1
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Quijada-Rodriguez AR, Fehsenfeld S, Marini AM, Wilson JM, Nash MT, Sachs M, Towle DW, Weihrauch D. Branchial CO 2 and ammonia excretion in crustaceans: Involvement of an apical Rhesus-like glycoprotein. Acta Physiol (Oxf) 2024; 240:e14078. [PMID: 38205922 DOI: 10.1111/apha.14078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 10/13/2023] [Accepted: 12/14/2023] [Indexed: 01/12/2024]
Abstract
AIM To determine whether the crustacean Rh1 protein functions as a dual CO2 /ammonia transporter and investigate its role in branchial ammonia excretion and acid-base regulation. METHODS Sequence analysis of decapod Rh1 proteins was used to determine the conservation of amino acid residues putatively involved in ammonia transport and CO2 binding in human and bacterial Rh proteins. Using the Carcinus maenas Rh1 protein (CmRh1) as a representative of decapod Rh1 proteins, we test the ammonia and CO2 transport capabilities of CmRh1 through heterologous expression in yeast and Xenopus oocytes coupled with site-directed mutagenesis. Quantitative PCR was used to assess the distribution of CmRh1 mRNA in various tissues. Western blotting was used to assess CmRh1 protein expression changes in response to high environmental ammonia and CO2 . Further, immunohistochemistry was used to assess sub-cellular localization of CmRh1 and a membrane-bound carbonic anhydrase (CmCAg). RESULTS Sequence analysis of decapod Rh proteins revealed high conservation of several amino acid residues putatively involved in conducting ammonia transport and CO2 binding. Expression of CmRh1 in Xenopus oocytes enhanced both ammonia and CO2 transport which was nullified in CmRh1 D180N mutant oocytes. Transport of the ammonia analog methylamine by CmRh1 is dependent on both ionized and un-ionized ammonia/methylamine species. CmRh1 was co-localized with CmCAg to the apical membrane of the crustacean gill and only experienced decreased protein expression in the anterior gills when exposed to high environmental ammonia. CONCLUSION CmRh1 is the first identified apical transporter-mediated route for ammonia and CO2 excretion in the crustacean gill. Our findings shed further light on the potential universality of dual ammonia and CO2 transport capacity of Rhesus glycoproteins in both vertebrates and invertebrates.
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Affiliation(s)
- Alex R Quijada-Rodriguez
- Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
- Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada
| | - Sandra Fehsenfeld
- Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
- Département de biologie, chimie et géographie, Université du Québec à Rimouski, Rimouski, Quebec, Canada
| | - Anna-Maria Marini
- Biology of Membrane Transport Laboratory, Molecular Biology Department, Université Libre de Bruxelles, Bruxelles, Belgium
- WELBIO, Wavre, Belgium
| | - Jonathan M Wilson
- Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada
| | - Mikyla T Nash
- Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - Maria Sachs
- Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
| | - David W Towle
- Mount Desert Island Biological Laboratory, Salisbury Cove, Maine, USA
| | - Dirk Weihrauch
- Department of Biological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada
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2
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Williamson G, Bizior A, Harris T, Pritchard L, Hoskisson P, Javelle A. Biological ammonium transporters from the Amt/Mep/Rh superfamily: mechanism, energetics, and technical limitations. Biosci Rep 2024; 44:BSR20211209. [PMID: 38131184 PMCID: PMC10794816 DOI: 10.1042/bsr20211209] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 12/12/2023] [Accepted: 12/21/2023] [Indexed: 12/23/2023] Open
Abstract
The exchange of ammonium across cellular membranes is a fundamental process in all domains of life and is facilitated by the ubiquitous Amt/Mep/Rh transporter superfamily. Remarkably, despite a high structural conservation in all domains of life, these proteins have gained various biological functions during evolution. It is tempting to hypothesise that the physiological functions gained by these proteins may be explained at least in part by differences in the energetics of their translocation mechanisms. Therefore, in this review, we will explore our current knowledge of energetics of the Amt/Mep/Rh family, discuss variations in observations between different organisms, and highlight some technical drawbacks which have hampered effects at mechanistic characterisation. Through the review, we aim to provide a comprehensive overview of current understanding of the mechanism of transport of this unique and extraordinary Amt/Mep/Rh superfamily of ammonium transporters.
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Affiliation(s)
- Gordon Williamson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Adriana Bizior
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Thomas Harris
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Leighton Pritchard
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Paul A. Hoskisson
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
| | - Arnaud Javelle
- Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, Glasgow, G4 0RE, U.K
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3
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Hu C, Dai W, Zhu X, Yao H, Lin Z, Dong Y, Lv L. Expression and Functional Analysis of AMT1 Gene Responding to High Ammonia Stress in Razor Clam ( Sinonovacula constricta). Animals (Basel) 2023; 13:ani13101638. [PMID: 37238069 DOI: 10.3390/ani13101638] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2023] [Revised: 05/01/2023] [Accepted: 05/11/2023] [Indexed: 05/28/2023] Open
Abstract
Ammonium transporter 1 (AMT1), a member of ammonia (NH3/NH4+) transport proteins, has been found to have ammonia transport activity in plants and microorganisms. However, the functional characteristics and molecular mechanisms of AMT1 in mollusks remain unclear. The razor clam (Sinonovacula constricta) is a suitable model species to explore the molecular mechanism of ammonia excretion because of the high concentration of ambient ammonia it is exposed to in the clam-fish-shrimp polyculture system. Here, the expression of AMT1 in S. constricta (Sc-AMT1) in response to high ammonia (12.85 mmol/L NH4Cl) stress was identified by real-time quantitative PCR (qRT-PCR), Western blotting, RNA interference, and immunofluorescence analysis. Additionally, the association between the SNP_g.15211125A > T linked with Sc-AMT1 and ammonia tolerance was validated by kompetitive allele-specific PCR (KASP). A significant upregulated expression of Sc-AMT1 was observed during ammonia exposure, and Sc-AMT1 was found to be localized in the flat cells of gill. Moreover, the interference with Sc-AMT1 significantly upregulated the hemolymph ammonia levels, accompanied by the increased mRNA expression of Rhesus glycoprotein (Rh). Taken together, our findings imply that AMT1 may be a primary contributor to ammonia excretion in S. constricta, which is the basis of their ability to inhabit benthic water with high ammonia levels.
