1
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Morris JA, Bardsley OJ, Salvage SC, Jackson AP, Matthews HR, Huang CLH. Nernst-Planck-Gaussian modelling of electrodiffusional recovery from ephaptic excitation between mammalian cardiomyocytes. Front Physiol 2024; 14:1280151. [PMID: 38235384 PMCID: PMC10791825 DOI: 10.3389/fphys.2023.1280151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2023] [Accepted: 12/01/2023] [Indexed: 01/19/2024] Open
Abstract
Introduction: In addition to gap junction conduction, recent reports implicate possible ephaptic coupling contributions to action potential (AP) propagation between successive adjacent cardiomyocytes. Here, AP generation in an active cell, withdraws Na+ from, creating a negative potential within, ephaptic spaces between the participating membranes, activating the initially quiescent neighbouring cardiomyocyte. However, sustainable ephaptic transmission requires subsequent complete recovery of the ephaptic charge difference. We explore physical contributions of passive electrodiffusive ion exchange with the remaining extracellular space to this recovery for the first time. Materials and Methods: Computational, finite element, analysis examined limiting, temporal and spatial, ephaptic [Na+], [Cl-], and the consequent Gaussian charge differences and membrane potential recovery patterns following a ΔV∼130 mV AP upstroke at physiological (37°C) temperatures. This incorporated Nernst-Planck formalisms into equations for the time-dependent spatial concentration gradient profiles. Results: Mammalian atrial, ventricular and purkinje cardiomyocyte ephaptic junctions were modelled by closely apposed circularly symmetric membranes, specific capacitance 1 μF cm-2, experimentally reported radii a = 8,000, 12,000 and 40,000 nm respectively and ephaptic axial distance w = 20 nm. This enclosed an ephaptic space containing principal ions initially at normal extracellular [Na+] = 153.1 mM and [Cl-] = 145.8 mM, respective diffusion coefficients D Na = 1.3 × 109 and D Cl = 2 × 109 nm2s-1. Stable, concordant computational solutions were confirmed exploring ≤1,600 nm mesh sizes and Δt≤0.08 ms stepsize intervals. The corresponding membrane voltage profile changes across the initially quiescent membrane were obtainable from computed, graphically represented a and w-dependent ionic concentration differences adapting Gauss's flux theorem. Further simulations explored biological variations in ephaptic dimensions, membrane anatomy, and diffusion restrictions within the ephaptic space. Atrial, ventricular and Purkinje cardiomyocytes gave 40, 180 and 2000 ms 99.9% recovery times, with 720 or 360 ms high limits from doubling ventricular radius or halving diffusion coefficient. Varying a, and D Na and D Cl markedly affected recovery time-courses with logarithmic and double-logarithmic relationships, Varying w exerted minimal effects. Conclusion: We thereby characterise the properties of, and through comparing atrial, ventricular and purkinje recovery times with interspecies in vivo background cardiac cycle duration data, (blue whale ∼2000, human∼90, Etruscan shrew, ∼40 ms) can determine physical limits to, electrodiffusive contributions to ephaptic recovery.
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Affiliation(s)
- Joshua A. Morris
- Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom
| | - Oliver J. Bardsley
- Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom
| | - Samantha C. Salvage
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Antony P. Jackson
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - Hugh R. Matthews
- Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom
| | - Christopher L-H. Huang
- Physiological Laboratory, University of Cambridge, Cambridge, United Kingdom
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
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2
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Murayama T, Kurebayashi N, Numaga-Tomita T, Kobayashi T, Okazaki S, Yamashiro K, Nakada T, Mori S, Ishida R, Kagechika H, Yamada M, Sakurai T. A reconstituted depolarization-induced Ca2+ release platform for validation of skeletal muscle disease mutations and drug discovery. J Gen Physiol 2022; 154:213630. [PMID: 36318155 PMCID: PMC9629852 DOI: 10.1085/jgp.202213230] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2022] [Revised: 09/06/2022] [Accepted: 10/03/2022] [Indexed: 11/06/2022] Open
Abstract
In skeletal muscle excitation-contraction (E-C) coupling, depolarization of the plasma membrane triggers Ca2+ release from the sarcoplasmic reticulum (SR), referred to as depolarization-induced Ca2+ release (DICR). DICR occurs through the type 1 ryanodine receptor (RyR1), which physically interacts with the dihydropyridine receptor Cav1.1 subunit in specific machinery formed with additional essential components including β1a, Stac3 adaptor protein, and junctophilins. Exome sequencing has accelerated the discovery of many novel mutations in genes encoding DICR machinery in various skeletal muscle diseases. However, functional validation is time-consuming because it must be performed in a skeletal muscle environment. In this study, we established a platform of the reconstituted DICR in HEK293 cells. The essential components were effectively transduced into HEK293 cells expressing RyR1 using baculovirus vectors, and Ca2+ release was quantitatively measured with R-CEPIA1er, a fluorescent ER Ca2+ indicator, without contaminant of extracellular Ca2+ influx. In these cells, [K+]-dependent Ca2+ release was triggered by chemical depolarization with the aid of inward rectifying potassium channel, indicating a successful reconstitution of DICR. Using the platform, we evaluated several Cav1.1 mutations that are implicated in malignant hyperthermia and myopathy. We also tested several RyR1 inhibitors; whereas dantrolene and Cpd1 inhibited DICR, procaine had no effect. Furthermore, twitch potentiators such as perchlorate and thiocyanate shifted the voltage dependence of DICR to more negative potentials without affecting Ca2+-induced Ca2+ release. These results well reproduced the findings with the muscle fibers and the cultured myotubes. Since the procedure is simple and reproducible, the reconstituted DICR platform will be highly useful for the validation of mutations and drug discovery for skeletal muscle diseases.
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Affiliation(s)
- Takashi Murayama
- Department of Pharmacology, Juntendo University School of Medicine, Tokyo, Japan
| | - Nagomi Kurebayashi
- Department of Pharmacology, Juntendo University School of Medicine, Tokyo, Japan
| | - Takuro Numaga-Tomita
- Department of Molecular Pharmacology, Shinshu University School of Medicine, Matsumoto, Japan
| | - Takuya Kobayashi
- Department of Pharmacology, Juntendo University School of Medicine, Tokyo, Japan
| | - Satoru Okazaki
- Department of Pharmacology, Juntendo University School of Medicine, Tokyo, Japan
| | - Kyosuke Yamashiro
- Department of Pharmacology, Juntendo University School of Medicine, Tokyo, Japan
| | - Tsutomu Nakada
- Department of Molecular Pharmacology, Shinshu University School of Medicine, Matsumoto, Japan
| | - Shuichi Mori
- Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo, Japan
| | - Ryosuke Ishida
- Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo, Japan
| | - Hiroyuki Kagechika
- Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University, Tokyo, Japan
| | - Mitsuhiko Yamada
- Department of Molecular Pharmacology, Shinshu University School of Medicine, Matsumoto, Japan
| | - Takashi Sakurai
- Department of Pharmacology, Juntendo University School of Medicine, Tokyo, Japan
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3
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McDonough AA, Fenton RA. Potassium homeostasis: sensors, mediators, and targets. Pflugers Arch 2022; 474:853-867. [PMID: 35727363 PMCID: PMC10163916 DOI: 10.1007/s00424-022-02718-3] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2022] [Revised: 06/08/2022] [Accepted: 06/12/2022] [Indexed: 12/16/2022]
Abstract
Transmembrane potassium (K) gradients are key determinants of membrane potential that can modulate action potentials, control muscle contractility, and influence ion channel and transporter activity. Daily K intake is normally equal to the amount of K in the entire extracellular fluid (ECF) creating a critical challenge - how to maintain ECF [K] and membrane potential in a narrow range during feast and famine. Adaptations to maintain ECF [K] include sensing the K intake, sensing ECF [K] vs. desired set-point and activating mediators that regulate K distribution between ECF and ICF, and regulate renal K excretion. In this focused review, we discuss the basis of these adaptions, including (1) potential mechanisms for rapid feedforward signaling to kidney and muscle after a meal (before a rise in ECF [K]), (2) how skeletal muscles sense and respond to changes in ECF [K], (3) effects of K on aldosterone biosynthesis, and (4) how the kidney responds to changes in ECF [K] to modify K excretion. The concepts of sexual dimorphisms in renal K handling adaptation are introduced, and the molecular mechanisms that can account for the benefits of a K-rich diet to maintain cardiovascular health are discussed. Although the big picture of K homeostasis is becoming more clear, we also highlight significant pieces of the puzzle that remain to be solved, including knowledge gaps in our understanding of initiating signals, sensors and their connection to homeostatic adjustments of ECF [K].
