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Contreras RG, Torres-Carrillo A, Flores-Maldonado C, Shoshani L, Ponce A. Na +/K +-ATPase: More than an Electrogenic Pump. Int J Mol Sci 2024; 25:6122. [PMID: 38892309 PMCID: PMC11172918 DOI: 10.3390/ijms25116122] [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: 03/26/2024] [Revised: 05/20/2024] [Accepted: 05/23/2024] [Indexed: 06/21/2024] Open
Abstract
The sodium pump, or Na+/K+-ATPase (NKA), is an essential enzyme found in the plasma membrane of all animal cells. Its primary role is to transport sodium (Na+) and potassium (K+) ions across the cell membrane, using energy from ATP hydrolysis. This transport creates and maintains an electrochemical gradient, which is crucial for various cellular processes, including cell volume regulation, electrical excitability, and secondary active transport. Although the role of NKA as a pump was discovered and demonstrated several decades ago, it remains the subject of intense research. Current studies aim to delve deeper into several aspects of this molecular entity, such as describing its structure and mode of operation in atomic detail, understanding its molecular and functional diversity, and examining the consequences of its malfunction due to structural alterations. Additionally, researchers are investigating the effects of various substances that amplify or decrease its pumping activity. Beyond its role as a pump, growing evidence indicates that in various cell types, NKA also functions as a receptor for cardiac glycosides like ouabain. This receptor activity triggers the activation of various signaling pathways, producing significant morphological and physiological effects. In this report, we present the results of a comprehensive review of the most outstanding studies of the past five years. We highlight the progress made regarding this new concept of NKA and the various cardiac glycosides that influence it. Furthermore, we emphasize NKA's role in epithelial physiology, particularly its function as a receptor for cardiac glycosides that trigger intracellular signals regulating cell-cell contacts, proliferation, differentiation, and adhesion. We also analyze the role of NKA β-subunits as cell adhesion molecules in glia and epithelial cells.
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Affiliation(s)
| | | | | | | | - Arturo Ponce
- Department of Physiology, Biophysics and Neurosciences, CINVESTAV-IPN, Mexico City 07360, Mexico; (R.G.C.); (A.T.-C.); (C.F.-M.); (L.S.)
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2
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Manoj KM, Gideon DA, Bazhin NM, Tamagawa H, Nirusimhan V, Kavdia M, Jaeken L. Na,K-ATPase: A murzyme facilitating thermodynamic equilibriums at the membrane-interface. J Cell Physiol 2023; 238:109-136. [PMID: 36502470 DOI: 10.1002/jcp.30925] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Revised: 11/08/2022] [Accepted: 11/14/2022] [Indexed: 12/14/2022]
Abstract
The redox metabolic paradigm of murburn concept advocates that diffusible reactive species (DRS, particularly oxygen-centric radicals) are mainstays of physiology, and not mere pathological manifestations. The murburn purview of cellular function also integrates the essential principles of bioenergetics, thermogenesis, homeostasis, electrophysiology, and coherence. In this context, any enzyme that generates/modulates/utilizes/sustains DRS functionality is called a murzyme. We have demonstrated that several water-soluble (peroxidases, lactate dehydrogenase, hemogoblin, etc.) and membrane-embedded (Complexes I-V in mitochondria, Photosystems I/II in chloroplasts, rhodopsin/transducin in rod cells, etc.) proteins serve as murzymes. The membrane protein of Na,K-ATPase (NKA, also known as sodium-potassium pump) is the focus of this article, owing to its centrality in neuro-cardio-musculo electrophysiology. Herein, via a series of critical queries starting from the geometric/spatio-temporal considerations of diffusion/mass transfer of solutes in cells to an update on structural/distributional features of NKA in diverse cellular systems, and from various mechanistic aspects of ion-transport (thermodynamics, osmoregulation, evolutionary dictates, etc.) to assays/explanations of inhibitory principles like cardiotonic steroids (CTS), we first highlight some unresolved problems in the field. Thereafter, we propose and apply a minimalist murburn model of trans-membrane ion-differentiation by NKA to address the physiological inhibitory effects of trans-dermal peptide, lithium ion, volatile anesthetics, confirmed interfacial DRS + proton modulators like nitrophenolics and unsaturated fatty acid, and the diverse classes of molecules like CTS, arginine, oximes, etc. These explanations find a pan-systemic connectivity with the inhibitions/uncouplings of other membrane proteins in cells.
