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Zajac M, Mukherjee S, Anees P, Oettinger D, Henn K, Srikumar J, Zou J, Saminathan A, Krishnan Y. A mechanism of lysosomal calcium entry. SCIENCE ADVANCES 2024; 10:eadk2317. [PMID: 38354239 PMCID: PMC10866540 DOI: 10.1126/sciadv.adk2317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2023] [Accepted: 01/16/2024] [Indexed: 02/16/2024]
Abstract
Lysosomal calcium (Ca2+) release is critical to cell signaling and is mediated by well-known lysosomal Ca2+ channels. Yet, how lysosomes refill their Ca2+ remains hitherto undescribed. Here, from an RNA interference screen in Caenorhabditis elegans, we identify an evolutionarily conserved gene, lci-1, that facilitates lysosomal Ca2+ entry in C. elegans and mammalian cells. We found that its human homolog TMEM165, previously designated as a Ca2+/H+ exchanger, imports Ca2+ pH dependently into lysosomes. Using two-ion mapping and electrophysiology, we show that TMEM165, hereafter referred to as human LCI, acts as a proton-activated, lysosomal Ca2+ importer. Defects in lysosomal Ca2+ channels cause several neurodegenerative diseases, and knowledge of lysosomal Ca2+ importers may provide previously unidentified avenues to explore the physiology of Ca2+ channels.
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Affiliation(s)
- Matthew Zajac
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Sourajit Mukherjee
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Palapuravan Anees
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Daphne Oettinger
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Katharine Henn
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Jainaha Srikumar
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Junyi Zou
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Anand Saminathan
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
| | - Yamuna Krishnan
- Department of Chemistry, The University of Chicago, Chicago, IL 60637, USA
- Neuroscience Institute, The University of Chicago, Chicago, IL 60637, USA
- Institute for Biophysical Dynamics, The University of Chicago, Chicago, IL 60637, USA
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Dong Y, Yu Z, Li Y, Huang B, Bai Q, Gao Y, Chen Q, Li N, He L, Zhao Y. Structural insight into the allosteric inhibition of human sodium-calcium exchanger NCX1 by XIP and SEA0400. EMBO J 2024; 43:14-31. [PMID: 38177313 PMCID: PMC10897212 DOI: 10.1038/s44318-023-00013-0] [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: 02/16/2023] [Revised: 11/10/2023] [Accepted: 11/15/2023] [Indexed: 01/06/2024] Open
Abstract
Sodium-calcium exchanger proteins influence calcium homeostasis in many cell types and participate in a wide range of physiological and pathological processes. Here, we elucidate the cryo-EM structure of the human Na+/Ca2+ exchanger NCX1.3 in the presence of a specific inhibitor, SEA0400. Conserved ion-coordinating residues are exposed on the cytoplasmic face of NCX1.3, indicating that the observed structure is stabilized in an inward-facing conformation. We show how regulatory calcium-binding domains (CBDs) assemble with the ion-translocation transmembrane domain (TMD). The exchanger-inhibitory peptide (XIP) is trapped within a groove between the TMD and CBD2 and predicted to clash with gating helices TMs1/6 at the outward-facing state, thus hindering conformational transition and promoting inactivation of the transporter. A bound SEA0400 molecule stiffens helix TM2ab and affects conformational rearrangements of TM2ab that are associated with the ion-exchange reaction, thus allosterically attenuating Ca2+-uptake activity of NCX1.3.
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Affiliation(s)
- Yanli Dong
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Zhuoya Yu
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yue Li
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Bo Huang
- Beijing StoneWise Technology Co Ltd., 15 Haidian street, Haidian district, Beijing, China
| | - Qinru Bai
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Yiwei Gao
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Qihao Chen
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Na Li
- Heart Center and Beijing Key Laboratory of Hypertension, Beijing Chaoyang Hospital, Capital Medical University, Beijing, 100020, China
| | - Lingli He
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China
| | - Yan Zhao
- Key Laboratory of Biomacromolecules (CAS), National Laboratory of Biomacromolecules, CAS Center for Excellence in Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China.
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Beijing, 100101, China.
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
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3
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Boutin JA, Bedut S, Jullian M, Galibert M, Frankiewicz L, Gloanec P, Ferry G, Puget K, Leprince J. Caloxin-derived peptides for the inhibition of plasma membrane calcium ATPases. Peptides 2022; 154:170813. [PMID: 35605801 DOI: 10.1016/j.peptides.2022.170813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 05/16/2022] [Accepted: 05/16/2022] [Indexed: 11/20/2022]
Abstract
Plasma membrane calcium ATPases (PMCAs) are a family of transmembrane proteins responsible for the extrusion of cytosolic Ca2+ to the extracellular milieu. They are important players of the calcium homeostasis possibly implicated in some important diseases. The reference inhibitors of PMCA extruding activity are on one hand ortho-vanadate (IC50 in the 30 mM range), and on the other a series of 12- to 20-mer peptides named caloxins (IC50 in the 100 µM scale). As for all integral membrane proteins, biochemistry and pharmacology are difficult to study on isolated and/or purified proteins. Using a series of reference blockers, we assessed a pharmacological window with which we could study the functionality of PMCAs in living cells. Using this system, we screened for alternative versions of caloxins, aiming at shortening the peptide backbone, introducing non-natural amino acids, and overall trying to get a glimpse at the structure-activity relationship between those new peptides and the protein in a cellular context. We describe a short series of equipotent 5-residue long analogues with IC50 in the low µM range.
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Affiliation(s)
- Jean A Boutin
- Institut de Recherches Servier, Croissy-sur-Seine, France; INSERM U1239, University of Rouen Normandy, Laboratory of Neuroendocrine Endocrine and Germinal Differentiation and Communication (NorDiC), Rouen, France.
| | | | | | | | | | | | - Gilles Ferry
- Institut de Recherches Servier, Croissy-sur-Seine, France
| | | | - Jérôme Leprince
- INSERM U1239, University of Rouen Normandy, Laboratory of Neuroendocrine Endocrine and Germinal Differentiation and Communication (NorDiC), Rouen, France; INSERM US51, University of Rouen Normandy, Cell Imaging Platform of Normandy (PRIMACEN), Rouen, France
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4
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Gök C, Main A, Gao X, Kerekes Z, Plain F, Kuo CW, Robertson AD, Fraser NJ, Fuller W. Insights into the molecular basis of the palmitoylation and depalmitoylation of NCX1. Cell Calcium 2021; 97:102408. [PMID: 33873072 PMCID: PMC8278489 DOI: 10.1016/j.ceca.2021.102408] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2020] [Revised: 03/30/2021] [Accepted: 04/06/2021] [Indexed: 11/23/2022]
Abstract
Catalyzed by zDHHC-PAT enzymes and reversed by thioesterases, protein palmitoylation is the only post-translational modification recognized to regulate the sodium/calcium exchanger NCX1. NCX1 palmitoylation occurs at a single site at position 739 in its large regulatory intracellular loop. An amphipathic ɑ-helix between residues 740-756 is a critical for NCX1 palmitoylation. Given the rich background of the structural elements involving in NCX1 palmitoylation, the molecular basis of NCX1 palmitoylation is still relatively poorly understood. Here we found that (1) the identity of palmitoylation machinery of NCX1 controls its spatial organization within the cell, (2) the NCX1 amphipathic ɑ-helix directly interacts with zDHHC-PATs, (3) NCX1 is still palmitoylated when it is arrested in either Golgi or ER, indicating that NCX1 is a substrate for multiple zDHHC-PATs, (4) the thioesterase APT1 but not APT2 as a part of NCX1-depalmitoylation machinery governs subcellular organization of NCX1, (5) APT1 catalyzes NCX1 depalmitoylation in the Golgi but not in the ER. We also report that NCX2 and NCX3 are dually palmitoylated, with important implications for substrate recognition and enzyme catalysis by zDHHC-PATs. Our results could support new molecular or pharmacological strategies targeting the NCX1 palmitoylation and depalmitoylation machinery.
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Affiliation(s)
- Caglar Gök
- Institute of Cardiovascular & Medical Sciences, Sir James Black Building, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - Alice Main
- Institute of Cardiovascular & Medical Sciences, Sir James Black Building, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - Xing Gao
- Institute of Cardiovascular & Medical Sciences, Sir James Black Building, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - Zsombor Kerekes
- Institute of Cardiovascular & Medical Sciences, Sir James Black Building, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - Fiona Plain
- School of Medicine, Ninewells Hospital, University of Dundee, Dundee, DD1 9SY, United Kingdom
| | - Chien-Wen Kuo
- Institute of Cardiovascular & Medical Sciences, Sir James Black Building, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - Alan D Robertson
- Institute of Cardiovascular & Medical Sciences, Sir James Black Building, University of Glasgow, Glasgow, G12 8QQ, United Kingdom
| | - Niall J Fraser
- School of Medicine, Ninewells Hospital, University of Dundee, Dundee, DD1 9SY, United Kingdom
| | - William Fuller
- Institute of Cardiovascular & Medical Sciences, Sir James Black Building, University of Glasgow, Glasgow, G12 8QQ, United Kingdom.
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5
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Peptide hormone sensors using human hormone receptor-carrying nanovesicles and graphene FETs. Sci Rep 2020; 10:388. [PMID: 31942024 PMCID: PMC6962399 DOI: 10.1038/s41598-019-57339-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2019] [Accepted: 12/19/2019] [Indexed: 11/09/2022] Open
Abstract
Hormones within very low levels regulate and control the activity of specific cells and organs of the human body. Hormone imbalance can cause many diseases. Therefore, hormone detection tools have been developed, particularly over the last decade. Peptide hormones have a short half-life, so it is important to detect them within a short time. In this study, we report two types of peptide hormone sensors using human hormone receptor-carrying nanovesicles and graphene field-effect transistors (FETs). Parathyroid hormone (PTH) and glucagon (GCG) are peptide hormones present in human blood that act as ligands to G protein-coupled receptors (GPCRs). In this paper, the parathyroid hormone receptor (PTHR) and the glucagon receptor (GCGR) were expressed in human embryonic kidney-293 (HEK-293) cells, and were constructed as nanovesicles carrying the respective receptors. They were then immobilized onto graphene-based FETs. The two hormone sensors developed were able to detect each target hormone with high sensitivity (ca. 100 fM of PTH and 1 pM of GCG). Also, the sensors accurately recognized target hormones among different types of peptide hormones. In the development of hormone detection tools, this approach, using human hormone receptor-carrying nanovesicles and graphene FETs, offers the possibility of detecting very low concentrations of hormones in real-time.
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Li S, Jiang X, Luo Y, Zhou B, Shi M, Liu F, Sha A. Sodium/calcium overload and Sirt1/Nrf2/OH-1 pathway are critical events in mercuric chloride-induced nephrotoxicity. CHEMOSPHERE 2019; 234:579-588. [PMID: 31229719 DOI: 10.1016/j.chemosphere.2019.06.095] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2019] [Revised: 05/20/2019] [Accepted: 06/12/2019] [Indexed: 06/09/2023]
Abstract
Mercury (Hg), a significant toxic metal for nephrotoxicity, can be found in food (vegetable and seafood) and drinking water by contamination. Oxidative stress is involved in inorganic Hg-induced nephrotoxicity, but the Sirtuin1 (Sirt1)/Nrf2/OH-1 pathway and sodium (Na)/calcium (Ca) ions actions in mercuric chloride (HgCl2)-induced nephrotoxicity remains unclear to date. In this study, Kunming mice were treated HgCl2 (5 mg/kg) for 24 h to evaluate potential mechanism. Here, along with Sirt1 activation, pale kidney, hisologic conditions, typical apoptotic changes and TUNEL positive nuclei were observed under acute HgCl2 exposure. Specifically, although HgCl2 increased the expression of Nrf2, Keap1, OH-1 and NQO1, the mRNA levels of GSS, GCLC and GCLM showed no significant alterations in mice kidney. Moreover, mice exposed to HgCl2 decreased the concentrations of Mg, K, P, Mn, Fe, Zn, and elevated Na, Ca, Cu and Se in kidney. It was also observed that HgCl2 suppressed the ATPases (Na+-K+-ATPase, Ca2+-ATPase, Mg2+-ATPase and Ca2+-Mg2+-ATPase) activities and decreased the mRNA levels of Atp1a1, Atp1a2 in the kidney. Further study showed that HgCl2 elevated Na+ concentrations by markedly increased the mRNA levels of Na+ transporter. The present study revealed that HgCl2 induced Sirt1/Nrf2/OH-1 pathway activation while did not inhibit apoptosis in kidney of mice. Additionally, HgCl2 regulates Na+ concentrations, which might create secondary disorders in absorption and excretion of other ions. Altogether we assume that Sirt1/Nrf2/Na+/Ca2+ pathway might be a potential therapeutic target for treating acute HgCl2 induced nephrotoxicity.