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Affiliation(s)
- Chenxin Hu
- Key Laboratory of Aquatic Germplasm Resource of Zhejiang, College of Biological and Environmental Sciences, Zhejiang Wanli University, Ningbo 315100, China
| | - Wenfang Dai
- Ninghai Institute of Mariculture Breeding and Seed Industry, Zhejiang Wanli University, Ningbo 315604, China
| | - Xiaojie Zhu
- Key Laboratory of Aquatic Germplasm Resource of Zhejiang, College of Biological and Environmental Sciences, Zhejiang Wanli University, Ningbo 315100, China
| | - Hanhan Yao
- Key Laboratory of Aquatic Germplasm Resource of Zhejiang, College of Biological and Environmental Sciences, Zhejiang Wanli University, Ningbo 315100, China
| | - Zhihua Lin
- Key Laboratory of Aquatic Germplasm Resource of Zhejiang, College of Biological and Environmental Sciences, Zhejiang Wanli University, Ningbo 315100, China
- Ninghai Institute of Mariculture Breeding and Seed Industry, Zhejiang Wanli University, Ningbo 315604, China
| | - Yinghui Dong
- Ninghai Institute of Mariculture Breeding and Seed Industry, Zhejiang Wanli University, Ningbo 315604, China
| | - Liyuan Lv
- Ninghai Institute of Mariculture Breeding and Seed Industry, Zhejiang Wanli University, Ningbo 315604, China
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4
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Potential Novel Role of Membrane-Associated Carbonic Anhydrases in the Kidney. Int J Mol Sci 2023; 24:ijms24044251. [PMID: 36835660 PMCID: PMC9961601 DOI: 10.3390/ijms24044251] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2023] [Revised: 02/06/2023] [Accepted: 02/06/2023] [Indexed: 02/23/2023] Open
Abstract
Carbonic anhydrases (CAs), because they catalyze the interconversion of carbon dioxide (CO2) and water into bicarbonate (HCO3-) and protons (H+), thereby influencing pH, are near the core of virtually all physiological processes in the body. In the kidneys, soluble and membrane-associated CAs and their synergy with acid-base transporters play important roles in urinary acid secretion, the largest component of which is the reabsorption of HCO3- in specific nephron segments. Among these transporters are the Na+-coupled HCO3- transporters (NCBTs) and the Cl--HCO3- exchangers (AEs)-members of the "solute-linked carrier" 4 (SLC4) family. All of these transporters have traditionally been regarded as "HCO3-" transporters. However, recently our group has demonstrated that two of the NCBTs carry CO32- rather than HCO3- and has hypothesized that all NCBTs follow suit. In this review, we examine current knowledge on the role of CAs and "HCO3-" transporters of the SLC4 family in renal acid-base physiology and discuss how our recent findings impact renal acid secretion, including HCO3- reabsorption. Traditionally, investigators have associated CAs with producing or consuming solutes (CO2, HCO3-, and H+) and thus ensuring their efficient transport across cell membranes. In the case of CO32- transport by NCBTs, however, we hypothesize that the role of membrane-associated CAs is not the appreciable production or consumption of substrates but the minimization of pH changes in nanodomains near the membrane.
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5
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Nash N, Klymasz-Swartz AK, Nash MT, Sachs M, Yoon GR, Weihrauch D. Impact of heatwaves and environmental ammonia on energy metabolism, nitrogen excretion, and mRNA expression of related genes in the indicator model system Daphnia magna. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2022; 249:106225. [PMID: 35724523 DOI: 10.1016/j.aquatox.2022.106225] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Revised: 05/11/2022] [Accepted: 06/12/2022] [Indexed: 06/15/2023]
Abstract
Due to increasing anthropogenic impacts, heatwaves and prolonged exposure to elevated concentrations of ammonia (HEA) may occur in aquatic environments as a single stressor or a combination thereof, potentially impacting the physiology of exposed animals. In the current study, common water fleas Daphnia magna were exposed for one week to either a 5°C increase in temperature, an increase of 300 µmol l-1 total environmental ammonia, or to both of these stressors simultaneously. Exposure to elevated temperature caused a decrease in MO2, ammonia excretion rates, a downregulation of mRNA coding for key Krebs cycle enzymes and the energy consuming Na+/K+-ATPase and V-type H+-ATPase, as well as the energy distributing crustacean hyperglycemic hormone Rh-protein. High environmental ammonia inflicted a lesser inhibitory effect on the energy metabolism of Daphnia, but initiated ammonia detoxification processes via urea synthesis evident by elevated urea excretion rates and a mRNA upregulation of arginase. Effects observed under the combined stressors resembled largely the effects seen after acclimation to elevated temperature alone, potentially due to the animals' capability to efficiently detoxify critical ammonia loads. The observed physiological effects and potential threats of the environmental stressor are discussed in detail.
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Affiliation(s)
- N Nash
- University of Manitoba, Winnipeg, Canada
| | | | - M T Nash
- University of Manitoba, Winnipeg, Canada
| | - M Sachs
- University of Manitoba, Winnipeg, Canada
| | - G R Yoon
- University of Manitoba, Winnipeg, Canada
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6
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Vallese F, Kim K, Yen LY, Johnston JD, Noble AJ, Calì T, Clarke OB. Architecture of the human erythrocyte ankyrin-1 complex. Nat Struct Mol Biol 2022; 29:706-718. [PMID: 35835865 PMCID: PMC10373098 DOI: 10.1038/s41594-022-00792-w] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2021] [Accepted: 05/24/2022] [Indexed: 12/28/2022]
Abstract
The stability and shape of the erythrocyte membrane is provided by the ankyrin-1 complex, but how it tethers the spectrin-actin cytoskeleton to the lipid bilayer and the nature of its association with the band 3 anion exchanger and the Rhesus glycoproteins remains unknown. Here we present structures of ankyrin-1 complexes purified from human erythrocytes. We reveal the architecture of a core complex of ankyrin-1, the Rhesus proteins RhAG and RhCE, the band 3 anion exchanger, protein 4.2, glycophorin A and glycophorin B. The distinct T-shaped conformation of membrane-bound ankyrin-1 facilitates recognition of RhCE and, unexpectedly, the water channel aquaporin-1. Together, our results uncover the molecular details of ankyrin-1 association with the erythrocyte membrane, and illustrate the mechanism of ankyrin-mediated membrane protein clustering.
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Affiliation(s)
- Francesca Vallese
- Department of Anesthesiology, Columbia University Irving Medical Center, New York, NY, USA.,Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, USA.,Irving Institute for Clinical and Translational Research, Columbia University, New York, NY, USA
| | - Kookjoo Kim
- Department of Anesthesiology, Columbia University Irving Medical Center, New York, NY, USA.,Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, USA.,Irving Institute for Clinical and Translational Research, Columbia University, New York, NY, USA
| | - Laura Y Yen
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, USA
| | - Jake D Johnston
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, USA.,Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY, USA
| | - Alex J Noble
- Simons Electron Microscopy Center, New York Structural Biology Center, New York, NY, USA
| | - Tito Calì
- Department of Biomedical Sciences, University of Padua, Padua, Italy.,Padua Neuroscience Center (PNC), University of Padua, Padua, Italy.,Study Center for Neurodegeneration (CESNE), University of Padua, Padua, Italy
| | - Oliver Biggs Clarke
- Department of Anesthesiology, Columbia University Irving Medical Center, New York, NY, USA. .,Department of Physiology and Cellular Biophysics, Columbia University, New York, NY, USA. .,Irving Institute for Clinical and Translational Research, Columbia University, New York, NY, USA.
