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Fahlke C. Reinhardt Rüdel : Muscle physiologist, mentor, role model. Pflugers Arch 2024; 476:1-2. [PMID: 38015255 PMCID: PMC10758359 DOI: 10.1007/s00424-023-02886-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Revised: 11/03/2023] [Accepted: 11/08/2023] [Indexed: 11/29/2023]
Affiliation(s)
- Christoph Fahlke
- Institute of Biological Information Processing, Molekular- und Zellphysiologie (IBI-1), Forschungszentrum Jülich, 52425, Jülich, Germany.
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2
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Gada KD, Kamuene JM, Chandrashekar A, Kissell RC, Yauch AK, Plant LD. PI(4,5)P2 regulates the gating of NaV1.4 channels. J Gen Physiol 2023; 155:e202213255. [PMID: 37043561 PMCID: PMC10103707 DOI: 10.1085/jgp.202213255] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Revised: 02/22/2023] [Accepted: 03/22/2023] [Indexed: 04/14/2023] Open
Abstract
Voltage-gated sodium (NaV) channels are densely expressed in most excitable cells and activate in response to depolarization, causing a rapid influx of Na+ ions that initiates the action potential. The voltage-dependent activation of NaV channels is followed almost instantaneously by fast inactivation, setting the refractory period of excitable tissues. The gating cycle of NaV channels is subject to tight regulation, with perturbations leading to a range of pathophysiological states. The gating properties of most ion channels are regulated by the membrane phospholipid, phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2). However, it is not known whether PI(4,5)P2 modulates the activity of NaV channels. Here, we utilize optogenetics to activate specific, membrane-associated phosphoinositide (PI)-phosphatases that dephosphorylate PI(4,5)P2 while simultaneously recording NaV1.4 channel currents. We show that dephosphorylating PI(4,5)P2 left-shifts the voltage-dependent gating of NaV1.4 to more hyperpolarized membrane potentials, augments the late current that persists after fast inactivation, and speeds the rate at which channels recover from fast inactivation. These effects are opposed by exogenous diC8PI(4,5)P2. We provide evidence that PI(4,5)P2 is a negative regulator that tunes the gating behavior of NaV1.4 channels.
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Affiliation(s)
- Kirin D. Gada
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Jordie M. Kamuene
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Aishwarya Chandrashekar
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - R. Charles Kissell
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Anne K. Yauch
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
| | - Leigh D. Plant
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, Bouvé College of Health Sciences, Northeastern University, Boston, MA, USA
- Center for Drug Discovery, Northeastern University, Boston, MA, USA
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3
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Trivedi JR. Muscle Channelopathies. Continuum (Minneap Minn) 2022; 28:1778-1799. [PMID: 36537980 DOI: 10.1212/con.0000000000001183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
PURPOSE OF REVIEW This article describes the clinical features, diagnosis, pathophysiology, and management of nondystrophic myotonia and periodic paralysis. RECENT FINDINGS An increasing awareness exists about the genotype-phenotype overlap in skeletal muscle channelopathies, and thus genetic testing is needed to make a definitive diagnosis. Electrodiagnostic testing in channelopathies is highly specialized with significant overlap in various mutation subtypes. Randomized clinical trials have now been conducted in these disorders with expanded treatment options for patients with muscle channelopathies. SUMMARY Skeletal muscle channelopathies are rare heterogeneous conditions characterized by lifelong symptoms that require a comprehensive management plan that includes pharmacologic and nonpharmacologic interventions. The significant variability in biophysical features of various mutations, coupled with the difficulties of performing clinical trials in rare diseases, makes it challenging to design and implement treatment trials for muscle channelopathies.
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4
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Nicole S, Lory P. New Challenges Resulting From the Loss of Function of Na v1.4 in Neuromuscular Diseases. Front Pharmacol 2021; 12:751095. [PMID: 34671263 PMCID: PMC8521073 DOI: 10.3389/fphar.2021.751095] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Accepted: 09/16/2021] [Indexed: 11/13/2022] Open
Abstract
The voltage-gated sodium channel Nav1.4 is a major actor in the excitability of skeletal myofibers, driving the muscle force in response to nerve stimulation. Supporting further this key role, mutations in SCN4A, the gene encoding the pore-forming α subunit of Nav1.4, are responsible for a clinical spectrum of human diseases ranging from muscle stiffness (sodium channel myotonia, SCM) to muscle weakness. For years, only dominantly-inherited diseases resulting from Nav1.4 gain of function (GoF) were known, i.e., non-dystrophic myotonia (delayed muscle relaxation due to myofiber hyperexcitability), paramyotonia congenita and hyperkalemic or hypokalemic periodic paralyses (episodic flaccid muscle weakness due to transient myofiber hypoexcitability). These last 5 years, SCN4A mutations inducing Nav1.4 loss of function (LoF) were identified as the cause of dominantly and recessively-inherited disorders with muscle weakness: periodic paralyses with hypokalemic attacks, congenital myasthenic syndromes and congenital myopathies. We propose to name this clinical spectrum sodium channel weakness (SCW) as the mirror of SCM. Nav1.4 LoF as a cause of permanent muscle weakness was quite unexpected as the Na+ current density in the sarcolemma is large, securing the ability to generate and propagate muscle action potentials. The properties of SCN4A LoF mutations are well documented at the channel level in cellular electrophysiological studies However, much less is known about the functional consequences of Nav1.4 LoF in skeletal myofibers with no available pertinent cell or animal models. Regarding the therapeutic issues for Nav1.4 channelopathies, former efforts were aimed at developing subtype-selective Nav channel antagonists to block myofiber hyperexcitability. Non-selective, Nav channel blockers are clinically efficient in SCM and paramyotonia congenita, whereas patient education and carbonic anhydrase inhibitors are helpful to prevent attacks in periodic paralyses. Developing therapeutic tools able to counteract Nav1.4 LoF in skeletal muscles is then a new challenge in the field of Nav channelopathies. Here, we review the current knowledge regarding Nav1.4 LoF and discuss the possible therapeutic strategies to be developed in order to improve muscle force in SCW.