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Affiliation(s)
- Kelath Murali Manoj
- Satyamjayatu: The Science & Ethics Foundation, Kulappully, Shoranur-2, Kerala, India
| | - Daniel A Gideon
- Satyamjayatu: The Science & Ethics Foundation, Kulappully, Shoranur-2, Kerala, India
| | - Nikolai M Bazhin
- Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Novosibirsk, Russia
| | - Hirohisa Tamagawa
- Department of Mechanical Engineering, Gifu University, Gifu City, Japan
| | - Vijay Nirusimhan
- Satyamjayatu: The Science & Ethics Foundation, Kulappully, Shoranur-2, Kerala, India
| | - Mahendra Kavdia
- Department of Biomedical Engineering, Wayne State University, Detroit, Michigan, USA
| | - Laurent Jaeken
- Department of Industrial Sciences and Technology, Karel de Grote-Hogeschool, Antwerp University Association, Antwerp, Belgium
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Schor NF, Scott P, Litvina EY, Torborg C, Kim JL, Zalutsky R, Adams AB. Planning and Implementing Strategically: Year 1 of the NINDS 2021-2026 Strategic Plan. Neurology 2022; 99:1099-1107. [PMID: 36257710 PMCID: PMC9757872 DOI: 10.1212/wnl.0000000000201380] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2022] [Accepted: 08/24/2022] [Indexed: 12/27/2022] Open
Abstract
At the end of 2020, the National Institute of Neurological Disorders and Stroke, an institute of the NIH, completed an 18-month-long strategic planning process that involved and engaged diverse internal and external biomedical and general stakeholders. The institute published and disseminated its 2021-2026 Strategic Plan online in December 2020. Now, 1 year into its implementation, this progress report presents accomplishments to date, new initiatives and opportunities, and a preview of the metrics and benchmarks we will use to gauge the future progress of the strategic plan's implementation.
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Affiliation(s)
- Nina F Schor
- From the National Institute of Neurological Disorders and Stroke, Bethesda, MD.
| | - Paul Scott
- From the National Institute of Neurological Disorders and Stroke, Bethesda, MD
| | - Elizabeth Y Litvina
- From the National Institute of Neurological Disorders and Stroke, Bethesda, MD
| | - Christine Torborg
- From the National Institute of Neurological Disorders and Stroke, Bethesda, MD
| | - Jenny L Kim
- From the National Institute of Neurological Disorders and Stroke, Bethesda, MD
| | - Robert Zalutsky
- From the National Institute of Neurological Disorders and Stroke, Bethesda, MD
| | - Amy Bany Adams
- From the National Institute of Neurological Disorders and Stroke, Bethesda, MD
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4
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Spontarelli K, Infield DT, Nielsen HN, Holm R, Young VC, Galpin JD, Ahern CA, Vilsen B, Artigas P. Role of a conserved ion-binding site tyrosine in ion selectivity of the Na+/K+ pump. J Gen Physiol 2022; 154:e202113039. [PMID: 35657726 PMCID: PMC9171065 DOI: 10.1085/jgp.202113039] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Revised: 04/19/2022] [Accepted: 05/16/2022] [Indexed: 01/07/2023] Open
Abstract
The essential transmembrane Na+ and K+ gradients in animal cells are established by the Na+/K+ pump, a P-type ATPase that exports three Na+ and imports two K+ per ATP hydrolyzed. The mechanism by which the Na+/K+ pump distinguishes between Na+ and K+ at the two membrane sides is poorly understood. Crystal structures identify two sites (sites I and II) that bind Na+ or K+ and a third (site III) specific for Na+. The side chain of a conserved tyrosine at site III of the catalytic α-subunit (Xenopus-α1 Y780) has been proposed to contribute to Na+ binding by cation-π interaction. We substituted Y780 with natural and unnatural amino acids, expressed the mutants in Xenopus oocytes and COS-1 cells, and used electrophysiology and biochemistry to evaluate their function. Substitutions disrupting H-bonds impaired Na+ interaction, while Y780Q strengthened it, likely by H-bond formation. Utilizing the non-sense suppression method previously used to incorporate unnatural derivatives in ion channels, we were able to analyze Na+/K+ pumps with fluorinated tyrosine or phenylalanine derivatives inserted at position 780 to diminish cation-π interaction strength. In line with the results of the analysis of mutants with natural amino acid substitutions, the results with the fluorinated derivatives indicate that Na+-π interaction with the phenol ring at position 780 contributes minimally, if at all, to the binding of Na+. All Y780 substitutions decreased K+ apparent affinity, highlighting that a state-dependent H-bond network is essential for the selectivity switch at sites I and II when the pump changes conformational state.