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Affiliation(s)
- Alicia A McDonough
- Department of Physiology and Neuroscience, University of Southern California Keck School of Medicine, Los Angeles, CA, USA.
| | - Robert A Fenton
- Department of Biomedicine, Aarhus University, Aarhus, Denmark
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4
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Suetterlin KJ, Männikkö R, Matthews E, Greensmith L, Hanna MG, Bostock H, Tan SV. Excitability properties of mouse and human skeletal muscle fibres compared by muscle velocity recovery cycles. Neuromuscul Disord 2022; 32:347-357. [PMID: 35339342 PMCID: PMC7614892 DOI: 10.1016/j.nmd.2022.02.011] [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: 07/11/2021] [Revised: 01/27/2022] [Accepted: 02/22/2022] [Indexed: 11/21/2022]
Abstract
Mouse models of skeletal muscle channelopathies are not phenocopies of human disease. In some cases (e.g. Myotonia Congenita) the phenotype is much more severe, whilst in others (e.g. Hypokalaemic periodic paralysis) rodent physiology is protective. This suggests a species' difference in muscle excitability properties. In humans these can be measured indirectly by the post-impulse changes in conduction velocity, using Muscle Velocity Recovery Cycles (MVRCs). We performed MVRCs in mice and compared their muscle excitability properties with humans. Mouse Tibialis Anterior MVRCs (n = 70) have only one phase of supernormality (increased conduction velocity), which is smaller in magnitude (p = 9 × 10-21), and shorter in duration (p = 3 × 10-24) than human (n = 26). This abbreviated supernormality is followed by a period of late subnormality (reduced velocity) in mice, which overlaps in time with the late supernormality seen in human MVRCs. The period of late subnormality suggests increased t-tubule Na+/K+-pump activity. The subnormal phase in mice was converted to supernormality by blocking ClC-1 chloride channels, suggesting relatively higher chloride conductance in skeletal muscle. Our findings help explain discrepancies in phenotype between mice and humans with skeletal muscle channelopathies and potentially other neuromuscular disorders. MVRCs are a valuable new tool to compare in vivo muscle membrane properties between species and will allow further dissection of the molecular mechanisms regulating muscle excitability.
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Affiliation(s)
- K J Suetterlin
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom; AGE Research Group, NIHR Newcastle Biomedical Research Centre, Newcastle upon Tyne Hospitals NHS Foundation Trust and Newcastle University, Newcastle upon Tyne, United Kingdom.
| | - R Männikkö
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom
| | - E Matthews
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom; Atkinson Morley Neuromuscular Centre, Department of Neurology, St Georges University Hospitals NHS Foundation Trust, London, United Kingdom
| | - L Greensmith
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom
| | - M G Hanna
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom
| | - H Bostock
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom
| | - S V Tan
- Department of Neuromuscular Diseases, UCL Queen Square Institute of Neurology, London, United Kingdom; Department of Neurology and Clinical Neurophysiology, Guy's & St Thomas' NHS Foundation Trust and Institute of Psychiatry, Psychology & Neuroscience, Division of Neuroscience, King's College London, United Kingdom
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5
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Gilles O. K + -independent Kir blockade by external Cs + and Ba 2. Physiol Rep 2022; 10:e15200. [PMID: 35274814 PMCID: PMC8915156 DOI: 10.14814/phy2.15200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 01/14/2022] [Accepted: 01/24/2022] [Indexed: 06/14/2023] Open
Abstract
Cations such as Cs+ and Ba2+ are known to block K+ currents by entering an open channel and binding to the selectivity filter, where they obstruct the pore and block diffusion of the permeant ion. This obstruction is voltage- and K+ -dependent and is relieved by the trans permeant ion flux. The present patch-clamp study on Xenopus muscle cells shows that, unlike the voltage-activated K+ (Kv) channels, blockade of the inward rectifier K+ (Kir) channels by external foreign cations results from the combination of pore obstruction with a new and independent mechanism. This new blockade is independent of the K+ concentrations and flux and acts indiscriminately on both the outward and the inward Kir components. External Cs+ and Ba2+ compete for this blockade with free access to common channel sites. These features suggest that the blocking cations do not need to enter the channel for this new mechanism, and should bind to the extracellular side of the channel. When K+ fluxes are flowing outward, the pore obstruction is relieved for both Kir and Kv currents, and the K+ -independent blockade here described is responsible for a selective Kir inhibition, justifying the use of these external cations as tools in cell physiology studies.
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Affiliation(s)
- Ouanounou Gilles
- Université Paris‐SaclayCNRSInstitut des Neurosciences Paris‐SaclaySaclayFrance
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6
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Morris CE, Wheeler JJ, Joos B. The Donnan-dominated resting state of skeletal muscle fibers contributes to resilience and longevity in dystrophic fibers. J Gen Physiol 2022; 154:212743. [PMID: 34731883 PMCID: PMC8570295 DOI: 10.1085/jgp.202112914] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2021] [Accepted: 09/30/2021] [Indexed: 11/28/2022] Open
Abstract
Duchenne muscular dystrophy (DMD) is an X-linked dystrophin-minus muscle-wasting disease. Ion homeostasis in skeletal muscle fibers underperforms as DMD progresses. But though DMD renders these excitable cells intolerant of exertion, sodium overloaded, depolarized, and spontaneously contractile, they can survive for several decades. We show computationally that underpinning this longevity is a strikingly frugal, robust Pump-Leak/Donnan (P-L/D) ion homeostatic process. Unlike neurons, which operate with a costly “Pump-Leak–dominated” ion homeostatic steady state, skeletal muscle fibers operate with a low-cost “Donnan-dominated” ion homeostatic steady state that combines a large chloride permeability with an exceptionally small sodium permeability. Simultaneously, this combination keeps fiber excitability low and minimizes pump expenditures. As mechanically active, long-lived multinucleate cells, skeletal muscle fibers have evolved to handle overexertion, sarcolemmal tears, ischemic bouts, etc.; the frugality of their Donnan dominated steady state lets them maintain the outsized pump reserves that make them resilient during these inevitable transient emergencies. Here, P-L/D model variants challenged with DMD-type insult/injury (low pump-strength, overstimulation, leaky Nav and cation channels) show how chronic “nonosmotic” sodium overload (observed in DMD patients) develops. Profoundly severe DMD ion homeostatic insult/injury causes spontaneous firing (and, consequently, unwanted excitation–contraction coupling) that elicits cytotoxic swelling. Therefore, boosting operational pump-strength and/or diminishing sodium and cation channel leaks should help extend DMD fiber longevity.