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Affiliation(s)
- Sophie Nicole
- Institut de Génomique Fonctionnelle (IGF), Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics (ICST), Montpellier, France
| | - Philippe Lory
- Institut de Génomique Fonctionnelle (IGF), Université de Montpellier, CNRS, INSERM, Montpellier, France.,LabEx 'Ion Channel Science and Therapeutics (ICST), Montpellier, France
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5
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Uwera F, Ammar T, McRae C, Hayward LJ, Renaud JM. Lower Ca2+ enhances the K+-induced force depression in normal and HyperKPP mouse muscles. J Gen Physiol 2021; 152:151656. [PMID: 32291438 PMCID: PMC7335014 DOI: 10.1085/jgp.201912511] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 02/18/2020] [Accepted: 03/21/2020] [Indexed: 12/20/2022] Open
Abstract
Hyperkalemic periodic paralysis (HyperKPP) manifests as stiffness or subclinical myotonic discharges before or during periods of episodic muscle weakness or paralysis. Ingestion of Ca2+ alleviates HyperKPP symptoms, but the mechanism is unknown because lowering extracellular [Ca2+] ([Ca2+]e) has no effect on force development in normal muscles under normal conditions. Lowering [Ca2+]e, however, is known to increase the inactivation of voltage-gated cation channels, especially when the membrane is depolarized. Two hypotheses were tested: (1) lowering [Ca2+]e depresses force in normal muscles under conditions that depolarize the cell membrane; and (2) HyperKPP muscles have a greater sensitivity to low Ca2+-induced force depression because many fibers are depolarized, even at a normal [K+]e. In wild type muscles, lowering [Ca2+]e from 2.4 to 0.3 mM had little effect on tetanic force and membrane excitability at a normal K+ concentration of 4.7 mM, whereas it significantly enhanced K+-induced depression of force and membrane excitability. In HyperKPP muscles, lowering [Ca2+]e enhanced the K+-induced loss of force and membrane excitability not only at elevated [K+]e but also at 4.7 mM K+. Lowering [Ca2+]e increased the incidence of generating fast and transient contractures and gave rise to a slower increase in unstimulated force, especially in HyperKPP muscles. Lowering [Ca2+]e reduced the efficacy of salbutamol, a β2 adrenergic receptor agonist and a treatment for HyperKPP, to increase force at elevated [K+]e. Replacing Ca2+ by an equivalent concentration of Mg2+ neither fully nor consistently reverses the effects of lowering [Ca2+]e. These results suggest that the greater Ca2+ sensitivity of HyperKPP muscles primarily relates to (1) a greater effect of Ca2+ in depolarized fibers and (2) an increased proportion of depolarized HyperKPP muscle fibers compared with control muscle fibers, even at normal [K+]e.
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Affiliation(s)
- Francine Uwera
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
| | - Tarek Ammar
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
| | - Callum McRae
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
| | - Lawrence J Hayward
- Department of Neurology, University of Massachusetts Medical School, Worcester, MA
| | - Jean-Marc Renaud
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
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6
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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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7
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Stunnenberg BC, LoRusso S, Arnold WD, Barohn RJ, Cannon SC, Fontaine B, Griggs RC, Hanna MG, Matthews E, Meola G, Sansone VA, Trivedi JR, van Engelen BG, Vicart S, Statland JM. Guidelines on clinical presentation and management of nondystrophic myotonias. Muscle Nerve 2020; 62:430-444. [PMID: 32270509 PMCID: PMC8117169 DOI: 10.1002/mus.26887] [Citation(s) in RCA: 46] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Revised: 04/01/2020] [Accepted: 04/04/2020] [Indexed: 12/26/2022]
Abstract
The nondystrophic myotonias are rare muscle hyperexcitability disorders caused by gain-of-function mutations in the SCN4A gene or loss-of-function mutations in the CLCN1 gene. Clinically, they are characterized by myotonia, defined as delayed muscle relaxation after voluntary contraction, which leads to symptoms of muscle stiffness, pain, fatigue, and weakness. Diagnosis is based on history and examination findings, the presence of electrical myotonia on electromyography, and genetic confirmation. In the absence of genetic confirmation, the diagnosis is supported by detailed electrophysiological testing, exclusion of other related disorders, and analysis of a variant of uncertain significance if present. Symptomatic treatment with a sodium channel blocker, such as mexiletine, is usually the first step in management, as well as educating patients about potential anesthetic complications.
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Affiliation(s)
- Bas C. Stunnenberg
- Department of Neurology, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Samantha LoRusso
- Department of Neurology, Ohio State University Wexner Medical Center, Columbus, Ohio
| | - W. David Arnold
- Department of Neurology, Ohio State University Wexner Medical Center, Columbus, Ohio
| | - Richard J. Barohn
- Department of Neurology, University of Kansas Medical Center, Kansas City, Kansas
| | - Stephen C. Cannon
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California
| | - Bertrand Fontaine
- Assistance Publique-Hôpitaix de Paris, Sorbonne Université, INSERM, Service of Neuro-Myology and UMR 974, Institute of Myology, University Hospital Pitié-Salpêtrière, Paris, France
| | - Robert C. Griggs
- Department of Neurology, University of Rochester, Rochester, New York
| | - Michael G. Hanna
- MRC Centre for Neuromuscular Diseases, Department of Neuromuscular diseases, UCL Queen Square Institute of Neurology, United Kingdom
| | - Emma Matthews
- MRC Centre for Neuromuscular Diseases, Department of Neuromuscular diseases, UCL Queen Square Institute of Neurology, United Kingdom
| | - Giovanni Meola
- Department of Neurorehabilitation Sciences, Casa Cura Policlinico, Milan, Italy
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
| | - Valeria A. Sansone
- Department of Biomedical Sciences for Health, University of Milan, Milan, Italy
- Neurorehabilitation Unit, University of Milan, NEuroMuscular Omnicentre (NEMO), Fondazione Serena Onlus, Milan, Italy
| | - Jaya R. Trivedi
- Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, Dallas, Texas
| | | | - Savine Vicart
- Assistance Publique-Hôpitaix de Paris, Sorbonne Université, INSERM, Service of Neuro-Myology and UMR 974, Institute of Myology, University Hospital Pitié-Salpêtrière, Paris, France
| | - Jeffrey M. Statland
- Department of Neurology, University of Kansas Medical Center, Kansas City, Kansas
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8