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Affiliation(s)
- Kerri Spontarelli
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Daniel T. Infield
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA
| | - Hang N. Nielsen
- Department of Biomedicine, Aarhus University, Aarhus C, Denmark
| | - Rikke Holm
- Department of Biomedicine, Aarhus University, Aarhus C, Denmark
| | - Victoria C. Young
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Jason D. Galpin
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA
| | - Christopher A. Ahern
- Department of Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA
| | - Bente Vilsen
- Department of Biomedicine, Aarhus University, Aarhus C, Denmark
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
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5
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Oshiyama NF, Pereira AHM, Cardoso AC, Franchini KG, Bassani JWM, Bassani RA. Developmental differences in myocardial transmembrane Na + transport: Implications for excitability and Na + handling. J Physiol 2022; 600:2651-2667. [PMID: 35489088 DOI: 10.1113/jp282661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Accepted: 04/20/2022] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Previous studies showed that myocardial preparations from immature rats are less sensitive to electrical field stimulation than adult preparations. Freshly-isolated ventricular myocytes from neonatal rats showed lower excitability than adult cells, e.g., less negative threshold membrane potential and greater membrane depolarization required for action potential triggering. In addition to differences in mRNA levels for Na+ channels isoforms and greater Na+ current (INa ) density, Na+ channel voltage-dependence was shifted to the right in immature myocytes, which seems to be sufficient to decrease excitability, according to computer simulations. Only in neonatal myocytes did cyclic activity promote marked cytosolic Na+ accumulation, which was prevented by abolition of systolic Ca2+ transients by blockade of Ca2+ currents. Developmental changes in INa may account for the difference in action potential initiation parameters, but not for cytosolic Na+ accumulation, which seems to be due mainly to Na+ /Ca2+ exchanger-mediated Na+ influx. ABSTRACT Little is currently known about possible developmental changes in myocardial Na+ handling, which may have impact on cell excitability and Ca2+ content. Resting intracellular Na+ concentration ([Na+ ]i ), measured in freshly-isolated rat ventricular myocytes with CoroNa-green, was not significantly different in neonates (3-5 days old) and adults, but electrical stimulation caused marked [Na+ ]i rise only in neonates. Inhibition of L-type Ca2+ current by CdCl2 abolished not only systolic Ca2+ transients, but also activity-dependent intracellular Na+ accumulation in immature cells. This indicates that the main Na+ influx pathway during activity is the Na+ /Ca2+ exchanger, rather than voltage-dependent Na+ current (INa ), which was not affected by CdCl2 . In immature myocytes, INa density was 2-fold greater, inactivation was faster, and the current peak occurred at less negative transmembrane potential (Em ) than in adults. Na+ channel steady-state activation and inactivation curves in neonates showed a rightward shift, which should increase channel availability at diastolic Em , but also require greater depolarization for excitation, which was observed experimentally and reproduced in computer simulations. Ventricular mRNA levels of Nav 1.1, Nav 1.4 and Nav 1.5 pore-forming isoforms were greater in neonate ventricles, while decrease was seen for the β1 subunit. Both molecular and biophysical changes in the channel profile may contribute to the differences in INa density and voltage-dependence, and also to the less negative threshold Em in neonates, compared to adults. The apparently lower excitability in immature ventricle may confer protection against the development of spontaneous activity in this tissue. Abstract