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Affiliation(s)
- Catherine E Morris
- Neuroscience, Ottawa Hospital Research Institute, Ottawa, Canada.,Center for Neural Dynamics, University of Ottawa, Ottawa, Canada
| | | | - Béla Joos
- Center for Neural Dynamics, University of Ottawa, Ottawa, Canada.,Department of Physics, University of Ottawa, Ottawa, Canada
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7
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Déri S, Borbás J, Hartai T, Hategan L, Csányi B, Visnyovszki Á, Madácsy T, Maléth J, Hegedűs Z, Nagy I, Arora R, Labro AJ, Környei L, Varró A, Sepp R, Ördög B. Impaired cytoplasmic domain interactions cause co-assembly defect and loss of function in the p.Glu293Lys KNCJ2 variant isolated from an Andersen-Tawil syndrome patient. Cardiovasc Res 2021; 117:1923-1934. [PMID: 32810216 DOI: 10.1093/cvr/cvaa249] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 07/16/2020] [Accepted: 08/12/2020] [Indexed: 02/07/2023] Open
Abstract
AIMS Subunit interactions at the cytoplasmic domain interface (CD-I) have recently been shown to control gating in inward rectifier potassium channels. Here we report the novel KCNJ2 variant p.Glu293Lys that has been found in a patient with Andersen-Tawil syndrome type 1 (ATS1), causing amino acid substitution at the CD-I of the inward rectifier potassium channel subunit Kir2.1. Neither has the role of Glu293 in gating control been investigated nor has a pathogenic variant been described at this position. This study aimed to assess the involvement of Glu293 in CD-I subunit interactions and to establish the pathogenic role of the p.Glu293Lys variant in ATS1. METHODS AND RESULTS The p.Glu293Lys variant produced no current in homomeric form and showed dominant-negative effect over wild-type (WT) subunits. Immunocytochemical labelling showed the p.Glu293Lys subunits to distribute in the subsarcolemmal space. Salt bridge prediction indicated the presence of an intersubunit salt bridge network at the CD-I of Kir2.1, with the involvement of Glu293. Subunit interactions were studied by the NanoLuc® Binary Technology (NanoBiT) split reporter assay. Reporter constructs carrying NanoBiT tags on the intracellular termini produced no bioluminescent signal above background with the p.Glu293Lys variant in homomeric configuration and significantly reduced signals in cells co-expressing WT and p.Glu293Lys subunits simultaneously. Extracellularly presented reporter tags, however, generated comparable bioluminescent signals with heteromeric WT and p.Glu293Lys subunits and with homomeric WT channels. CONCLUSIONS Loss of function and dominant-negative effect confirm the causative role of p.Glu293Lys in ATS1. Co-assembly of Kir2.1 subunits is impaired in homomeric channels consisting of p.Glu293Lys subunits and is partially rescued in heteromeric complexes of WT and p.Glu293Lys Kir2.1 variants. These data point to an important role of Glu293 in mediating subunit assembly, as well as in gating of Kir2.1 channels.
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Affiliation(s)
- Szilvia Déri
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, Dóm tér 12, 6720 Szeged, Hungary
| | - János Borbás
- 2nd Department of Internal Medicine and Cardiology Centre, University of Szeged, Semmelweis u. 8, 6725 Szeged, Hungary
| | - Teodóra Hartai
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
| | - Lidia Hategan
- 2nd Department of Internal Medicine and Cardiology Centre, University of Szeged, Semmelweis u. 8, 6725 Szeged, Hungary
| | - Beáta Csányi
- 2nd Department of Internal Medicine and Cardiology Centre, University of Szeged, Semmelweis u. 8, 6725 Szeged, Hungary
| | - Ádám Visnyovszki
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
| | - Tamara Madácsy
- 1st Department of Internal Medicine, University of Szeged, Korányi fasor 8-10, 6720 Szeged, Hungary, Hungary
| | - József Maléth
- 1st Department of Internal Medicine, University of Szeged, Korányi fasor 8-10, 6720 Szeged, Hungary, Hungary
| | - Zoltán Hegedűs
- Institute of Biophysics, Biological Research Centre of the Hungarian Academy of Sciences, Temesvári krt. 62, 6726 Szeged, Hungary
- Department of Biochemistry and Medical Chemistry, University of Pécs, Szigeti út 12, 7624 Pécs, Hungary
| | - István Nagy
- Institute of Biochemistry, Biological Research Centre the Hungarian Academy of Sciences, Temesvári krt. 62, 6726 Szeged, Hungary
- Seqomics Biotechnology Ltd, Vállalkozók útja 7, 6782 Mórahalom, Hungary
| | - Rohit Arora
- Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium
| | - Alain J Labro
- Department of Biomedical Sciences, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium
- Department of Basic Medical Sciences, University of Ghent, C. Heymanslaan 10, 9000 Ghent, Belgium
| | - László Környei
- Gottsegen György National Institute of Cardiology, Haller u. 9, 1096 Budapest, Hungary
| | - András Varró
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, Dóm tér 12, 6720 Szeged, Hungary
- MTA-SZTE Research Group for Cardiovascular Pharmacology, Hungarian Academy of Sciences, Dóm tér 12, 6720 Szeged, Hungary
| | - Róbert Sepp
- 2nd Department of Internal Medicine and Cardiology Centre, University of Szeged, Semmelweis u. 8, 6725 Szeged, Hungary
| | - Balázs Ördög
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Dóm tér 12, PO Box 427, Szeged 6720, Hungary
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Hostrup M, Cairns SP, Bangsbo J. Muscle Ionic Shifts During Exercise: Implications for Fatigue and Exercise Performance. Compr Physiol 2021; 11:1895-1959. [PMID: 34190344 DOI: 10.1002/cphy.c190024] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Exercise causes major shifts in multiple ions (e.g., K+ , Na+ , H+ , lactate- , Ca2+ , and Cl- ) during muscle activity that contributes to development of muscle fatigue. Sarcolemmal processes can be impaired by the trans-sarcolemmal rundown of ion gradients for K+ , Na+ , and Ca2+ during fatiguing exercise, while changes in gradients for Cl- and Cl- conductance may exert either protective or detrimental effects on fatigue. Myocellular H+ accumulation may also contribute to fatigue development by lowering glycolytic rate and has been shown to act synergistically with inorganic phosphate (Pi) to compromise cross-bridge function. In addition, sarcoplasmic reticulum Ca2+ release function is severely affected by fatiguing exercise. Skeletal muscle has a multitude of ion transport systems that counter exercise-related ionic shifts of which the Na+ /K+ -ATPase is of major importance. Metabolic perturbations occurring during exercise can exacerbate trans-sarcolemmal ionic shifts, in particular for K+ and Cl- , respectively via metabolic regulation of the ATP-sensitive K+ channel (KATP ) and the chloride channel isoform 1 (ClC-1). Ion transport systems are highly adaptable to exercise training resulting in an enhanced ability to counter ionic disturbances to delay fatigue and improve exercise performance. In this article, we discuss (i) the ionic shifts occurring during exercise, (ii) the role of ion transport systems in skeletal muscle for ionic regulation, (iii) how ionic disturbances affect sarcolemmal processes and muscle fatigue, (iv) how metabolic perturbations exacerbate ionic shifts during exercise, and (v) how pharmacological manipulation and exercise training regulate ion transport systems to influence exercise performance in humans. © 2021 American Physiological Society. Compr Physiol 11:1895-1959, 2021.