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Mi W, Wu F, Quinonez M, DiFranco M, Cannon SC. Recovery from acidosis is a robust trigger for loss of force in murine hypokalemic periodic paralysis. J Gen Physiol 2019; 151:555-566. [PMID: 30733232 PMCID: PMC6445579 DOI: 10.1085/jgp.201812231] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Accepted: 01/28/2019] [Indexed: 01/12/2023] Open
Abstract
Hypokalemic periodic paralysis causes episodes of muscle weakness. Mi et al. investigate the rest-induced weakness that occurs after vigorous exercise and find that acidosis, as occurs with exercise, leads to accumulation of myoplasmic Cl−, which favors a depolarized resting potential when pH returns to normal. Periodic paralysis is an ion channelopathy of skeletal muscle in which recurrent episodes of weakness or paralysis are caused by sustained depolarization of the resting potential and thus reduction of fiber excitability. Episodes are often triggered by environmental stresses, such as changes in extracellular K+, cooling, or exercise. Rest after vigorous exercise is the most common trigger for weakness in periodic paralysis, but the mechanism is unknown. Here, we use knock-in mutant mouse models of hypokalemic periodic paralysis (HypoKPP; NaV1.4-R669H or CaV1.1-R528H) and hyperkalemic periodic paralysis (HyperKPP; NaV1.4-M1592V) to investigate whether the coupling between pH and susceptibility to loss of muscle force is a possible contributor to exercise-induced weakness. In both mouse models, acidosis (pH 6.7 in 25% CO2) is mildly protective, but a return to pH 7.4 (5% CO2) unexpectedly elicits a robust loss of force in HypoKPP but not HyperKPP muscle. Prolonged exposure to low pH (tens of minutes) is required to cause susceptibility to post-acidosis loss of force, and the force decrement can be prevented by maneuvers that impede Cl− entry. Based on these data, we propose a mechanism for post-acidosis loss of force wherein the reduced Cl− conductance in acidosis leads to a slow accumulation of myoplasmic Cl−. A rapid recovery of both pH and Cl− conductance, in the context of increased [Cl]in/[Cl]out, favors the anomalously depolarized state of the bistable resting potential in HypoKPP muscle, which reduces fiber excitability. This mechanism is consistent with the delayed onset of exercise-induced weakness that occurs with rest after vigorous activity.
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Affiliation(s)
- Wentao Mi
- Department of Neurology & Neurotherapeutics, UT Southwestern Medical Center, Dallas, TX
| | - Fenfen Wu
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Marbella Quinonez
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Marino DiFranco
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
| | - Stephen C Cannon
- Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA
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9
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Abstract
Skeletal muscle channelopathies are rare heterogeneous diseases with marked genotypic and phenotypic variability. These disorders cause lifetime disability and impact quality of life. Despite advances in understanding of the molecular pathology of these disorders, the diverse phenotypic manifestations remain a challenge in diagnosis, therapeutic, genetic counseling, and research planning. Electrodiagnostic testing is useful in directing the diagnosis, but has several limitations: patient discomfort, time consuming, and significant overlap of findings in muscle channelopathies. Although genetic testing is the gold standard in making a definitive diagnosis, a mutation might not be identified in many patients with a well-supported clinical diagnosis of periodic paralysis. In the recent past, there have been landmark clinical trials in non-dystrophic myotonia and periodic paralysis which are encouraging as they demonstrate the ability of robust clinical research consortia to conduct well-controlled trials of rare diseases.
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Affiliation(s)
- Lauren Phillips
- Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas, 75390, USA
| | - Jaya R Trivedi
- Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas, 75390, USA.
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10
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Marakhonov AV, Varenikov GG, Skoblov MY. Sodium Channelopathies: From Molecular Physiology towards Medical Genetics. RUSS J GENET+ 2018. [DOI: 10.1134/s102279541801009x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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11
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Ammar T, Lin W, Higgins A, Hayward LJ, Renaud JM. Understanding the physiology of the asymptomatic diaphragm of the M1592V hyperkalemic periodic paralysis mouse. ACTA ACUST UNITED AC 2017; 146:509-25. [PMID: 26621775 PMCID: PMC4664826 DOI: 10.1085/jgp.201511476] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
When muscles become paralyzed in crises of hyperkalemic periodic paralysis, patients do not stop breathing. Here is why. The diaphragm muscle of hyperkalemic periodic paralysis (HyperKPP) patients and of the M1592V HyperKPP mouse model rarely suffers from the myotonic and paralytic symptoms that occur in limb muscles. Enigmatically, HyperKPP diaphragm expresses the mutant NaV1.4 channel and, more importantly, has an abnormally high Na+ influx similar to that in extensor digitorum longus (EDL) and soleus, two hindlimb muscles suffering from the robust HyperKPP abnormalities. The objective was to uncover the physiological mechanisms that render HyperKPP diaphragm asymptomatic. A first mechanism involves efficient maintenance of resting membrane polarization in HyperKPP diaphragm at various extracellular K+ concentrations compared with larger membrane depolarizations in HyperKPP EDL and soleus. The improved resting membrane potential (EM) results from significantly increased Na+ K+ pump electrogenic activity, and not from an increased protein content. Action potential amplitude was greater in HyperKPP diaphragm than in HyperKPP soleus and EDL, providing a second mechanism for the asymptomatic behavior of the HyperKPP diaphragm. One suggested mechanism for the greater action potential amplitude is lower intracellular Na+ concentration because of greater Na+ K+ pump activity, allowing better Na+ current during the action potential depolarization phase. Finally, HyperKPP diaphragm had a greater capacity to generate force at depolarized EM compared with wild-type diaphragm. Action potential amplitude was not different between wild-type and HyperKPP diaphragm. There was also no evidence for an increased activity of the Na+–Ca2+ exchanger working in the reverse mode in the HyperKPP diaphragm compared with the wild-type diaphragm. So, a third mechanism remains to be elucidated to fully understand how HyperKPP diaphragm generates more force compared with wild type. Although the mechanism for the greater force at depolarized resting EM remains to be determined, this study provides support for the modulation of the Na+ K+ pump as a component of therapy to alleviate weakness in HyperKPP.