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7
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Thies AB, Quijada-Rodriguez AR, Zhouyao H, Weihrauch D, Tresguerres M. A Rhesus channel in the coral symbiosome membrane suggests a novel mechanism to regulate NH 3 and CO 2 delivery to algal symbionts. SCIENCE ADVANCES 2022; 8:eabm0303. [PMID: 35275725 PMCID: PMC8916725 DOI: 10.1126/sciadv.abm0303] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Reef-building corals maintain an intracellular photosymbiotic association with dinoflagellate algae. As the algae are hosted inside the symbiosome, all metabolic exchanges must take place across the symbiosome membrane. Using functional studies in Xenopus oocytes, immunolocalization, and confocal Airyscan microscopy, we established that Acropora yongei Rh (ayRhp1) facilitates transmembrane NH3 and CO2 diffusion and that it is present in the symbiosome membrane. Furthermore, ayRhp1 abundance in the symbiosome membrane was highest around midday and lowest around midnight. We conclude that ayRhp1 mediates a symbiosomal NH4+-trapping mechanism that promotes nitrogen delivery to algae during the day-necessary to sustain photosynthesis-and restricts nitrogen delivery at night-to keep algae under nitrogen limitation. The role of ayRhp1-facilitated CO2 diffusion is less clear, but it may have implications for metabolic dysregulation between symbiotic partners and bleaching. This previously unknown mechanism expands our understanding of symbioses at the immediate animal-microbe interface, the symbiosome.
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Affiliation(s)
- Angus B. Thies
- Marine Biology research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA
- Corresponding author. (A.B.T.); (M.T.)
| | | | - Haonan Zhouyao
- Department of Biological Sciences, University of Manitoba, Winnipeg, MB, Canada
| | - Dirk Weihrauch
- Department of Biological Sciences, University of Manitoba, Winnipeg, MB, Canada
| | - Martin Tresguerres
- Marine Biology research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093, USA
- Corresponding author. (A.B.T.); (M.T.)
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8
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Effects of butyrate− on ruminal Ca2+ transport: evidence for the involvement of apically expressed TRPV3 and TRPV4 channels. Pflugers Arch 2022; 474:315-342. [PMID: 35098357 PMCID: PMC8837523 DOI: 10.1007/s00424-021-02647-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2021] [Revised: 11/04/2021] [Accepted: 11/24/2021] [Indexed: 11/29/2022]
Abstract
The ruminal epithelium absorbs large quantities of NH4+ and Ca2+. A role for TRPV3 has emerged, but data on TRPV4 are lacking. Furthermore, short-chain fatty acids (SCFA) stimulate ruminal Ca2+ and NH4+ uptake in vivo and in vitro, but the pathway is unclear. Sequencing of the bovine homologue (bTRPV4) revealed 96.79% homology to human TRPV4. Two commercial antibodies were tested using HEK-293 cells overexpressing bTRPV4, which in ruminal protein detected a weak band at the expected ~ 100 kDa and several bands ≤ 60 kDa. Immunofluorescence imaging revealed staining of the apical membrane of the stratum granulosum for bTRPV3 and bTRPV4, with cytosolic staining in other layers of the ruminal epithelium. A similar expression pattern was observed in a multilayered ruminal cell culture which developed resistances of > 700 Ω · cm2 with expression of zonula occludens-1 and claudin-4. In Ussing chambers, 2-APB and the TRPV4 agonist GSK1016790A stimulated the short-circuit current across native bovine ruminal epithelia. In whole-cell patch-clamp recordings on HEK-293 cells, bTRPV4 was shown to be permeable to NH4+, K+, and Na+ and highly sensitive to GSK1016790A, while effects of butyrate− were insignificant. Conversely, bTRPV3 was strongly stimulated by 2-APB and by butyrate− (pH 6.4 > pH 7.4), but not by GSK1016790A. Fluorescence calcium imaging experiments suggest that butyrate− stimulates both bTRPV3 and bTRPV4. While expression of bTRPV4 appears to be weaker, both channels are candidates for the ruminal transport of NH4+ and Ca2+. Stimulation by SCFA may involve cytosolic acidification (bTRPV3) and cell swelling (bTRPV4).
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9
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Liebe H, Liebe F, Sponder G, Hedtrich S, Stumpff F. Beyond Ca 2+ signalling: the role of TRPV3 in the transport of NH 4. Pflugers Arch 2021; 473:1859-1884. [PMID: 34664138 PMCID: PMC8599221 DOI: 10.1007/s00424-021-02616-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Revised: 08/17/2021] [Accepted: 08/18/2021] [Indexed: 12/11/2022]
Abstract
Mutations of TRPV3 lead to severe dermal hyperkeratosis in Olmsted syndrome, but whether the mutants are trafficked to the cell membrane or not is controversial. Even less is known about TRPV3 function in intestinal epithelia, although research on ruminants and pigs suggests an involvement in the uptake of NH4+. It was the purpose of this study to measure the permeability of the human homologue (hTRPV3) to NH4+, to localize hTRPV3 in human skin equivalents, and to investigate trafficking of the Olmsted mutant G573S. Immunoblotting and immunostaining verified the successful expression of hTRPV3 in HEK-293 cells and Xenopus oocytes with trafficking to the cell membrane. Human skin equivalents showed distinct staining of the apical membrane of the top layer of keratinocytes with cytosolic staining in the middle layers. Experiments with pH-sensitive microelectrodes on Xenopus oocytes demonstrated that acidification by NH4+ was significantly greater when hTRPV3 was expressed. Single-channel measurements showed larger conductances in overexpressing Xenopus oocytes than in controls. In whole-cell experiments on HEK-293 cells, both enantiomers of menthol stimulated influx of NH4+ in hTRPV3 expressing cells, but not in controls. Expression of the mutant G573S greatly reduced cell viability with partial rescue via ruthenium red. Immunofluorescence confirmed cytosolic expression, with membrane staining observed in a very small number of cells. We suggest that expression of TRPV3 by epithelia may have implications not just for Ca2+ signalling, but also for nitrogen metabolism. Models suggesting how influx of NH4+ via TRPV3 might stimulate skin cornification or intestinal NH4+ transport are discussed.
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Affiliation(s)
- Hendrik Liebe
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany.,Department of Biology, Chemistry, and Pharmacy, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany
| | - Franziska Liebe
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany
| | - Gerhard Sponder
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany
| | - Sarah Hedtrich
- Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada
| | - Friederike Stumpff
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany.