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Affiliation(s)
- Siwen Li
- Department of Physiology, College of Basic Medical Sciences, Southwest Medical University, Luzhou, 646000, Sichuan Province, PR China.
| | - Xia Jiang
- Department of Physiology, College of Basic Medical Sciences, Southwest Medical University, Luzhou, 646000, Sichuan Province, PR China
| | - Yonghong Luo
- Department of Physiology, College of Basic Medical Sciences, Southwest Medical University, Luzhou, 646000, Sichuan Province, PR China
| | - Bingru Zhou
- Department of Physiology, College of Basic Medical Sciences, Southwest Medical University, Luzhou, 646000, Sichuan Province, PR China
| | - Mei Shi
- Department of Physiology, College of Basic Medical Sciences, Southwest Medical University, Luzhou, 646000, Sichuan Province, PR China
| | - Fangyuan Liu
- Department of Physiology, College of Basic Medical Sciences, Southwest Medical University, Luzhou, 646000, Sichuan Province, PR China
| | - Ailong Sha
- Department of Physiology, College of Basic Medical Sciences, Southwest Medical University, Luzhou, 646000, Sichuan Province, PR China
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Ahn SR, An JH, Song HS, Park JW, Lee SH, Kim JH, Jang J, Park TH. Duplex Bioelectronic Tongue for Sensing Umami and Sweet Tastes Based on Human Taste Receptor Nanovesicles. ACS NANO 2016; 10:7287-7296. [PMID: 27327579 DOI: 10.1021/acsnano.6b02547] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
For several decades, significant efforts have been made in developing artificial taste sensors to recognize the five basic tastes. So far, the well-established taste sensor is an E-tongue, which is constructed with polymer and lipid membranes. However, the previous artificial taste sensors have limitations in various food, beverage, and cosmetic industries because of their failure to mimic human taste reception. There are many interactions between tastants. Therefore, detecting the interactions in a multiplexing system is required. Herein, we developed a duplex bioelectronic tongue (DBT) based on graphene field-effect transistors that were functionalized with heterodimeric human umami taste and sweet taste receptor nanovesicles. Two types of nanovesicles, which have human T1R1/T1R3 for the umami taste and human T1R2/T1R3 for the sweet taste on their membranes, immobilized on micropatterned graphene surfaces were used for the simultaneous detection of the umami and sweet tastants. The DBT platform led to highly sensitive and selective recognition of target tastants at low concentrations (ca. 100 nM). Moreover, our DBT was able to detect the enhancing effect of taste enhancers as in a human taste sensory system. This technique can be a useful tool for the detection of tastes instead of sensory evaluation and development of new artificial tastants in the food and beverage industry.
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Affiliation(s)
- Sae Ryun Ahn
- School of Chemical and Biological Engineering, Bio-MAX Institute, Seoul National University , Seoul 151-744, Republic of Korea
| | - Ji Hyun An
- School of Chemical and Biological Engineering, Seoul National University , Seoul 151-744, Republic of Korea
| | - Hyun Seok Song
- Division of Bioconvergence Analysis, Korea Basic Science Institute (KBSI) , Yuseong, Daejeon 169-148, Republic of Korea
| | - Jin Wook Park
- School of Chemical and Biological Engineering, Seoul National University , Seoul 151-744, Republic of Korea
| | - Sang Hun Lee
- Department of Bioengineering, University of California , Berkeley, California 94720, United States
| | - Jae Hyun Kim
- S.LSI Material Technology Group, Device Solutions, Samsung Electronics , 1, Samsung-ro, Giheung-gu, Yongin-si, Gyeonggi-do 446-711, Korea
| | - Jyongsik Jang
- School of Chemical and Biological Engineering, Seoul National University , Seoul 151-744, Republic of Korea
| | - Tai Hyun Park
- School of Chemical and Biological Engineering, Bio-MAX Institute, Seoul National University , Seoul 151-744, Republic of Korea
- Advanced Institutes of Convergence Technology , Suwon, Gyeonggi-do 443-270, Republic of Korea
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Abstract
Na(+)/Ca(2+) exchangers (NCXs) have traditionally been viewed principally as a means of Ca(2+) removal from non-excitable cells. However there has recently been increasing interest in the operation of NCXs in reverse mode acting as a means of eliciting Ca(2+) entry into these cells. Reverse mode exchange requires a significant change in the normal resting transmembrane ion gradients and membrane potential, which has been suggested to occur principally via the coupling of NCXs to localised Na(+) entry through non-selective cation channels such as canonical transient receptor potential (TRPC) channels. Here we review evidence for functional or physical coupling of NCXs to non-selective cation channels, and how this affects NCX activity in non-excitable cells. In particular we focus on the potential role of nanojunctions, where the close apposition of plasma and intracellular membranes may help create the conditions needed for the generation of localised rises in Na(+) concentration that would be required to trigger reverse mode exchange.
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Lee M, Jung JW, Kim D, Ahn YJ, Hong S, Kwon HW. Discrimination of Umami Tastants Using Floating Electrode-Based Bioelectronic Tongue Mimicking Insect Taste Systems. ACS NANO 2015; 9:11728-11736. [PMID: 26563753 DOI: 10.1021/acsnano.5b03031] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report a floating electrode-based bioelectronic tongue mimicking insect taste systems for the detection and discrimination of umami substances. Here, carbon nanotube field-effect transistors with floating electrodes were hybridized with nanovesicles containing honeybee umami taste receptor, gustatory receptor 10 of Apis mellifera (AmGr10). This strategy enables us to discriminate between l-monosodium glutamate (MSG), best-known umami tastant, and non-umami substances with a high sensitivity and selectivity. It could also be utilized for the detection of MSG in liquid food such as chicken stock. Moreover, we demonstrated the synergism between MSG and disodium 5'-inosinate (IMP) for the umami taste using this platform. This floating electrode-based bioelectronic tongue mimicking insect taste systems can be a powerful platform for various applications such as food screening, and it also can provide valuable insights on insect taste systems.
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Affiliation(s)
- Minju Lee
- Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University , Seoul 151-747, Korea
| | - Je Won Jung
- Biomodulation Major, Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, College of Agriculture & Life Sciences, Seoul National University , Seoul 151-921, Korea
| | - Daesan Kim
- Department of Biophysics and Chemical Biology, Seoul National University , Seoul 151-747, Korea
| | - Young-Joon Ahn
- Biomodulation Major, Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, College of Agriculture & Life Sciences, Seoul National University , Seoul 151-921, Korea
| | - Seunghun Hong
- Department of Physics and Astronomy, and Institute of Applied Physics, Seoul National University , Seoul 151-747, Korea
| | - Hyung Wook Kwon
- Biomodulation Major, Department of Agricultural Biotechnology and Research Institute of Agriculture and Life Sciences, College of Agriculture & Life Sciences, Seoul National University , Seoul 151-921, Korea
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Shao XM, Kao L, Kurtz I. A novel delta current method for transport stoichiometry estimation. BMC BIOPHYSICS 2015; 7:14. [PMID: 25558372 PMCID: PMC4274721 DOI: 10.1186/s13628-014-0014-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Accepted: 11/19/2014] [Indexed: 11/23/2022]
Abstract
Background The ion transport stoichiometry (q) of electrogenic transporters is an important determinant of their function. q can be determined by the reversal potential (Erev) if the transporter under study is the only electrogenic transport mechanism or a specific inhibitor is available. An alternative approach is to calculate delta reversal potential (ΔErev) by altering the concentrations of the transported substrates. This approach is based on the hypothesis that the contributions of other channels and transporters on the membrane to Erev are additive. However, Erev is a complicated function of the sum of different conductances rather than being additive. Results We propose a new delta current (ΔI) method based on a simplified model for electrogenic secondary active transport by Heinz (Electrical Potentials in Biological Membrane Transport, 1981). ΔI is the difference between two currents obtained from altering the external concentration of a transported substrate thereby eliminating other currents without the need for a specific inhibitor. q is determined by the ratio of ΔI at two different membrane voltages (V1 and V2) where q = 2RT/(F(V2 –V1))ln(ΔI2/ΔI1) + 1. We tested this ΔI methodology in HEK-293 cells expressing the elctrogenic SLC4 sodium bicarbonate cotransporters NBCe2-C and NBCe1-A, the results were consistent with those obtained with the Erev inhibitor method. Furthermore, using computational simulations, we compared the estimates of q with the ΔErev and ΔI methods. The results showed that the ΔErev method introduces significant error when other channels or electrogenic transporters are present on the membrane and that the ΔI equation accurately calculates the stoichiometric ratio. Conclusions We developed a ΔI method for estimating transport stoichiometry of electrogenic transporters based on the Heinz model. This model reduces to the conventional reversal potential method when the transporter under study is the only electrogenic transport process in the membrane. When there are other electrogenic transport pathways, ΔI method eliminates their contribution in estimating q. Computational simulations demonstrated that the ΔErev method introduces significant error when other channels or electrogenic transporters are present and that the ΔI equation accurately calculates the stoichiometric ratio. This new ΔI method can be readily extended to the analysis of other electrogenic transporters in other tissues.
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Affiliation(s)
- Xuesi M Shao
- Department of Neurobiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 USA
| | - Liyo Kao
- Division of Nephrology, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 USA
| | - Ira Kurtz
- Division of Nephrology, Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 USA ; Brain Research Institute, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095 USA
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11
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Sodium recognition by the Na+/Ca2+ exchanger in the outward-facing conformation. Proc Natl Acad Sci U S A 2014; 111:E5354-62. [PMID: 25468964 DOI: 10.1073/pnas.1415751111] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Na(+)/Ca(2+) exchangers (NCXs) are ubiquitous membrane transporters with a key role in Ca(2+) homeostasis and signaling. NCXs mediate the bidirectional translocation of either Na(+) or Ca(2+), and thus can catalyze uphill Ca(2+) transport driven by a Na(+) gradient, or vice versa. In a major breakthrough, a prokaryotic NCX homolog (NCX_Mj) was recently isolated and its crystal structure determined at atomic resolution. The structure revealed an intriguing architecture consisting of two inverted-topology repeats, each comprising five transmembrane helices. These repeats adopt asymmetric conformations, yielding an outward-facing occluded state. The crystal structure also revealed four putative ion-binding sites, but the occupancy and specificity thereof could not be conclusively established. Here, we use molecular-dynamics simulations and free-energy calculations to identify the ion configuration that best corresponds to the crystallographic data and that is also thermodynamically optimal. In this most probable configuration, three Na(+) ions occupy the so-called Sext, SCa, and Sint sites, whereas the Smid site is occupied by one water molecule and one H(+), which protonates an adjacent aspartate side chain (D240). Experimental measurements of Na(+)/Ca(2+) and Ca(2+)/Ca(2+) exchange by wild-type and mutagenized NCX_Mj confirm that transport of both Na(+) and Ca(2+) requires protonation of D240, and that this side chain does not coordinate either ion at Smid. These results imply that the ion exchange stoichiometry of NCX_Mj is 3:1 and that translocation of Na(+) across the membrane is electrogenic, whereas transport of Ca(2+) is not. Altogether, these findings provide the basis for further experimental and computational studies of the conformational mechanism of this exchanger.
