1
|
Sudnitsyna J, Ruzhnikova TO, Panteleev MA, Kharazova A, Gambaryan S, Mindukshev IV. Chloride Gradient Is Involved in Ammonium Influx in Human Erythrocytes. Int J Mol Sci 2024; 25:7390. [PMID: 39000500 PMCID: PMC11242273 DOI: 10.3390/ijms25137390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2024] [Revised: 06/20/2024] [Accepted: 06/29/2024] [Indexed: 07/16/2024] Open
Abstract
The ammonia/ammonium (NH3/NH4+, AM) concentration in human erythrocytes (RBCs) is significantly higher than in plasma. Two main possible mechanisms for AM transport, including simple and facilitated diffusion, are described; however, the driving force for AM transport is not yet fully characterized. Since the erythroid ammonium channel RhAG forms a structural unit with anion exchanger 1 (eAE1) within the ankyrin core complex, we hypothesized the involvement of eAE1 in AM transport. To evaluate the functional interaction between eAE1 and RhAG, we used a unique feature of RBCs to swell and lyse in isotonic NH4+ buffer. The kinetics of cell swelling and lysis were analyzed by flow cytometry and an original laser diffraction method, adapted for accurate volume sensing. The eAE1 role was revealed according to (i) the changes in cell swelling and lysis kinetics, and (ii) changes in intracellular pH, triggered by eAE1 inhibition or the modulation of eAE1 main ligand concentrations (Cl- and HCO3-). Additionally, the AM import kinetics was analyzed enzymatically and colorimetrically. In NH4+ buffer, RBCs concentration-dependently swelled and lysed when [NH4+] exceeded 100 mM. Cell swelling and hemolysis were tightly regulated by chloride concentration. The complete substitution of chloride with glutamate prevented NH4+-induced cell swelling and hemolysis, and the restoration of [Cl-] dose-dependently amplified the rates of RBC swelling and lysis and the percentage of hemolyzed cells. Similarly, eAE1 inhibition impeded cell swelling and completely prevented hemolysis. Accordingly, eAE1 inhibition, or a lack of chloride anions in the buffer, significantly decreased NH4+ import. Our data indicate that the eAE1-mediated chloride gradient is required for AM transport. Taken together, our data reveal a new player in AM transport in RBCs.
Collapse
Affiliation(s)
- Julia Sudnitsyna
- Center for Theoretical Problems of Physicochemical Pharmacology, Russian Academy of Sciences, 30 Srednyaya Kalitnikovskaya St., 109029 Moscow, Russia
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 Thorez Ave., 194223 Saint Petersburg, Russia
| | - Tamara O Ruzhnikova
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 Thorez Ave., 194223 Saint Petersburg, Russia
- Department of Cytology and Histology, Saint Petersburg State University, 7/9 Universitetskaya Emb., 199034 Saint Petersburg, Russia
| | - Mikhail A Panteleev
- Center for Theoretical Problems of Physicochemical Pharmacology, Russian Academy of Sciences, 30 Srednyaya Kalitnikovskaya St., 109029 Moscow, Russia
| | - Alexandra Kharazova
- Department of Cytology and Histology, Saint Petersburg State University, 7/9 Universitetskaya Emb., 199034 Saint Petersburg, Russia
| | - Stepan Gambaryan
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 Thorez Ave., 194223 Saint Petersburg, Russia
| | - Igor V Mindukshev
- Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, 44 Thorez Ave., 194223 Saint Petersburg, Russia
| |
Collapse
|
2
|
Pflüger T, Gschell M, Zhang L, Shnitsar V, Zabadné AJ, Zierep P, Günther S, Einsle O, Andrade SLA. How sensor Amt-like proteins integrate ammonium signals. SCIENCE ADVANCES 2024; 10:eadm9441. [PMID: 38838143 DOI: 10.1126/sciadv.adm9441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 04/30/2024] [Indexed: 06/07/2024]
Abstract
Unlike aquaporins or potassium channels, ammonium transporters (Amts) uniquely discriminate ammonium from potassium and water. This feature has certainly contributed to their repurposing as ammonium receptors during evolution. Here, we describe the ammonium receptor Sd-Amt1, where an Amt module connects to a cytoplasmic diguanylate cyclase transducer module via an HAMP domain. Structures of the protein with and without bound ammonium were determined to 1.7- and 1.9-Ångstrom resolution, depicting the ON and OFF states of the receptor and confirming the presence of a binding site for two ammonium cations that is pivotal for signal perception and receptor activation. The transducer domain was disordered in the crystals, and an AlphaFold2 prediction suggests that the helices linking both domains are flexible. While the sensor domain retains the trimeric fold formed by all Amt family members, the HAMP domains interact as pairs and serve to dimerize the transducer domain upon activation.
Collapse
Affiliation(s)
- Tobias Pflüger
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Mathias Gschell
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Lin Zhang
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Volodymyr Shnitsar
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Annas J Zabadné
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
| | - Paul Zierep
- Faculty of Chemistry and Pharmacy, Institute for Pharmaceutical Sciences, University Freiburg, Hermann-Herder-Str. 9, 79104 Freiburg, Germany
| | - Stefan Günther
- Faculty of Chemistry and Pharmacy, Institute for Pharmaceutical Sciences, University Freiburg, Hermann-Herder-Str. 9, 79104 Freiburg, Germany
| | - Oliver Einsle
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
- BIOSS Centre for Biological Signaling Studies, University Freiburg, Schänzlerstr. 1, 79104 Freiburg, Germany
| | - Susana L A Andrade
- Faculty of Chemistry and Pharmacy, Institute for Biochemistry, University Freiburg, Albertstr. 21, 79104 Freiburg, Germany
- BIOSS Centre for Biological Signaling Studies, University Freiburg, Schänzlerstr. 1, 79104 Freiburg, Germany
| |
Collapse
|
3
|
Bourgeois S, Houillier P. State of knowledge on ammonia handling by the kidney. Pflugers Arch 2024; 476:517-531. [PMID: 38448728 PMCID: PMC11006756 DOI: 10.1007/s00424-024-02940-1] [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: 12/21/2023] [Revised: 02/28/2024] [Accepted: 03/01/2024] [Indexed: 03/08/2024]
Abstract
The disposal of ammonia, the main proton buffer in the urine, is important for acid-base homeostasis. Renal ammonia excretion is the predominant contributor to renal net acid excretion, both under basal condition and in response to acidosis. New insights into the mechanisms of renal ammonia production and transport have been gained in the past decades. Ammonia is the only urinary solute known to be produced in the kidney and selectively transported through the different parts of the nephron. Both molecular forms of total ammonia, NH3 and NH4+, are transported by specific proteins. Proximal tubular ammoniagenesis and the activity of these transport processes determine the eventual fate of total ammonia produced and excreted by the kidney. In this review, we summarized the state of the art of ammonia handling by the kidney and highlighted the newest processes described in the last decade.