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Affiliation(s)
- Morten Hostrup
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
| | - Simeon Peter Cairns
- SPRINZ, School of Sport and Recreation, Auckland University of Technology, Auckland, New Zealand.,Health and Rehabilitation Research Institute, Auckland University of Technology, Auckland, New Zealand
| | - Jens Bangsbo
- Section of Integrative Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Copenhagen, Denmark
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9
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Lindinger MI, Cairns SP. Regulation of muscle potassium: exercise performance, fatigue and health implications. Eur J Appl Physiol 2021; 121:721-748. [PMID: 33392745 DOI: 10.1007/s00421-020-04546-8] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Accepted: 10/29/2020] [Indexed: 12/30/2022]
Abstract
This review integrates from the single muscle fibre to exercising human the current understanding of the role of skeletal muscle for whole-body potassium (K+) regulation, and specifically the regulation of skeletal muscle [K+]. We describe the K+ transport proteins in skeletal muscle and how they contribute to, or modulate, K+ disturbances during exercise. Muscle and plasma K+ balance are markedly altered during and after high-intensity dynamic exercise (including sports), static contractions and ischaemia, which have implications for skeletal and cardiac muscle contractile performance. Moderate elevations of plasma and interstitial [K+] during exercise have beneficial effects on multiple physiological systems. Severe reductions of the trans-sarcolemmal K+ gradient likely contributes to muscle and whole-body fatigue, i.e. impaired exercise performance. Chronic or acute changes of arterial plasma [K+] (hyperkalaemia or hypokalaemia) have dangerous health implications for cardiac function. The current mechanisms to explain how raised extracellular [K+] impairs cardiac and skeletal muscle function are discussed, along with the latest cell physiology research explaining how calcium, β-adrenergic agonists, insulin or glucose act as clinical treatments for hyperkalaemia to protect the heart and skeletal muscle in vivo. Finally, whether these agents can also modulate K+-induced muscle fatigue are evaluated.
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Affiliation(s)
- Michael I Lindinger
- Research and Development, The Nutraceutical Alliance, Burlington, ON, L7N 2Z9, Canada
| | - Simeon P Cairns
- SPRINZ, School of Sport and Recreation, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, 1020, New Zealand.
- Health and Rehabilitation Research Institute, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, 1020, New Zealand.
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10
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Miranda DR, Reed E, Jama A, Bottomley M, Ren H, Rich MM, Voss AA. Mechanisms of altered skeletal muscle action potentials in the R6/2 mouse model of Huntington's disease. Am J Physiol Cell Physiol 2020; 319:C218-C232. [PMID: 32432924 DOI: 10.1152/ajpcell.00153.2020] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Huntington's disease (HD) patients suffer from progressive and debilitating motor dysfunction for which only palliative treatment is currently available. Previously, we discovered reduced skeletal muscle Cl- channel (ClC-1) and inwardly rectifying K+ channel (Kir) currents in R6/2 HD transgenic mice. To further investigate the role of ClC-1 and Kir currents in HD skeletal muscle pathology, we measured the effect of reduced ClC-1 and Kir currents on action potential (AP) repetitive firing in R6/2 mice using a two-electrode current clamp. We found that R6/2 APs had a significantly lower peak amplitude, depolarized maximum repolarization, and prolonged decay time compared with wild type (WT). Of these differences, only the maximum repolarization was accounted for by the reduction in ClC-1 and Kir currents, indicating the presence of additional ion channel defects. We found that both KV1.5 and KV3.4 mRNA levels were significantly reduced in R6/2 skeletal muscle compared with WT, which explains the prolonged decay time of R6/2 APs. Overall, we found that APs in WT and R6/2 muscle significantly and progressively change during activity to maintain peak amplitude despite buildup of Na+ channel inactivation. Even with this resilience, the persistently reduced peak amplitude of R6/2 APs is expected to result in earlier fatigue and may help explain the motor impersistence experienced by HD patients. This work lays the foundation to link electrical changes to force generation defects in R6/2 HD mice and to examine the regulatory events controlling APs in WT muscle.
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Affiliation(s)
- Daniel R Miranda
- Department of Biological Sciences, Wright State University, Dayton, Ohio
| | - Eric Reed
- Department of Biological Sciences, Wright State University, Dayton, Ohio
| | - Abdulrahman Jama
- Department of Biochemistry and Molecular Biology, Wright State University, Dayton, Ohio
| | - Michael Bottomley
- Department of Mathematics and Statistics, Wright State University, Dayton, Ohio
| | - Hongmei Ren
- Department of Biochemistry and Molecular Biology, Wright State University, Dayton, Ohio
| | - Mark M Rich
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, Ohio
| | - Andrew A Voss
- Department of Biological Sciences, Wright State University, Dayton, Ohio
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Terwoord JD, Hearon CM, Racine ML, Ketelhut NB, Luckasen GJ, Richards JC, Dinenno FA. K IR channel activation links local vasodilatation with muscle fibre recruitment during exercise in humans. J Physiol 2020; 598:2621-2636. [PMID: 32329892 DOI: 10.1113/jp279682] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2020] [Accepted: 04/17/2020] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS During exercise, blood flow to working skeletal muscle increases in parallel with contractile activity such that oxygen delivery is sufficient to meet metabolic demand. K+ released from active skeletal muscle fibres could facilitate vasodilatation in proportion to the degree of muscle fibre recruitment. Once released, K+ stimulates inwardly rectifying K+ (KIR ) channels on the vasculature to elicit an increase in blood flow. In the present study, we demonstrate that KIR channels mediate the rapid vasodilatory response to an increase in exercise intensity. We also show that KIR channels augment vasodilatation during exercise which demands greater muscle fibre recruitment independent of the total amount of work performed. These results suggest that K+ plays a key role in coupling the magnitude of vasodilatation to the degree of contractile activity. Ultimately, the findings from this study help us understand the signalling mechanisms that regulate muscle blood flow in humans. ABSTRACT Blood flow to active skeletal muscle is augmented with greater muscle fibre recruitment. We tested whether activation of inwardly rectifying potassium (KIR ) channels underlies vasodilatation with elevated muscle fibre recruitment when work rate is increased (Protocol 1) or held constant (Protocol 2). We assessed forearm vascular conductance (FVC) during rhythmic handgrip exercise under control conditions and during local inhibition of KIR channels (intra-arterial BaCl2 ). In Protocol 1, healthy volunteers performed mild handgrip exercise for 3 min, then transitioned to moderate intensity for 30 s. BaCl2 eliminated vasodilatation during the first contraction at the moderate workload (ΔFVC, BaCl2 : -1 ± 17 vs. control: 30 ± 28 ml min-1 100 mmHg-1 ; n = 9; P = 0.004) and attenuated the 30 s area under the curve by 56 ± 14% (n = 9; P < 0.0001). In Protocol 2, participants performed two exercise bouts in which muscle fibre recruitment was manipulated while total contractile work was held constant via reciprocal changes in contraction frequency: (1) low fibre recruitment, with contractions at 12.5% maximal voluntary contraction once every 4 s and (2) high fibre recruitment, with contractions at 25% maximal voluntary contraction once every 8 s. Under control conditions, steady-state FVC was augmented in high vs. low fibre recruitment (211 ± 90 vs. 166 ± 73 ml min-1 ⋅100 mmHg-1 ; n = 10; P = 0.0006), whereas BaCl2 abolished the difference between high and low fibre recruitment (134 ± 59 vs. 134 ± 63 ml min-1 100 mmHg-1 ; n = 10; P = 0.85). These findings demonstrate that KIR channel activation is a key mechanism linking local vasodilatation with muscle fibre recruitment during exercise.