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Song HS, Jin HJ, Ahn SR, Kim D, Lee SH, Kim UK, Simons CT, Hong S, Park TH. Bioelectronic tongue using heterodimeric human taste receptor for the discrimination of sweeteners with human-like performance. ACS NANO 2014; 8:9781-9789. [PMID: 25126667 DOI: 10.1021/nn502926x] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The sense of taste helps humans to obtain information and form a picture of the world by recognizing chemicals in their environments. Over the past decade, large advances have been made in understanding the mechanisms of taste detection and mimicking its capability using artificial sensor devices. However, the detection capability of previous artificial taste sensors has been far inferior to that of animal tongues, in terms of its sensitivity and selectivity. Herein, we developed a bioelectronic tongue using heterodimeric human sweet taste receptors for the detection and discrimination of sweeteners with human-like performance, where single-walled carbon nanotube field-effect transistors were functionalized with nanovesicles containing human sweet taste receptors and used to detect the binding of sweeteners to the taste receptors. The receptors are heterodimeric G-protein-coupled receptors (GPCRs) composed of human taste receptor type 1 member 2 (hTAS1R2) and human taste receptor type 1 member 3 (hTAS1R3), which have multiple binding sites and allow a human tongue-like broad selectivity for the detection of sweeteners. This nanovesicle-based bioelectronic tongue can be a powerful tool for the detection of sweeteners as an alternative to labor-intensive and time-consuming cell-based assays and the sensory evaluation panels used in the food and beverage industry. Furthermore, this study also allows the artificial sensor to exam the functional activity of dimeric GPCRs.
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Affiliation(s)
- Hyun Seok Song
- School of Chemical and Biological Engineering, Bio-MAX Institute, ‡Department of Physics and Astronomy, and Institute of Applied Physics, and §Department of Biophysics and Chemical Biology, Seoul National University , Seoul, 151-747, Republic of Korea
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13
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Alexander SPH, Benson HE, Faccenda E, Pawson AJ, Sharman JL, Spedding M, Peters JA, Harmar AJ. The Concise Guide to PHARMACOLOGY 2013/14: transporters. Br J Pharmacol 2013; 170:1706-96. [PMID: 24528242 PMCID: PMC3892292 DOI: 10.1111/bph.12450] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. Transporters are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.
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Affiliation(s)
- Stephen PH Alexander
- School of Life Sciences, University of Nottingham Medical SchoolNottingham, NG7 2UH, UK
| | - Helen E Benson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Elena Faccenda
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Adam J Pawson
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | - Joanna L Sharman
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
| | | | - John A Peters
- Neuroscience Division, Medical Education Institute, Ninewells Hospital and Medical School, University of DundeeDundee, DD1 9SY, UK
| | - Anthony J Harmar
- The University/BHF Centre for Cardiovascular Science, University of EdinburghEdinburgh, EH16 4TJ, UK
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14
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Dixit M, Kim S, Matthews GF, Erreger K, Galli A, Cobb CE, Hustedt EJ, Beth AH. Structural arrangement of the intracellular Ca2+ binding domains of the cardiac Na+/Ca2+ exchanger (NCX1.1): effects of Ca2+ binding. J Biol Chem 2012; 288:4194-207. [PMID: 23233681 DOI: 10.1074/jbc.m112.423293] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cardiac Na(+)/Ca(2+) exchanger (NCX1.1) serves as the primary means of Ca(2+) extrusion across the plasma membrane of cardiomyocytes after the rise in intracellular Ca(2+) during contraction. The exchanger is regulated by binding of Ca(2+) to its intracellular domain, which contains two structurally homologous Ca(2+) binding domains denoted as CBD1 and CBD2. NMR and x-ray crystallographic studies have provided structures for the isolated CBD1 and CBD2 domains and have shown how Ca(2+) binding affects their structures and motional dynamics. However, structural information on the entire Ca(2+) binding domain, denoted CBD12, and how binding of Ca(2+) alters its structure and dynamics is more limited. Site-directed spin labeling has been employed in this work to address these questions. Electron paramagnetic resonance measurements on singly labeled constructs of CBD12 have identified the regions that undergo changes in dynamics as a result of Ca(2+) binding. Double electron-electron resonance (DEER) measurements on doubly labeled constructs of CBD12 have shown that the β-sandwich regions of the CBD1 and CBD2 domains are largely insensitive to Ca(2+) binding and that these two domains are widely separated at their N and C termini. Interdomain distances measured by DEER have been employed to construct structural models for CBD12 in the presence and absence of Ca(2+). These models show that there is not a major change in the relative orientation of the two Ca(2+) binding domains as a result of Ca(2+) binding in the NCX1.1 isoform. Additional measurements have shown that there are significant changes in the dynamics of the F-G loop region of CBD2 that merit further characterization with regard to their possible involvement in regulation of NCX1.1 activity.
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Affiliation(s)
- Mrinalini Dixit
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee 37232, USA
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15
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Besserer GM, Nicoll DA, Abramson J, Philipson KD. Characterization and purification of a Na+/Ca2+ exchanger from an archaebacterium. J Biol Chem 2012; 287:8652-9. [PMID: 22287543 DOI: 10.1074/jbc.m111.331280] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The superfamily of cation/Ca(2+) exchangers includes both Na(+)/Ca(2+) exchangers (NCXs) and Na(+)/Ca(2+),K(+) exchangers (NCKX) as the families characterized in most detail. These Ca(2+) transporters have prominent physiological roles. For example, NCX and NCKX are important in regulation of cardiac contractility and visual processes, respectively. The superfamily also has a large number of members of the YrbG family expressed in prokaryotes. However, no members of this family have been functionally expressed, and their transport properties are unknown. We have expressed, purified, and characterized a member of the YrbG family, MaX1 from Methanosarcina acetivorans. MaX1 catalyzes Ca(2+) uptake into membrane vesicles. The Ca(2+) uptake requires intravesicular Na(+) and is stimulated by an inside positive membrane potential. Despite very limited sequence similarity, MaX1 is a Na(+)/Ca(2+) exchanger with kinetic properties similar to those of NCX. The availability of a prokaryotic Na(+)/Ca(2+) exchanger should facilitate structural and mechanistic investigations.
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Affiliation(s)
- Gabriel Mercado Besserer
- Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095-1751, USA
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16
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Song WY, Choi KS, Alexis DA, Martinoia E, Lee Y. Brassica juncea plant cadmium resistance 1 protein (BjPCR1) facilitates the radial transport of calcium in the root. Proc Natl Acad Sci U S A 2011; 108:19808-13. [PMID: 22089235 PMCID: PMC3241789 DOI: 10.1073/pnas.1104905108] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Calcium (Ca) is an important structural component of plant cell walls and an intracellular messenger in plants and animals. Therefore, plants tightly control the balance of Ca by regulating Ca uptake and its transfer from cell to cell and organ to organ. Here, we propose that Brassica juncea PCR1 (PCR1), a member of the plant cadmium resistance (PCR) protein family in Indian mustard, is a Ca(2+) efflux transporter that is required for the efficient radial transfer of Ca(2+) in the root and is implicated in the translocation of Ca to the shoot. Knock-down lines of BjPCR1 were greatly stunted and translocated less Ca to the shoot than did the corresponding WT. The localization of BjPCR1 to the plasma membrane and the preferential expression of BjPCR1 in the root epidermal cells of WT plants suggest that BjPCR1 antisense plants could not efficiently transfer Ca(2+) from the root epidermis to the cells located inside the root. Protoplasts isolated from BjPCR1 antisense lines had lower Ca(2+) efflux activity than did those of the WT, and membrane vesicles isolated from BjPCR1-expressing yeast exhibited increased Ca(2+) transport activity. Inhibitor studies, together with theoretical considerations, indicate that BjPCR1 exports one Ca(2+) in exchange for three protons. Root hair-specific expression of BjPCR1 in Arabidopsis results in plants that exhibit increased Ca(2+) resistance and translocation. In conclusion, our data support the hypothesis that BjPCR1 is an exporter required for the translocation of Ca(2+) from the root epidermis to the inner cells, and ultimately to the shoot.
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Affiliation(s)
- Won-Yong Song
- Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland
- Pohang University of Science and Technology-University of Zurich Cooperative Laboratory, Department of Integrative Bioscience and Biotechnology, World Class University Program, Pohang University of Science and Technology, Pohang 790-784, Korea; and
- Division of Applied Biology, College of Agriculture and Life Sciences, Chungnam National University, Daejeon 305-764, Korea
| | - Kwan-Sam Choi
- Division of Applied Biology, College of Agriculture and Life Sciences, Chungnam National University, Daejeon 305-764, Korea
| | - De Angeli Alexis
- Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland
| | - Enrico Martinoia
- Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland
- Pohang University of Science and Technology-University of Zurich Cooperative Laboratory, Department of Integrative Bioscience and Biotechnology, World Class University Program, Pohang University of Science and Technology, Pohang 790-784, Korea; and
| | - Youngsook Lee
- Pohang University of Science and Technology-University of Zurich Cooperative Laboratory, Department of Integrative Bioscience and Biotechnology, World Class University Program, Pohang University of Science and Technology, Pohang 790-784, Korea; and
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17
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O'Hara T, Virág L, Varró A, Rudy Y. Simulation of the undiseased human cardiac ventricular action potential: model formulation and experimental validation. PLoS Comput Biol 2011; 7:e1002061. [PMID: 21637795 PMCID: PMC3102752 DOI: 10.1371/journal.pcbi.1002061] [Citation(s) in RCA: 701] [Impact Index Per Article: 53.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2010] [Accepted: 04/05/2011] [Indexed: 11/19/2022] Open
Abstract
Cellular electrophysiology experiments, important for understanding cardiac arrhythmia mechanisms, are usually performed with channels expressed in non myocytes, or with non-human myocytes. Differences between cell types and species affect results. Thus, an accurate model for the undiseased human ventricular action potential (AP) which reproduces a broad range of physiological behaviors is needed. Such a model requires extensive experimental data, but essential elements have been unavailable. Here, we develop a human ventricular AP model using new undiseased human ventricular data: Ca(2+) versus voltage dependent inactivation of L-type Ca(2+) current (I(CaL)); kinetics for the transient outward, rapid delayed rectifier (I(Kr)), Na(+)/Ca(2+) exchange (I(NaCa)), and inward rectifier currents; AP recordings at all physiological cycle lengths; and rate dependence and restitution of AP duration (APD) with and without a variety of specific channel blockers. Simulated APs reproduced the experimental AP morphology, APD rate dependence, and restitution. Using undiseased human mRNA and protein data, models for different transmural cell types were developed. Experiments for rate dependence of Ca(2+) (including peak and decay) and intracellular sodium ([Na(+)](i)) in undiseased human myocytes were quantitatively reproduced by the model. Early afterdepolarizations were induced by I(Kr) block during slow pacing, and AP and Ca(2+) alternans appeared at rates >200 bpm, as observed in the nonfailing human ventricle. Ca(2+)/calmodulin-dependent protein kinase II (CaMK) modulated rate dependence of Ca(2+) cycling. I(NaCa) linked Ca(2+) alternation to AP alternans. CaMK suppression or SERCA upregulation eliminated alternans. Steady state APD rate dependence was caused primarily by changes in [Na(+)](i), via its modulation of the electrogenic Na(+)/K(+) ATPase current. At fast pacing rates, late Na(+) current and I(CaL) were also contributors. APD shortening during restitution was primarily dependent on reduced late Na(+) and I(CaL) currents due to inactivation at short diastolic intervals, with additional contribution from elevated I(Kr) due to incomplete deactivation.