Collapse
Affiliation(s)
- Soline Bourgeois
- Institut of Physiology, University of Zurich, Zurich, Switzerland.
| | - Pascal Houillier
- Centre de Recherche Des Cordeliers, INSERM, Sorbonne Université, Université Paris Cité, Paris, France
- Centre National de La Recherche Scientifique (CNRS), EMR 8228, Paris, France
| |
Collapse
|
4
|
Zhang Q, Liu J, Yao D, Shi JX, Liu YJ, Wei YG, Guo S. Comprehensive Analysis to Identify Rh Family C Glycoprotein ( RHCG) as the Causative Gene for Psoriasis and Search for Alternative Treatment Modalities. Drug Des Devel Ther 2023; 17:2593-2611. [PMID: 37664450 PMCID: PMC10473404 DOI: 10.2147/dddt.s421300] [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: 05/30/2023] [Accepted: 08/17/2023] [Indexed: 09/05/2023] Open
Abstract
Background Psoriasis is a complex autoimmune disease. Frequent interactions between epidermal and immune cells are likely to be responsible for the strong heterogeneity of psoriasis. Therefore, our work aims to build on current knowledge and further search for new molecular mechanisms related to psoriasis pathogenesis in order to develop new targeted drugs. Methods Data from psoriasis samples were obtained from the Gene Expression Omnibus (GEO) database, and batch effects were corrected using the "Combat" algorithm in the "SVA" package. Functional annotation of differential genes in psoriasis was performed by Gene set enrichment analysis (GSEA). Core functional modules were identified using the Multiscale Embedded Gene Co-Expression Network Analysis (MEGENA) algorithm for selection from the differential gene interaction network. The expression and potential function of Rh Family C Glycoprotein (RHCG) was predicted in single cell data by the "Seurat" package and validated in psoriasis samples by multiplex immunofluorescence. In addition, the regulatory function of HOP Homeobox (HOPX) on RHCG in keratinocytes was confirmed using RNA interference. Using immune infiltration analysis, RHCG and DC cells were analyzed for their association. Finally, the molecular mechanisms of treatment of psoriasis using Tripterygii Radix (TR) and Cinnamomi Ramulus (CR) were explored through network pharmacology and experimental validation. Results Immune response (represented by C1_2) and collagen matrix formation (represented by C1_3) were identified as two important pathogenic factors in psoriasis and helped to define new biological subtypes of psoriasis. One important psoriasis hub gene, RHCG, was obtained and found to be closely associated with keratinocyte differentiation as well as DC cell maturation. And RHCG was regulated by HOPX in keratinocytes. In addition, the mechanism of action of CR and TR in the treatment of psoriasis was tentatively confirmed to be related to TRPV3, NFKB2, and YAP1. Conclusions Our study identifies a new causal disease gene (RHCG) and offers potential alternatives for the treatment of psoriasis.
Collapse
Affiliation(s)
- Qian Zhang
- Department of Dermatology, Affiliated Hospital of Nanjing University of Chinese Medicine, Jiangsu Province Hospital of Chinese Medicine, Nanjing, Jiangsu, 210029, People’s Republic of China
- No. 1 Clinical Medical College, Nanjing University of Chinese Medicine, Nanjing, Jiangsu, 210023, People’s Republic of China
| | - Jia Liu
- Department of Dermatology, Affiliated Hospital of Nanjing University of Chinese Medicine, Jiangsu Province Hospital of Chinese Medicine, Nanjing, Jiangsu, 210029, People’s Republic of China
| | - Dan Yao
- Department of Dermatology, Affiliated Hospital of Nanjing University of Chinese Medicine, Jiangsu Province Hospital of Chinese Medicine, Nanjing, Jiangsu, 210029, People’s Republic of China
- No. 1 Clinical Medical College, Nanjing University of Chinese Medicine, Nanjing, Jiangsu, 210023, People’s Republic of China
| | - Jian-Xin Shi
- Department of Dermatology, Affiliated Hospital of Nanjing University of Chinese Medicine, Jiangsu Province Hospital of Chinese Medicine, Nanjing, Jiangsu, 210029, People’s Republic of China
| | - Yuan-Jie Liu
- No. 1 Clinical Medical College, Nanjing University of Chinese Medicine, Nanjing, Jiangsu, 210023, People’s Republic of China
- Department of Oncology, Affiliated Hospital of Nanjing University of Chinese Medicine, Jiangsu Province Hospital of Chinese Medicine, Nanjing, Jiangsu, 210029, People’s Republic of China
- Key Laboratory of Tumor System Biology of Traditional Chinese Medicine, Nanjing, Jiangsu, 210029, People’s Republic of China
| | - Yue-Gang Wei
- Department of Dermatology, Affiliated Hospital of Nanjing University of Chinese Medicine, Jiangsu Province Hospital of Chinese Medicine, Nanjing, Jiangsu, 210029, People’s Republic of China
| | - Shun Guo
- Department of Dermatology, Affiliated Hospital of Nanjing University of Chinese Medicine, Jiangsu Province Hospital of Chinese Medicine, Nanjing, Jiangsu, 210029, People’s Republic of China
- No. 1 Clinical Medical College, Nanjing University of Chinese Medicine, Nanjing, Jiangsu, 210023, People’s Republic of China
| |
Collapse
|
5
|
Sinha R, Pradhan S, Banerjee S, Jahan A, Akhtar S, Pahari A, Raut S, Parakh P, Basu S, Srivastava P, Nayak S, Thenral SG, Ramprasad V, Ashton E, Bockenhauer D, Mandal K. Whole-exome sequencing and variant spectrum in children with suspected inherited renal tubular disorder: the East India Tubulopathy Gene Study. Pediatr Nephrol 2022; 37:1811-1836. [PMID: 35006361 DOI: 10.1007/s00467-021-05388-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/05/2021] [Revised: 09/29/2021] [Accepted: 11/10/2021] [Indexed: 12/15/2022]
Abstract
BACKGROUND Inherited tubulopathies are a heterogeneous group of genetic disorders making whole-exome sequencing (WES) the preferred diagnostic methodology. METHODS This was a multicenter descriptive study wherein children (< 18 years) with clinically suspected tubular disorders were recruited for molecular testing through WES. Multiplex ligation-dependent probe amplification (MLPA) and Sanger sequencing were done when required. Variants were classified as per American College of Medical Genetics 2015 guidelines and pathogenic (P)/likely pathogenic (LP) variants were considered causative. RESULTS There were 77 index cases (male =73%). Median age at diagnosis was 48 months (IQR 18.5 to 108 months). At recruitment, the number of children in each clinical group was as follows: distal renal tubular acidosis (dRTA) = 25; Bartter syndrome = 18; isolated hypophosphatemic rickets (HP) = 6; proximal tubular dysfunction (pTD) = 12; nephrogenic diabetes insipidus (NDI) = 6; kidney stone/nephrocalcinosis (NC) = 6; others = 4. We detected 55 (24 novel) P/LP variants, providing genetic diagnoses in 54 children (70%). The diagnostic yield of WES was highest for NDI (100%), followed by HP (83%; all X-linked HP), Bartter syndrome (78%), pTD (75%), dRTA (64%), and NC (33%). Molecular testing had a definite impact on clinical management in 24 (31%) children. This included revising clinical diagnosis among 14 children (26% of those with a confirmed genetic diagnosis and 18% of the overall cohort), detection of previously unrecognized co-morbidities among 8 children (sensorineural deafness n = 5, hemolytic anemia n = 2, and dental changes n = 1) and facilitating specific medical treatment for 7 children (primary hyperoxaluria n = 1, cystinosis n = 4, tyrosinemia n = 2). CONCLUSION WES is a powerful tool in the diagnosis and management of children with inherited tubulopathies in the Indian population. A higher resolution version of the Graphical abstract is available as Supplementary information.