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Affiliation(s)
- Janée D Terwoord
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA
| | - Christopher M Hearon
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA
| | - Matthew L Racine
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA
| | - Nathaniel B Ketelhut
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA
| | - Gary J Luckasen
- Medical Center of the Rockies Foundation, University of Colorado Health, Loveland, CO, USA
| | - Jennifer C Richards
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA
| | - Frank A Dinenno
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University, Fort Collins, CO, USA
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Wang M, Sun J, Yang Q. Modeling and simulation of excitation- contraction coupling of fast-twitch skeletal muscle fibers. Technol Health Care 2020; 28:13-24. [PMID: 32364140 PMCID: PMC7369047 DOI: 10.3233/thc-209003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND: The current excitation-contraction coupling model of fast-twitch skeletal muscle fibers cannot completely simulate the excitation-contraction process. OBJECTIVE: To solve this problem, this study proposes an excitation-contraction model of fast-twitch skeletal muscle fibers based on the physiological structure and contractile properties of half-sarcomeres. METHODS: The model includes the action potential model of fast-twitch fiber membranes and transverse tubule membranes, the cycle model of 𝐶𝑎2+ in myofibril, the cross-bridge cycle model, and the fatigue model of metabolism. RESULTS: Finally, detailed analyses of the results from the simulation are conducted using the Simulink toolbox in MATLAB. Two conditions, non-coincidence and coincidence, are analyzed for both the thick and thin myofilaments. CONCLUSIONS: The simulation results of two groups of models are the same as the previous research results, which validates the accuracy of models.
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Affiliation(s)
- Monan Wang
- Corresponding author: Monan Wang, Key Laboratory of Medical Biomechanics and Materials of Heilongjiang Province, Harbin University of Science and Technology, Xuefu Road, Harbin, Heilongjiang, 150080, China. Tel.: +86 451 86390530; Fax: +86 451 86390500; E-mail:
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13
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Zagorchev P, Petkov GV, Gagov HS. Bitter Taste Receptors as Regulators of Abdominal Muscles Contraction. Physiol Res 2019; 68:991-995. [PMID: 31647294 DOI: 10.33549/physiolres.934156] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Bitter taste receptors (TAS2R) are expressed in many non-sensor tissues including skeletal muscles but their function remains unexplored. The aim of this study is to investigate the role of TAS2R in rat abdominal skeletal muscles contractions using denatonium, a TAS2R agonist. Low concentration of denatonium (0.01 mmol/l) caused a significant decrease of amplitudes of the electrical field stimulation (EFS)-induced contractions in abdominal skeletal muscles preparations in vitro. This inhibitory effect was significantly reduced when the preparations were pre-incubated with gentamicin (0.02 mmol/l) used as a non-specific inhibitor of IP3 formation or with BaCl(2) (0.03 mmol/l) applied to block the inward-rectifier potassium current. All experiments were performed in the presence of pipecuronium in order to block the nerve stimulation of the contractions. The data obtained suggest that denatonium decreases the force of rat abdominal muscles contractions mainly via activation of TAS2R, phosphatidylinositol 4,5-biphosphate and its downstream signal metabolites.
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Affiliation(s)
- P Zagorchev
- Faculty of Biology, Sofia University, Sofia, Bulgaria.
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14
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Heiny JA, Cannon SC, DiFranco M. A four-electrode method to study dynamics of ion activity and transport in skeletal muscle fibers. J Gen Physiol 2019; 151:1146-1155. [PMID: 31320390 PMCID: PMC6719403 DOI: 10.1085/jgp.201912398] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 06/18/2019] [Indexed: 11/20/2022] Open
Abstract
Ion movements across biological membranes, driven by electrochemical gradients or active transport mechanisms, control essential cell functions. Membrane ion movements can manifest as electrogenic currents or electroneutral fluxes, and either process can alter the extracellular and/or intracellular concentration of the transported ions. Classic electrophysiological methods allow accurate measurement of membrane ion movements when the transport mechanism produces a net ionic current; however, they cannot directly measure electroneutral fluxes and do not detect any accompanying change in intracellular ion concentrations. Here, we developed a method for simultaneously measuring ion movements and the accompanying dynamic changes in intracellular ion concentrations in intact skeletal muscle fibers under voltage or current clamp in real time. The method combines a two-microelectrode voltage clamp with ion-selective and reference microelectrodes (four-electrode system). We validate the electrical stability of the system and the viability of the preparation for periods of ∼1 h. We demonstrate the power of this method with measurements of intracellular Cl-, H+, and Na+ to show (a) voltage-dependent redistribution of Cl- ions; (b) intracellular pH changes induced by changes in extracellular pCO2; and (c) electroneutral and electrogenic Na+ movements controlled by the Na,K-ATPase. The method is useful for studying a range of transport mechanisms in many cell types, particularly when the transmembrane ion movements are electrically silent and/or when the transport activity measurably changes the intracellular activity of a transported ion.
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Affiliation(s)
- Judith A Heiny
- Department of Pharmacology and Systems Physiology, University of Cincinnati, Cincinnati, OH
| | - Stephen C Cannon
- Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA
| | - Marino DiFranco
- Department of Physiology, David Geffen School of Medicine at University of California, Los Angeles, Los Angeles, CA
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Kir2.2 p.Thr140Met: a genetic susceptibility to sporadic periodic paralysis. ACTA MYOLOGICA : MYOPATHIES AND CARDIOMYOPATHIES : OFFICIAL JOURNAL OF THE MEDITERRANEAN SOCIETY OF MYOLOGY 2018; 37:193-203. [PMID: 30838349 PMCID: PMC6390110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
INTRODUCTION Periodic paralyses (PP) are recurrent episodes of flaccid limb muscle weakness. Next to autosomal dominant forms, sporadic PP (SPP) cases are known but their genetics are unclear. METHODS In a patient with hypokalemic SPP, we performed exome sequencing to identify a candidate gene. We sequenced this gene in 263 unrelated PP patients without any known causative mutations. Then we performed functional analysis of all variants found and molecular modelling for interpretation. RESULTS Exome sequencing in the proband yielded three heterozygous variants predicted to be linked to disease. These encoded p.Thr140Met in the Kir2.2 potassium channel, p.Asp229Asn in protein kinase C theta, and p.Thr15943Ile in titin. Since all hitherto known causative PP genes code for ion channels, we studied the Kir2.2-encoding gene, KCNJ12, for involvement in PP pathogenesis. KCNJ12 screening in 263 PP patients revealed three further variants, each in a single individual and coding for p.Gly419Ser, p.Cys75Tyr, and p.Ile283Val. All four Kir2.2 variants were functionally expressed. Only p.Thr140Met displayed relevant functional alterations, i.e. homo-tetrameric channels produced almost no current, and hetero-tetrameric channels suppressed co-expressed wildtype Kir2.1 in a dominant-negative manner. Molecular modelling showed Kir2.2 p.Thr140Met to reduce movement of potassium ions towards binding sites in the hetero-tetramer pore compatible with a reduced maximal current. MD simulations revealed loss of hydrogen bonding with the p.Thr140Met substitution. DISCUSSION The electrophysiological findings of p.Thr140Met are similar to those found in thyrotoxic PP caused by Kir2.6 mutations. Also, the homologous Thr140 residue is mutated in Kir2.6. This supports the idea that Kir2.2 p.Thr140Met conveys susceptibility to SPP and should be included in genetic screening.