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Affiliation(s)
- Tarek Ammar
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Wei Lin
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Amanda Higgins
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
| | - Lawrence J Hayward
- Department of Neurology, University of Massachusetts Medical School, Worcester, MA 01655
| | - Jean-Marc Renaud
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada
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12
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Abstract
Familial disorders of skeletal muscle excitability were initially described early in the last century and are now known to be caused by mutations of voltage-gated ion channels. The clinical manifestations are often striking, with an inability to relax after voluntary contraction (myotonia) or transient attacks of severe weakness (periodic paralysis). An essential feature of these disorders is fluctuation of symptoms that are strongly impacted by environmental triggers such as exercise, temperature, or serum K(+) levels. These phenomena have intrigued physiologists for decades, and in the past 25 years the molecular lesions underlying these disorders have been identified and mechanistic studies are providing insights for therapeutic strategies of disease modification. These familial disorders of muscle fiber excitability are "channelopathies" caused by mutations of a chloride channel (ClC-1), sodium channel (NaV1.4), calcium channel (CaV1.1), and several potassium channels (Kir2.1, Kir2.6, and Kir3.4). This review provides a synthesis of the mechanistic connections between functional defects of mutant ion channels, their impact on muscle excitability, how these changes cause clinical phenotypes, and approaches toward therapeutics.
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Affiliation(s)
- Stephen C Cannon
- Department of Physiology, David Geffen School of Medicine, UCLA, Los Angeles, CA, USA
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13
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Khogali S, Lucas B, Ammar T, Dejong D, Barbalinardo M, Hayward LJ, Renaud JM. Physiological basis for muscle stiffness and weakness in a knock-in M1592V mouse model of hyperkalemic periodic paralysis. Physiol Rep 2015; 3:3/12/e12656. [PMID: 26702073 PMCID: PMC4760441 DOI: 10.14814/phy2.12656] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 11/18/2015] [Indexed: 11/24/2022] Open
Abstract
The mechanisms responsible for the onset and progressive worsening of episodic muscle stiffness and weakness in hyperkalemic periodic paralysis (HyperKPP) are not fully understood. Using a knock‐in HyperKPP mouse model harboring the M1592V NaV1.4 channel mutant, we interrogated changes in physiological defects during the first year, including tetrodotoxin‐sensitive Na+ influx, hindlimb electromyographic (EMG) activity and immobility, muscle weakness induced by elevated [K+]e, myofiber‐type composition, and myofiber damage. In situ EMG activity was greater in HyperKPP than wild‐type gastrocnemius, whereas spontaneous muscle contractions were observed in vitro. We suggest that both the greater EMG activity and spontaneous contractions are related to periods of hyperexcitability during which fibers generate action potentials by themselves in the absence of any stimulation and that these periods are the cause of the muscle stiffness reported by patients. HyperKPP muscles had a greater sensitivity to the K+‐induced force depression than wild‐type muscles. So, an increased interstitial K+ concentration locally near subsets of myofibers as a result of the hyperexcitability likely produced partial loss of force rather than complete paralysis. NaV1.4 channel protein content reached adult level by 3 weeks postnatal in both wild type and HyperKPP and apparent symptoms did not worsen after the first month of age suggesting (i) that the phenotypic behavior of M1592V HyperKPP muscles results from defective function of mutant NaV1.4 channels rather than other changes in protein expression after the first month and (ii) that the lag in onset during the first decade and the progression of human HyperKPP symptoms during adolescence are a function of NaV1.4 channel content.
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Affiliation(s)
- Shiemaa Khogali
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Brooke Lucas
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Tarek Ammar
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Danica Dejong
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Michael Barbalinardo
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Lawrence J Hayward
- Department of Neurology, University of Massachusetts Medical School, Worcester, Massachusetts
| | - Jean-Marc Renaud
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
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15
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Lucas B, Ammar T, Khogali S, DeJong D, Barbalinardo M, Nishi C, Hayward LJ, Renaud JM. Contractile abnormalities of mouse muscles expressing hyperkalemic periodic paralysis mutant NaV1.4 channels do not correlate with Na+ influx or channel content. Physiol Genomics 2014; 46:385-97. [PMID: 24714718 DOI: 10.1152/physiolgenomics.00166.2013] [Citation(s) in RCA: 12] [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
Hyperkalemic periodic paralysis (HyperKPP) is characterized by myotonic discharges that occur between episodic attacks of paralysis. Individuals with HyperKPP rarely suffer respiratory distress even though diaphragm muscle expresses the same defective Na(+) channel isoform (NaV1.4) that causes symptoms in limb muscles. We tested the hypothesis that the extent of the HyperKPP phenotype (low force generation and shift toward oxidative type I and IIA fibers) in muscle is a function of 1) the NaV1.4 channel content and 2) the Na(+) influx through the defective channels [i.e., the tetrodotoxin (TTX)-sensitive Na(+) influx]. We measured NaV1.4 channel protein content, TTX-sensitive Na(+) influx, force generation, and myosin isoform expression in four muscles from knock-in mice expressing a NaV1.4 isoform corresponding to the human M1592V mutant. The HyperKPP flexor digitorum brevis muscle showed no contractile abnormalities, which correlated well with its low NaV1.4 protein content and by far the lowest TTX-sensitive Na(+) influx. In contrast, diaphragm muscle expressing the HyperKPP mutant contained high levels of NaV1.4 protein and exhibited a TTX-sensitive Na(+) influx that was 22% higher compared with affected extensor digitorum longus (EDL) and soleus muscles. Surprisingly, despite this high burden of Na(+) influx, the contractility phenotype was very mild in mutant diaphragm compared with the robust abnormalities observed in EDL and soleus. This study provides evidence that HyperKPP phenotype does not depend solely on the NaV1.4 content or Na(+) influx and that the diaphragm does not depend solely on Na(+)-K(+) pumps to ameliorate the phenotype.
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Affiliation(s)
- Brooke Lucas
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; and
| | - Tarek Ammar
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; and
| | - Shiemaa Khogali
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; and
| | - Danica DeJong
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; and
| | - Michael Barbalinardo
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; and
| | - Cameron Nishi
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; and
| | - Lawrence J Hayward
- Department of Neurology, University of Massachusetts Medical School, Worcester, Massachusetts
| | - Jean-Marc Renaud
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada; and
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16
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Abstract
Mutations in the skeletal muscle voltage-gated calcium channel (CaV1.1) have been associated with hypokalemic periodic paralysis, but how the pathogenesis of this disorder relates to the functional consequences of mutations was unclear. In this issue of the JCI, Wu and colleagues recapitulate the disease by generating a novel knock-in CaV1.1 mutant mouse and use this model to investigate the cellular and molecular features of pathogenesis. They demonstrated an aberrant muscle cell current conducted through the CaV1.1 voltage-sensor domain (gating pore current) that explains an abnormally depolarized muscle membrane and the failure of muscle action potential firing during challenge with agents known to provoke periodic paralysis. Their work advances understanding of molecular and cellular mechanisms underlying an inherited channelopathy.