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Affiliation(s)
- Thomas O'Hara
- Cardiac Bioelectricity and Arrhythmia Center, Department of Biomedical
Engineering, Washington University in St. Louis, St. Louis, Missouri, United
States of America
| | - László Virág
- Department of Pharmacology and Pharmacotherapy, University of Szeged,
Szeged, Hungary
| | - András Varró
- Department of Pharmacology and Pharmacotherapy, University of Szeged,
Szeged, Hungary
- Division of Cardiovascular Pharmacology, Hungarian Academy of Sciences,
Szeged, Hungary
| | - Yoram Rudy
- Cardiac Bioelectricity and Arrhythmia Center, Department of Biomedical
Engineering, Washington University in St. Louis, St. Louis, Missouri, United
States of America
- * E-mail:
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18
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Wang W, Gao J, Entcheva E, Cohen IS, Gordon C, Mathias RT. A transmural gradient in the cardiac Na/K pump generates a transmural gradient in Na/Ca exchange. J Membr Biol 2010; 233:51-62. [PMID: 20130849 DOI: 10.1007/s00232-010-9224-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2009] [Accepted: 01/08/2010] [Indexed: 10/19/2022]
Abstract
We previously demonstrated a transmural gradient in Na/K pump current (I (P)) and [Na(+)]( i ), with the highest maximum I (P) and lowest [Na(+)]( i ) in epicardium. The present study examines the relationship between the transmural gradient in I (P) and Na/Ca exchange (NCX). Myocytes were isolated from canine left ventricle. Whole-cell patch clamp was used to measure current generated by NCX (I (NCX)) and inward background calcium current (I (ibCa)), defined as inward current through Ca(2+) channels less outward current through Ca(2+)-ATPase. When resting myocytes from endocardium (Endo), midmyocardium (Mid) or epicardium (Epi) were studied in the same conditions, I (NCX) was the same and I (ibCa) was zero. Moreover, Western blots were consistent with NCX protein being uniform across the wall. However, the gradient in [Na(+)]( i ), with I (ibCa) = 0, should create a gradient in [Ca(2+)]( i ). To test this hypothesis, we measured resting [Ca(2+)]( i ) using two methods, based on either transport or the Ca(2+)-sensitive dye Fura2. Both methods demonstrated a significant transmural gradient in resting [Ca(2+)]( i ), with Endo > Mid > Epi. This gradient was eliminated by exposing Epi to sufficient ouabain to partially inhibit Na/K pumps, thus increasing [Na(+)]( i ) to values similar to those in Endo. These data support the existence of a transmural gradient for Ca(2+) removal by NCX. This gradient is not due to differences in expression of NCX; rather, it is generated by a transmural gradient in [Na(+)]( i ), which is due to a transmural gradient in plasma membrane expression of the Na/K pump.
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Affiliation(s)
- Wei Wang
- Department of Physiology and Biophysics, SUNY at Stony Brook, NY 11794-8661, USA
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19
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Soliman D, Hamming KS, Matemisz LC, Light PE. Reactive oxygen species directly modify sodium–calcium exchanger activity in a splice variant-dependent manner. J Mol Cell Cardiol 2009; 47:595-602. [DOI: 10.1016/j.yjmcc.2009.05.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2009] [Revised: 05/15/2009] [Accepted: 05/16/2009] [Indexed: 11/15/2022]
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20
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Sakamoto K, Owada Y, Shikama Y, Wada I, Waguri S, Iwamoto T, Kimura J. Involvement of Na+/Ca2+ exchanger in migration and contraction of rat cultured tendon fibroblasts. J Physiol 2009; 587:5345-59. [PMID: 19770194 DOI: 10.1113/jphysiol.2009.172080] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In response to injury and inflammation of tendons, tendon fibroblasts are activated, migrate to the wound, and eventually induce contraction of the extracellular matrices to repair the tissue. Under such conditions, Ca(2+) signalling is involved in motility and contractility of tendon fibroblasts. Using cultured tendon fibroblasts isolated from rat Achilles tendons, we investigated functional expression of Na(+)/Ca(2+) exchangers (NCX). The fluorometric study showed that the intracellular Ca(2+) concentration ([Ca(2+)](i)) was increased by reducing extracellular Na(+) concentration ([Na(+)](o)) in tendon fibroblasts. Selective NCX inhibitors, KB-R7943 and SEA0400, both attenuated [Na(+)](o)-dependent [Ca(2+)](i) elevation and the resting [Ca(2+)](i) in tendon fibroblasts. RT-PCR, Western blots and sequence analyses revealed that NCX1.3 and NCX1.7 were expressed in cultured tendon fibroblasts. NCX2 mRNA was undetected. NCX3 expression was negligibly low. Immunofluorescence microscopy indicated that NCX1 protein localized in the plasma membrane especially at the microspikes of tendon fibroblasts. In the wound-healing scratch assay, the cells migrated toward the space created by a scratch and almost completely filled the space within 48 h. This phenomenon was significantly suppressed by KB-R7943 and SEA0400. Furthermore, the NCX inhibitors abrogated the tendon fibroblast-mediated collagen-matrix contractions. Two types of siRNAs for NCX1 also suppressed the migration and contraction of tendon fibroblasts. We conclude that NCX is expressed and mediates Ca(2+) influx in cultured tendon fibroblasts. Since the pharmacological inhibitors and siRNA for NCX1 suppressed motility and contractility of tendon fibroblasts, NCX may play an important role in the function of tendon fibroblasts in the wound healing.
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Affiliation(s)
- Kazuho Sakamoto
- Department of Pharmacology, Fukushima Medical University, School of Medicine, Hikarigaoka, Fukushima, Japan.
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21
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Qayyum F, Al-Bondokji I, Kuszczak I, Samson SE, Grover AK. Sodium-calcium exchange mediated contraction in left anterior descending and left ventricular branch arteries. J Cell Mol Med 2009; 13:3742-52. [PMID: 19659456 PMCID: PMC4516523 DOI: 10.1111/j.1582-4934.2009.00872.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We tested the hypothesis that the de-endothelialized artery rings from the left anterior descending (LAD) coronary artery and its left ventricular branch (LVB) differ in their contractile responses to Na+–Ca2+-exchanger (NCX) mediated Ca2+-entry, muscarinic receptor activation with carbachol, and sarco/endoplasmic reticulum Ca2+ pump (SERCA) inhibition with thapsigargin. In LVB, the force of contraction (in N/g tissue) produced by the NCX mediated Ca2+-entry (17.5 ± 1.4) and carbachol (18 ± 1.5) was only slightly smaller than that due to membrane depolarization with KCl (24.0 ± 1.0). In contrast, in LAD the force of contraction produced with NCX (8.7 ± 0.7) and carbachol (6.1 ± 1.1) was much smaller than with KCl (15.7 ± 0.7). Thapsigargin also contracted LVB with greater force than LAD. When isolated microsomes were used, the binding to the muscarinic receptor antagonist quinuclidinyl benzilate was greater in LVB than in LAD. Microsomes were also used for Western blots. The intensities of signals for both SERCA and NCX were greater in LVB than in LAD. These biochemical observations were consistent with the contractile experiments. Thus, it appears that the differences between LAD and the resistance arteries may begin as early as LVB.
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Affiliation(s)
- Fareeha Qayyum
- Department of Medicine, McMaster University, Hamilton, ON, Canada
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22
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Zhang XQ, Wang J, Carl LL, Song J, Ahlers BA, Cheung JY. Phospholemman regulates cardiac Na+/Ca2+ exchanger by interacting with the exchanger's proximal linker domain. Am J Physiol Cell Physiol 2009; 296:C911-21. [PMID: 19158404 DOI: 10.1152/ajpcell.00196.2008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phospholemman (PLM) belongs to the FXYD family of small ion transport regulators. When phosphorylated at Ser(68), PLM inhibits cardiac Na(+)/Ca(2+) exchanger (NCX1). We previously demonstrated that the cytoplasmic tail of PLM interacts with the proximal intracellular loop (residues 218-358), but not the transmembrane (residues 1-217 and 765-938) or Ca(2+)-binding (residues 371-508) domains, of NCX1. In this study, we used intact Na(+)/Ca(2+) exchanger with various deletions in the intracellular loop to map the interaction sites with PLM. We first demonstrated by Western blotting and confocal immunofluorescence microscopy that wild-type (WT) NCX1 and its deletion mutants were expressed in transfected HEK-293 cells. Cotransfection with PLM and NCX1 (or its deletion mutants) in HEK-293 cells did not decrease expression of NCX1 (or its deletion mutants). Coexpression of PLM with WT NCX1 inhibited NCX1 current (I(NaCa)). Deletion of residues 240-679, 265-373, 250-300, or 300-373 from WT NCX1 resulted in loss of inhibition of I(NaCa) by PLM. Inhibition of I(NaCa) by PLM was preserved when residues 229-237, 270-300, 328-330, or 330-373 were deleted from the intracellular loop of NCX1. These results suggest that PLM mediated inhibition of I(NaCa) by interacting with two distinct regions (residues 238-270 and 300-328) of NCX1. Indeed, I(NaCa) measured in mutants lacking residues 238-270, 300-328, or 238-270 + 300-328 was not affected by PLM. Glutathione S-transferase pull-down assays confirmed that PLM bound to fragments corresponding to residues 218-371, 218-320, 218-270, 238-371, and 300-373, but not to fragments encompassing residues 250-300 and 371-508 of NCX1, indicating that residues 218-270 and 300-373 physically associated with PLM. Finally, acute regulation of I(NaCa) by PLM phosphorylation observed with WT NCX1 was absent in 250-300 deletion mutant but preserved in 229-237 deletion mutant. We conclude that PLM mediates its inhibition of NCX1 by interacting with residues 238-270 and 300-328.
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Affiliation(s)
- Xue-Qian Zhang
- Division of Nephrology, Thomas Jefferson Univ., 833 Chestnut St., Suite 700, Philadelphia, PA 19107, USA
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23
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Reeves JP, Abdellatif M, Condrescu M. The sodium-calcium exchanger is a mechanosensitive transporter. J Physiol 2008; 586:1549-63. [PMID: 18238815 DOI: 10.1113/jphysiol.2008.151274] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
This report describes the influence of fluid flow and osmotically induced volume changes on Na(+)-Ca(2+) exchange (NCX) activity in transfected CHO cells. Exchange activity was measured as Na(+)-dependent Ca(2+) or Ba(2+) fluxes using the fluorescent probe fura-2. When exchange activity was initiated by superfusing Ba(2+)-containing solutions over the cells for a 20 s interval, a high rate of Ba(2+) uptake was observed while the solution was being applied but the rate of Ba(2+) uptake declined > 10-fold when the solution flow ceased. Ba(2+) efflux in exchange for extracellular Na(+) or Ca(2+) (Ba(2+)-Ca(2+) exchange) was similarly biphasic. During NCX-mediated Ca(2+) uptake, a rapid increase in cytosolic [Ca(2+)] to a peak value occurred, followed by a decline in [Ca(2+)](i) to a lower steady-state value after solution flow ceased. When NCX activity was initiated by an alternate procedure that minimized the duration of solution flow, the rapid phase of Ba(2+) influx was greatly reduced in magnitude and Ca(2+) uptake became nearly monophasic. Solution superfusion did not produce any obvious changes in cell shape or volume. NCX-mediated Ba(2+) and Ca(2+) influx were also sensitive to osmotically induced changes in cell volume. NCX activity was stimulated in hypotonic media and inhibited in hypertonic media; the osmotically induced changes in activity occurred within seconds and were rapidly reversible. We conclude that NCX activity is modulated by both solution flow and osmotically induced volume changes.
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Affiliation(s)
- John P Reeves
- Department of Pharmacology & Physiology, University of Medicine and Dentistry of New Jersey, Graduate School of Biomedical Sciences, 185 South Orange Avenue, Newark, NJ 07101-1709, USA.
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24
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Dietz RM, Kiedrowski L, Shuttleworth CW. Contribution of Na(+)/Ca(2+) exchange to excessive Ca(2+) loading in dendrites and somata of CA1 neurons in acute slice. Hippocampus 2008; 17:1049-59. [PMID: 17598158 DOI: 10.1002/hipo.20336] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Multiple Ca(2+) entry routes have been implicated in excitotoxic Ca(2+) loading in neurons and reverse-operation of sodium-calcium exchangers (NCX) has been shown to contribute under conditions where intracellular Na(+) levels are enhanced. We have investigated effects of KB-R7943, an inhibitor of reverse-operation NCX activity, on Ca(2+) elevations in single CA1 neurons in acute hippocampal slices. KB-R7943 had no significant effect on input resistance, action potential waveform, or action potential frequency adaptation, but reduced L-type Ca(2+) entry in somata. Nimodipine was therefore included in subsequent experiments to prevent complication from effects of L-type influx on evaluation of NCX activity. NMDA produced transient primary Ca(2+) increases, followed by propagating secondary Ca(2+) increases that initiated in apical dendrites. KB-R7943 had no significant effect on primary or secondary Ca(2+) increases generated by NMDA. The Na(+)/K(+) ATPase inhibitor ouabain (30 microM) produced degenerative Ca(2+) overload that was initiated in basal dendrites. KB-R7943 significantly reduced initial Ca(2+) increases and delayed the propagation of degenerative Ca(2+) loads triggered by ouabain, raising the possibility that excessive intracellular Na(+) loading can trigger reverse-operation NCX activity. A combination of NMDA and ouabain produced more rapid Ca(2+) overload, that was contributed to by NCX activity. These results suggest that degenerative Ca(2+) signaling can be triggered by NMDA in dendrites, before intracellular Na(+) levels become sufficient to reverse NCX activity. However, since Na(+)/K(+) ATPase inhibition does appear to produce significant reverse-operation NCX activity, this additional Ca(2+) influx pathway may operate in ATP-deprived CA1 neurons and play a role in ischemic neurodegeneration.