figure legend Little is currently known about possible developmental changes in myocardial Na+ transport, which may have impact on cell excitability and other physiological aspects. At the mRNA level, neonatal rat ventricle expresses a greater variety of Na+ channel isoforms than in adults. In immature ventricular cardiomyocytes, Na+ current (INa ) density was greater, but voltage-dependence is shifted to less negative potentials than in adults. This should increase channel availability at diastolic membrane potential, but also require greater depolarization for excitation, which was observed experimentally and reproduced in computer simulation. We also observed that electrical stimulation caused marked intracellular Na+ accumulation only in neonates, which was abolished when Ca2+ transients and the Na+ /Ca2+ exchanger (NCX) were inhibited by Cd2+ + Ni2+ . Thus, it seems that the main Na+ influx pathway during activity in neonates is the NCX, rather than voltage-dependent INa , which was not affected by these blockers. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Natália F Oshiyama
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
| | - Ana H M Pereira
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil
| | - Alisson C Cardoso
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil
| | - Kleber G Franchini
- Brazilian Biosciences National Laboratory, Brazilian Center for Research in Energy and Materials (LNBio/CNPEM), Campinas, SP, Brazil.,Department of Internal Medicine, School of Medicine, University of Campinas, Campinas, SP, Brazil
| | - José W M Bassani
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
| | - Rosana A Bassani
- Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.,National Laboratory for Cell Calcium Study, (LabNECC), Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
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Chen W, Wang L, Liang P, Mast J, Mathis C, Liu CY, Wei J, Zhang J, Fu L, Juncos LA, Buggs J, Liu R. Reducing ischemic kidney injury through application of a synchronization modulation electric field to maintain Na +/K +-ATPase functions. Sci Transl Med 2022; 14:eabj4906. [PMID: 35263146 PMCID: PMC9994383 DOI: 10.1126/scitranslmed.abj4906] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Renal ischemia-reperfusion injury is an important contributor to the development of delayed graft function after transplantation, which is associated with higher rejection rates and poorer long-term outcomes. One of the earliest impairments during ischemia is Na+/K+-ATPase (Na/K pump) dysfunction due to insufficient ATP supply, resulting in subsequent cellular damage. Therefore, strategies that preserve ATP or maintain Na/K pump function may limit the extent of renal injury during ischemia-reperfusion. Here, we applied a synchronization modulation electric field to activate Na/K pumps, thereby maintaining cellular functions under ATP-insufficient conditions. We tested the effectiveness of this technique in two models of ischemic renal injury: an in situ renal ischemia-reperfusion injury model (predominantly warm ischemia) and a kidney transplantation model (predominantly cold ischemia). Application of the synchronization modulation electric field to a renal ischemia-reperfusion injury mouse model preserved Na/K pump activity, thereby reducing kidney injury, as reflected by 40% lower plasma creatinine (1.17 ± 0.03 mg/dl) in the electric field-treated group as compared to the untreated control group (1.89 ± 0.06 mg/dl). In a mouse kidney transplantation model, renal graft function was improved by more than 50% with the application of the synchronization modulation electric field according to glomerular filtration rate measurements (85.40 ± 12.18 μl/min in the untreated group versus 142.80 ± 11.65 μl/min in the electric field-treated group). This technique for preserving Na/K pump function may have therapeutic potential not only for ischemic kidney injury but also for other diseases associated with Na/K pump dysfunction due to inadequate ATP supply.