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Affiliation(s)
- Alfred L George
- Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232, USA.
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17
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Jurkat-Rott K, Lerche H, Weber Y, Lehmann-Horn F. Hereditary channelopathies in neurology. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 686:305-34. [PMID: 20824453 DOI: 10.1007/978-90-481-9485-8_18] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Ion channelopathies are caused by malfunction or altered regulation of ion channel proteins due to hereditary or acquired protein changes. In neurology, main phenotypes include certain forms of epilepsy, ataxia, migraine, neuropathic pain, myotonia, and muscle weakness including myasthenia and periodic paralyses. The total prevalence of monogenic channelopathies in neurology is about 35:100,000. Susceptibility-related mutations further increase the relevance of channel genes in medicine considerably. As many disease mechanisms have been elucidated by functional characterization on the molecular level, the channelopathies are regarded as model disorders for pathogenesis and treatment of non-monogenic forms of epilepsy and migraine. As more than 35% of marketed drugs target ion channels, there is a high chance to identify compounds that counteract the effects of the mutations.
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18
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Cannon SC, Bean BP. Sodium channels gone wild: resurgent current from neuronal and muscle channelopathies. J Clin Invest 2009; 120:80-3. [PMID: 20038809 DOI: 10.1172/jci41340] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Voltage-dependent sodium channels are the central players in the excitability of neurons, cardiac muscle, and skeletal muscle. Hundreds of mutations in sodium channels have been associated with human disease, particularly genetic forms of epilepsy, arrhythmias, myotonia, and periodic paralysis. In this issue of the JCI, Jarecki and colleagues present evidence suggesting that many such mutations alter the gating of sodium channels to produce resurgent sodium current, an unusual form of gating in which sodium channels reopen following an action potential, thus promoting the firing of another action potential (see the related article beginning on page 369). The results of this study suggest a widespread pathophysiological role for this mechanism, previously described to occur normally in only a few types of neurons.
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Affiliation(s)
- Stephen C Cannon
- Department of Neurology, University of Texas Southwestern Medical Center, 5223 Harry Hines Blvd., Dallas, Texas 75390-8813, USA.
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19
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Rudolph JA, Spier SJ, Byrns G, Hoffman EP. Linkage of hyperkalaemic periodic paralysis in quarter horses to the horse adult skeletal muscle sodium channel gene. Anim Genet 2009; 23:241-50. [PMID: 1323940 DOI: 10.1111/j.1365-2052.1992.tb00136.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A genetic disease observed in certain Quarter horses is hyperkalaemic periodic paralysis (HYPP). This disease causes attacks of paralysis which can be induced by ingestion of potassium. Recent studies have shown that HYPP in humans is due to single base changes within the adult skeletal muscle sodium channel gene. A large Quarter horse pedigree segregating dominant HYPP was studied to determine if mutations of the sodium channel gene are similarly responsible for HYPP in horses. We used cross-species, PCR-mediated, cDNA cloning and sequencing of the horse adult skeletal muscle sodium channel alpha-subunit gene to identify a polymorphism, and then used this polymorphism to see if the horse sodium channel gene was genetically linked to HYPP in horses. The sodium channel gene was indeed found to be tightly linked to HYPP (LOD = 2.7, theta = 0). Our results suggest that HYPP in horses involves the same gene as the clinically similar human disease, and indicates that these are homologous disorders. The future identification of the specific sodium channel mutation causing HYPP in Quarter horses will permit the development of accurate molecular diagnostics of this condition, as has been recently shown for humans.
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Affiliation(s)
- J A Rudolph
- Department of Molecular Genetics & Biochemistry, University of Pittsburgh School of Medicine, Pennsylvania 15261
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21
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Hayward LJ, Kim JS, Lee MY, Zhou H, Kim JW, Misra K, Salajegheh M, Wu FF, Matsuda C, Reid V, Cros D, Hoffman EP, Renaud JM, Cannon SC, Brown RH. Targeted mutation of mouse skeletal muscle sodium channel produces myotonia and potassium-sensitive weakness. J Clin Invest 2008; 118:1437-49. [PMID: 18317596 DOI: 10.1172/jci32638] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2007] [Accepted: 01/16/2008] [Indexed: 11/17/2022] Open
Abstract
Hyperkalemic periodic paralysis (HyperKPP) produces myotonia and attacks of muscle weakness triggered by rest after exercise or by K+ ingestion. We introduced a missense substitution corresponding to a human familial HyperKPP mutation (Met1592Val) into the mouse gene encoding the skeletal muscle voltage-gated Na+ channel NaV1.4. Mice heterozygous for this mutation exhibited prominent myotonia at rest and muscle fiber-type switching to a more oxidative phenotype compared with controls. Isolated mutant extensor digitorum longus muscles were abnormally sensitive to the Na+/K+ pump inhibitor ouabain and exhibited age-dependent changes, including delayed relaxation and altered generation of tetanic force. Moreover, rapid and sustained weakness of isolated mutant muscles was induced when the extracellular K+ concentration was increased from 4 mM to 10 mM, a level observed in the muscle interstitium of humans during exercise. Mutant muscle recovered from stimulation-induced fatigue more slowly than did control muscle, and the extent of recovery was decreased in the presence of high extracellular K+ levels. These findings demonstrate that expression of the Met1592ValNa+ channel in mouse muscle is sufficient to produce important features of HyperKPP, including myotonia, K+-sensitive paralysis, and susceptibility to delayed weakness during recovery from fatigue.