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Affiliation(s)
- Robert M Dietz
- Department of Neurosciences, University of New Mexico School of Medicine, Albuquerque, New Mexico, USA
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25
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Abstract
Mammalian Na+/Ca2+ exchangers are members of three branches of a much larger family of transport proteins [the CaCA (Ca2+/cation antiporter) superfamily] whose main role is to provide control of Ca2+ flux across the plasma membranes or intracellular compartments. Since cytosolic levels of Ca2+ are much lower than those found extracellularly or in sequestered stores, the major function of Na+/Ca2+ exchangers is to extrude Ca2+ from the cytoplasm. The exchangers are, however, fully reversible and thus, under special conditions of subcellular localization and compartmentalized ion gradients, Na+/Ca2+ exchangers may allow Ca2+ entry and may play more specialized roles in Ca2+ movement between compartments. The NCX (Na+/Ca2+ exchanger) [SLC (solute carrier) 8] branch of Na+/Ca2+ exchangers comprises three members: NCX1 has been most extensively studied, and is broadly expressed with particular abundance in heart, brain and kidney, NCX2 is expressed in brain, and NCX3 is expressed in brain and skeletal muscle. The NCX proteins subserve a variety of roles, depending upon the site of expression. These include cardiac excitation-contraction coupling, neuronal signalling and Ca2+ reabsorption in the kidney. The NCKX (Na2+/Ca2+-K+ exchanger) (SLC24) branch of Na+/Ca2+ exchangers transport K+ and Ca2+ in exchange for Na+, and comprises five members: NCKX1 is expressed in retinal rod photoreceptors, NCKX2 is expressed in cone photoreceptors and in neurons throughout the brain, NCKX3 and NCKX4 are abundant in brain, but have a broader tissue distribution, and NCKX5 is expressed in skin, retinal epithelium and brain. The NCKX proteins probably play a particularly prominent role in regulating Ca2+ flux in environments which experience wide and frequent fluctuations in Na+ concentration. Until recently, the range of functions that NCKX proteins play was generally underappreciated. This situation is now changing rapidly as evidence emerges for roles including photoreceptor adaptation, synaptic plasticity and skin pigmentation. The CCX (Ca2+/cation exchanger) branch has only one mammalian member, NCKX6 or NCLX (Na+/Ca2+-Li+ exchanger), whose physiological function remains unclear, despite a broad pattern of expression.
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Affiliation(s)
- Jonathan Lytton
- Department of Biochemistry and Molecular Biology, Libin Cardiovascular Institute of Alberta, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta, Canada T2N 4N1.
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Török TL. Electrogenic Na+/Ca2+-exchange of nerve and muscle cells. Prog Neurobiol 2007; 82:287-347. [PMID: 17673353 DOI: 10.1016/j.pneurobio.2007.06.003] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 04/12/2007] [Accepted: 06/12/2007] [Indexed: 12/19/2022]
Abstract
The plasma membrane Na(+)/Ca(2+)-exchanger is a bi-directional electrogenic (3Na(+):1Ca(2+)) and voltage-sensitive ion transport mechanism, which is mainly responsible for Ca(2+)-extrusion. The Na(+)-gradient, required for normal mode operation, is created by the Na(+)-pump, which is also electrogenic (3Na(+):2K(+)) and voltage-sensitive. The Na(+)/Ca(2+)-exchanger operational modes are very similar to those of the Na(+)-pump, except that the uncoupled flux (Na(+)-influx or -efflux?) is missing. The reversal potential of the exchanger is around -40 mV; therefore, during the upstroke of the AP it is probably transiently activated, leading to Ca(2+)-influx. The Na(+)/Ca(2+)-exchange is regulated by transported and non-transported external and internal cations, and shows ATP(i)-, pH- and temperature-dependence. The main problem in determining the role of Na(+)/Ca(2+)-exchange in excitation-secretion/contraction coupling is the lack of specific (mode-selective) blockers. During recent years, evidence has been accumulated for co-localisation of the Na(+)-pump, and the Na(+)/Ca(2+)-exchanger and their possible functional interaction in the "restricted" or "fuzzy space." In cardiac failure, the Na(+)-pump is down-regulated, while the exchanger is up-regulated. If the exchanger is working in normal mode (Ca(2+)-extrusion) during most of the cardiac cycle, upregulation of the exchanger may result in SR Ca(2+)-store depletion and further impairment in contractility. If so, a normal mode selective Na(+)/Ca(2+)-exchange inhibitor would be useful therapy for decompensation, and unlike CGs would not increase internal Na(+). In peripheral sympathetic nerves, pre-synaptic alpha(2)-receptors may regulate not only the VSCCs but possibly the reverse Na(+)/Ca(2+)-exchange as well.
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Affiliation(s)
- Tamás L Török
- Department of Pharmacodynamics, Semmelweis University, P.O. Box 370, VIII. Nagyvárad-tér 4, H-1445 Budapest, Hungary.
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Cheung JY, Rothblum LI, Moorman JR, Tucker AL, Song J, Ahlers BA, Carl LL, Wang J, Zhang XQ. Regulation of cardiac Na+/Ca2+ exchanger by phospholemman. Ann N Y Acad Sci 2007; 1099:119-34. [PMID: 17446450 DOI: 10.1196/annals.1387.004] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Phospholemman (PLM) is the first sequenced member of the FXYD family of regulators of ion transport. The mature protein has 72 amino acids and consists of an extracellular N terminus containing the signature FXYD motif, a single transmembrane (TM) domain, and a cytoplasmic C-terminal domain containing four potential sites for phosphorylation. PLM and other members of the FXYD family are known to regulate Na+-K+-ATPase. Using adenovirus-mediated gene transfer into adult rat cardiac myocytes, we showed that changes in contractility and intracellular Ca2+ homeostasis associated with PLM overexpression or downregulation are not consistent with the effects expected from inhibition of Na+-K+-ATPase by PLM. Additional studies with heterologous expression of PLM and cardiac Na+/Ca2+ exchanger 1 (NCX1) in HEK293 cells and cardiac myocytes isolated from PLM-deficient mice demonstrated by co-localization, co-immunoprecipitation, and electrophysiological and radioactive tracer uptake techniques that PLM associates with NCX1 in the sarcolemma and transverse tubules and that PLM inhibits NCX1, independent of its effects on Na+-K+-ATPase. Mutational analysis indicates that the cytoplasmic domain of PLM is required for its regulation of NCX1. In addition, experiments using phosphomimetic and phospho-deficient PLM mutants, as well as activators of protein kinases A and C, indicate that PLM phosphorylated at serine68 is the active form that inhibits NCX1. This is in sharp contrast to the finding that the unphosphorylated PLM form inhibits Na+-K+-ATPase. We conclude that PLM regulates cardiac contractility by modulating the activities of NCX and Na+-K+-ATPase.
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Affiliation(s)
- Joseph Y Cheung
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
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Szewczyk MM, Davis KA, Samson SE, Simpson F, Rangachari PK, Grover AK. Ca2+-pumps and Na2+-Ca2+-exchangers in coronary artery endothelium versus smooth muscle. J Cell Mol Med 2007; 11:129-38. [PMID: 17367507 PMCID: PMC4401226 DOI: 10.1111/j.1582-4934.2007.00010.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Vascular endothelial cells (EC) and smooth muscle cells (SMC) require a decrease in cytoplasmic Ca2+ concentration after activation. This can be achieved by Ca2+ sequestration by the sarco-/endoplasmic reticulum Ca2+ pumps (SERCA) and Ca2+ extrusion by plasma membrane Ca2+ pumps (PMCA) and Na+–Ca2+-exchangers (NCX). Since the two cell types differ in their structure and function, we compared the activities of PMCA, NCX and SERCA in pig coronary artery EC and SMC, the types of isoforms expressed using RT-PCR, and their protein abundance using Western blots. The activity of NCX is higher in EC than in SMC but those of PMCA and SERCA is lower. Consistently, the protein abundance for NCX protein is higher in EC than in SMC and those of PMCA and SERCA is lower. Based on RT-PCR experiments, the types of RNA present are as follows: EC for PMCA1 while SMC for PMCA4 and PMCA1; EC for SERCA2 and SERCA3 and SMC for SERCA2. Both EC and SMC express NCX1 (mainly NCX1.3). PMCA, SERCA and NCX differ in their affinities for Ca2+ and regulation. Based on these observations and the literature, we conclude that the tightly regulated Ca2+ removal systems in SMC are consistent with the cyclical control of contractility of the filaments and those in EC are consistent with Ca2+ regulation of the endothelial nitric oxide synthase near the cell surface. The differences between EC and SMC should be considered in therapeutic interventions of cardiovascular diseases.
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Affiliation(s)
- Magdalena M Szewczyk
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
- *Correspondence to Dr A.K. GROVER Department of Medicine, HSC 4N41, McMaster University, 1200 Main Street West Hamilton, Ontario L8N 3Z5 Canada. Tel.: 905-525-9140 x22238 Fax: 905-522-3114 E-mail:
| | - Kim A Davis
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Sue E Samson
- Department of Medicine, McMaster University, Hamilton, Ontario, Canada
| | - Fiona Simpson
- Department of Medicine, McMaster University, Hamilton, Ontario, Canada
| | | | - Ashok K Grover
- Department of Medicine, McMaster University, Hamilton, Ontario, Canada
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
- *Correspondence to Dr A.K. GROVER Department of Medicine, HSC 4N41, McMaster University, 1200 Main Street West Hamilton, Ontario L8N 3Z5 Canada. Tel.: 905-525-9140 x22238 Fax: 905-522-3114 E-mail:
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Bers DM, Ginsburg KS. Na:Ca Stoichiometry and Cytosolic Ca-Dependent Activation of NCX in Intact Cardiomyocytes. Ann N Y Acad Sci 2007; 1099:326-38. [PMID: 17303827 DOI: 10.1196/annals.1387.060] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We are studying both Na:Ca exchange stoichiometry and cytosolic [Ca] ([Ca]i)-dependent regulation of Na-Ca exchange (NCX) in intact rabbit ventricular myocytes. Analysis of NCX fluxes in subcellular systems strongly supports a dominant 3Na:1Ca exchange, and our measurements in intact cells confirm this. However, in intact native cells, local ion gradients and other factors complicate the process of inferring stoichiometry. From a functional viewpoint, NCX stoichiometry is near 3:1 but is affected by ion accumulation/depletion as well as non-NCX fluxes. We and others have viewed [Ca]i-dependent NCX regulation as a static process (dependent on instantaneous local [Ca]i). However, evidence from subcellular and expression systems shows the process to be dynamic, and our observations confirm this to be the case in intact cardiac cells as well.
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Affiliation(s)
- Donald M Bers
- Department of Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Avenue, Maywood, IL 60153, USA.
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Riedel MJ, Baczkó I, Searle GJ, Webster N, Fercho M, Jones L, Lang J, Lytton J, Dyck JRB, Light PE. Metabolic regulation of sodium-calcium exchange by intracellular acyl CoAs. EMBO J 2006; 25:4605-14. [PMID: 16977318 PMCID: PMC1589979 DOI: 10.1038/sj.emboj.7601321] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2006] [Accepted: 08/09/2006] [Indexed: 11/09/2022] Open
Abstract
The sodium-calcium exchanger (NCX) is a critical mediator of calcium homeostasis. In the heart, NCX1 predominantly operates in forward mode to extrude Ca(2+); however, reverse-mode NCX1 activity during ischemia/reperfusion (IR) contributes to Ca(2+) loading and electrical and contractile dysfunction. IR injury has also been associated with altered fat metabolism and accumulation of long-chain acyl CoA esters. Here, we show that acyl CoAs are novel, endogenous activators of reverse-mode NCX1 activity, exhibiting chain length and saturation dependence, with longer chain saturated acyl moieties being the most effective NCX1 activators. These results implicate dietary fat composition as a plausible determinant of IR injury. We further show that acyl CoAs may interact directly with the XIP (exchanger inhibitory peptide) sequence, a known region of anionic lipid modulation, to dynamically regulate NCX1 activity and Ca(2+) homeostasis. Additionally, our findings have broad implications for the coupling of Ca(2+) homeostasis to fat metabolism in a variety of tissues.