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16
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Terwoord JD, Hearon CM, Luckasen GJ, Richards JC, Joyner MJ, Dinenno FA. Elevated extracellular potassium prior to muscle contraction reduces onset and steady-state exercise hyperemia in humans. J Appl Physiol (1985) 2018; 125:615-623. [PMID: 29722620 DOI: 10.1152/japplphysiol.00183.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The increase in interstitial potassium (K+) during muscle contractions is thought to be a vasodilatory signal that contributes to exercise hyperemia. To determine the role of extracellular K+ in exercise hyperemia, we perfused skeletal muscle with K+ before contractions, such that the effect of any endogenously-released K+ would be minimized. We tested the hypothesis that local, intra-arterial infusion of potassium chloride (KCl) at rest would impair vasodilation in response to subsequent rhythmic handgrip exercise in humans. In 11 young adults, we determined forearm blood flow (FBF) (Doppler ultrasound) and forearm vascular conductance (FVC) (FBF/mean arterial pressure) during 4 min of rhythmic handgrip exercise at 10% of maximal voluntary contraction during 1) control conditions, 2) infusion of KCl before the initiation of exercise, and 3) infusion of sodium nitroprusside (SNP) as a control vasodilator. Infusion of KCl or SNP elevated resting FVC similarly before the onset of exercise (control: 39 ± 6 vs. KCl: 81 ± 12 and SNP: 82 ± 13 ml·min-1·100 mmHg-1; both P < 0.05 vs. control). Infusion of KCl at rest diminished the hyperemic (ΔFBF) and vasodilatory (ΔFVC) response to subsequent exercise by 22 ± 5% and 30 ± 5%, respectively (both P < 0.05 vs. control), whereas SNP did not affect the change in FBF ( P = 0.74 vs. control) or FVC ( P = 0.61 vs. control) from rest to steady-state exercise. These findings implicate the K+ ion as an essential vasodilator substance contributing to exercise hyperemia in humans. NEW & NOTEWORTHY Our findings support a significant and obligatory role for potassium signaling in the local vasodilatory and hyperemic response to exercise in humans.
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Affiliation(s)
- Janée D Terwoord
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University , Fort Collins, Colorado
| | - Christopher M Hearon
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University , Fort Collins, Colorado.,Institute for Exercise and Environmental Medicine, University of Texas Southwestern Medical Center , Dallas, Texas
| | - Gary J Luckasen
- Medical Center of the Rockies Foundation, University of Colorado Health, Loveland, Colorado
| | - Jennifer C Richards
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University , Fort Collins, Colorado
| | - Michael J Joyner
- Department of Anesthesiology, Mayo Clinic , Rochester, Minnesota
| | - Frank A Dinenno
- Human Cardiovascular Physiology Laboratory, Department of Health and Exercise Science, Colorado State University , Fort Collins, Colorado
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17
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Joos B, Markham MR, Lewis JE, Morris CE. A model for studying the energetics of sustained high frequency firing. PLoS One 2018; 13:e0196508. [PMID: 29708986 PMCID: PMC5927439 DOI: 10.1371/journal.pone.0196508] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2017] [Accepted: 04/13/2018] [Indexed: 11/25/2022] Open
Abstract
Regulating membrane potential and synaptic function contributes significantly to the energetic costs of brain signaling, but the relative costs of action potentials (APs) and synaptic transmission during high-frequency firing are unknown. The continuous high-frequency (200-600Hz) electric organ discharge (EOD) of Eigenmannia, a weakly electric fish, underlies its electrosensing and communication. EODs reflect APs fired by the muscle-derived electrocytes of the electric organ (EO). Cholinergic synapses at the excitable posterior membranes of the elongated electrocytes control AP frequency. Based on whole-fish O2 consumption, ATP demand per EOD-linked AP increases exponentially with AP frequency. Continual EOD-AP generation implies first, that ion homeostatic processes reliably counteract any dissipation of posterior membrane ENa and EK and second that high frequency synaptic activation is reliably supported. Both of these processes require energy. To facilitate an exploration of the expected energy demands of each, we modify a previous excitability model and include synaptic currents able to drive APs at frequencies as high as 600 Hz. Synaptic stimuli are modeled as pulsatile cation conductance changes, with or without a small (sustained) background conductance. Over the full species range of EOD frequencies (200–600 Hz) we calculate frequency-dependent “Na+-entry budgets” for an electrocyte AP as a surrogate for required 3Na+/2K+-ATPase activity. We find that the cost per AP of maintaining constant-amplitude APs increases nonlinearly with frequency, whereas the cost per AP for synaptic input current is essentially constant. This predicts that Na+ channel density should correlate positively with EOD frequency, whereas AChR density should be the same across fish. Importantly, calculated costs (inferred from Na+-entry through Nav and ACh channels) for electrocyte APs as frequencies rise are much less than expected from published whole-fish EOD-linked O2 consumption. For APs at increasingly high frequencies, we suggest that EOD-related costs external to electrocytes (including packaging of synaptic transmitter) substantially exceed the direct cost of electrocyte ion homeostasis.
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Affiliation(s)
- Bela Joos
- Department of Physics, University of Ottawa, Ottawa, Ontario, Canada
- Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada
- * E-mail:
| | - Michael R. Markham
- Department of Biology, The University of Oklahoma, Norman, Oklahoma, United States of America
| | - John E. Lewis
- Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Catherine E. Morris
- Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada
- Neuroscience, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
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18
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Beqollari D, Dockstader K, Bannister RA. A skeletal muscle L-type Ca 2+ channel with a mutation in the selectivity filter (Ca V1.1 E1014K) conducts K<sup/>. J Biol Chem 2018; 293:3126-3133. [PMID: 29326166 DOI: 10.1074/jbc.m117.812446] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2017] [Revised: 01/04/2018] [Indexed: 12/17/2022] Open
Abstract
A glutamate-to-lysine substitution at position 1014 within the selectivity filter of the skeletal muscle L-type Ca2+ channel (CaV1.1) abolishes Ca2+ flux through the channel pore. Mice engineered to exclusively express the mutant channel display accelerated muscle fatigue, changes in muscle composition, and altered metabolism relative to wildtype littermates. By contrast, mice expressing another mutant CaV1.1 channel that is impermeable to Ca2+ (CaV1.1 N617D) have shown no detectable phenotypic differences from wildtype mice to date. The major biophysical difference between the CaV1.1 E1014K and CaV1.1 N617D mutants elucidated thus far is that the former channel conducts robust Na+ and Cs+ currents in patch-clamp experiments, but neither of these monovalent conductances seems to be of relevance in vivo Thus, the basis for the different phenotypes of these mutants has remained enigmatic. We now show that CaV1.1 E1014K readily conducts 1,4-dihydropyridine-sensitive K+ currents at depolarizing test potentials, whereas CaV1.1 N617D does not. Our observations, coupled with a large body of work by others regarding the role of K+ accumulation in muscle fatigue, raise the possibility that the introduction of an additional K+ flux from the myoplasm into the transverse-tubule lumen accelerates the onset of fatigue and precipitates the metabolic changes observed in CaV1.1 E1014K muscle. These results, highlighting an unexpected consequence of a channel mutation, may help define the complex mechanisms underlying skeletal muscle fatigue and related dysfunctions.