Collapse
Affiliation(s)
- Rajiv Sinha
- Institute of Child Health, Kolkata, India
- Apollo Hospital, Kolkata, India
| | | | - Sushmita Banerjee
- Institute of Child Health, Kolkata, India
- Calcutta Medical and Research Institute, Kolkata, India
| | - Afsana Jahan
- Renowell Clinic and Pratiksha Hospital, Gauhati, India
| | | | | | | | | | | | - Priyanka Srivastava
- Post Graduate Institute of Medical Education and Research, Chandigarh, India
| | | | | | | | - Emma Ashton
- Rare & Inherited Disease Laboratory, NHS North Thames Genomic Laboratory Hub, Great Ormond Street Hospital for Children, NHS Foundation Trust, London, UK
| | - Detlef Bockenhauer
- UCL Department of Renal Medicine and Renal Unit, Great Ormond Street Hospital for Children, NHS Foundation Trust, London, UK
| | - Kausik Mandal
- Department of Medical Genetics, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, 226014, India.
| |
Collapse
|
6
|
Kell DB. A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation. Adv Microb Physiol 2021; 78:1-177. [PMID: 34147184 DOI: 10.1016/bs.ampbs.2021.01.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.
Collapse
Affiliation(s)
- Douglas B Kell
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative, Biology, University of Liverpool, Liverpool, United Kingdom; The Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Lyngby, Denmark.
| |
Collapse
|
7
|
Abstract
Renal tubular acidosis should be suspected in poorly thriving young children with hyperchloremic and hypokalemic normal anion gap metabolic acidosis, with/without syndromic features. Further workup is needed to determine the type of renal tubular acidosis and the presumed etiopathogenesis, which informs treatment choices and prognosis. The risk of nephrolithiasis and calcinosis is linked to the presence (proximal renal tubular acidosis, negligible stone risk) or absence (distal renal tubular acidosis, high stone risk) of urine citrate excretion. New formulations of slow-release alkali and potassium combination supplements are being tested that are expected to simplify treatment and lead to sustained acidosis correction.
Collapse
Affiliation(s)
- Robert Todd Alexander
- Department of Pediatrics and Physiology, Stollery Children's Hospital, 11405-87 Avenue, Edmonton, Alberta T6G 1C9, Canada
| | - Martin Bitzan
- Division of Nephrology, Department of Pediatrics, The Montreal Children's Hospital, McGill University Health Centre, Room B RC.6651, Montreal, Quebec H4A 3J1, Canada; Al Jalila Children's Hospital, Al Jadaf PO Box 7662, Dubai, UAE.
| |
Collapse
|
8
|
Lister A, Bourgeois S, Imenez Silva PH, Rubio-Aliaga I, Marbet P, Walsh J, Shelton LM, Keller B, Verrey F, Devuyst O, Giesbertz P, Daniel H, Goldring CE, Copple IM, Wagner CA, Odermatt A. NRF2 regulates the glutamine transporter Slc38a3 (SNAT3) in kidney in response to metabolic acidosis. Sci Rep 2018; 8:5629. [PMID: 29618784 PMCID: PMC5884861 DOI: 10.1038/s41598-018-24000-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 03/19/2018] [Indexed: 12/28/2022] Open
Abstract
Expression of the glutamine transporter SNAT3 increases in kidney during metabolic acidosis, suggesting a role during ammoniagenesis. Microarray analysis of Nrf2 knock-out (KO) mouse kidney identified Snat3 as the most significantly down-regulated transcript compared to wild-type (WT). We hypothesized that in the absence of NRF2 the kidney would be unable to induce SNAT3 under conditions of metabolic acidosis and therefore reduce the availability of glutamine for ammoniagenesis. Metabolic acidosis was induced for 7 days in WT and Nrf2 KO mice. Nrf2 KO mice failed to induce Snat3 mRNA and protein expression during metabolic acidosis. However, there were no differences in blood pH, bicarbonate, pCO2, chloride and calcium or urinary pH, ammonium and phosphate levels. Normal induction of ammoniagenic enzymes was observed whereas several amino acid transporters showed differential regulation. Moreover, Nrf2 KO mice during acidosis showed increased expression of renal markers of oxidative stress and injury and NRF2 activity was increased during metabolic acidosis in WT kidney. We conclude that NRF2 is required to adapt the levels of SNAT3 in response to metabolic acidosis. In the absence of NRF2 and SNAT3, the kidney does not have any major acid handling defect; however, increased oxidative stress and renal injury may occur.