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Affiliation(s)
- Michael J Riedel
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - István Baczkó
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology and Pharmacotherapy, Albert Szent-Györgyi Medical Center, University of Szeged, Szeged, Hungary
| | - Gavin J Searle
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Nicola Webster
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Matthew Fercho
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Lynn Jones
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Jessica Lang
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Jonathan Lytton
- Departments of Biochemistry & Molecular Biology and Physiology & Biophysics, University of Calgary, Alberta, Canada
| | - Jason R B Dyck
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
| | - Peter E Light
- Departments of Pharmacology and Pediatrics, University of Alberta, Edmonton, Alberta, Canada
- Department of Pharmacology, Faculty of Medicine and Dentistry, University of Alberta, 9-58 Medical Sciences Bldg, Edmonton, Edmonton, Alberta, Canada T6G 2H7. Tel.: +1 780 492 0638; Fax: +1 780 492 4325; E-mail:
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Dong H, Jiang Y, Triggle CR, Li X, Lytton J. Novel role for K+-dependent Na+/Ca2+ exchangers in regulation of cytoplasmic free Ca2+ and contractility in arterial smooth muscle. Am J Physiol Heart Circ Physiol 2006; 291:H1226-35. [PMID: 16617138 DOI: 10.1152/ajpheart.00196.2006] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Cytoplasmic free Ca2+ ([Ca2+]cyt) is essential for the contraction and relaxation of blood vessels. The role of plasma membrane Na+/Ca2+ exchange (NCX) activity in the regulation of vascular Ca2+ homeostasis was previously ascribed to the NCX1 protein. However, recent studies suggest that a relatively newly discovered K+-dependent Na+/Ca2+ exchanger, NCKX (gene family SLC24), is also present in vascular smooth muscle. The purpose of the present study was to identify the expression and function of NCKX in arteries. mRNA encoding NCKX3 and NCKX4 was demonstrated by RT-PCR and Northern blot in both rat mesenteric and aortic smooth muscle. NCXK3 and NCKX4 proteins were also demonstrated by immunoblot and immunofluorescence. After voltage-gated Ca2+ channels, store-operated Ca2+ channels, and Na+ pump were pharmacologically blocked, when the extracellular Na+ was replaced with Li+ (0 Na+) to induce reverse mode (Ca2+ entry) activity of Na+/Ca2+ exchangers, a large increase in [Ca2+]cyt signal was observed in primary cultured aortic smooth muscle cells. About one-half of this [Ca2+]cyt signal depended on the extracellular K+. In addition, after the activity of NCX was inhibited by KB-R7943, Na+ replacement-induced Ca2+ entry was absolutely dependent on extracellular K+. In arterial rings denuded of endothelium, a significant fraction of the phenylephrine-induced and nifedipine-resistant aortic or mesenteric contraction could be prevented by removal of extracellular K+. Taken together, these data provide strong evidence for the expression of NCKX proteins in the vascular smooth muscle and their novel role in mediating agonist-stimulated [Ca2+]cyt and thereby vascular tone.
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Affiliation(s)
- Hui Dong
- Division of Gastroenterology, Department of Medicine, University of California, San Diego School of Medicine, La Jolla, CA 92093-0063, USA.
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Accardi A, Walden M, Nguitragool W, Jayaram H, Williams C, Miller C. Separate ion pathways in a Cl-/H+ exchanger. ACTA ACUST UNITED AC 2006; 126:563-70. [PMID: 16316975 PMCID: PMC2266597 DOI: 10.1085/jgp.200509417] [Citation(s) in RCA: 162] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
CLC-ec1 is a prokaryotic CLC-type Cl−/H+ exchange transporter. Little is known about the mechanism of H+ coupling to Cl−. A critical glutamate residue, E148, was previously shown to be required for Cl−/H+ exchange by mediating proton transfer between the protein and the extracellular solution. To test whether an analogous H+ acceptor exists near the intracellular side of the protein, we performed a mutagenesis scan of inward-facing carboxyl-bearing residues and identified E203 as the unique residue whose neutralization abolishes H+ coupling to Cl− transport. Glutamate at this position is strictly conserved in all known CLCs of the transporter subclass, while valine is always found here in CLC channels. The x-ray crystal structure of the E203Q mutant is similar to that of the wild-type protein. Cl− transport rate in E203Q is inhibited at neutral pH, and the double mutant, E148A/E203Q, shows maximal Cl− transport, independent of pH, as does the single mutant E148A. The results argue that substrate exchange by CLC-ec1 involves two separate but partially overlapping permeation pathways, one for Cl− and one for H+. These pathways are congruent from the protein's extracellular surface to E148, and they diverge beyond this point toward the intracellular side. This picture demands a transport mechanism fundamentally different from familiar alternating-access schemes.
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Affiliation(s)
- Alessio Accardi
- Department of Biochemistry, Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02454, USA
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Egger M, Porzig H, Niggli E, Schwaller B. Rapid turnover of the "functional" Na(+)-Ca2+ exchanger in cardiac myocytes revealed by an antisense oligodeoxynucleotide approach. Cell Calcium 2005; 37:233-43. [PMID: 15670870 DOI: 10.1016/j.ceca.2004.10.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2004] [Revised: 10/07/2004] [Accepted: 10/12/2004] [Indexed: 11/28/2022]
Abstract
Antisense oligodeoxynucleotides (AS-ODNs) were used in combination with transient functional expression of the cardiac Na(+)-Ca2+ exchanger (NCX1) to correlate suppression of the Na(+)-Ca2+ exchange function with down-regulation of NCX1 protein expression. In a de-novo expression system (Sf9 cells), a decrease in both, NCX1 mRNA and protein after AS-ODN application was paralleled by diminished NCX1 activity, a typical hallmark of a true "antisense effect". Although AS-ODN uptake was also efficient in rat neonatal cardiac myocytes, in whole-cell extracts of these cells treated with AS-ODNs, the amount of NCX1 protein determined in a quantitative binding assay remained almost unchanged, despite a prompt loss of NCX1 function. Immunocytochemical staining of myocytes revealed that most of the immunoreactivity was not localized in the plasma membrane, but in intracellular compartments and was barely affected by AS-ODN treatment. These results indicate that the "functional half-life" of the NCX1 protein in the plasma membrane of neonatal cardiac myocytes is surprisingly short, much shorter than reported half-lifes of about 30 h for other membrane proteins.
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Affiliation(s)
- Marcel Egger
- University of Bern, Department of Physiology, Bühlplatz 5, CH-3012 Bern, Switzerland.
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Baczkó I, Jones L, McGuigan CF, Manning Fox JE, Gandhi M, Giles WR, Clanachan AS, Light PE. Plasma membrane KATP channel-mediated cardioprotection involves posthypoxic reductions in calcium overload and contractile dysfunction: mechanistic insights into cardioplegia. FASEB J 2005; 19:980-2. [PMID: 15774423 DOI: 10.1096/fj.04-3008fje] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Our recent data demonstrate that activation of pmKATP channels polarizes the membrane of cardiomyocytes and reduces Na+/Ca2+ exchange-mediated Ca2+ overload. However, it is important that these findings be extended into contractile models of hypoxia/reoxygenation injury to further test the notion that pmKATP channel activation affords protection against contractile dysfunction and calcium overload. Single rat heart right ventricular myocytes were enzymatically isolated, and cell contractility and Ca2+ transients in field-stimulated myocytes were measured in a cellular model of metabolic inhibition and reoxygenation. Activation of pmKATP with P-1075 (5 microM) or inhibition of the Na+/Ca2+ exchanger with KB-R7943 (5 microM)reduced reoxygenation-induced diastolic Ca2+ overload and improved the rate and magnitude of posthypoxic contractile recovery during the first few minutes of reoxygenation. Moreover,diastolic Ca2+ overload and posthypoxic contractile dysfunction were aggravated in ventricular myocytes either subjected to specific blockade of pmKATP with HMR1098 (20 microM) or expressing the dominant-negative pmKATP construct Kir6.2(AAA) in the presence of P-1075. Our results suggest that a common mechanism, involving resting membrane potential-modulated increases in diastolic [Ca2+]i, is responsible for the development of contractile dysfunction during reoxygenation following metabolic inhibition. This novel and highly plausible cellular mechanism for pmKATP-mediated cardioprotection may have direct clinical relevance as evidenced by the following findings: a hypokalemic polarizing cardioplegia solution supplemented with the pmKATP opener P-1075 improved Ca2+ homeostasis and recovery of function compared with hyperkalemic depolarizing St. Thomas' cardioplegia following contractile arrest in single ventricular myocytes and working rat hearts. We therefore propose that activation of pmKATP channels improves posthypoxic cardiac function via reductions in abnormal diastolic Ca2+ homeostasis mediated by reverse-mode Na+/Ca2+ exchange.
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Affiliation(s)
- István Baczkó
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
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Xiao YF, Ke Q, Chen Y, Morgan JP, Leaf A. Inhibitory effect of n-3 fish oil fatty acids on cardiac Na+/Ca2+ exchange currents in HEK293t cells. Biochem Biophys Res Commun 2004; 321:116-23. [PMID: 15358223 DOI: 10.1016/j.bbrc.2004.06.114] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2004] [Indexed: 10/26/2022]
Abstract
Abnormal activity of the cardiac Na+/Ca2+ exchanger (NCX1) can affect intracellular Ca2+ homeostasis and cause arrhythmias. The n-3 polyunsaturated fatty acids (PUFAs), however, may prevent arrhythmias. To test the effect of PUFAs on the cardiac NCX1 current (I(NCX1)), the canine NCX1 cDNA was expressed in human embryonic kidney (HEK293t) cells. The average density of I(NCX1) was 10.9+/-2.6 pA/pF (n=44) in NCX1-transfected cells and eicosapentaenoic acid (EPA, C20:5n-3) significantly inhibited I(NCX1) The suppression of I(NCX1) by EPA was concentration-dependent with an IC50 of 0.82+/-0.27 microM. EPA had a similar effect on outward or inward I(NCX1). Docosahexaenoic acid (DHA, C22:6n-3) and arachidonic acid (AA, C20:4n-6) also significantly inhibited I(NCX1), whereas the saturated fatty acid, stearic acid (SA, C18:0), did not. Our data demonstrate that the n-3 PUFAs significantly suppress cardiac I(NCX1), which is probably one of their protective effects against lethal arrhythmias.
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Hinata M, Kimura J. Forefront of Na+/Ca2+ exchanger studies: stoichiometry of cardiac Na+/Ca2+ exchanger; 3:1 or 4:1? J Pharmacol Sci 2004; 96:15-8. [PMID: 15359081 DOI: 10.1254/jphs.fmj04002x3] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
The stoichiometry of the Na+/Ca2+ exchanger (NCX) had been generally accepted as 3 Na+:1 Ca2+. However, recently a challenging stoichiometry of 4:1 was proposed. Therefore, using guinea pig ventricular cells, we re-examined the stoichiometry by measuring the reversal potential of the NCX current and intracellular Ca2+ concentrations under the whole-cell voltage clamp. We confirmed that the stoichiometry of NCX is 3:1 not 4:1. In addition, we explored the possible reasons for obtaining erroneous results of a 4:1 stoichiometry.