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Affiliation(s)
- Donald Beqollari
- From the Department of Medicine, Cardiology Division, University of Colorado School of Medicine, Aurora, Colorado 80045
| | - Karen Dockstader
- From the Department of Medicine, Cardiology Division, University of Colorado School of Medicine, Aurora, Colorado 80045
| | - Roger A Bannister
- From the Department of Medicine, Cardiology Division, University of Colorado School of Medicine, Aurora, Colorado 80045
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Simkin D, Robin G, Giuliano S, Vukolic A, Moceri P, Guy N, Wagner KD, Lacampagne A, Allard B, Bendahhou S. Andersen's syndrome mutants produce a knockdown of inwardly rectifying K + channel in mouse skeletal muscle in vivo. Cell Tissue Res 2017; 371:309-323. [PMID: 29018970 DOI: 10.1007/s00441-017-2696-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Accepted: 09/05/2017] [Indexed: 11/30/2022]
Abstract
Andersen's syndrome (AS) is a rare autosomal disorder that has been defined by the triad of periodic paralysis, cardiac arrhythmia, and developmental anomalies. AS has been directly linked to over 40 different autosomal dominant negative loss-of-function mutations in the KCNJ2 gene, encoding for the tetrameric strong inward rectifying K+ channel KIR2.1. While KIR2.1 channels have been suggested to contribute to setting the resting membrane potential (RMP) and to control the duration of the action potential (AP) in skeletal and cardiac muscle, the mechanism by which AS mutations produce such complex pathophysiological symptoms is poorly understood. Thus, we use an adenoviral transduction strategy to study in vivo subcellular distribution of wild-type (WT) and AS-associated mutant KIR2.1 channels in mouse skeletal muscle. We determined that WT and D71V AS mutant KIR2.1 channels are localized to the sarcolemma and the transverse tubules (T-tubules) of skeletal muscle fibers, while the ∆314-315 AS KIR2.1 mutation prevents proper trafficking of the homo- or hetero-meric channel complexes. Whole-cell voltage-clamp recordings in individual skeletal muscle fibers confirmed the reduction of inwardly rectifying K+ current (IK1) after transduction with ∆314-315 KIR2.1 as compared to WT channels. Analysis of skeletal muscle function revealed reduced force generation during isometric contraction as well as reduced resistance to muscle fatigue in extensor digitorum longus muscles transduced with AS mutant KIR2.1. Together, these results suggest that KIR2.1 channels may be involved in the excitation-contraction coupling process required for proper skeletal muscle function. Our findings provide clues to mechanisms associated with periodic paralysis in AS.
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Affiliation(s)
- Dina Simkin
- UMR 7370 CNRS, LP2M, Laboratoire d'Excellence - ICST, Université Côte d'Azur, Faculté de Médecine, 06107, Nice, France.,Department of Pharmacology, Feinberg School of Medicine, Northwestern University, Chicago, IL, 60611, USA
| | - Gaëlle Robin
- UMR CNRS 5534, Université Claude Bernard Lyon 1, 69622, Lyon, France
| | - Serena Giuliano
- UMR 7370 CNRS, LP2M, Laboratoire d'Excellence - ICST, Université Côte d'Azur, Faculté de Médecine, 06107, Nice, France
| | - Ana Vukolic
- Institute for Molecular Health Science, ETH Zurich, 8093, Zurich, Switzerland
| | - Pamela Moceri
- UMR 7370 CNRS, LP2M, Laboratoire d'Excellence - ICST, Université Côte d'Azur, Faculté de Médecine, 06107, Nice, France.,Service de Cardiologie, Pasteur Hospital, CHU de Nice, 06107, Nice, France
| | - Nicolas Guy
- UMR 7275 CNRS, IPMC, Université Côte d'Azur, 06560, Valbonne, France
| | - Kay-Dietrich Wagner
- UMR 7284 CNRS, INSERM, IBV, Université Côte d'Azur, Faculté de Médecine, 06107, Nice, France
| | - Alain Lacampagne
- INSERM U1046, UMR CNRS 9214, Université de Montpellier, CHRU de Montpellier, 34295, Montpellier, France
| | - Bruno Allard
- UMR CNRS 5534, Université Claude Bernard Lyon 1, 69622, Lyon, France
| | - Saïd Bendahhou
- UMR 7370 CNRS, LP2M, Laboratoire d'Excellence - ICST, Université Côte d'Azur, Faculté de Médecine, 06107, Nice, France.
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Defects in Neuromuscular Transmission May Underlie Motor Dysfunction in Spinal and Bulbar Muscular Atrophy. J Neurosci 2017; 36:5094-106. [PMID: 27147661 DOI: 10.1523/jneurosci.3485-15.2016] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 03/22/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Spinal and bulbar muscular atrophy (SBMA) in men is an androgen-dependent neuromuscular disease caused by expanded CAG repeats in the androgen receptor (AR). Whether muscle or motor neuron dysfunction or both underlies motor impairment in SBMA is unknown. Muscles of SBMA mice show significant contractile dysfunction, implicating them as a likely source of motor dysfunction, but whether disease also impairs neuromuscular transmission is an open question. Thus, we examined synaptic function in three well-studied SBMA mouse models-the AR97Q, knock-in (KI), and myogenic141 models-by recording in vitro miniature and evoked end-plate potentials (MEPPs and EPPs, respectively) intracellularly from adult muscle fibers. We found striking defects in neuromuscular transmission suggesting that toxic AR in SBMA impairs both presynaptic and postsynaptic mechanisms. Notably, SBMA causes neuromuscular synapses to become weak and muscles to become hyperexcitable in all three models. Presynaptic defects included deficits in quantal content, reduced size of the readily releasable pool, and impaired short-term facilitation. Postsynaptic defects included prolonged decay times for both MEPPs and EPPs, marked resistance to μ-conotoxin (a sodium channel blocker), and enhanced membrane excitability. Quantitative PCR revealed robust upregulation of mRNAs encoding neonatal isoforms of the AChR (γ-subunit) and the voltage-gated sodium channel (NaV1.5) in diseased adult muscles of all three models, consistent with the observed slowing of synaptic potentials and resistance to μ-conotoxin. These findings suggest that muscles of SBMA patients regress to an immature state that impairs neuromuscular function. SIGNIFICANCE STATEMENT We have discovered that SBMA is accompanied by marked defects in neuromuscular synaptic transmission involving both presynaptic and postsynaptic mechanisms. For three different mouse models, we find that diseased synapses are weak, having reduced quantal content due to reductions in the size of the readily releasable pool and/or probability of release. Synaptic potentials in diseased adult fibers are slowed, explained by an aberrant upregulation of the neonatal isoform of the acetylcholine receptor. Diseased fibers also show marked resistance to μ-conotoxin, explained by an aberrant upregulation in the neonatal isoform of the sodium channel, and are hyperexcitable, reminiscent of myotonic dystrophy, showing anode-break action potentials. This work identifies several new molecular targets for recovering function in SBMA.