Collapse
Affiliation(s)
- Adam Lister
- Department of Pharmaceutical Sciences, Division of Molecular and Systems Toxicology, University of Basel, Klingelbergstrasse 50, 4056, Basel, Switzerland.,National Center for Competence in Research Kidney.CH, Zürich, Switzerland
| | - Soline Bourgeois
- Institute of Physiology, Zürich Centre for Integrative Human Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland.,National Center for Competence in Research Kidney.CH, Zürich, Switzerland
| | - Pedro H Imenez Silva
- Institute of Physiology, Zürich Centre for Integrative Human Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland.,National Center for Competence in Research Kidney.CH, Zürich, Switzerland
| | - Isabel Rubio-Aliaga
- Institute of Physiology, Zürich Centre for Integrative Human Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland.,National Center for Competence in Research Kidney.CH, Zürich, Switzerland
| | - Philippe Marbet
- Department of Pharmaceutical Sciences, Division of Molecular and Systems Toxicology, University of Basel, Klingelbergstrasse 50, 4056, Basel, Switzerland.,National Center for Competence in Research Kidney.CH, Zürich, Switzerland
| | - Joanne Walsh
- Department of Molecular and Clinical Pharmacology, MRC Centre for Drug Safety Science, University of Liverpool, Liverpool, L69 3GE, UK
| | - Luke M Shelton
- Department of Molecular and Clinical Pharmacology, MRC Centre for Drug Safety Science, University of Liverpool, Liverpool, L69 3GE, UK
| | - Bettina Keller
- Institute of Physiology, Zürich Centre for Integrative Human Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland
| | - Francois Verrey
- Institute of Physiology, Zürich Centre for Integrative Human Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland.,National Center for Competence in Research Kidney.CH, Zürich, Switzerland
| | - Olivier Devuyst
- Institute of Physiology, Zürich Centre for Integrative Human Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland.,National Center for Competence in Research Kidney.CH, Zürich, Switzerland
| | - Pieter Giesbertz
- Department of Biochemistry, ZIEL Research Center of Nutrition and Food Sciences, Technische Universität München, Freising, Germany
| | - Hannelore Daniel
- Department of Biochemistry, ZIEL Research Center of Nutrition and Food Sciences, Technische Universität München, Freising, Germany
| | - Christopher E Goldring
- Department of Molecular and Clinical Pharmacology, MRC Centre for Drug Safety Science, University of Liverpool, Liverpool, L69 3GE, UK
| | - Ian M Copple
- Department of Molecular and Clinical Pharmacology, MRC Centre for Drug Safety Science, University of Liverpool, Liverpool, L69 3GE, UK
| | - Carsten A Wagner
- Institute of Physiology, Zürich Centre for Integrative Human Physiology, University of Zürich, Winterthurerstrasse 190, 8057, Zürich, Switzerland. .,National Center for Competence in Research Kidney.CH, Zürich, Switzerland.
| | - Alex Odermatt
- Department of Pharmaceutical Sciences, Division of Molecular and Systems Toxicology, University of Basel, Klingelbergstrasse 50, 4056, Basel, Switzerland. .,National Center for Competence in Research Kidney.CH, Zürich, Switzerland.
| |
Collapse
|
9
|
Bourgeois S, Bounoure L, Mouro-Chanteloup I, Colin Y, Brown D, Wagner CA. The ammonia transporter RhCG modulates urinary acidification by interacting with the vacuolar proton-ATPases in renal intercalated cells. Kidney Int 2018; 93:390-402. [PMID: 29054531 PMCID: PMC6166241 DOI: 10.1016/j.kint.2017.07.027] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 07/08/2017] [Accepted: 07/27/2017] [Indexed: 12/19/2022]
Abstract
Ammonium, stemming from renal ammoniagenesis, is a major urinary proton buffer and is excreted along the collecting duct. This process depends on the concomitant secretion of ammonia by the ammonia channel RhCG and of protons by the vacuolar-type proton-ATPase pump. Thus, urinary ammonium content and urinary acidification are tightly linked. However, mice lacking Rhcg excrete more alkaline urine despite lower urinary ammonium, suggesting an unexpected role of Rhcg in urinary acidification. RhCG and the B1 and B2 proton-ATPase subunits could be co-immunoprecipitated from kidney. In ex vivo microperfused cortical collecting ducts (CCD) proton-ATPase activity was drastically reduced in the absence of Rhcg. Conversely, overexpression of RhCG in HEK293 cells resulted in higher proton secretion rates and increased B1 proton-ATPase mRNA expression. However, in kidneys from Rhcg-/- mice the expression of only B1 and B2 subunits was altered. Immunolocalization of proton-ATPase subunits together with immuno-gold detection of the A proton-ATPase subunit showed similar localization and density of staining in kidneys from Rhcg+/+ and Rhcg-/-mice. In order to test for a reciprocal effect of intercalated cell proton-ATPases on Rhcg activity, we assessed Rhcg and proton-ATPase activities in microperfused CCD from Atp6v1b1-/- mice and showed reduced proton-ATPase activity without altering Rhcg activity. Thus, RhCG and proton-ATPase are located within the same cellular protein complex. RhCG may modulate proton-ATPase function and urinary acidification, whereas proton-ATPase activity does not affect RhCG function. This mechanism may help to coordinate ammonia and proton secretion beyond physicochemical driving forces.
Collapse
Affiliation(s)
- Soline Bourgeois
- Institute of Physiology, University of Zurich, Zurich, Switzerland
| | - Lisa Bounoure
- Institute of Physiology, University of Zurich, Zurich, Switzerland
| | | | - Yves Colin
- UMR_S1134, INSERM, Université Paris Diderot, INTS, Labex GR-Ex, Paris, France
| | - Dennis Brown
- Center for Systems Biology, Program in Membrane Biology, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA
| | - Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland.
| |
Collapse
|
10
|
Pourafshar N, Pourafshar S, Soleimani M. Urine Ammonium, Metabolic Acidosis and Progression of Chronic Kidney Disease. Nephron Clin Pract 2017; 138:222-228. [PMID: 29050011 DOI: 10.1159/000481892] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Accepted: 09/28/2017] [Indexed: 11/19/2022] Open
Abstract
The metabolism of a typical Western diet generates 50-100 mEq of acid (H+) per day, which must be excreted in the urine for the systemic acid-base to remain in balance. The 2 major mechanisms that are responsible for the renal elimination of daily acid under normal conditions are ammonium (NH4+) excretion and titratable acidity. In the presence of systemic acidosis, ammonium excretion is intensified and becomes the crucial mechanism for the elimination of acid. The impairment in NH4+ excretion is therefore associated with reduced acid excretion, which causes excess accumulation of acid in the body and consequently results in metabolic acidosis. Chronic kidney disease (CKD) is associated with the impairment in acid excretion and precipitation of metabolic acidosis, which has an adverse effect on the progression of CKD. Recent studies suggest that the progressive decline in renal ammonium excretion in CKD is an important determinant of the ensuing systemic metabolic acidosis and is an independent factor for predicting the worsening of kidney function. While these studies have been primarily performed in hypertensive individuals with CKD, a closer look at renal NH4+ excretion in non-hypertensive individuals with CKD is warranted to ascertain its role in the progression of kidney disease.