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10
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Weihrauch D, O'Donnell MJ. Mechanisms of nitrogen excretion in insects. CURRENT OPINION IN INSECT SCIENCE 2021; 47:25-30. [PMID: 33609767 DOI: 10.1016/j.cois.2021.02.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 02/03/2021] [Accepted: 02/08/2021] [Indexed: 06/12/2023]
Abstract
Avoiding the toxic effects of ammonia derived from catabolism of proteins and nucleic acids typically involves synthesis of the less soluble compound uric acid in insects, although some species which are not water stressed excrete ammonia directly. Some dipterans metabolize uric acid further to allantoin or urea. Uric acid plays diverse roles as a nitrogenous waste, nitrogen store, pigment, antioxidant and possibly a signaling molecule. Multiple transporters are implicated in urate transport, including members of the ABC and SLC families. Excretion of ammonia by the Malpighian tubules, hindgut, or anal papillae involves multiple transporters, including Na+/K+-ATPase, Rhesus glycoproteins, ammonia transporters (AMTs) and possibly a hyperpolarization-activated cyclic nucleotide-gated K+ channel (HCN).
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Affiliation(s)
- Dirk Weihrauch
- Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
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11
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Michenkova M, Taki S, Blosser MC, Hwang HJ, Kowatz T, Moss FJ, Occhipinti R, Qin X, Sen S, Shinn E, Wang D, Zeise BS, Zhao P, Malmstadt N, Vahedi-Faridi A, Tajkhorshid E, Boron WF. Carbon dioxide transport across membranes. Interface Focus 2021; 11:20200090. [PMID: 33633837 PMCID: PMC7898146 DOI: 10.1098/rsfs.2020.0090] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/04/2021] [Indexed: 12/30/2022] Open
Abstract
Carbon dioxide (CO2) movement across cellular membranes is passive and governed by Fick's law of diffusion. Until recently, we believed that gases cross biological membranes exclusively by dissolving in and then diffusing through membrane lipid. However, the observation that some membranes are CO2 impermeable led to the discovery of a gas molecule moving through a channel; namely, CO2 diffusion through aquaporin-1 (AQP1). Later work demonstrated CO2 diffusion through rhesus (Rh) proteins and NH3 diffusion through both AQPs and Rh proteins. The tetrameric AQPs exhibit differential selectivity for CO2 versus NH3 versus H2O, reflecting physico-chemical differences among the small molecules as well as among the hydrophilic monomeric pores and hydrophobic central pores of various AQPs. Preliminary work suggests that NH3 moves through the monomeric pores of AQP1, whereas CO2 moves through both monomeric and central pores. Initial work on AQP5 indicates that it is possible to create a metal-binding site on the central pore's extracellular face, thereby blocking CO2 movement. The trimeric Rh proteins have monomers with hydrophilic pores surrounding a hydrophobic central pore. Preliminary work on the bacterial Rh homologue AmtB suggests that gas can diffuse through the central pore and three sets of interfacial clefts between monomers. Finally, initial work indicates that CO2 diffuses through the electrogenic Na/HCO3 cotransporter NBCe1. At least in some cells, CO2-permeable proteins could provide important pathways for transmembrane CO2 movements. Such pathways could be amenable to cellular regulation and could become valuable drug targets.
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Affiliation(s)
- Marie Michenkova
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Sara Taki
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Matthew C. Blosser
- Mork Family Department of Chemical Engineering & Materials Science, University of Southern California, Los Angeles, CA, USA
| | - Hyea J. Hwang
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Thomas Kowatz
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Fraser. J. Moss
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Rossana Occhipinti
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Xue Qin
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Soumyo Sen
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Eric Shinn
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Dengke Wang
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Brian S. Zeise
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Pan Zhao
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Noah Malmstadt
- Mork Family Department of Chemical Engineering & Materials Science, University of Southern California, Los Angeles, CA, USA
| | - Ardeschir Vahedi-Faridi
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
| | - Emad Tajkhorshid
- NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA
| | - Walter F. Boron
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, USA
- Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH, USA
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, OH, USA
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12
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Lin LY, Zheng JA, Huang SC, Hung GY, Horng JL. Ammonia exposure impairs lateral-line hair cells and mechanotransduction in zebrafish embryos. CHEMOSPHERE 2020; 257:127170. [PMID: 32497837 DOI: 10.1016/j.chemosphere.2020.127170] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Revised: 05/18/2020] [Accepted: 05/20/2020] [Indexed: 06/11/2023]
Abstract
Ammonia (including NH3 and NH4+) is a major pollutant of freshwater environments. However, the toxic effects of ammonia on the early stages of fish are not fully understood, and little is known about the effects on the sensory system. In this study, we hypothesized that ammonia exposure can cause adverse effects on embryonic development and impair the lateral line system of fish. Zebrafish embryos were exposed to high-ammonia water (10, 15, 20, 25, and 30 mM NH4Cl; pH 7.0) for 96 h (0-96 h post-fertilization). The body length, heart rate, and otic vesicle size had significantly decreased with ≥15 mM NH4Cl, while the number and function of lateral-line hair cells had decreased with ≥10 mM NH4Cl. The mechanoelectrical transduction (MET) channel-mediated Ca2+ influx was measured with a scanning ion-selective microelectrode technique to reveal the function of hair cells. We found that NH4+ (≥5 mM NH4Cl) entered hair cells and suppressed the Ca2+ influx of hair cells. Neomycin and La3+ (MET channel blockers) suppressed NH4+ influx, suggesting that NH4+ enters hair cells via MET channels in hair bundles. In conclusion, this study showed that ammonia exposure (≥10 mM NH4Cl) can cause adverse effects in zebrafish embryos, and lateral-line hair cells are sensitive to ammonia exposure.
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Affiliation(s)
- Li-Yih Lin
- Department of Life Science, School of Life Science, National Taiwan Normal University, Taipei, 11677, Taiwan
| | - Jie-An Zheng
- Department of Life Science, School of Life Science, National Taiwan Normal University, Taipei, 11677, Taiwan
| | - Shun-Chih Huang
- Department of Life Science, School of Life Science, National Taiwan Normal University, Taipei, 11677, Taiwan
| | - Giun-Yi Hung
- Division of Pediatric Hematology and Oncology, Department of Pediatrics, Taipei Veterans General Hospital, Taipei, 11217, Taiwan; Department of Pediatrics, Faculty of Medicine, School of Medicine, National Yang-Ming University, Taipei, 11221, Taiwan
| | - Jiun-Lin Horng
- Department of Anatomy and Cell Biology, School of Medicine, College of Medicine, Taipei Medical University, Taipei, 11031, Taiwan.
