbow trout (Oncorhynchus mykiss): evidence for Rh glycoprotein and H+-ATPase involvement. Physiol Genomics 2007; 31:463-74. [PMID: 17712040 DOI: 10.1152/physiolgenomics.00061.2007] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Branchial ammonia transport in freshwater teleosts is not well understood. Most studies conclude that NH(3) diffuses out of the gill and becomes protonated to NH(4)(+) in an acidified gill boundary layer. Rhesus (Rh) proteins are new members of the ammonia transporter superfamily and rainbow trout possess genes encoding for Rh30-like1 and Rhcg2. We identified seven additional full-length trout Rh cDNA sequences: one Rhag and two each of Rhbg, Rhcg1, and Rh30-like. The mRNA expression of Rhbg, Rhcg1, and Rhcg2 was examined in trout tissues (blood, brain, eye, gill, heart, intestine, kidney, liver, muscle, skin, spleen) exposed to high external ammonia (HEA; 1.5 mmol/l NH(4)HCO(3), pH 7.95, 15 degrees C). Rhbg was expressed in all tissues, Rhcg1 was expressed in brain, gill, liver, and skin, and Rhcg2 was expressed in gill and skin. Brain Rhbg and Rhcg1 were downregulated, blood Rh30-like and Rhag were downregulated, and skin Rhbg and Rhcg2 were upregulated with HEA. After an initial uptake of ammonia into the fish during HEA, excretion was reestablished, coinciding with upregulations of gill Rh mRNA in the pavement cell fraction: Rhcg2 at 12 and 48 h, and Rhbg at 48 h. NHE2 expression remained unchanged, but upregulated H(+)-ATPase (V-type, B-subunit) and downregulated carbonic anhydrase (CA2) expression and activity were noted in the gill and again expression changes occurred in pavement cells, and not in mitochondria-rich cells. Together, these results indicate Rh glycoprotein involvement in ammonia transport and excretion in the rainbow trout while underscoring the significance of gill boundary layer acidification by H(+)-ATPase.
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Affiliation(s)
- C Michele Nawata
- Department of Biology, McMaster University, Hamilton, Ontario, Canada.
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40
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Wolfe DM, Zhang Y, Roberts GP. Specificity and regulation of interaction between the PII and AmtB1 proteins in Rhodospirillum rubrum. J Bacteriol 2007; 189:6861-9. [PMID: 17644595 PMCID: PMC2045211 DOI: 10.1128/jb.00759-07] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The nitrogen regulatory protein P(II) and the ammonia gas channel AmtB are both found in most prokaryotes. Interaction between these two proteins has been observed in several organisms and may regulate the activities of both proteins. The regulation of their interaction is only partially understood, and we show that in Rhodospirillum rubrum one P(II) homolog, GlnJ, has higher affinity for an AmtB(1)-containing membrane than the other two P(II) homologs, GlnB and GlnK. This interaction strongly favors the nonuridylylated form of GlnJ and is disrupted by high levels of 2-ketoglutarate (2-KG) in the absence of ATP or low levels of 2-KG in the presence of ATP. ADP inhibits the destabilization of the GlnJ-AmtB(1) complex in the presence of ATP and 2-KG, supporting a role for P(II) as an energy sensor measuring the ratio of ATP to ADP. In the presence of saturating levels of ATP, the estimated K(d) of 2-KG for GlnJ bound to AmtB(1) is 340 microM, which is higher than that required for uridylylation of GlnJ in vitro, about 5 microM. This supports a model where multiple 2-KG and ATP molecules must bind a P(II) trimer to stimulate release of P(II) from AmtB(1), in contrast to the lower 2-KG requirement for productive uridylylation of P(II) by GlnD.
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Affiliation(s)
- David M Wolfe
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, USA
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41
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Abstract
Acid-base homeostasis to a great extent relies on renal ammonia metabolism. In the past several years, seminal studies have generated important new insights into the mechanisms of renal ammonia transport. In particular, the theory that ammonia transport occurs almost exclusively through nonionic NH(3) diffusion and NH(4)(+) trapping has given way to a model postulating that a variety of proteins specifically transport NH(3) and NH(4)(+) and that this transport is critical for normal ammonia metabolism. Many of these proteins transport primarily H(+) or K(+) but also transport NH(4)(+). Nonerythroid Rh glycoproteins transport ammonia and may represent critical facilitators of ammonia transport in the kidney. This review discusses the underlying aspects of renal ammonia transport as well as specific proteins with important roles in renal ammonia transport.