Collapse
Affiliation(s)
- Negiin Pourafshar
- Department of Medicine at University of Virginia, Charlottesville, Virginia, USA
| | - Shirin Pourafshar
- Department of Medicine at University of Virginia, Charlottesville, Virginia, USA
| | - Manoocher Soleimani
- Department of Medicine, University of Cincinnati, Cincinnati, Ohio, USA.,Department of Medicine Services, Veterans Medical Center, Cincinnati, Ohio, USA
| |
Collapse
|
11
|
Pathophysiology, diagnosis and treatment of inherited distal renal tubular acidosis. J Nephrol 2017; 31:511-522. [DOI: 10.1007/s40620-017-0447-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 09/21/2017] [Indexed: 10/18/2022]
|
12
|
Hu MY, Hwang PP, Tseng YC. Recent advances in understanding trans-epithelial acid-base regulation and excretion mechanisms in cephalopods. Tissue Barriers 2015; 3:e1064196. [PMID: 26716070 DOI: 10.1080/21688370.2015.1064196] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2015] [Revised: 06/09/2015] [Accepted: 06/15/2015] [Indexed: 01/17/2023] Open
Abstract
Cephalopods have evolved complex sensory systems and an active lifestyle to compete with fish for similar resources in the marine environment. Their highly active lifestyle and their extensive protein metabolism has led to substantial acid-base regulatory abilities enabling these organisms to cope with CO2 induced acid-base disturbances. In convergence to teleost, cephalopods possess an ontogeny-dependent shift in ion-regulatory epithelia with epidermal ionocytes being the major site of embryonic acid-base regulation and ammonia excretion, while gill epithelia take these functions in adults. Although the basic morphology and excretory function of gill epithelia in cephalopods were outlined almost half a century ago, modern immunohistological and molecular techniques are bringing new insights to the mechanistic basis of acid-base regulation and excretion of nitrogenous waste products (e.g. NH3/NH4 (+)) across ion regulatory epithelia of cephalopods. Using cephalopods as an invertebrate model, recent findings reveal partly conserved mechanisms but also novel aspects of acid-base regulation and nitrogen excretion in these exclusively marine animals. Comparative studies using a range of marine invertebrates will create a novel and exciting research direction addressing the evolution of pH regulatory and excretory systems.
Collapse
Affiliation(s)
- Marian Y Hu
- Institute of Physiology; Christian-Albrechts University Kiel ; Kiel, Germany ; Institute of Cellular and Organismic Biology; Academia Sinica ; Taipei City, Taiwan
| | - Pung-Pung Hwang
- Institute of Cellular and Organismic Biology; Academia Sinica ; Taipei City, Taiwan
| | - Yung-Che Tseng
- Department of Life Science; National Taiwan Normal University ; Taipei City, Taiwan
| |
Collapse
|
13
|
Wagner CA, Mohebbi N, Bourgeois S. The ugly duckling of urinary acidification: what is the contribution of the thick ascending limb of the loop of Henle to urinary acidification? Am J Physiol Renal Physiol 2015; 309:F431-3. [PMID: 26155846 DOI: 10.1152/ajprenal.00296.2015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 07/07/2015] [Indexed: 11/22/2022] Open
Affiliation(s)
- Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, Switzerland; and
| | - Nilufar Mohebbi
- Division of Nephrology, University Hospital Zurich, Zurich, Switzerland
| | - Soline Bourgeois
- Institute of Physiology, University of Zurich, Zurich, Switzerland; and
| |
Collapse
|
14
|
Furukawa F, Tseng YC, Liu ST, Chou YL, Lin CC, Sung PH, Uchida K, Lin LY, Hwang PP. Induction of Phosphoenolpyruvate Carboxykinase (PEPCK) during Acute Acidosis and Its Role in Acid Secretion by V-ATPase-Expressing Ionocytes. Int J Biol Sci 2015; 11:712-25. [PMID: 25999794 PMCID: PMC4440261 DOI: 10.7150/ijbs.11827] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2015] [Accepted: 04/09/2015] [Indexed: 12/21/2022] Open
Abstract
Vacuolar-Type H+-ATPase (V-ATPase) takes the central role in pumping H+ through cell membranes of diverse organisms, which is essential for surviving acid-base fluctuating lifestyles or environments. In mammals, although glucose is believed to be an important energy source to drive V-ATPase, and phosphoenolpyruvate carboxykinase (PEPCK), a key enzyme for gluconeogenesis, is known to be activated in response to acidosis, the link between acid secretion and PEPCK activation remains unclear. In the present study, we used zebrafish larva as an in vivo model to show the role of acid-inducible PEPCK activity in glucose production to support higher rate of H+ secretion via V-ATPase, by utilizing gene knockdown, glucose supplementation, and non-invasive scanning ion-selective electrode technique (SIET). Zebrafish larvae increased V-ATPase-mediated acid secretion and transiently expression of Pck1, a zebrafish homolog of PEPCK, in response to acid stress. When pck1 gene was knocked down by specific morpholino, the H+ secretion via V-ATPase decreased, but this effect was rescued by supplementation of glucose into the yolk. By assessing changes in amino acid content and gene expression of respective enzymes, glutamine and glutamate appeared to be the major source for replenishment of Krebs cycle intermediates, which are subtracted by Pck1 activity. Unexpectedly, pck1 knockdown did not affect glutamine/glutamate catalysis, which implies that Pck1 does not necessarily drive this process. The present study provides the first in vivo evidence that acid-induced PEPCK provides glucose for acid-base homeostasis at an individual level, which is supported by rapid pumping of H+ via V-ATPase at the cellular level.
Collapse
Affiliation(s)
- Fumiya Furukawa
- 1. Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan ; 2. Department of Marine Biology and Environmental Sciences, Faculty of Agriculture, University of Miyazaki, Miyazaki, Japan
| | - Yung-Che Tseng
- 3. Department of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Sian-Tai Liu
- 3. Department of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Yi-Ling Chou
- 1. Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan
| | - Ching-Chun Lin
- 1. Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan
| | - Po-Hsuan Sung
- 4. Department of Life Science, National Taiwan University, Taipei, Taiwan
| | - Katsuhisa Uchida
- 2. Department of Marine Biology and Environmental Sciences, Faculty of Agriculture, University of Miyazaki, Miyazaki, Japan
| | - Li-Yih Lin
- 3. Department of Life Science, National Taiwan Normal University, Taipei, Taiwan
| | - Pung-Pung Hwang
- 1. Institute of Cellular and Organismic Biology, Academia Sinica, Nankang, Taipei, Taiwan
| |
Collapse
|
15
|
|
16
|
Bürki R, Mohebbi N, Bettoni C, Wang X, Serra AL, Wagner CA. Impaired expression of key molecules of ammoniagenesis underlies renal acidosis in a rat model of chronic kidney disease. Nephrol Dial Transplant 2014; 30:770-81. [PMID: 25523450 DOI: 10.1093/ndt/gfu384] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Accepted: 11/19/2014] [Indexed: 11/14/2022] Open
Abstract
BACKGROUND Advanced chronic kidney disease (CKD) is associated with the development of renal metabolic acidosis. Metabolic acidosis per se may represent a trigger for progression of CKD. Renal acidosis of CKD is characterized by low urinary ammonium excretion with preserved urinary acidification indicating a defect in renal ammoniagenesis, ammonia excretion or both. The underlying molecular mechanisms, however, have not been addressed to date. METHODS We examined the Han:SPRD rat model and used a combination of metabolic studies, mRNA and protein analysis of renal molecules involved in acid-base handling. RESULTS We demonstrate that rats with reduced kidney function as evident from lower creatinine clearance, lower haematocrit, higher plasma blood urea nitrogen, creatinine, phosphate and potassium had metabolic acidosis that could be aggravated by HCl acid loading. Urinary ammonium excretion was highly reduced whereas urinary pH was more acidic in CKD compared with control animals. The abundance of key enzymes and transporters of proximal tubular ammoniagenesis (phosphate-dependent glutaminase, PEPCK and SNAT3) and bicarbonate transport (NBCe1) was reduced in CKD compared with control animals. In the collecting duct, normal expression of the B1 H(+)-ATPase subunit is in agreement with low urinary pH. In contrast, the RhCG ammonia transporter, critical for the final secretion of ammonia into urine was strongly down-regulated in CKD animals. CONCLUSION In the Han:SPRD rat model for CKD, key molecules required for renal ammoniagenesis and ammonia excretion are highly down-regulated providing a possible molecular explanation for the development and maintenance of renal acidosis in CKD patients.