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13
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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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14
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Liebe F, Liebe H, Kaessmeyer S, Sponder G, Stumpff F. The TRPV3 channel of the bovine rumen: localization and functional characterization of a protein relevant for ruminal ammonia transport. Pflugers Arch 2020; 472:693-710. [PMID: 32458085 PMCID: PMC7293678 DOI: 10.1007/s00424-020-02393-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 03/31/2020] [Accepted: 05/06/2020] [Indexed: 12/28/2022]
Abstract
Large quantities of ammonia (NH3 or NH4+) are absorbed from the gut, associated with encephalitis in hepatic disease, poor protein efficiency in livestock, and emissions of nitrogenous climate gasses. Identifying the transport mechanisms appears urgent. Recent functional and mRNA data suggest that absorption of ammonia from the forestomach of cattle may involve TRPV3 channels. The purpose of the present study was to sequence the bovine homologue of TRPV3 (bTRPV3), localize the protein in ruminal tissue, and confirm transport of NH4+. After sequencing, bTRPV3 was overexpressed in HEK-293 cells and Xenopus oocytes. An antibody was selected via epitope screening and used to detect the protein in immunoblots of overexpressing cells and bovine rumen, revealing a signal of the predicted ~ 90 kDa. In rumen only, an additional ~ 60 kDa band appeared, which may represent a previously described bTRPV3 splice variant of equal length. Immunohistochemistry revealed staining from the ruminal stratum basale to stratum granulosum. Measurements with pH-sensitive microelectrodes showed that NH4+ acidifies Xenopus oocytes, with overexpression of bTRPV3 enhancing permeability to NH4+. Single-channel measurements revealed that Xenopus oocytes endogenously expressed small cation channels in addition to fourfold-larger channels only observed after expression of bTRPV3. Both endogenous and bTRPV3 channels conducted NH4+, Na+, and K+. We conclude that bTRPV3 is expressed by the ruminal epithelium on the protein level. In conjunction with data from previous studies, a role in the transport of Na+, Ca2+, and NH4+ emerges. Consequences for calcium homeostasis, ruminal pH, and nitrogen efficiency in cattle are discussed.
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Affiliation(s)
- Franziska Liebe
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany
| | - Hendrik Liebe
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany
- Department of Biology, Chemistry, and Pharmacy, Freie Universität Berlin, Arnimallee 22, 14195, Berlin, Germany
| | - Sabine Kaessmeyer
- Institute of Veterinary Anatomy, Freie Universität Berlin, Koserstraße 20, 14195, Berlin, Germany
| | - Gerhard Sponder
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany
| | - Friederike Stumpff
- Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany.
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15
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Occhipinti R, Boron WF. Role of Carbonic Anhydrases and Inhibitors in Acid-Base Physiology: Insights from Mathematical Modeling. Int J Mol Sci 2019; 20:E3841. [PMID: 31390837 PMCID: PMC6695913 DOI: 10.3390/ijms20153841] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Revised: 07/24/2019] [Accepted: 07/25/2019] [Indexed: 01/25/2023] Open
Abstract
Carbonic anhydrases (CAs) catalyze a reaction fundamental for life: the bidirectional conversion of carbon dioxide (CO2) and water (H2O) into bicarbonate (HCO3-) and protons (H+). These enzymes impact numerous physiological processes that occur within and across the many compartments in the body. Within compartments, CAs promote rapid H+ buffering and thus the stability of pH-sensitive processes. Between compartments, CAs promote movements of H+, CO2, HCO3-, and related species. This traffic is central to respiration, digestion, and whole-body/cellular pH regulation. Here, we focus on the role of mathematical modeling in understanding how CA enhances buffering as well as gradients that drive fluxes of CO2 and other solutes (facilitated diffusion). We also examine urinary acid secretion and the carriage of CO2 by the respiratory system. We propose that the broad physiological impact of CAs stem from three fundamental actions: promoting H+ buffering, enhancing H+ exchange between buffer systems, and facilitating diffusion. Mathematical modeling can be a powerful tool for: (1) clarifying the complex interdependencies among reaction, diffusion, and protein-mediated components of physiological processes; (2) formulating hypotheses and making predictions to be tested in wet-lab experiments; and (3) inferring data that are impossible to measure.
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Affiliation(s)
- Rossana Occhipinti
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
| | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
- Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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16
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Abdulnour‐Nakhoul S, Hering‐Smith K, Hamm LL, Nakhoul NL. Effects of chronic hypercapnia on ammonium transport in the mouse kidney. Physiol Rep 2019; 7:e14221. [PMID: 31456326 PMCID: PMC6712239 DOI: 10.14814/phy2.14221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2019] [Revised: 08/06/2019] [Accepted: 08/07/2019] [Indexed: 11/24/2022] Open
Abstract
Hypercapnia and subsequent respiratory acidosis are serious complications in many patients with respiratory disorders. The acute response to hypercapnia is buffering of H+ by hemoglobin and cellular proteins but this effect is limited. The chronic response is renal compensation that increases HCO3- reabsorption, and stimulates urinary excretion of titratable acids (TA) and NH4+ . However, the main effective pathway is the excretion of NH4+ in the collecting duct. Our hypothesis is that, the renal NH3 /NH4+ transporters, Rhbg and Rhcg, in the collecting duct mediate this response. The effect of hypercapnia on these transporters is unknown. We conducted in vivo experiments on mice subjected to chronic hypercapnia. One group breathed 8% CO2 and the other breathed normal air as control (0.04% CO2 ). After 3 days, the mice were euthanized and kidneys, blood, and urine samples were collected. We used immunohistochemistry and Western blot analysis to determine the effects of high CO2 on localization and expression of the Rh proteins, carbonic anhydrase IV, and pendrin. In hypercapnic animals, there was a significant increase in urinary NH4+ excretion but no change in TA. Western blot analysis showed a significant increase in cortical expression of Rhbg (43%) but not of Rhcg. Expression of CA-IV was increased but pendrin was reduced. These data suggest that hypercapnia leads to compensatory upregulation of Rhbg that contributes to excretion of NH3 /NH4+ in the kidney. These studies are the first to show a link among hypercapnia, NH4+ excretion, and Rh expression.