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Affiliation(s)
- Lawrence J Hayward
- Department of Neurology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
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22
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Shang LL, Pfahnl AE, Sanyal S, Jiao Z, Allen J, Banach K, Fahrenbach J, Weiss D, Taylor WR, Zafari AM, Dudley SC. Human heart failure is associated with abnormal C-terminal splicing variants in the cardiac sodium channel. Circ Res 2007; 101:1146-54. [PMID: 17901361 PMCID: PMC3157752 DOI: 10.1161/circresaha.107.152918] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Heart failure (HF) is associated with reduced cardiac Na+ channel (SCN5A) current. We hypothesized that abnormal transcriptional regulation of this ion channel during HF could help explain the reduced current. Using human hearts explanted at the transplantation, we have identified 3 human C-terminal SCN5A mRNA splicing variants predicted to result in truncated, nonfunctional channels. As compared with normal hearts, the explanted ventricles showed an upregulation of 2 of the variants and a downregulation of the full-length mRNA transcript such that the E28A transcript represented only 48.5% (P<0.01) of the total SCN5A mRNA. This correlated with a 62.8% (P<0.01) reduction in Na+ channel protein. Lymphoblasts and skeletal muscle expressing SCN5A also showed identical C-terminal splicing variants. Variants showed reduced membrane protein and no functional current. Transfection of truncation variants into a cell line stably transfected with the full-length Na+ channel resulted in dose-dependent reductions in channel mRNA and current. Introduction of a premature truncation in the C-terminal region in a single allele of the mouse SCN5A resulted in embryonic lethality. Embryonic stem cell-derived cardiomyocytes expressing the construct showed reductions in Na+ channel-dependent electrophysiological parameters, suggesting that the presence of truncated Na+ channel mRNA at levels seen in HF is likely to be physiologically significant. In summary, chronic HF was associated with an increase in 2 truncated SCN5A variants and a decrease in the native mRNA. These splice variations may help explain a loss of Na+ channel protein and may contribute to the increased arrhythmic risk in clinical HF.
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Affiliation(s)
- Lijuan L Shang
- Division of Cardiology, Department of Medicine, Emory University, Atlanta, GA, USA
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23
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Cleland JC, Griggs RC. Channelopathies of the Nervous System. Neurobiol Dis 2007. [DOI: 10.1016/b978-012088592-3/50033-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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24
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Abstract
Ion channelopathies are a diverse array of human disorders caused by mutations in ion channel genes. This review focuses on the pathogenic mechanisms of channelopathies affecting skeletal muscle and brain arising from mutations of voltage-gated ion channels and fast ligand-gated ion channels expressed at the surface membrane. Derangements in channel function alter the electrical excitability of the cell and thereby increase susceptibility to transient symptomatic attacks including myasthenia, periodic paralysis, myotonic stiffness, seizures, headache, dyskinesia, or episodic ataxia. Although these disorders are rare, they stand out as exemplary cases for which disease pathogenesis can be traced from a point mutation to altered protein function, to altered cellular activity, and to clinical phenotype. The study of these disorders has provided insights on channel structure-function relations, the physiological roles of ion channels, and rational approaches toward therapeutic intervention for many disorders of cellular excitability.
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Affiliation(s)
- Stephen C Cannon
- Department of Neurology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
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25
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Abstract
A variety of inherited human disorders affecting skeletal muscle contraction, heart rhythm, and nervous system function have been traced to mutations in genes encoding voltage-gated sodium channels. Clinical severity among these conditions ranges from mild or even latent disease to life-threatening or incapacitating conditions. The sodium channelopathies were among the first recognized ion channel diseases and continue to attract widespread clinical and scientific interest. An expanding knowledge base has substantially advanced our understanding of structure-function and genotype-phenotype relationships for voltage-gated sodium channels and provided new insights into the pathophysiological basis for common diseases such as cardiac arrhythmias and epilepsy.
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Affiliation(s)
- Alfred L George
- Division of Genetic Medicine, Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232-0275, USA.
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26
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Abstract
The periodic paralyses are rare disorders of skeletal muscle characterized by episodic attacks of weakness due to intermittent failure of electrical excitability. Familial forms of periodic paralysis are all caused by mutations in genes coding for voltage-gated ion channels. New discoveries in the past 2 years have broadened our views on the diversity of phenotypes produced by mutations of a single channel gene and have led to the identification of potassium channel mutations, in addition to those previously found in sodium and calcium channels. This review focuses on the clinical features, molecular genetic defects, and pathophysiologic mechanisms that underlie familial periodic paralysis.
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Affiliation(s)
- Stephen C Cannon
- Department of Neurology, Massachusetts General Hospital/Wellman 423, 50 Blossom Street, Boston, MA 02114, USA.
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27
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28
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Abstract
Several heritable forms of myotonia and periodic paralysis are caused by missense mutations in the voltage-gated sodium channel of skeletal muscle. Mutations produce gain-of-function defects, either disrupted inactivation or enhanced activation. Both defects result in too much inward Na current which may either initiate pathologic bursts of action potentials (myotonia) or cause flaccid paralysis by depolarizing fibers to a refractory inexcitable state. Myotonic stiffness and periodic paralysis occur as paroxysmal attacks often triggered by environmental factors such as serum K+, cold, or exercise. Many gaps remain in our understanding of the interactions between genetic predisposition and these environmental influences. Targeted gene manipulation in animals may provide the tools to fill in these gaps.
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Affiliation(s)
- S C Cannon
- Department of Neurobiology, Harvard Medical School, Massachusetts General Hospital, Boston, USA.
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29
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Abstract
The periodic paralyses are a group of muscle diseases with abnormalities of channels. These abnormalities result in paralysis or weakness with or without poor relaxation of muscle. Hypokalemic periodic paralyses, potassium-sensitive periodic paralyses, and paramyotonia congenita are reviewed. The clinical findings, pathophysiologic abnormalities, diagnostic evaluations, and possible treatments are included in this article.
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Affiliation(s)
- L Gutmann
- Department of Neurology, West Virginia University School of Medicine, Morgantown, WV 26506, USA
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30
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Rojas CV, Neely A, Velasco-Loyden G, Palma V, Kukuljan M. Hyperkalemic periodic paralysis M1592V mutation modifies activation in human skeletal muscle Na+ channel. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:C259-66. [PMID: 9886942 DOI: 10.1152/ajpcell.1999.276.1.c259] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mutations in the human skeletal muscle Na+ channel underlie the autosomal dominant disease hyperkalemic periodic paralysis (HPP). Muscle fibers from affected individuals exhibit sustained Na+ currents thought to depolarize the sarcolemma and thus inactivate normal Na+ channels. We expressed human wild-type or M1592V mutant alpha-subunits with the beta1-subunit in Xenopus laevis oocytes and recorded Na+ currents using two-electrode and cut-open oocyte voltage-clamp techniques. The most prominent functional difference between M1592V mutant and wild-type channels is a 5- to 10-mV shift in the hyperpolarized direction of the steady-state activation curve. The shift in the activation curve for the mutant results in a larger overlap with the inactivation curve than that observed for wild-type channels. Accordingly, the current through M1592V channels displays a larger noninactivating component than does that through wild-type channels at membrane potentials near -40 mV. The functional properties of the M1592V mutant resemble those of the previously characterized HPP T704M mutant. Both clinically similar phenotypes arise from mutations located at a distance from the putative voltage sensor of the channel.