Collapse
Affiliation(s)
- Remy Bürki
- Institute of Physiology and ZIHP, University of Zurich, Zurich, Switzerland
| | - Nilufar Mohebbi
- Institute of Physiology and ZIHP, University of Zurich, Zurich, Switzerland Division of Nephrology, University Hospital Zurich, Zurich, Switzerland
| | - Carla Bettoni
- Institute of Physiology and ZIHP, University of Zurich, Zurich, Switzerland
| | - Xueqi Wang
- Division of Nephrology, University Hospital Zurich, Zurich, Switzerland Department of Nephrology, Changzheng Hospital, Second Military Medical University, Shanghai, China
| | - Andreas L Serra
- Division of Nephrology, University Hospital Zurich, Zurich, Switzerland
| | - Carsten A Wagner
- Institute of Physiology and ZIHP, University of Zurich, Zurich, Switzerland
| |
Collapse
|
17
|
|
18
|
Hu MY, Guh YJ, Stumpp M, Lee JR, Chen RD, Sung PH, Chen YC, Hwang PP, Tseng YC. Branchial NH4+-dependent acid–base transport mechanisms and energy metabolism of squid (Sepioteuthis lessoniana) affected by seawater acidification. Front Zool 2014. [DOI: 10.1186/s12983-014-0055-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
|
19
|
Geyer RR, Parker MD, Toye AM, Boron WF, Musa-Aziz R. Relative CO₂/NH₃ permeabilities of human RhAG, RhBG and RhCG. J Membr Biol 2014; 246:915-26. [PMID: 24077989 DOI: 10.1007/s00232-013-9593-0] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2013] [Accepted: 09/05/2013] [Indexed: 10/26/2022]
Abstract
Mammalian glycosylated rhesus (Rh) proteins include the erythroid RhAG and the nonerythroid RhBG and RhCG. RhBG and RhCG are expressed in multiple tissues, including hepatocytes and the collecting duct (CD) of the kidney. Here, we expressed human RhAG, RhBG and RhCG in Xenopus oocytes (vs. H2O-injected control oocytes) and used microelectrodes to monitor the maximum transient change in surface pH (DpHS) caused by exposing the same oocyte to 5 % CO₂/33 mM HCO₃⁻ (an increase) or 0.5 mM NH₃/NH₄⁺ (a decrease). Subtracting the respective values for day-matched, H₂O-injected control oocytes yielded channel-specific values (*). (ΔpH*(S))(CO₂) and (-ΔpH*(S))(NH₃) were each significantly >0 for all channels, indicating that RhBG and RhCG--like RhAG--can carry CO₂ and NH₃. We also investigated the role of a conserved aspartate residue, which was reported to inhibit NH₃ transport. However, surface biotinylation experiments indicate the mutants RhBG(D178N) and RhCG(D177N) have at most a very low abundance in the oocyte plasma membrane. We demonstrate for the first time that RhBG and RhCG--like RhAG--have significant CO₂ permeability, and we confirm that RhAG, RhBG and RhCG all have significant NH₃ permeability. However, as evidenced by (ΔpH*(S))(CO₂)/ (-ΔpH*(S))(NH₃) values, we could not distinguish among the CO₂/ NH₃ permeability ratios for RhAG, RhBG and RhCG. Finally, we propose a mechanism whereby RhBG and RhCG contribute to acid secretion in the CD by enhancing the transport of not only NH₃ but also CO₂ across the membranes of CD cells.
Collapse
|
20
|
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.
| | | |
Collapse
|
21
|
Everything you need to know about distal renal tubular acidosis in autoimmune disease. Rheumatol Int 2014; 34:1037-45. [PMID: 24682397 PMCID: PMC4107275 DOI: 10.1007/s00296-014-2993-3] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Accepted: 03/14/2014] [Indexed: 11/24/2022]
Abstract
Renal acid–base homeostasis is a complex process, effectuated by bicarbonate reabsorption and acid secretion. Impairment of urinary acidification is called renal tubular acidosis (RTA). Distal renal tubular acidosis (dRTA) is the most common form of the RTA syndromes. Multiple pathophysiologic mechanisms, each associated with various etiologies, can lead to dRTA. The most important consequence of dRTA is (recurrent) nephrolithiasis. The diagnosis is based on a urinary acidification test. Potassium citrate is the treatment of choice.
Collapse
|
22
|
Bounoure L, Ruffoni D, Müller R, Kuhn GA, Bourgeois S, Devuyst O, Wagner CA. The role of the renal ammonia transporter Rhcg in metabolic responses to dietary protein. J Am Soc Nephrol 2014; 25:2040-52. [PMID: 24652796 DOI: 10.1681/asn.2013050466] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
High dietary protein imposes a metabolic acid load requiring excretion and buffering by the kidney. Impaired acid excretion in CKD, with potential metabolic acidosis, may contribute to the progression of CKD. Here, we investigated the renal adaptive response of acid excretory pathways in mice to high-protein diets containing normal or low amounts of acid-producing sulfur amino acids (SAA) and examined how this adaption requires the RhCG ammonia transporter. Diets rich in SAA stimulated expression of enzymes and transporters involved in mediating NH4 (+) reabsorption in the thick ascending limb of the loop of Henle. The SAA-rich diet increased diuresis paralleled by downregulation of aquaporin-2 (AQP2) water channels. The absence of Rhcg transiently reduced NH4 (+) excretion, stimulated the ammoniagenic pathway more strongly, and further enhanced diuresis by exacerbating the downregulation of the Na(+)/K(+)/2Cl(-) cotransporter (NKCC2) and AQP2, with less phosphorylation of AQP2 at serine 256. The high protein acid load affected bone turnover, as indicated by higher Ca(2+) and deoxypyridinoline excretion, phenomena exaggerated in the absence of Rhcg. In animals receiving a high-protein diet with low SAA content, the kidney excreted alkaline urine, with low levels of NH4 (+) and no change in bone metabolism. Thus, the acid load associated with high-protein diets causes a concerted response of various nephron segments to excrete acid, mostly in the form of NH4 (+), that requires Rhcg. Furthermore, bone metabolism is altered by a high-protein acidogenic diet, presumably to buffer the acid load.