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Affiliation(s)
- Masamitsu Hinata
- Department of Pharmacology, School of Medicine, Fukushima Medical University, Japan
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Uehara A, Iwamoto T, Nakamura Y, Imanaga I. Forefront of Na+/Ca2+ exchanger studies: physiology and molecular biology of monovalent cation sensitivities in Na+/Ca2+ exchangers. J Pharmacol Sci 2004; 96:19-22. [PMID: 15359082 DOI: 10.1254/jphs.fmj04002x4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Sensitivities of the reverse-mode Na+/Ca2+ exchange activity measured as the Na+i-dependent Ca2+ uptake to extracellular monovalent cations K+, Li+, and Na+ were compared between the K+ -dependent (NCKX2) and the K+ -independent Na+/Ca2+ exchanger (NCX1) overexpressed in a fibroblast cell. Interestingly, the exchange activity of NCKX2 was not influenced by Li+ while it was increased by K+. On the contrary, the activity of NCX1 was increased by Li+. Thus, the cation sensitivities to K+ and Li+ markedly differed between NCKX2 and NCX1. In addition, Na+ exerted a significantly smaller inhibitory effect on the activity in NCKX2 than in NCX1. The Na+/Ca2+ exchange activities of NCKX2 and NCX1 are considered to be regulated differentially via the respective binding site domains that have distinct sensitivities to the external monovalent cations.
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Affiliation(s)
- Akira Uehara
- Department of Physiology, School of Medicine, Fukuoka University, 7-chome Nanakuma, Jonan-ku, Japan.
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Kiedrowski L, Czyz A, Baranauskas G, Li XF, Lytton J. Differential contribution of plasmalemmal Na/Ca exchange isoforms to sodium-dependent calcium influx and NMDA excitotoxicity in depolarized neurons. J Neurochem 2004; 90:117-28. [PMID: 15198672 DOI: 10.1111/j.1471-4159.2004.02462.x] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Inhibition of Na(+),K(+)-ATPase during NMDA applications greatly increased NMDA-induced excitotoxicity in primary cultures of forebrain neurons (FNs), but not in cerebellar granule cells (CGCs). Because Na(+),K(+)-ATPase inhibition promotes reversal of plasmalemmal Na(+)/Ca(2+) exchangers, we compared the activities of reversed K(+)-independent (NCX) and K(+)-dependent (NCKX) Na(+)/Ca(2+) exchangers in these cultures. To this end, we measured gramicidin-induced and Na(+)-dependent elevation in cytosolic [Ca(2+)] ([Ca(2+)](c)) that represents Ca(2+) influx via reversed NCX and NCKX; NCX activity was dissected out by removing external K(+). The [Ca(2+)](c) elevations mediated by NCX alone, and NCX plus NCKX combined, were 17 and 6 times more rapid in FNs than in CGCs, respectively. Northern blot analysis showed that FNs preferentially express NCX1 whereas CGCs expressed NCX3. Differences in expression of other isoforms (NCX2, NCKX2, NCKX3 and NCKX4) were less pronounced. We tested whether the NCX or NCKX family of exchangers contributes most to the toxic NMDA-induced Ca(2+) influx in depolarized neurons. We found that in FNs, inhibition of NCX alone was sufficient to significantly limit NMDA excitotoxicity, whereas in CGCs, inhibition of both NCX and NCKX was required. The data suggest that the high activity of NCX isoforms expressed in FNs, possibly NCX1, sensitizes these neurons to NMDA excitotoxicity.
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Affiliation(s)
- Lech Kiedrowski
- The Psychiatric Institute, Department of Psychiatry, The University of Illinois at Chicago, Chicago, Illinois, USA.
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Cai X, Lytton J. The cation/Ca(2+) exchanger superfamily: phylogenetic analysis and structural implications. Mol Biol Evol 2004; 21:1692-703. [PMID: 15163769 DOI: 10.1093/molbev/msh177] [Citation(s) in RCA: 157] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Cation/Ca(2+) exchangers are an essential component of Ca(2+) signaling pathways and function to transport cytosolic Ca(2+) across membranes against its electrochemical gradient by utilizing the downhill gradients of other cation species such as H(+), Na(+), or K(+). The cation/Ca(2+) exchanger superfamily is composed of H(+)/Ca(2+) exchangers and Na(+)/Ca(2+) exchangers, which have been investigated extensively in both plant cells and animal cells. Recently, information from completely sequenced genomes of bacteria, archaea, and eukaryotes has revealed the presence of genes that encode homologues of cation/Ca(2+) exchangers in many organisms in which the role of these exchangers has not been clearly demonstrated. In this study, we report a comprehensive sequence alignment and the first phylogenetic analysis of the cation/Ca(2+) exchanger superfamily of 147 sequences. The results present a framework for structure-function relationships of cation/Ca(2+) exchangers, suggesting unique signature motifs of conserved residues that may underlie divergent functional properties. Construction of a phylogenetic tree with inclusion of cation/Ca(2+) exchangers with known functional properties defines five protein families and the evolutionary relationships between the members. Based on this analysis, the cation/Ca(2+) exchanger superfamily is classified into the YRBG, CAX, NCX, and NCKX families and a newly recognized family, designated CCX. These findings will provide guides for future studies concerning structures, functions, and evolutionary origins of the cation/Ca(2+) exchangers.
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Affiliation(s)
- Xinjiang Cai
- The Cardiovascular Research Group, Departments of Biochemistry and Molecular Biology and Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada.
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40
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Kang TM, Hilgemann DW. Multiple transport modes of the cardiac Na+/Ca2+ exchanger. Nature 2004; 427:544-8. [PMID: 14765196 DOI: 10.1038/nature02271] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2003] [Accepted: 12/05/2003] [Indexed: 11/08/2022]
Abstract
The cardiac Na+/Ca2+ exchanger (NCX1; ref. 2) is a bi-directional Ca2+ transporter that contributes to the electrical activity of the heart. When, and if, Ca2+ is exported or imported depends on the Na+/Ca2+ exchange ratio. Whereas a ratio of 3:1 (Na+:Ca2+) has been indicated by Ca2+ flux equilibrium studies, a ratio closer to 4:1 has been indicated by exchange current reversal potentials. Here we show, using an ion-selective electrode technique to quantify ion fluxes in giant patches, that ion flux ratios are approximately 3.2 for maximal transport in either direction. With Na+ and Ca2+ on both sides of the membrane, net current and Ca2+ flux can reverse at different membrane potentials, and inward current can be generated in the absence of cytoplasmic Ca2+, but not Na+. We propose that NCX1 can transport not only 1 Ca2+ or 3 Na+ ions, but also 1 Ca2+ with 1 Na+ ion at a low rate. Therefore, in addition to the major 3:1 transport mode, import of 1 Na+ with 1 Ca2+ defines a Na+-conducting mode that exports 1 Ca2+, and an electroneutral Ca2+ influx mode that exports 3 Na+. The two minor transport modes can potentially determine resting free Ca2+ and background inward current in heart.
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Affiliation(s)
- Tong Mook Kang
- Department of Physiology, Center for Molecular Medicine, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Korea
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41
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Cai X, Lytton J. Molecular cloning of a sixth member of the K+-dependent Na+/Ca2+ exchanger gene family, NCKX6. J Biol Chem 2003; 279:5867-76. [PMID: 14625281 DOI: 10.1074/jbc.m310908200] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bioinformatic and molecular cloning tools were used to identify and isolate cDNA clones from mouse and human tissues that encode the sixth member of the K(+)-dependent Na+/Ca2+ exchanger family, NCKX6. The mouse NCKX6 protein is 585 amino acids long and shares about 62% sequence similarity with previously identified exchangers in the alpha-repeat regions but has little primary sequence similarity outside these regions. NCKX6 transcripts of 4 kb are abundantly expressed in all tissues examined and are thus more broadly distributed than previously described NC(K)X family members. Two alternatively spliced products of this novel gene were identified that encode proteins of different length. The short isoform differs from the full-length isoform at the C-terminal hydrophobic domain as a result of a shift in the reading frame caused by the deletion of two exons. Both NCKX6 isoforms were expressed in HEK-293 cells. Functional analysis by digital imaging of fura-2 loaded transfected HEK-293 cells demonstrated that the short isoform exhibited K(+)-dependent Na+/Ca2+ exchange activity whereas the full-length isoform did not. The latter was retained within the endoplasmic reticulum, whereas the short isoform was present at the plasma membrane in transfected cells. Immunofluorescence studies examining NCKX6 expression in native tissue using an NCKX6-specific antibody showed intense labeling of the cardiac sarcolemmal membrane. The discovery of NCKX6 therefore reveals a novel member of the Na+/Ca2+ exchanger superfamily whose ubiquitous expression in all tissues suggests an important role for K(+)-dependent Na+/Ca2+ exchange in maintaining cellular Ca2+ homeostasis in diverse tissues and cell types.
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Affiliation(s)
- Xinjiang Cai
- Cardiovascular Research Group, Department of Biochemistry and Molecular Biology, University of Calgary, Calgary, Alberta T2N 4N1, Canada
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42
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Reeves JP, Condrescu M. Allosteric activation of sodium-calcium exchange activity by calcium: persistence at low calcium concentrations. J Gen Physiol 2003; 122:621-39. [PMID: 14581586 PMCID: PMC2229582 DOI: 10.1085/jgp.200308915] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2003] [Accepted: 10/03/2003] [Indexed: 11/25/2022] Open
Abstract
The activity of the cardiac Na+/Ca2+ exchanger is stimulated allosterically by Ca2+, but estimates of the half-maximal activating concentration have varied over a wide range. In Chinese hamster ovary cells expressing the cardiac Na+/Ca2+ exchanger, the time course of exchange-mediated Ca2+ influx showed a pronounced lag period followed by an acceleration of Ca2+ uptake. Lag periods were absent in cells expressing an exchanger mutant that was not dependent on regulatory Ca2+ activation. We assumed that the rate of Ca2+ uptake during the acceleration phase reflected the degree of allosteric activation of the exchanger and determined the value of cytosolic Ca2+ ([Ca2+]i) at which the rate of Ca2+ influx was half-maximal (Kh). After correcting for the effects of mitochondrial Ca2+ uptake and fura-2 buffering, Kh values of approximately 300 nM were obtained. After an increase in [Ca2+]i, the activated state of the exchanger persisted following a subsequent reduction in [Ca2+]i to values <100 nM. Thus, within 30 s after termination of a transient increase in [Ca2+]i, exchange-mediated Ca2+ entry began without a lag period and displayed a linear rate of Ca2+ uptake in most cells; a sigmoidal time course of Ca2+ uptake returned 60-90 s after the transient increase in [Ca2+]i was terminated. Relaxation of the activated state was accelerated by the activity of the endoplasmic reticulum Ca2+ pump, suggesting that local Ca2+ gradients contribute to maintaining exchanger activation after the return of global [Ca2+]i to low values.
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Affiliation(s)
- John P Reeves
- Department of Pharmacology and Physiology, UMDNJ - NJ Medical School, Newark, NJ 07101-1709, USA.
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43
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Baczkó I, Giles WR, Light PE. Resting membrane potential regulates Na(+)-Ca2+ exchange-mediated Ca2+ overload during hypoxia-reoxygenation in rat ventricular myocytes. J Physiol 2003; 550:889-98. [PMID: 12807988 PMCID: PMC2343092 DOI: 10.1113/jphysiol.2003.043372] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
In the heart, reperfusion following an ischaemic episode can result in a marked increase in [Ca2+]i and cause myocyte dysfunction and death. Although the Na(+)-Ca2+ exchanger has been implicated in this response, the ionic mechanisms that are responsible have not been identified. In this study, the hypothesis that the diastolic membrane potential can influence Na(+)-Ca2+ exchange and Ca2+ homeostasis during chemically induced hypoxia-reoxygenation has been tested using right ventricular myocytes isolated from adult rat hearts. Superfusion with selected [K+]o of 0.5, 2.5, 5, 7, 10 and 15 mM yielded the following resting membrane potentials: -27.6+/-1.63 mV, -102.2+/-1.89, -86.5+/-1.03, -80.1+/-1.25, -73.6+/-1.02 and -66.4+/-1.03, respectively. In a second set of experiments myocytes were subjected to chemically induced hypoxia-reoxygenation at these different [K+]o, while [Ca2+]i was monitored using fura-2. These results demonstrated that after chemically induced hypoxia-reoxygenation had caused a marked increase in [Ca2+]i, hyperpolarization of myocytes with 2.5 mM [K+]o significantly reduced [Ca2+]i (7.5+/-0.32 vs. 16.9+/-0.55%); while depolarization (with either 0.5 or 15 mM [K+]o) significantly increased [Ca2+]i (31.8+/-3.21 and 20.8+/-0.36 vs. 16.9+/-0.55%, respectively). As expected, at depolarized membrane potentials myocyte hypercontracture and death increased in parallel with Ca2+ overload. The involvement of the Na(+)-Ca2+ exchanger in Ca2+ homeostasis was evaluated using the Na(+)-Ca2+ exchanger inhibitor KB-R7943. During reoxygenation KB-R7943 (5 microM) almost completely prevented the increase in [Ca2+]i both in control conditions (in 5 mM [K+]o: 2.2+/-0.40 vs. 10.8+/-0.14%) and in depolarized myocytes (in 15 mM [K+]o: -2.1+/-0.51 vs. 11.3+/-0.05%). These findings demonstrate that the resting membrane potential of ventricular myocytes is a critical determinant of [Ca2+]i during hypoxia-reoxygenation. This appears to be due mainly to an effect of diastolic membrane potential on the Na(+)-Ca2+ exchanger, since at depolarized potentials this exchanger mechanism operates in the reverse mode, causing a significant Ca2+ influx.