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Affiliation(s)
- Wei Chen
- Department of Physics, College of Arts and Sciences, University of South Florida, Tampa, FL 33620, USA
| | - Lei Wang
- Department of Molecular Pharmacology and Physiology, College of Medicine, University of South Florida, Tampa, FL 33620, USA
| | - Pengfei Liang
- Department of Physics, College of Arts and Sciences, University of South Florida, Tampa, FL 33620, USA
| | - Jason Mast
- Department of Physics, College of Arts and Sciences, University of South Florida, Tampa, FL 33620, USA
| | - Clausell Mathis
- Department of Physics, College of Arts and Sciences, University of South Florida, Tampa, FL 33620, USA
| | - Catherine Y Liu
- Department of Molecular Pharmacology and Physiology, College of Medicine, University of South Florida, Tampa, FL 33620, USA
| | - Jin Wei
- Department of Molecular Pharmacology and Physiology, College of Medicine, University of South Florida, Tampa, FL 33620, USA
| | - Jie Zhang
- Department of Molecular Pharmacology and Physiology, College of Medicine, University of South Florida, Tampa, FL 33620, USA
| | - Liying Fu
- Department of Pathology, Scripps Green Hospital, La Jolla, CA 92037, USA
| | - Luis A Juncos
- Department of Internal Medicine, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | | | - Ruisheng Liu
- Department of Molecular Pharmacology and Physiology, College of Medicine, University of South Florida, Tampa, FL 33620, USA
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Kubota T, Nabatame S, Sato R, Hama M, Nishiike U, Mochizuki H, Takahashi MP, Takeshima T. Hemiplegic migraine type 2 caused by a novel variant within the P-type ATPase motif in ATP1A2 concomitant with a CACNA1A variant. Brain Dev 2021; 43:952-957. [PMID: 34092402 DOI: 10.1016/j.braindev.2021.05.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/09/2021] [Revised: 05/15/2021] [Accepted: 05/18/2021] [Indexed: 10/21/2022]
Abstract
BACKGROUND Familial hemiplegic migraine (FHM) is an inherited autosomal dominant disorder characterized by migraine with reversible hemiplegia. FHM1 is caused by variants in CACNA1A, encoding a P/Q type neuronal voltage-gated calcium channel α subunit, which is also associated with episodic ataxia type 2 (EA2). FHM2 is associated with ATP1A2, which codes for an Na+/K+-ATPase isoform 2 subunit. CASE PRESENTATION We identified an FHM2 family, the mother and her daughter, with a novel variant in ATP1A2, p.Gly377Asp, located in a well-conserved P-type ATPase motif. Additionally, the mother harbored deletion in the CACNA1A, associated with EA2, but her daughter did not. The mother presented migraine with typical aura without motor deficit, whereas her daughter had migraine accompanied by recurrent motor deficit and altered consciousness. The additional CACNA1A deletion in the mother might serve as a modifier. CONCLUSION Our report emphasizes the importance of genetic analysis to diagnose neurological ion channel/transporter diseases.
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Affiliation(s)
- Tomoya Kubota
- Department of Clinical Laboratory and Biomedical Sciences, Division of Health Sciences, Osaka University Graduate School of Medicine, 1-7, Yamadaoka, Suita, Osaka 5650871, Japan; Department of Neurology, Osaka University Graduate School of Medicine, 2-2, Yamadaoka, Suita, Osaka 5650871, Japan
| | - Shin Nabatame
- Department of Pediatrics, Osaka University Graduate School of Medicine, 2-2, Yamadaoka, Suita, Osaka 5650871, Japan
| | - Ruka Sato
- Department of Clinical Laboratory and Biomedical Sciences, Division of Health Sciences, Osaka University Graduate School of Medicine, 1-7, Yamadaoka, Suita, Osaka 5650871, Japan
| | - Manami Hama
- Department of Clinical Laboratory and Biomedical Sciences, Division of Health Sciences, Osaka University Graduate School of Medicine, 1-7, Yamadaoka, Suita, Osaka 5650871, Japan
| | - Ujiakira Nishiike
- Department of Neurology, Osaka University Graduate School of Medicine, 2-2, Yamadaoka, Suita, Osaka 5650871, Japan
| | - Hideki Mochizuki
- Department of Neurology, Osaka University Graduate School of Medicine, 2-2, Yamadaoka, Suita, Osaka 5650871, Japan
| | - Masanori P Takahashi
- Department of Clinical Laboratory and Biomedical Sciences, Division of Health Sciences, Osaka University Graduate School of Medicine, 1-7, Yamadaoka, Suita, Osaka 5650871, Japan; Department of Neurology, Osaka University Graduate School of Medicine, 2-2, Yamadaoka, Suita, Osaka 5650871, Japan.