Collapse
Affiliation(s)
- Lisa Bounoure
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland; and
| | - Davide Ruffoni
- Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | - Ralph Müller
- Institute for Biomechanics, ETH Zurich, Zurich, Switzerland
| | | | - Soline Bourgeois
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland; and
| | - Olivier Devuyst
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland; and
| | - Carsten A Wagner
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, Zurich, Switzerland; and
| |
Collapse
|
23
|
Liu ST, Tsung L, Horng JL, Lin LY. Proton-facilitated ammonia excretion by ionocytes of medaka (Oryzias latipes) acclimated to seawater. Am J Physiol Regul Integr Comp Physiol 2013; 305:R242-51. [DOI: 10.1152/ajpregu.00047.2013] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The proton-facilitated ammonia excretion is critical for a fish's ability to excrete ammonia in freshwater. However, it remains unclear whether that mechanism is also critical for ammonia excretion in seawater (SW). Using a scanning ion-selective electrode technique (SIET) to measure H+ gradients, an acidic boundary layer was detected at the yolk-sac surface of SW-acclimated medaka ( Oryzias latipes) larvae. The H+ gradient detected at the surface of ionocytes was higher than that of keratinocytes in the yolk sac. Treatment with Tricine buffer or EIPA (a NHE inhibitor) reduced the H+ gradient and ammonia excretion of larvae. In situ hybridization and immunochemistry showed that slc9a2 (NHE2) and slc9a3 (NHE3) were expressed in the same SW-type ionocytes. A real-time PCR analysis showed that transfer to SW downregulated branchial mRNA expressions of slc9a3 and Rhesus glycoproteins ( rhcg1, rhcg2, and rhbg) but upregulated that of slc9a2. However, slc9a3, rhcg1, rhcg2, and rhbg expressions were induced by high ammonia in SW. This study suggests that SW-type ionocytes play a role in acid and ammonia excretion and that the Na+/H+ exchanger and Rh glycoproteins are involved in the proton-facilitated ammonia excretion mechanism.
Collapse
Affiliation(s)
- Sian-Tai Liu
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan; and
| | - Lin Tsung
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan; and
| | - Jiun-Lin Horng
- Department of Anatomy, Taipei Medical University, Taipei, Taiwan
| | - Li-Yih Lin
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan; and
| |
Collapse
|
24
|
Bourgeois S, Bounoure L, Christensen EI, Ramakrishnan SK, Houillier P, Devuyst O, Wagner CA. Haploinsufficiency of the ammonia transporter Rhcg predisposes to chronic acidosis: Rhcg is critical for apical and basolateral ammonia transport in the mouse collecting duct. J Biol Chem 2012; 288:5518-29. [PMID: 23281477 DOI: 10.1074/jbc.m112.441782] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Ammonia secretion by the collecting duct (CD) is critical for acid-base homeostasis and, when defective, causes distal renal tubular acidosis (dRTA). The Rhesus protein RhCG mediates NH(3) transport as evident from cell-free and cellular models as well as from Rhcg-null mice. Here, we investigated in a Rhcg mouse model the metabolic effects of Rhcg haploinsufficiency, the role of Rhcg in basolateral NH(3) transport, and the mechanisms of adaptation to the lack of Rhcg. Both Rhcg(+/+) and Rhcg(+/-) mice were able to handle an acute acid load, whereas Rhcg(-/-) mice developed severe metabolic acidosis with reduced ammonuria and high mortality. However, chronic acid loading revealed that Rhcg(+/-) mice did not fully recover, showing lower blood HCO(3)(-) concentration and more alkaline urine. Microperfusion studies demonstrated that transepithelial NH(3) permeability was reduced by 80 and 40%, respectively, in CDs from Rhcg(-/-) and Rhcg(+/-) mice compared with controls. Basolateral membrane permeability to NH(3) was reduced in CDs from Rhcg(-/-) mice consistent with basolateral Rhcg localization. Rhcg(-/-) responded to acid loading with normal expression of enzymes and transporters involved in proximal tubular ammoniagenesis but reduced abundance of the NKCC2 transporter responsible for medullary accumulation of ammonium. Consequently, tissue ammonium content was decreased. These data demonstrate a role for apical and basolateral Rhcg in transepithelial NH(3) transport and uncover an incomplete dRTA phenotype in Rhcg(+/-) mice. Haploinsufficiency or reduced expression of RhCG may underlie human forms of (in)complete dRTA.
Collapse
Affiliation(s)
- Soline Bourgeois
- Institute of Physiology and Zurich Center for Integrative Human Physiology, University of Zurich, CH-8057 Zurich, Switzerland
| | | | | | | | | | | | | |
Collapse
|
25
|
The promiscuous binding of pharmaceutical drugs and their transporter-mediated uptake into cells: what we (need to) know and how we can do so. Drug Discov Today 2012. [PMID: 23207804 DOI: 10.1016/j.drudis.2012.11.008] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
A recent paper in this journal sought to counter evidence for the role of transport proteins in effecting drug uptake into cells, and questions that transporters can recognize drug molecules in addition to their endogenous substrates. However, there is abundant evidence that both drugs and proteins are highly promiscuous. Most proteins bind to many drugs and most drugs bind to multiple proteins (on average more than six), including transporters (mutations in these can determine resistance); most drugs are known to recognise at least one transporter. In this response, we alert readers to the relevant evidence that exists or is required. This needs to be acquired in cells that contain the relevant proteins, and we highlight an experimental system for simultaneous genome-wide assessment of carrier-mediated uptake in a eukaryotic cell (yeast).