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Affiliation(s)
- C V Rojas
- Instituto de Nutrición y Tecnología de los Alimentos, Universidad de Chile, Casilla 138-11, Santiago, Chile
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31
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Abstract
Hyperkalemic periodic paralysis, paramyotonia congenita, and the potassium-aggravated myotonias are all caused by point mutations in the alpha-subunit of a sodium channel expressed selectively in skeletal muscle. This review updates the growing list of genotype-phenotype correlations for these mutations and summarizes the alterations in channel function they produce. A toxin-based in vitro model demonstrates that subtle defects in sodium channel inactivation are sufficient to cause myotonia and computer modeling suggests that specific types of inactivation defect may predispose to paralysis or myotonia.
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Affiliation(s)
- S C Cannon
- Department of Neurobiology, Harvard Medical School, Massachusetts General Hospital, Boston 02114, USA
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32
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Saito M, Ohmura M, Kondo A. Effects of alterations in potassium and calcium concentrations on the pressure generated in rat whole bladder in vitro. Int J Urol 1996; 3:478-83. [PMID: 9170577 DOI: 10.1111/j.1442-2042.1996.tb00580.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND Various physiologic systems maintain the ionic equilibrium essential for normal neuron and smooth muscle function. These systems are impaired by nonphysiologic concentrations of extracellular cations. This study investigated the effects of altered extracellular concentrations of potassium and calcium on the in vitro pressure generation in the whole bladder of rats. METHODS Pressure increases in response to field stimulation, as well as low and high doses of bethanechol, were determined in a Krebs solution containing a normal amount of potassium, and in excess of 10 mmol/L and 20 mmol/L of potassium. Each of these solutions had calcium concentrations, that were low (0.8 mmol/L), normal (2.5 mmol/L), or high (7.5 mmol/L). RESULTS The response to field stimulation was significantly decreased at the 20-mmol/L concentration of potassium in the presence of the different concentrations of calcium. The response to field stimulation increased as the extracellular concentration of calcium increased. The pressure increase caused by a low dose of bethanechol was significantly enhanced by elevations in the concentrations of both potassium and calcium. There was no difference in the response to a high dose of bethanechol in the presence of the various concentrations of potassium and calcium. CONCLUSION These findings indicated that changes in the cationic equilibrium that result in blocking of the neuronal sodium channels, as well as increasing the level of intracellular bound calcium in smooth muscle, alter bladder function in vitro.
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Affiliation(s)
- M Saito
- Department of Urology, Nagoya University School of Medicine, Japan
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33
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Abstract
Hyperkalemic periodic paralysis (HyperPP) is a disorder in which current through Na+ channels causes a prolonged depolarization of skeletal muscle fibers, resulting in membrane inexcitability and muscle paralysis. Although HyperPP mutations can enhance persistent sodium currents, unaltered slow inactivation would effectively eliminate any sustained currents through the mutant channels. We now report that rat skeletal muscle channels containing the mutation T698M, which corresponds to the human T704M HyperPP mutation, recover very quickly from prolonged depolarizations. Even after holding at -20 mV for 20 min, approximately 25% of the maximal sodium current is available subsequent to a 10-ms hyperpolarization (-100 mV). Under the same conditions, recovery is less than 3% in wild-type channels and in the F1304Q mutant, which has impaired fast inactivation. This effect of the T698M mutation on slow inactivation, in combination with its effects on activation, is expected to result in persistent currents such as that seen in HyperPP muscle.
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Affiliation(s)
- T R Cummins
- Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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34
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Abstract
The myotonias and periodic paralyses are a diverse group of skeletal muscle disorders that share a common pathophysiological mechanism: all are caused by derangements in the electrical excitability of the sarcolemma. Mutations within coding regions of ion-channel genes have been identified recently as the underlying molecular defects in these heritable disorders. Chloride-channel mutations cause a reduction in the resting conductance, which enhances excitability and gives rise to myotonia. By contrast, missense mutations in the L-type Ca2+ channel reduce the electrical excitability of the fiber and cause a form of periodic paralysis. Mutations of the sodium channel impair inactivation of the channel, which, depending on the type and severity of the functional defect, results in either paralysis or myotonia.
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Affiliation(s)
- S C Cannon
- Dept of Neurobiology, Harvard Medical School, Massachusetts General Hospital, Boston 02114, USA
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35
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Lehmann-Horn F, Rüdel R. Molecular pathophysiology of voltage-gated ion channels. Rev Physiol Biochem Pharmacol 1996; 128:195-268. [PMID: 8791722 DOI: 10.1007/3-540-61343-9_9] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
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36
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Abstract
Many physiological processes depend upon the proper functioning of plasma membrane ion channels. This is most apparent in absorptive and secretory epithelia, and in electrically excitable tissues such as nerve and muscle. Disturbances in the operation of ion channels in these settings can alter normal physiology and cause disease. This review illustrates the use of molecular genetics in identifying hereditary diseases caused by mutations in genes which encode various skeletal muscle ion channels. Recent advances in the discovery of genetic mutations in the skeletal muscle voltage-gated sodium channel in certain forms of periodic paralysis, mutations in the skeletal muscle chloride channel gene in myotonia congenita, and defects in two distinct calcium channels that underlie disorders of excitation-contraction coupling (murine muscular dysgenesis, malignant hyperthermia susceptibility) will be presented. In each case, prior knowledge of abnormal ion channel function prompted the search for mutations in candidate genes. This work is beginning to shed new light on the relationship between ion channel structure and function by studies of naturally occurring channel mutations.