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21
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DiFranco M, Kramerova I, Vergara JL, Spencer MJ. Attenuated Ca(2+) release in a mouse model of limb girdle muscular dystrophy 2A. Skelet Muscle 2016; 6:11. [PMID: 26913171 PMCID: PMC4765215 DOI: 10.1186/s13395-016-0081-y] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 01/30/2016] [Indexed: 02/02/2023] Open
Abstract
Background Mutations in CAPN3 cause limb girdle muscular dystrophy type 2A (LGMD2A), a progressive muscle wasting disease. CAPN3 is a non-lysosomal, Ca-dependent, muscle-specific proteinase. Ablation of CAPN3 (calpain-3 knockout (C3KO) mice) leads to reduced ryanodine receptor (RyR1) expression and abnormal Ca2+/calmodulin-dependent protein kinase II (Ca-CaMKII)-mediated signaling. We previously reported that Ca2+ release measured by fura2-FF imaging in response to single action potential stimulation was reduced in old C3KO mice; however, the use of field stimulation prevented investigation of the mechanisms underlying this impairment. Furthermore, our prior studies were conducted on older animals, whose muscles showed advanced muscular dystrophy, which prevented us from establishing whether impaired Ca2+ handling is an early feature of disease. In the current study, we sought to overcome these matters by studying single fibers isolated from young wild-type (WT) and C3KO mice using a low affinity calcium dye and high intracellular ethylene glycol-bis(2-aminoethylether)-n,n,n′,n′-tetraacetic acid (EGTA) to measure Ca2+ fluxes. Muscles were subjected to both current and voltage clamp conditions. Methods Standard and confocal fluorescence microscopy was used to study Ca2+ release in single fibers enzymatically isolated from hind limb muscles of wild-type and C3KO mice. Two microelectrode amplifier and experiments were performed under current or voltage clamp conditions. Calcium concentration changes were detected with an impermeant low affinity dye in the presence of high EGTA intracellular concentrations, and fluxes were calculated with a single compartment model. Standard Western blotting analysis was used to measure the concentration of RyR1 and the α subunit of the dihydropyridine (αDHPR) receptors. Data are presented as mean ± SEM and compared with the Student’s test with significance set at p < 0.05. Results We found that the peak value of Ca2+ fluxes elicited by single action potentials was significantly reduced by 15–20 % in C3KO fibers, but the kinetics was unaltered. Ca2+ release elicited by tetanic stimulation was also impaired in C3KO fibers. Confocal studies confirmed that Ca2+ release was similarly reduced in all triads of C3KO mice. Voltage clamp experiments revealed a normal voltage dependence of Ca2+ release in C3KO mice but reduced peak Ca2+ fluxes as with action potential stimulation. These findings concur with biochemical observations of reduced RyR1 and αDHPR levels in C3KO muscles and reduced mechanical output. Confocal studies revealed a similar decrease in Ca2+ release at all triads consistent with a homogenous reduction of functional voltage activated Ca2+ release sites. Conclusions Overall, these results suggest that decreased Ca2+ release is an early defect in calpainopathy and may contribute to the observed reduction of CaMKII activation in C3KO mice.
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Affiliation(s)
- Marino DiFranco
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095 USA ; Center for Duchenne Muscular Dystrophy at UCLA, 635 Charles E. Young Dr. South, NRB Rm. 401, Los Angeles, CA 90095 USA
| | - Irina Kramerova
- Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, 90095 USA ; Center for Duchenne Muscular Dystrophy at UCLA, 635 Charles E. Young Dr. South, NRB Rm. 401, Los Angeles, CA 90095 USA
| | - Julio L Vergara
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, CA 90095 USA ; Center for Duchenne Muscular Dystrophy at UCLA, 635 Charles E. Young Dr. South, NRB Rm. 401, Los Angeles, CA 90095 USA
| | - Melissa Jan Spencer
- Department of Neurology, David Geffen School of Medicine, University of California, Los Angeles, 90095 USA ; Center for Duchenne Muscular Dystrophy at UCLA, 635 Charles E. Young Dr. South, NRB Rm. 401, Los Angeles, CA 90095 USA
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DiFranco M, Hakimjavadi H, Lingrel JB, Heiny JA. Na,K-ATPase α2 activity in mammalian skeletal muscle T-tubules is acutely stimulated by extracellular K+. ACTA ACUST UNITED AC 2015; 146:281-94. [PMID: 26371210 PMCID: PMC4586590 DOI: 10.1085/jgp.201511407] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2015] [Accepted: 08/21/2015] [Indexed: 11/20/2022]
Abstract
The K+ affinity of the Na,K-ATPase α2 isoform matches its activity to the range of extracellular K+ concentrations in the T-tubules at rest and during contraction, maintaining the excitability of active muscle. The Na,K-ATPase α2 isoform is the predominant Na,K-ATPase in adult skeletal muscle and the sole Na,K-ATPase in the transverse tubules (T-tubules). In quiescent muscles, the α2 isozyme operates substantially below its maximal transport capacity. Unlike the α1 isoform, the α2 isoform is not required for maintaining resting ion gradients or the resting membrane potential, canonical roles of the Na,K-ATPase in most other cells. However, α2 activity is stimulated immediately upon the start of contraction and, in working muscles, its contribution is crucial to maintaining excitation and resisting fatigue. Here, we show that α2 activity is determined in part by the K+ concentration in the T-tubules, through its K+ substrate affinity. Apparent K+ affinity was determined from measurements of the K1/2 for K+ activation of pump current in intact, voltage-clamped mouse flexor digitorum brevis muscle fibers. Pump current generated by the α2 Na,K-ATPase, Ip, was identified as the outward current activated by K+ and inhibited by micromolar ouabain. Ip was outward at all potentials studied (−90 to −30 mV) and increased with depolarization in the subthreshold range, −90 to −50 mV. The Q10 was 2.1 over the range of 22–37°C. The K1/2,K of Ip was 4.3 ± 0.3 mM at −90 mV and was relatively voltage independent. This K+ affinity is lower than that reported for other cell types but closely matches the dynamic range of extracellular K+ concentrations in the T-tubules. During muscle contraction, T-tubule luminal K+ increases in proportion to the frequency and duration of action potential firing. This K1/2,K predicts a low fractional occupancy of K+ substrate sites at the resting extracellular K+ concentration, with occupancy increasing in proportion to the frequency of membrane excitation. The stimulation of preexisting pumps by greater K+ site occupancy thus provides a rapid mechanism for increasing α2 activity in working muscles.
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Affiliation(s)
- Marino DiFranco
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095
| | - Hesamedin Hakimjavadi
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267
| | - Jerry B Lingrel
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267
| | - Judith A Heiny
- Department of Molecular and Cellular Physiology, University of Cincinnati College of Medicine, Cincinnati, OH 45267
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