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Affiliation(s)
- I. David Weiner
- Nephrology Section, North Florida/South Georgia Veterans Health System, University of Florida, Gainesville, Florida 32608
- Division of Nephrology, Hypertension and Transplantation, University of Florida, Gainesville, Florida 32608
| | - L. Lee Hamm
- Department of Medicine, Tulane University School of Medicine, New Orleans, Louisiana 70112
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42
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Abstract
The brain ammonium production is detoxified by astrocytes, the gut ammonium production is detoxified by hepatic cells, and the renal ammonium production plays a major role in renal acid excretion. As a result of ammonium handling in these organs, the ammonium and pH values are strictly regulated in plasma. Up until recently, it was accepted that mammalian cell transmembrane ammonium transport was due to NH(4)(+) transport by non-specific transporting systems, and to non-ionic NH(3) diffusion, whereas lower organisms (such as bacteria, yeasts and plants) were endowed with specific ammonium transporters (Amts). Sequence homologies between Amts and human Rhesus (Rh) glycoproteins (RhAG, from erythroid cells, and RhBG and RhCG from epithelial cells) raised the hypothesis that Rh glycoproteins act as specific ammonium transporters, further sustained by the polarized distribution of RhBG and RhCG in gut, kidney and liver. Results from functional studies agree that Rh glycoproteins are the first ammonium transporters reported in mammals. However, the nature of the transported specie(s) is much debated: in particular, it is proposed that Rh glycoproteins mediate a direct NH(3) transport, or that they mediate an indirect NH(3) transport (resulting from NH(4)(+) for H(+) exchange). Direct NH(3) transport (associated or not with NH(4)(+) transport) raises the exciting hypothesis that Rh glycoproteins may also transport other gases than NH(3) (namely, CO(2)).
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Affiliation(s)
- Gabrielle Planelles
- Inserm, U806 et Université Paris Descartes, Faculté de Médecine René Descartes, Paris, France.
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Callebaut I, Dulin F, Bertrand O, Ripoche P, Mouro I, Colin Y, Mornon JP, Cartron JP. Hydrophobic cluster analysis and modeling of the human Rh protein three-dimensional structures. Transfus Clin Biol 2006; 13:70-84. [PMID: 16584906 DOI: 10.1016/j.tracli.2006.02.001] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
Rh (Rhesus) is a major blood group system in man, which is clinically significant in transfusion medicine. Rh antigens are carried by an oligomer of two major erythroid specific polypeptides, the Rh (D and CcEe) proteins and the RhAG glycoprotein, that shared a common predicted structure with 12 transmembrane a-helices (M0 to M11). Non erythroid homologues of these proteins have been identified (RhBG and RhCG), notably in diverse organs specialized in ammonia production and excretion, such as kidney, liver and intestine. Phylogenetic studies and experimental evidence have shown that these proteins belong to the Amt/Mep/Rh protein superfamily of ammonium/methylammonium permease, but another view suggests that Rh proteins might function as CO2 gas channels. Until recently no information on the structure of these proteins were available. However, in the last two years, new insight has been gained into the structural features of Rh proteins (through the determination of the crystal structures of bacterial AmtB and archeaebacterial Amt-1. Here, models of the subunit and oligomeric architecture of human Rh proteins are proposed, based on a refined alignment with and crystal structure of the bacterial ammonia transporter AmtB, a member of the Amt/Mep/Rh superfamily. This alignment was performed considering invariant structural features, which were revealed through Hydrophobic Cluster Analysis, and led to propose alternative predictions for the less conserved regions, particularly in the N-terminal sequences. The Rh models, on which an additional Rh-specific, N-terminal helix M0 was tentatively positioned, were further assessed through the consideration of biochemical and immunochemical data, as well as of stereochemical and topological constraints. These models highlighted some Rh specific features that have not yet been reported. Among these, are the prediction of some critical residues, which may play a role in the channel function, but also in the stability of the subunit structure and oligomeric assembly. These results provide a basis to further understand the structure/function relationships of Rh proteins, and the alterations occurring in variant phenotypes.