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Affiliation(s)
- Solange Abdulnour‐Nakhoul
- Section of Nephrology, Departments of Medicine and PhysiologyTulane University School of MedicineNew OrleansLouisiana
| | - Kathleen Hering‐Smith
- Section of Nephrology, Departments of Medicine and PhysiologyTulane University School of MedicineNew OrleansLouisiana
| | - L. Lee Hamm
- Section of Nephrology, Departments of Medicine and PhysiologyTulane University School of MedicineNew OrleansLouisiana
| | - Nazih L. Nakhoul
- Section of Nephrology, Departments of Medicine and PhysiologyTulane University School of MedicineNew OrleansLouisiana
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17
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Brauner CJ, Shartau RB, Damsgaard C, Esbaugh AJ, Wilson RW, Grosell M. Acid-base physiology and CO2 homeostasis: Regulation and compensation in response to elevated environmental CO2. FISH PHYSIOLOGY 2019. [DOI: 10.1016/bs.fp.2019.08.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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18
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Weihrauch D, Allen GJP. Ammonia excretion in aquatic invertebrates: new insights and questions. J Exp Biol 2018; 221:221/2/jeb169219. [DOI: 10.1242/jeb.169219] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
ABSTRACT
Invertebrates employ a variety of ammonia excretion strategies to facilitate their survival in diverse aquatic environments, including freshwater, seawater and the water film surrounding soil particles. Various environmental properties set innate challenges for an organism's ammonia excretory capacity. These include the availability of NaCl and the respective ion-permeability of the organism's transport epithelia, and the buffering capacity of their immediate surrounding medium. To this end, some transporters seem to be conserved in the excretory process. This includes the Na+/K+(NH4+)-ATPase (NKA), the NH3/CO2 dual gas-channel Rhesus (Rh)-proteins and novel ammonia transporters (AMTs), which have been identified in several invertebrates but appear to be absent from vertebrates. In addition, recent evidence strongly suggests that the hyperpolarization-activated cyclic nucleotide-gated K+ channel (HCN) plays a significant role in ammonia excretion and is highly conserved throughout the animal kingdom. Furthermore, microtubule-dependent vesicular excretion pathways have been found in marine and soil-dwelling species, where, unlike freshwater systems, acid-trapping of excreted ammonia is difficult or absent owing to the high environmental buffering capacity of the surroundings. Finally, although ammonia is known to be a toxic nitrogenous waste product, certain marine species readily maintain potentially toxic hemolymph ammonia as a sort of ammonia homeostasis, which suggests that ammonia is involved in physiological processes and does not exist simply for excretion. Such findings are discussed within this Commentary and are hypothesized to be involved in acid–base regulation. We also describe excretory organs and processes that are dependent on environmental constraints and indicate gaps in the current knowledge in these topics.
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Affiliation(s)
- Dirk Weihrauch
- University of Manitoba, Department of Biological Sciences, Winnipeg, R3T2N2, MB, Canada
| | - Garett J. P. Allen
- University of Manitoba, Department of Biological Sciences, Winnipeg, R3T2N2, MB, Canada
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19
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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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20
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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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21
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Talbot K, Kwong RWM, Gilmour KM, Perry SF. The water channel aquaporin-1a1 facilitates movement of CO₂ and ammonia in zebrafish (Danio rerio) larvae. ACTA ACUST UNITED AC 2017; 218:3931-40. [PMID: 26677259 DOI: 10.1242/jeb.129759] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The present study tested the hypothesis that zebrafish (Danio rerio) aquaporin-1a1 (AQP1a1) serves as a multi-functional channel for the transfer of the small gaseous molecules, CO2 and ammonia, as well as water, across biological membranes. Zebrafish embryos were microinjected with a translation-blocking morpholino oligonucleotide targeted to AQP1a1. Knockdown of AQP1a1 significantly reduced rates of CO2 and ammonia excretion, as well as water fluxes, in larvae at 4 days post fertilization (dpf). Because AQP1a1 is expressed both in ionocytes present on the body surface and in red blood cells, the haemolytic agent phenylhydrazine was used to distinguish between the contributions of AQP1a1 to gas transfer in these two locations. Phenylhydrazine treatment had no effect on AQP1a1-linked excretion of CO2 or ammonia, providing evidence that AQP1a1 localized to the yolk sac epithelium, rather than red blood cell AQP1a1, is the major site of CO2 and ammonia movements. The possibility that AQP1a1 and the rhesus glycoprotein Rhcg1, which also serves as a dual CO2 and ammonia channel, act in concert to facilitate CO2 and ammonia excretion was explored. Although knockdown of each protein did not affect the abundance of mRNA and protein of the other protein under control conditions, impairment of ammonia excretion by chronic exposure to high external ammonia triggered a significant increase in the abundance of AQP1a1 mRNA and protein in 4 dpf larvae experiencing Rhcg1 knockdown. Collectively, these results suggest that AQP1a1 in zebrafish larvae facilitates the movement of CO2 and ammonia, as well as water, in a physiologically relevant fashion.
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Affiliation(s)
- Krystle Talbot
- Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Raymond W M Kwong
- Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Kathleen M Gilmour
- Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
| | - Steve F Perry
- Department of Biology, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada
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22
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Satchwell TJ, Bell AJ, Hawley BR, Pellegrin S, Mordue KE, van Deursen CTBM, Braak NHT, Huls G, Leers MPG, Overwater E, Tamminga RYJ, van der Zwaag B, Fermo E, Bianchi P, van Wijk R, Toye AM. Severe Ankyrin-R deficiency results in impaired surface retention and lysosomal degradation of RhAG in human erythroblasts. Haematologica 2016; 101:1018-27. [PMID: 27247322 DOI: 10.3324/haematol.2016.146209] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Accepted: 05/25/2016] [Indexed: 11/09/2022] Open
Abstract
Ankyrin-R provides a key link between band 3 and the spectrin cytoskeleton that helps to maintain the highly specialized erythrocyte biconcave shape. Ankyrin deficiency results in fragile spherocytic erythrocytes with reduced band 3 and protein 4.2 expression. We use in vitro differentiation of erythroblasts transduced with shRNAs targeting ANK1 to generate erythroblasts and reticulocytes with a novel ankyrin-R 'near null' human phenotype with less than 5% of normal ankyrin expression. Using this model, we demonstrate that absence of ankyrin negatively impacts the reticulocyte expression of a variety of proteins, including band 3, glycophorin A, spectrin, adducin and, more strikingly, protein 4.2, CD44, CD47 and Rh/RhAG. Loss of band 3, which fails to form tetrameric complexes in the absence of ankyrin, alongside GPA, occurs due to reduced retention within the reticulocyte membrane during erythroblast enucleation. However, loss of RhAG is temporally and mechanistically distinct, occurring predominantly as a result of instability at the plasma membrane and lysosomal degradation prior to enucleation. Loss of Rh/RhAG was identified as common to erythrocytes with naturally occurring ankyrin deficiency and demonstrated to occur prior to enucleation in cultures of erythroblasts from a hereditary spherocytosis patient with severe ankyrin deficiency but not in those exhibiting milder reductions in expression. The identification of prominently reduced surface expression of Rh/RhAG in combination with direct evaluation of ankyrin expression using flow cytometry provides an efficient and rapid approach for the categorization of hereditary spherocytosis arising from ankyrin deficiency.