Collapse
|
26
|
Lin CC, Lin LY, Hsu HH, Thermes V, Prunet P, Horng JL, Hwang PP. Acid secretion by mitochondrion-rich cells of medaka (Oryzias latipes) acclimated to acidic freshwater. Am J Physiol Regul Integr Comp Physiol 2012; 302:R283-91. [DOI: 10.1152/ajpregu.00483.2011] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the present study, medaka embryos were exposed to acidified freshwater (pH 5) to investigate the mechanism of acid secretion by mitochondrion-rich (MR) cells in embryonic skin. With double or triple in situ hybridization/immunocytochemistry, the Na+/H+ exchanger 3 (NHE3) and H+-ATPase were localized in two distinct subtypes of MR cells. NHE3 was expressed in apical membranes of a major proportion of MR cells, whereas H+-ATPase was expressed in basolateral membranes of a much smaller proportion of MR cells. Gill mRNA levels of NHE3 and H+-ATPase and the two subtypes of MR cells in yolk sac skin were increased by acid acclimation; however, the mRNA level of NHE3 was remarkably higher than that of H+-ATPase. A scanning ion-selective electrode technique was used to measure H+, Na+, and NH4+ transport by individual MR cells in larval skin. Results showed that Na+ uptake and NH4+ excretion by MR cells increased after acid acclimation. These findings suggested that the NHE3/Rh glycoprotein-mediated Na+ uptake/NH4+ excretion mechanism plays a critical role in acidic equivalent (H+/NH4+) excretion by MR cells of the freshwater medaka.
Collapse
Affiliation(s)
- Chia-Cheng Lin
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan, Republic of China
| | - Li-Yih Lin
- Department of Life Science, National Taiwan Normal University, Taipei, Taiwan, Republic of China; and
| | - Hao-Hsuan Hsu
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan, Republic of China
| | - Violette Thermes
- Institut National de la Recherche Agronomique, Station Commune de Recherches en Ichtyophysiologie, Biodiversité et Environnement, Campus de Beaulieu, Rennes, France
| | - Patrick Prunet
- Institut National de la Recherche Agronomique, UR1037, SCRIBE, IFR140, Biogenouest, Rennes, France; and
| | - Jiun-Lin Horng
- Department of Anatomy, Taipei Medical University, Taipei, Taiwan, Republic of China
| | - Pung-Pung Hwang
- Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan, Republic of China
| |
Collapse
|
27
|
Han KH. Mechanisms of the effects of acidosis and hypokalemia on renal ammonia metabolism. Electrolyte Blood Press 2011; 9:45-9. [PMID: 22438855 PMCID: PMC3302905 DOI: 10.5049/ebp.2011.9.2.45] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Accepted: 12/18/2011] [Indexed: 01/29/2023] Open
Abstract
Renal ammonia metabolism is the predominant component of net acid excretion and new bicarbonate generation. Renal ammonia metabolism is regulated by acid-base balance. Both acute and chronic acid loads enhance ammonia production in the proximal tubule and secretion into the urine. In contrast, alkalosis reduces ammoniagenesis. Hypokalemia is a common electrolyte disorder that significantly increases renal ammonia production and excretion, despite causing metabolic alkalosis. Although the net effects of hypokalemia are similar to metabolic acidosis, molecular mechanisms of renal ammonia production and transport have not been well understood. This mini review summarizes recent findings regarding renal ammonia metabolism in response to chronic hypokalemia.
Collapse
Affiliation(s)
- Ki-Hwan Han
- Department of Anatomy, Ewha Womans University School of Medicine, Seoul, Korea
| |
Collapse
|
28
|
Lee SY, Shin JA, Kwon HM, Weiner ID, Han KH. Renal ischemia-reperfusion injury causes intercalated cell-specific disruption of occludin in the collecting duct. Histochem Cell Biol 2011; 136:637-47. [PMID: 22048282 PMCID: PMC3214267 DOI: 10.1007/s00418-011-0881-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/23/2011] [Indexed: 11/30/2022]
Abstract
Renal ischemic events open tight junctions and disrupt epithelial polarity. The purpose of this study was to examine the effects of ischemia–reperfusion (IR) injury on expression and distribution of the tight junction proteins, occludin and ZO-1, in the rat kidney. IR injury was induced by clamping both renal pedicles for 30 min and animals were killed at 6 h after the reperfusion. IR injury decreased blood bicarbonate level, but did not persistently alter pH, Na+, K+, or Cl−. In control kidneys, occludin immunoreactivity was intense in the tight junctions in the thick ascending limb, distal convoluted tubule, and collecting duct, moderate in the thin limbs of the loop of Henle, and was not detected in the proximal tubule, glomerulus, and blood vessels. ZO-1 was expressed in the same sites in which occludin was expressed, and additionally was also expressed in the proximal tubule, glomerulus, and vascular endothelial cells. IR kidneys exhibited damaged renal tubular epithelial cells in both proximal tubule and collecting duct segments in the outer medulla. In the collecting duct, the response of intercalated cells and principal cells differed. Following IR injury, intercalated cells, but not principal cells, lost their normal epithelial polarity and were frequently extruded into the tubule lumen. Occludin, instead of being localized to tight junctions, was localized diffusely in the cytoplasm in intercalated cells of IR kidneys. Principal cells, in contrast, were not detectably affected and neither occludin nor ZO-1 expression were altered in response to IR injury. The normal localization of ZO-1 expression to tight junction sites in both the proximal tubule and collecting duct was altered in response to IR, and, instead, ZO-1 expression was present diffusely in the cytoplasm. IR injury did not alter detectably either occludin or ZO-1 localization to the tight junction of the thick ascending limb cells. The abundance of total occludin protein by immunoblot analysis was not changed with IR injury. These results demonstrate that renal IR injury causes tight junction disruptions in both the proximal tubule and the collecting duct, and that altered distribution of the tight junction protein, occludin, may play a critical role in the collecting duct dysfunction which IR induces.
Collapse
Affiliation(s)
- Su-Youn Lee
- Department of Anatomy, Ewha Womans University School of Medicine, 911-1 Mok-6-dong, Yangcheon-ku, Seoul, 158-710 Korea
| | - Jung-A Shin
- Department of Anatomy, Ewha Womans University School of Medicine, 911-1 Mok-6-dong, Yangcheon-ku, Seoul, 158-710 Korea
| | - H. Moo Kwon
- Division of Nephrology, University of Maryland School of Medicine, Baltimore, MD USA
| | - I. David Weiner
- Division of Nephrology, University of Florida College of Medicine, Gainesville, FL USA
- Nephrology Section, NF/SGVHS, Gainesville, FL USA
| | - Ki-Hwan Han
- Department of Anatomy, Ewha Womans University School of Medicine, 911-1 Mok-6-dong, Yangcheon-ku, Seoul, 158-710 Korea
| |
Collapse
|
29
|
Rastegar A. Attending Rounds: Patient with Hypokalemia and Metabolic Acidosis. Clin J Am Soc Nephrol 2011; 6:2516-21. [DOI: 10.2215/cjn.04150511] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
|
30
|
Devuyst O, Wang X, Serra A. Vasopressin-2 receptor antagonists in autosomal dominant polycystic kidney disease: from man to mouse and back. Nephrol Dial Transplant 2011; 26:2423-5. [DOI: 10.1093/ndt/gfr380] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
|