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Affiliation(s)
- István Baczkó
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada
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44
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Abstract
Na+ influx via INa during cardiac action potentials can raise bulk [Na+]i by 10 to 15 micromol/L. However, larger rises in submembrane [Na+] ([Na+]sm) local to Na+-Ca2+ exchangers (NCX) could enhance Ca2+ influx via NCX (and Ca2+-induced Ca2+ release). We tested whether INa could increase [Na+]sm, using NCX current (INCX) as a biosensor in rabbit ventricular myocytes (with [Ca2+]i buffered, [Na+]i=10 mmol/L, and other currents blocked). We measured INCX as early as 5 ms after INa. Prior INa activation did not affect INCX at physiological membrane potentials (Em=-100 to +50 mV), but for Em >+50 mV (where INCX is especially sensitive to [Na+]i), INCX shifted outward. At 5 ms and +100 mV, INa shifted INCX outward by 0.23 A/F (corresponding to Delta[Na+]sm=0.24 mmol/L). The effect of INa dissipated with a time constant of approximately 15 ms. Thus, the impact of INa on NCX is almost undetectable at physiological Em and short lived. This suggests that INa effects on excitation-contraction coupling (via outward INCX) are minimal and limited to early during the action potential. However, local Delta[Na+]sm during INa may be 60 times higher than bulk Delta[Na+]i.
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Affiliation(s)
- Christopher R Weber
- Department of Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave, Maywood, Ill 60153, USA
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45
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Kang TM, Markin VS, Hilgemann DW. Ion fluxes in giant excised cardiac membrane patches detected and quantified with ion-selective microelectrodes. J Gen Physiol 2003; 121:325-47. [PMID: 12668735 PMCID: PMC2217369 DOI: 10.1085/jgp.200208777] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
We have used ion-selective electrodes (ISEs) to quantify ion fluxes across giant membrane patches by measuring and simulating ion gradients on both membrane sides. Experimental conditions are selected with low concentrations of the ions detected on the membrane side being monitored. For detection from the cytoplasmic (bath) side, the patch pipette is oscillated laterally in front of an ISE. For detection on the extracellular (pipette) side, ISEs are fabricated from flexible quartz capillary tubing (tip diameters, 2-3 microns), and an ISE is positioned carefully within the patch pipette with the tip at a controlled distance from the mouth of the patch pipette. Transport activity is then manipulated by solution changes on the cytoplasmic side. Ion fluxes can be quantified by simulating the ion gradients with appropriate diffusion models. For extracellular (intrapatch pipette) recordings, ion diffusion coefficients can be determined from the time courses of concentration changes. The sensitivity and utility of the methods are demonstrated with cardiac membrane patches by measuring (a) potassium fluxes via ion channels, valinomycin, and Na/K pumps; (b) calcium fluxes mediated by Na/Ca exchangers; (c) sodium fluxes mediated by gramicidin and Na/K pumps; and (d) proton fluxes mediated by an unknown electrogenic mechanism. The potassium flux-to-current ratio for the Na/K pump is approximately twice that determined for potassium channels and valinomycin, as expected for a 3Na/2K pump stoichiometery (i.e., 2K/charge moved). For valinomycin-mediated potassium currents and gramicidin-mediated sodium currents, the ion fluxes calculated from diffusion models are typically 10-15% smaller than expected from the membrane currents. As presently implemented, the ISE methods allow reliable detection of calcium and proton fluxes equivalent to monovalent cation currents <1 pA in magnitude, and they allow detection of sodium and potassium fluxes equivalent to <5 pA currents. The capability to monitor ion fluxes, independent of membrane currents, should facilitate studies of both electrogenic and electroneutral ion-coupled transporters in giant patches.
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Affiliation(s)
- Tong Mook Kang
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390-9040, USA
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46
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Cai X, Zhang K, Lytton J. A novel topology and redox regulation of the rat brain K+-dependent Na+/Ca2+ exchanger, NCKX2. J Biol Chem 2002; 277:48923-30. [PMID: 12377762 DOI: 10.1074/jbc.m208818200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In this study we have examined the roles of endogenous cysteine residues in the rat brain K(+)-dependent Na(+)/Ca(2+) exchanger protein, NCKX2, by site-directed mutagenesis. We found that mutation of Cys-614 or Cys-666 to Ala inhibited expression of the exchanger protein in HEK-293 cells, but not in an in vitro translation system. We speculated that Cys-614 and Cys-666 might form an extracellular disulfide bond that stabilized protein structure. Such an arrangement would place the C terminus of the exchanger outside the cell, contrary to the original topological model. This hypothesis was tested by adding a hemagglutinin A epitope to the C terminus of the protein. The hemagglutinin A epitope could be recognized with a specific antibody without permeabilization of the cell membrane, supporting an extracellular location for the C terminus. Additionally, the exchanger molecule could be labeled with biotin maleimide only following extracellular application of beta-mercaptoethanol. Surprisingly, mutation of Cys-395, located in the large intracellular loop, to Ala, prevented reduction-dependent labeling of the protein. The activity of wild-type exchanger, but not the Cys-395 --> Ala mutant, was stimulated after application of beta-mercaptoethanol. Co-immunoprecipitation experiments demonstrated self-association between wild-type and FLAG-tagged exchanger proteins that could not be inhibited by Cys-395 --> Ala mutation. These results suggest that NCKX2 associates as a dimer, an interaction that does not require, but may be stabilized by, a disulfide linkage through Cys-395. This linkage, perhaps by limiting protein mobility along the dimer interface, reduces the transport activity of NCKX2.
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Affiliation(s)
- Xinjiang Cai
- Cardiovascular Research Group, Department of Biochemistry and Molecular Biology, University of Calgary, Alberta T2N 4N1, Canada
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47
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Li XF, Kraev AS, Lytton J. Molecular cloning of a fourth member of the potassium-dependent sodium-calcium exchanger gene family, NCKX4. J Biol Chem 2002; 277:48410-7. [PMID: 12379639 DOI: 10.1074/jbc.m210011200] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We report here the identification and characterization of a fourth member of the potassium-dependent sodium-calcium exchanger gene family, NCKX4 (gene SLC24A4), which mapped to the chromosomal region 14q32. Human NCKX4 encoded a protein of 605 amino acids that displayed a high level of sequence identity to previously described family members, rod NCKX1 (gene SLC24A1), cone/neuronal NCKX2 (gene SLC24A2), and ubiquitous NCKX3 (gene SLC24A3), in the hydrophobic regions surrounding the alpha-repeat sequences thought to form the ion-binding pocket used for transport. The protein product of the NCKX4 gene shared the highest level of amino acid identity, as well as an almost identical arrangement of exon boundaries, with NCKX3, indicating that these two genes have arisen from a recent duplication event. NCKX4 transcripts were abundantly expressed in all brain regions, aorta, lung, and thymus, as well as at a lower level in many other tissues. The NCKX4 protein demonstrated potassium-dependent sodium calcium exchanger activity when assayed in transfected HEK293 cells using digital imaging of fura-2 fluorescence. The discovery of NCKX4, as far as can be ascertained from the current version of the human genome sequence, completes the mammalian potassium-dependent sodium-calcium exchanger gene family.
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Affiliation(s)
- Xiao-Fang Li
- Department of Biochemistry and Molecular Biology, University of Calgary, Alberta T2N 4N1, Canada
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48
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Hinata M, Yamamura H, Li L, Watanabe Y, Watano T, Imaizumi Y, Kimura J. Stoichiometry of Na+-Ca2+ exchange is 3:1 in guinea-pig ventricular myocytes. J Physiol 2002; 545:453-61. [PMID: 12456825 PMCID: PMC2290698 DOI: 10.1113/jphysiol.2002.025866] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In single guinea-pig ventricular myocytes, we examined the stoichiometry of Na(+)-Ca(2+) exchange (NCX) by measuring the reversal potential (E(NCX)) of NCX current (I(NCX)) and intracellular Ca(2+) concentration ([Ca(2+)](i)) with the whole-cell voltage-clamp technique and confocal microscopy, respectively. With given ionic concentrations in the external and pipette solutions, the predicted E(NCX) were -73 and -11 mV at 3:1 and 4:1 stoichiometries, respectively. E(NCX) measured were -69 +/- 2 mV (n = 11), -47 +/- 1 mV (n = 14) and -15 +/- 1 mV (n = 15) at holding potentials (HP) of -73, -42 and -11 mV, respectively. Thus, E(NCX) almost coincided with HP, indicating that [Ca(2+)](i) and/or [Na(+)](i) changed due to I(NCX) flow. Shifts of E(NCX) (deltaE(NCX)) were measured by changing [Ca(2+)](o) or [Na(+)](o). The measured values of deltaE(NCX) were almost always smaller than those expected theoretically at a stoichiometry of either 3:1 or 4:1. Using indo-1 fluorescence, [Ca(2+)](i) measured under the whole-cell voltage-clamp supported a 3:1 but not 4:1 stoichiometry. To prevent Ca(2+) accumulation, we inhibited I(NCX) with Ni(2+) and re-examined E(NCX) during washing out Ni(2+). With HP at predicted E(NCX) at a 3:1 stoichiometry, E(NCX) developed was close to predicted E(NCX) and did not change with time. However, with HP at predicted E(NCX) for a 4:1 stoichiometry, E(NCX) developed initially near a predicted E(NCX) for a 3:1 stoichiometry and shifted toward E(NCX) for a 4:1 stoichiometry with time. We conclude that the stoichiometry of cardiac NCX is 3:1.
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Affiliation(s)
- Masamitsu Hinata
- Department of Pharmacology, School of Medicine, School of Nursing, Fukushima Medical University, Fukushima 960-1295, Japan.
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Affiliation(s)
- Jonathan Lytton
- Department of Biochemistry and Molecular Biology, University of Calgary Health Sciences Centre, 3330 Hospital Drive NW, Calgary, AB, Canada T2N 4N1.
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Abstract
Expression of cDNA encoding the rat heart NCX1.1 protein in HEK-293 cells provides a simple system in which properties of the expressed protein can be determined in the absence of contaminating ionic conductances or parallel transport pathways. Using this system, we have determined that NCX1.1 transports 4 Na(+) in exchange for 1 Ca(2+) and accompanied by the movement of 2 positive charges. The measured stoichiometry is constant over a range of different intracellular Na(+) and Ca(2+) concentrations, independent of the nature of the Ca(2+) buffer used and not affected by the direction of the applied voltage ramp. We conclude that our measurements are unlikely to be confounded by poor control over ionic conditions close to the intracellular surface of the membrane. A stoichiometry of 4:1 for NCX1 has important implications for models of the role of NCX1 in cellular Ca(2+) handling and suggests that in the heart the exchanger will be cardioprotective over a wider range of conditions and have a greater contribution to action potential shape than previously appreciated.
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Affiliation(s)
- Jonathan Lytton
- Cardiovascular Research Group, Department of Biochemistry Molecular Biology, University of Calgary, Calgary, AB, Canada T2N 4N1.
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