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Affiliation(s)
- I Callebaut
- Département de biologie structurale, IMPMC, CNRS UMR7590, universités Paris VI et Paris VII, case 115, 4, place Jussieu, 75252 Paris cedex 05, France
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Ripoche P, Goossens D, Devuyst O, Gane P, Colin Y, Verkman AS, Cartron JP. Role of RhAG and AQP1 in NH3 and CO2 gas transport in red cell ghosts: a stopped-flow analysis. Transfus Clin Biol 2006; 13:117-22. [PMID: 16574458 DOI: 10.1016/j.tracli.2006.03.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
To clarify the potential role Rh/RhAG and AQP1 proteins in erythrocyte gas transport, NH3 and CO2 transport was measured in erythrocyte ghost membrane vesicles from rare human variants (Rh(null), CO(null),) and knockout mice (homozygous AQP1-/-, Rh-/- and Rhag-/-) exhibiting well-characterized protein defects. Transport was measured from intracellular pH (pHi) changes in a stopped-flow fluorimeter. NH3 transport was measured in chloride-free conditions with ghosts exposed to 20 mM inwardly directed gradients of gluconate salts of ammonium, hydrazine and methylammonium at 15 degrees C. Alkalinization rates of control samples were 6.5+/-0.3, 4.03+/-0.17, 0.95+/-0.08 s(-1) for each solute, respectively, but were significantly reduced for Rh(null) and CO(null) samples that are deficient in RhAG and AQP1 proteins, respectively. Alkalinization rates of Rh(null) ghosts were about 60%, 83% and 94% lower than that in control ghosts, respectively, for each solute. In CO(null) ghosts, the lack of AQP1 resulted in about 30% reduction of the alkalinization rates as compared to controls, but the transport selectivity of RhAG for the three solutes was preserved. Similar observations were made with ghosts from KO mice Rhag-/- and AQP1-/-. These results confirm the major contribution of RhAG/Rhag in the NH3 conductance of erythrocytes and suggest that the reduction of transport rates in the absence of AQP1 would be better explained by a direct or indirect effect on RhAG/Rhag-mediated transport. When ghosts were preloaded with carbonic anhydrase and exposed to a 25 mM CO2/HCO3- gradient at 6 degrees C, an extremely rapid kinetics of acidification corresponding to CO2 influx was observed. The rate constants were not significantly different between controls and human variants (125+/-6 s(-1)), or between wild-type and KO mice, suggesting no major role of RhAG or AQP1 in CO2 transport, at least in our experimental conditions.
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Affiliation(s)
- P Ripoche
- Institut national de la transfusion sanguine, Paris F-75015, France
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Kaunitz JD, Akiba Y. Duodenal Carbonic Anhydrase: Mucosal Protection, Luminal Chemosensing, and Gastric Acid Disposal. Keio J Med 2006; 55:96-106. [PMID: 17008801 DOI: 10.2302/kjm.55.96] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The duodenum serves as a buffer zone between the stomach and jejunum. Over a length of only 25 cm, large volumes of strong acid secreted by the stomach must be converted to the neutral-alkaline chyme of the hindgut lumen, generating large volumes of CO2, which the duodenum then absorbs. The duodenal mucosa consists of epithelial cells connected by low-resistance tight junctions, forming a leaky epithelial barrier. Despite this high permeability, the epithelial cells, under intense stress from luminal mineral acid and highly elevated P(CO2), maintain normal functioning. Furthermore, the duodenum plays an active role in foregut acid-base homeostasis, absorbing large amounts of H+ and CO2 that are recycled by the gastric parietal cells. Prompted by the high expression of cytosolic and membrane carbonic anhydrase (CAs) in duodenal epithelial cells, and the intriguing observation that CA activity appears to augment cellular acid stress, we formulated a novel hypothesis regarding the role of CA in duodenal acid absorption, epithelial protection, and chemosensing. In this review, we will describe how luminal CO2/H+ traverses the duodenal epithelial cell brush border membrane, acidifies the cytoplasm, and is sensed in the subepithelium.
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Affiliation(s)
- Jonathan D Kaunitz
- Greater Los Angeles Veterans Affairs Healthcare System, Los Angeles, CA, USA.
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