| | - Takao Takeshima
- Department of Neurology, Tominaga Hospital, 1-4-48, Minato-cho, Naniwa-ku, Osaka, Osaka 5560017, Japan.
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Meyer DJ, Bijlani S, de Sautu M, Spontarelli K, Young VC, Gatto C, Artigas P. FXYD protein isoforms differentially modulate human Na/K pump function. J Gen Physiol 2021; 152:211559. [PMID: 33231612 PMCID: PMC7690937 DOI: 10.1085/jgp.202012660] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 10/29/2020] [Indexed: 12/28/2022] Open
Abstract
Tight regulation of the Na/K pump is essential for cellular function because this heteromeric protein builds and maintains the electrochemical gradients for Na+ and K+ that energize electrical signaling and secondary active transport. We studied the regulation of the ubiquitous human α1β1 pump isoform by five human FXYD proteins normally located in muscle, kidney, and neurons. The function of Na/K pump α1β1 expressed in Xenopus oocytes with or without FXYD isoforms was evaluated using two-electrode voltage clamp and patch clamp. Through evaluation of the partial reactions in the absence of K+ but presence of Na+ in the external milieu, we demonstrate that each FXYD subunit alters the equilibrium between E1P(3Na) and E2P, the phosphorylated conformations with Na+ occluded and free from Na+, respectively, thereby altering the apparent affinity for Na+. This modification of Na+ interaction shapes the small effects of FXYD proteins on the apparent affinity for external K+ at physiological Na+. FXYD6 distinctively accelerated both the Na+-deocclusion and the pump-turnover rates. All FXYD isoforms altered the apparent affinity for intracellular Na+ in patches, an effect that was observed only in the presence of intracellular K+. Therefore, FXYD proteins alter the selectivity of the pump for intracellular ions, an effect that could be due to the altered equilibrium between E1 and E2, the two major pump conformations, and/or to small changes in ion affinities that are exacerbated when both ions are present. Lastly, we observed a drastic reduction of Na/K pump surface expression when it was coexpressed with FXYD1 or FXYD6, with the former being relieved by injection of PKA's catalytic subunit into the oocyte. Our results indicate that a prominent effect of FXYD1 and FXYD6, and plausibly other FXYDs, is the regulation of Na/K pump trafficking.
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Affiliation(s)
- Dylan J Meyer
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Sharan Bijlani
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Marilina de Sautu
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Kerri Spontarelli
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Victoria C Young
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
| | - Craig Gatto
- School of Biological Sciences, Illinois State University. Normal, IL
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock TX
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9
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Displacement of the Na +/K + pump's transmembrane domains demonstrates conserved conformational changes in P-type 2 ATPases. Proc Natl Acad Sci U S A 2021; 118:2019317118. [PMID: 33597302 DOI: 10.1073/pnas.2019317118] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Cellular survival requires the ion gradients built by the Na+/K+ pump, an ATPase that alternates between two major conformations (E1 and E2). Here we use state-specific engineered-disulfide cross-linking to demonstrate that transmembrane segment 2 (M2) of the pump's α-subunit moves in directions that are inconsistent with distances observed in existing crystal structures of the Na+/K+ pump in E1 and E2. We characterize this movement with voltage-clamp fluorometry in single-cysteine mutants. Most mutants in the M1-M2 loop produced state-dependent fluorescence changes upon labeling with tetramethylrhodamine-6-maleimide (TMRM), which were due to quenching by multiple endogenous tryptophans. To avoid complications arising from multiple potential quenchers, we analyzed quenching of TMRM conjugated to R977C (in the static M9-M10 loop) by tryptophans introduced, one at a time, in M1-M2. This approach showed that tryptophans introduced in M2 quench TMRM only in E2, with D126W and L130W on the same helix producing the largest fluorescence changes. These observations indicate that M2 moves outward as Na+ is deoccluded from the E1 conformation, a mechanism consistent with cross-linking results and with proposals for other P-type 2 ATPases.