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Affiliation(s)
- Timothy J Satchwell
- School of Biochemistry, University of Bristol, UK National Institute for Health Research Blood and Transplant Research Unit (NIHR BTRU) in Red Blood Cell Products, University of Bristol, UK
| | | | - Bethan R Hawley
- School of Biochemistry, University of Bristol, UK National Institute for Health Research Blood and Transplant Research Unit (NIHR BTRU) in Red Blood Cell Products, University of Bristol, UK
| | - Stephanie Pellegrin
- School of Biochemistry, University of Bristol, UK National Institute for Health Research Blood and Transplant Research Unit (NIHR BTRU) in Red Blood Cell Products, University of Bristol, UK
| | - Kathryn E Mordue
- School of Biochemistry, University of Bristol, UK National Institute for Health Research Blood and Transplant Research Unit (NIHR BTRU) in Red Blood Cell Products, University of Bristol, UK
| | | | | | - Gerwin Huls
- Department of Hematology, University Medical Center Groningen, The Netherlands
| | - Mathie P G Leers
- Department of Clinical Chemistry and Hematology, Atrium Medical Center Parkstad, Heerlen, The Netherlands
| | - Eline Overwater
- Department of Clinical Genetics, VU University Medical Center, and Department of Clinical Genetics, Academic Medical Center, Amsterdam, The Netherlands
| | - Rienk Y J Tamminga
- Department of Pediatric Hematology, Beatrix Childrens Hospital, University Medical Center Groningen, The Netherlands
| | - Bert van der Zwaag
- Department of Medical Genetics, University Medical Center Utrecht, The Netherlands
| | - Elisa Fermo
- Oncohematology Unit - Physiopathology of Anemias Unit, Foundation IRCCS Cà Granda, Ospedale Maggiore Policlinico, Milan, Italy
| | - Paola Bianchi
- Oncohematology Unit - Physiopathology of Anemias Unit, Foundation IRCCS Cà Granda, Ospedale Maggiore Policlinico, Milan, Italy
| | - Richard van Wijk
- Department of Clinical Chemistry and Haematology, Laboratory for Red Blood Cell Research, University Medical Center Utrecht, The Netherlands
| | - Ashley M Toye
- School of Biochemistry, University of Bristol, UK National Institute for Health Research Blood and Transplant Research Unit (NIHR BTRU) in Red Blood Cell Products, University of Bristol, UK
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23
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Boeckstaens M. [From the discovery of microbial Mep-Amt ammonium transporters to human Rhesus factors]. Med Sci (Paris) 2016; 32:394-400. [PMID: 27137697 DOI: 10.1051/medsci/20163204018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Ammonium, ubiquitous on Earth, plays major and distinct roles in most organisms. While it can be a nitrogen source for many microorganisms and plants, it is a cytotoxic metabolic product actively detoxified by the liver in animals. Furthermore, in the latter, ammonium synthesis in the kidney is involved in acid/base homeostasis. Ammonium transport is ensured by a family of proteins, called Mep-Amt-Rh. This family is conserved in all domains of life and comprises the human Rh factors, notably known in transfusional medicine. While the study of bacterial, fungal and vegetal Mep-Amt transporters reveals a fine-tuned and rapid regulation of these proteins in function of environmental changes, the regulation of animal Rh proteins has been poorly addressed. This review notably highlights the importance of the yeast model in the study of the regulation of these proteins as well as in the functional characterization of Mep-Amt-Rh members of diverse origins.
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Affiliation(s)
- Mélanie Boeckstaens
- Laboratoire de biologie du transport membranaire, IBMM, université Libre de Bruxelles, 12, rue des Professeurs Jeener et Brachet, 6041 Gosselies, Belgique
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24
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Cooper GJ, Occhipinti R, Boron WF. CrossTalk proposal: Physiological CO2 exchange can depend on membrane channels. J Physiol 2015; 593:5025-8. [PMID: 26568076 DOI: 10.1113/jp270059] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 09/22/2015] [Indexed: 12/18/2022] Open
Affiliation(s)
- Gordon J Cooper
- Department of Biomedical Science, University of Sheffield, Sheffield, S10 2TN, UK
| | - Rossana Occhipinti
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA.,Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
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25
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Lee HW, Osis G, Handlogten ME, Guo H, Verlander JW, Weiner ID. Effect of dietary protein restriction on renal ammonia metabolism. Am J Physiol Renal Physiol 2015; 308:F1463-73. [PMID: 25925252 DOI: 10.1152/ajprenal.00077.2015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 04/20/2015] [Indexed: 11/22/2022] Open
Abstract
Dietary protein restriction has multiple benefits in kidney disease. Because protein intake is a major determinant of endogenous acid production, it is important that net acid excretion change in parallel during protein restriction. Ammonia is the primary component of net acid excretion, and inappropriate ammonia excretion can lead to negative nitrogen balance. Accordingly, we examined ammonia excretion in response to protein restriction and then we determined the molecular mechanism of the changes observed. Wild-type C57Bl/6 mice fed a 20% protein diet and then changed to 6% protein developed an 85% reduction in ammonia excretion within 2 days, which persisted during a 10-day study. The expression of multiple proteins involved in renal ammonia metabolism was altered, including the ammonia-generating enzymes phosphate-dependent glutaminase (PDG) and phosphoenolpyruvate carboxykinase (PEPCK) and the ammonia-metabolizing enzyme glutamine synthetase. Rhbg, an ammonia transporter, increased in expression in the inner stripe of outer medullary collecting duct intercalated cell (OMCDis-IC). However, collecting duct-specific Rhbg deletion did not alter the response to protein restriction. Rhcg deletion did not alter ammonia excretion in response to dietary protein restriction. These results indicate 1) dietary protein restriction decreases renal ammonia excretion through coordinated regulation of multiple components of ammonia metabolism; 2) increased Rhbg expression in the OMCDis-IC may indicate a biological role in addition to ammonia transport; and 3) Rhcg expression is not necessary to decrease ammonia excretion during dietary protein restriction.