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10
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Biondo ED, Spontarelli K, Ababioh G, Méndez L, Artigas P. Diseases caused by mutations in the Na +/K + pump α1 gene ATP1A1. Am J Physiol Cell Physiol 2021; 321:C394-C408. [PMID: 34232746 DOI: 10.1152/ajpcell.00059.2021] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Human cell survival requires function of the Na+/K+ pump; the heteromeric protein that hydrolyzes ATP to extrude Na+ and import K+ across the plasmalemma, thereby building and maintaining these ions' electrochemical gradients. Numerous dominant diseases caused by mutations in genes encoding for Na+/K+ pump catalytic (α) subunit isoforms highlight the importance of this protein. Here, we review literature describing disorders caused by missense mutations in ATP1A1, the gene encoding the ubiquitously expressed α1 isoform of the Na+/K+ pump. These various maladies include primary aldosteronism with secondary hypertension, an endocrine syndrome, Charcot-Marie-Tooth disease, a peripheral neuropathy, complex spastic paraplegia, another neuromuscular disorder, as well as hypomagnesemia accompanied by seizures and cognitive delay, a condition affecting the renal and central nervous systems. This article focuses on observed commonalities among these mutations' functional effects, as well as on the special characteristics that enable each particular mutation to exclusively affect a certain system, without affecting others. In this respect, it is clear how somatic mutations localized to adrenal adenomas increase aldosterone production without compromising other systems. However, it remains largely unknown how and why some but not all de novo germline or familial mutations (where the mutant must be expressed in numerous tissues) produce a specific disease and not the other diseases. We propose hypotheses to explain this observation and the approaches that we think will drive future research on these debilitating disorders to develop novel patient-specific treatments by combining the use of heterologous protein-expression systems, patient-derived pluripotent cells, and gene-edited cell and mouse models.
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Affiliation(s)
- Elisa D Biondo
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Kerri Spontarelli
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Giovanna Ababioh
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Lois Méndez
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, Texas
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Structural Insights into the Interactions of Digoxin and Na +/K +-ATPase and Other Targets for the Inhibition of Cancer Cell Proliferation. Molecules 2021; 26:molecules26123672. [PMID: 34208576 PMCID: PMC8234910 DOI: 10.3390/molecules26123672] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2021] [Revised: 06/01/2021] [Accepted: 06/09/2021] [Indexed: 12/12/2022] Open
Abstract
Digoxin is a cardiac glycoside long used to treat congestive heart failure and found recently to show antitumor potential. The hydroxy groups connected at the C-12, C-14, and C-3′a positions; the C-17 unsaturated lactone unit; the conformation of the steroid core; and the C-3 saccharide moiety have been demonstrated as being important for digoxin’s cytotoxicity and interactions with Na+/K+-ATPase. The docking profiles for digoxin and several derivatives and Na+/K+-ATPase were investigated; an additional small Asn130 side pocket was revealed, which could be useful in the design of novel digoxin-like antitumor agents. In addition, the docking scores for digoxin and its derivatives were found to correlate with their cytotoxicity, indicating a potential use of these values in the prediction of the cancer cell cytotoxicity of other cardiac glycosides. Moreover, in these docking studies, digoxin was found to bind to FIH-1 and NF-κB but not HDAC, IAP, and PI3K, suggesting that this cardiac glycoside directly targets FIH-1, Na+/K+-ATPase, and NF-κB to mediate its antitumor potential. Differentially, digoxigenin, the aglycon of digoxin, binds to HDAC and PI3K, but not FIH-1, IAP, Na+/K+-ATPase, and NF-κB, indicating that this compound may target tumor autophagy and metabolism to mediate its antitumor propensity.