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Affiliation(s)
- Hyun-Wook Lee
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Gunars Osis
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Mary E Handlogten
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - Hui Guo
- Division of Nephrology, Second Hospital of Shanxi Medical University, Yaiyuan, Shanxi, Peoples Republic of China; and
| | - Jill W Verlander
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida
| | - I David Weiner
- Division of Nephrology, Hypertension and Transplantation, University of Florida College of Medicine, Gainesville, Florida, Nephrology and Hypertension Section, Medical Service, North Florida/South Georgia Veterans Health System, Gainesville, Florida
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26
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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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Occhipinti R, Boron WF. Mathematical modeling of acid-base physiology. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2015; 117:43-58. [PMID: 25617697 PMCID: PMC4666298 DOI: 10.1016/j.pbiomolbio.2015.01.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 01/05/2015] [Accepted: 01/12/2015] [Indexed: 01/22/2023]
Abstract
pH is one of the most important parameters in life, influencing virtually every biological process at the cellular, tissue, and whole-body level. Thus, for cells, it is critical to regulate intracellular pH (pHi) and, for multicellular organisms, to regulate extracellular pH (pHo). pHi regulation depends on the opposing actions of plasma-membrane transporters that tend to increase pHi, and others that tend to decrease pHi. In addition, passive fluxes of uncharged species (e.g., CO2, NH3) and charged species (e.g., HCO3(-), [Formula: see text] ) perturb pHi. These movements not only influence one another, but also perturb the equilibria of a multitude of intracellular and extracellular buffers. Thus, even at the level of a single cell, perturbations in acid-base reactions, diffusion, and transport are so complex that it is impossible to understand them without a quantitative model. Here we summarize some mathematical models developed to shed light onto the complex interconnected events triggered by acids-base movements. We then describe a mathematical model of a spherical cells-which to our knowledge is the first one capable of handling a multitude of buffer reactions-that our team has recently developed to simulate changes in pHi and pHo caused by movements of acid-base equivalents across the plasma membrane of a Xenopus oocyte. Finally, we extend our work to a consideration of the effects of simultaneous CO2 and HCO3(-) influx into a cell, and envision how future models might extend to other cell types (e.g., erythrocytes) or tissues (e.g., renal proximal-tubule epithelium) important for whole-body pH homeostasis.
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Affiliation(s)
- Rossana Occhipinti
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
| | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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Renal acid-base regulation: new insights from animal models. Pflugers Arch 2014; 467:1623-41. [PMID: 25515081 DOI: 10.1007/s00424-014-1669-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 12/02/2014] [Accepted: 12/03/2014] [Indexed: 12/16/2022]
Abstract
Because majority of biological processes are dependent on pH, maintaining systemic acid-base balance is critical. The kidney contributes to systemic acid-base regulation, by reabsorbing HCO3 (-) (both filtered by glomeruli and generated within a nephron) and acidifying urine. Abnormalities in those processes will eventually lead to a disruption in systemic acid-base balance and provoke metabolic acid-base disorders. Research over the past 30 years advanced our understanding on cellular and molecular mechanisms responsible for those processes. In particular, a variety of transgenic animal models, where target genes are deleted either globally or conditionally, provided significant insights into how specific transporters are contributing to the renal acid-base regulation. Here, we broadly overview the mechanisms of renal ion transport participating to acid-base regulation, with emphasis on data obtained from transgenic mice models.
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Musa-Aziz R, Occhipinti R, Boron WF. Evidence from simultaneous intracellular- and surface-pH transients that carbonic anhydrase II enhances CO2 fluxes across Xenopus oocyte plasma membranes. Am J Physiol Cell Physiol 2014; 307:C791-813. [PMID: 24965587 DOI: 10.1152/ajpcell.00051.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The α-carbonic anhydrases (CAs) are zinc-containing enzymes that catalyze the interconversion of CO2 and HCO3 (-). Here, we focus on human CA II (CA II), a ubiquitous cytoplasmic enzyme. In the second paper in this series, we examine CA IV at the extracellular surface. After microinjecting recombinant CA II in a Tris solution (or just Tris) into oocytes, we expose oocytes to 1.5% CO2/10 mM HCO3 (-)/pH 7.50 while using microelectrodes to monitor intracellular pH (pHi) and surface pH (pHS). CO2 influx causes the familiar sustained pHi fall as well as a transient pHS rise; CO2 efflux does the opposite. Both during CO2 addition and removal, CA II increases the magnitudes of the maximal rate of pHi change, (dpHi/dt)max, and the maximal change in pHS, ΔpHS. Preincubating oocytes with the inhibitor ethoxzolamide eliminates the effects of CA II. Compared with pHS, pHi begins to change only after a delay of ~9 s and its relaxation has a larger (i.e., slower) time constant (τpHi > τpHS ). Simultaneous measurements with two pHi electrodes, one superficial and one deep, suggest that impalement depth contributes to pHi delay and higher τpHi . Using higher CO2/HCO3 (-) levels, i.e., 5%/33 mM HCO3 (-) or 10%/66 mM HCO3 (-), increases (dpHi/dt)max and ΔpHS, though not in proportion to the increase in [CO2]. A reaction-diffusion mathematical model (described in the third paper in this series) accounts for the above general features and supports the conclusion that cytosolic CA-consuming entering CO2 or replenishing exiting CO2-increases CO2 fluxes across the cell membrane.
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Affiliation(s)
- Raif Musa-Aziz
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio; Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut; and Department of Physiology and Biophysics, University of Sao Paulo, Institute of Biomedical Sciences, Sao Paulo, Brazil
| | - Rossana Occhipinti
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio
| | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, Ohio; Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio; Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut; and
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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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Wagner CA, Bourgeois S. Two Rhesus protein ammonia transporters team up to eliminate ammonium into urine. Am J Physiol Renal Physiol 2014; 306:F721-3. [PMID: 24431200 DOI: 10.1152/ajprenal.00681.2013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- Carsten A Wagner
- Institute of Physiology, Univ. of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
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Hulikova A, Swietach P. Rapid CO2 permeation across biological membranes: implications for CO2 venting from tissue. FASEB J 2014; 28:2762-74. [PMID: 24652949 DOI: 10.1096/fj.13-241752] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The degree to which cell membranes are barriers to CO2 transport remains controversial. Proteins, such as aquaporins and Rh complex, have been proposed to facilitate CO2 transport, implying that the nonchannel component of membranes must have greatly reduced CO2 permeability. To determine whether membrane CO2 permeation is rate limiting for gas transport, the spread of CO2 across multicellular tissue growths (spheroids) was measured using intracellular pH as a spatial readout. Colorectal HCT116 cells have basal water and NH3 permeability, indicating the functional absence of aquaporins and gas channels. However, CO2 diffusivity in HCT116 spheroids was only 24 ± 4% lower than in pure water, which can be accounted for fully by volume exclusion due to proteins. Diffusivity was unaffected by blockers of aquaporins and Rh complex (Hg(2+), p-chloromercuribenzoic acid, and 4,4'-diisothiocyano-2,2'-stilbene-disulfonic acid) but decreased under hypertonic conditions (by addition of 300 mOsm mannitol), which increases intracellular protein crowding. Similar CO2 diffusivity was measured in spheroids of T47D breast cells (basal water permeability) and NHDF-Ad fibroblasts (aquaporin-facilitated water permeability). In contrast, diffusivity of NH3, a smaller but less lipophilic gas, was considerably slower than in pure water, as expected from rate-limiting membrane permeation. In conclusion, membranes, even in the functional absence of proposed gas channels, do not restrict CO2 venting from tissue growths.-Hulikova, A., Swietach, P. Rapid CO2 permeation across biological membranes: implications for CO2 venting from tissue.
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Affiliation(s)
- Alzbeta Hulikova
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, United Kingdom
| | - Pawel Swietach
- Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, United Kingdom
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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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