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Yap JQ, Seflova J, Sweazey R, Artigas P, Robia SL. FXYD proteins and sodium pump regulatory mechanisms. J Gen Physiol 2021; 153:211866. [PMID: 33688925 PMCID: PMC7953255 DOI: 10.1085/jgp.202012633] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2020] [Accepted: 02/03/2021] [Indexed: 12/12/2022] Open
Abstract
The sodium/potassium-ATPase (NKA) is the enzyme that establishes gradients of sodium and potassium across the plasma membrane. NKA activity is tightly regulated for different physiological contexts through interactions with single-span transmembrane peptides, the FXYD proteins. This diverse family of regulators has in common a domain containing a Phe-X-Tyr-Asp (FXYD) motif, two conserved glycines, and one serine residue. In humans, there are seven tissue-specific FXYD proteins that differentially modulate NKA kinetics as appropriate for each system, providing dynamic responsiveness to changing physiological conditions. Our understanding of how FXYD proteins contribute to homeostasis has benefitted from recent advances described in this review: biochemical and biophysical studies have provided insight into regulatory mechanisms, genetic models have uncovered remarkable complexity of FXYD function in integrated physiological systems, new posttranslational modifications have been identified, high-resolution structural studies have revealed new details of the regulatory interaction with NKA, and new clinical correlations have been uncovered. In this review, we address the structural determinants of diverse FXYD functions and the special roles of FXYDs in various physiological systems. We also discuss the possible roles of FXYDs in protein trafficking and regulation of non-NKA targets.
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Affiliation(s)
- John Q Yap
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Jaroslava Seflova
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
| | - Ryan Sweazey
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Pablo Artigas
- Department of Cell Physiology and Molecular Biophysics, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX
| | - Seth L Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, IL
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Maleckar MM, Martín-Vasallo P, Giles WR, Mobasheri A. Physiological Effects of the Electrogenic Current Generated by the Na +/K + Pump in Mammalian Articular Chondrocytes. Bioelectricity 2020; 2:258-268. [PMID: 34471850 PMCID: PMC8370340 DOI: 10.1089/bioe.2020.0036] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Background: Although the chondrocyte is a nonexcitable cell, there is strong interest in gaining detailed knowledge of its ion pumps, channels, exchangers, and transporters. In combination, these transport mechanisms set the resting potential, regulate cell volume, and strongly modulate responses of the chondrocyte to endocrine agents and physicochemical alterations in the surrounding extracellular microenvironment. Materials and Methods: Mathematical modeling was used to assess the functional roles of energy-requiring active transport, the Na+/K+ pump, in chondrocytes. Results: Our findings illustrate plausible physiological roles for the Na+/K+ pump in regulating the resting membrane potential and suggest ways in which specific molecular components of pump can respond to the unique electrochemical environment of the chondrocyte. Conclusion: This analysis provides a basis for linking chondrocyte electrophysiology to metabolism and yields insights into novel ways of manipulating or regulating responsiveness to external stimuli both under baseline conditions and in chronic diseases such as osteoarthritis.
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Affiliation(s)
| | - Pablo Martín-Vasallo
- UD of Biochemistry and Molecular Biology, Universidad de La Laguna, San Cristóbal de La Laguna, Spain.,Instituto de Tecnologías Biomédicas de Canarias, Universidad de La Laguna, San Cristóbal de La Laguna, Spain
| | - Wayne R Giles
- Department of Physiology and Pharmacology, University of Calgary, Calgary, Canada
| | - Ali Mobasheri
- Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland.,Department of Regenerative Medicine, State Research Institute Centre for Innovative Medicine, Vilnius, Lithuania.,Department of Orthopedics, Rheumatology and Clinical Immunology, University Medical Center Utrecht, Utrecht, The Netherlands
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