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Affiliation(s)
- A L George
- Division of Nephrology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
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37
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Yang N, Ji S, Zhou M, Ptácek LJ, Barchi RL, Horn R, George AL. Sodium channel mutations in paramyotonia congenita exhibit similar biophysical phenotypes in vitro. Proc Natl Acad Sci U S A 1994; 91:12785-9. [PMID: 7809121 PMCID: PMC45524 DOI: 10.1073/pnas.91.26.12785] [Citation(s) in RCA: 155] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Mutations in the skeletal muscle voltage-gated Na+ channel alpha-subunit have been found in patients with two distinct hereditary disorders of sarcolemmal excitation: hyperkalemic periodic paralysis (HYPP) and paramyotonia congenita (PC). Six of these mutations have been functionally expressed in a heterologous cell line (tsA201 cells) using the recombinant human skeletal muscle Na+ channel alpha-subunit cDNA hSkM1. PC mutants from diverse locations in this subunit (T1313M, L1433R, R1448H, R1448C, A1156T) all exhibit a similar disturbance in channel inactivation characterized by reduced macroscopic rate, accelerated recovery, and altered voltage dependence. PC mutants had no significant abnormality in activation. In contrast, one HYPP mutation studied (T704M) has a normal inactivation rate but exhibits shifts in the midpoints of steady-state activation and inactivation along the voltage axis. These findings help to explain the phenotypic differences between HYPP and PC at the molecular and biophysical level and contribute to our understanding of Na+ channel structure and function.
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Affiliation(s)
- N Yang
- Department of Physiology, Jefferson Medical College, Philadelphia, PA 19107
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38
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Sonoda Y, Gotow T, Kuriyama M, Nakahara K, Arimura K, Osame M. Electrical myotonia of rabbit skeletal muscles by HMG-CoA reductase inhibitors. Muscle Nerve 1994; 17:891-7. [PMID: 8041396 DOI: 10.1002/mus.880170808] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
HMG-CoA reductase (HCR) inhibitors are effective cholesterol-lowering agents in the treatment of hypercholesterolemia. Using intracellular microelectrodes, we studied the pathomechanism of myotonia experimentally induced in rabbits by HCR inhibitors, simvastatin, and pravastatin. The external intercostal muscle of rabbits showed some electrophysiologic characteristics of myotonia including repetitive firing after administration of simvastatin (50 mg/kg per day, for 4 weeks). The relative chloride conductance, though reduced in both, was more affected in simvastatin-administered muscles. In normal muscles perfused with a solution containing the inhibitors, both simvastatin and pravastatin produced membrane hyperexcitability with repetitive firing similar to that seen in simvastatin-administered rabbits. The minimum concentrations required to cause repetitive firing was 0.3 mg/L for simvastatin and 30 mg/L for pravastatin. These results indicate that HCR inhibitors induce some characteristics of myotonia by blocking the chloride channel in the muscle membrane.
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Affiliation(s)
- Y Sonoda
- Third Department of Internal Medicine, Kagoshima University School of Medicine, Japan
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39
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Chahine M, George AL, Zhou M, Ji S, Sun W, Barchi RL, Horn R. Sodium channel mutations in paramyotonia congenita uncouple inactivation from activation. Neuron 1994; 12:281-94. [PMID: 8110459 DOI: 10.1016/0896-6273(94)90271-2] [Citation(s) in RCA: 239] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Mutations in the adult human skeletal muscle Na+ channel alpha subunit cause the disease paramyotonia congenita. Two paramyotonia congenita mutations, R1448H and R1448C, substitute histidine and cysteine for arginine in the S4 segment of domain 4. These mutations, expressed in a cell line, have only small effects on the activation of Na+ currents, but mutant channels inactivate more slowly with less voltage dependence than wild-type channels and exhibit an enhanced rate of recovery from inactivation. Increase of extracellular pH made the rate of inactivation of R1448H similar to that of R1448C, suggesting that this residue has an extracellular location and that its charge is important for normal inactivation. Analysis of single-channel data reveals that mutant channels inactivate normally from closed states, but poorly from the open state. The data suggest a critical role for the S4 helix of domain 4 in coupling between activation and inactivation.
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Affiliation(s)
- M Chahine
- Department of Physiology, Jefferson Medical College, Philadelphia, Pennsylvania 19107
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40
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Affiliation(s)
- R H Brown
- Harvard Medical School, Department of Neurology, Massachusetts General Hospital-East, Charlestown 02112, USA
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41
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Cannon SC, Brown RH, Corey DP. Theoretical reconstruction of myotonia and paralysis caused by incomplete inactivation of sodium channels. Biophys J 1993; 65:270-88. [PMID: 8396455 PMCID: PMC1225722 DOI: 10.1016/s0006-3495(93)81045-2] [Citation(s) in RCA: 136] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Muscle fibers from individuals with hyperkalemic periodic paralysis generate repetitive trains of action potentials (myotonia) or large depolarizations and block of spike production (paralysis) when the extracellular K+ is elevated. These pathologic features are thought to arise from mutations of the sodium channel alpha subunit which cause a partial loss of inactivation (steady-state Popen approximately 0.02, compared to < 0.001 in normal channels). We present a model that provides a possible mechanism for how this small persistent sodium current leads to repetitive firing, why the integrity of the T-tubule system is required to produce myotonia, and why paralysis will occur when a slightly larger proportion of channels fails to inactivate. The model consists of a two-compartment system to simulate the surface and T-tubule membranes. When the steady-state sodium channel open probability exceeds 0.0075, trains of repetitive discharges occur in response to constant current injection. At the end of the current injection, the membrane potential may either return to the normal resting value, continue to discharge repetitive spikes, or settle to a new depolarized equilibrium potential. This after-response depends on both the proportion of noninactivating sodium channels and the magnitude of the activity-driven K+ accumulation in the T-tubular space. A reduced form of model is presented in which a two-dimensional phase-plane analysis shows graphically how this diversity of after-responses arises as extracellular [K+] and the proportion of noninactivating sodium channels are varied.
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Affiliation(s)
- S C Cannon
- Department of Neurology, Massachusetts General Hospital, Boston 02114
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Cannon SC, Strittmatter SM. Functional expression of sodium channel mutations identified in families with periodic paralysis. Neuron 1993; 10:317-26. [PMID: 8382500 DOI: 10.1016/0896-6273(93)90321-h] [Citation(s) in RCA: 174] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Two mutations in the sodium channel alpha subunit that have been implicated as the cause of periodic paralysis were studied by functional expression in a mammalian cell line. Both mutations disrupted inactivation without affecting the time course of the onset of the sodium current or the single-channel conductance. This is the same functional defect that was observed in myotubes cultured from affected patients and proves that these mutations are not benign polymorphisms. Unlike the currents in the myotubes, however, there was no consistent potassium dependence for the noninactivating component. These mutations also define new regions of the sodium channel alpha subunit that are involved in the process of inactivation.
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Affiliation(s)
- S C Cannon
- Department of Neurology, Howard Hughes Medical Institute, Massachusetts General Hospital, Boston 02114
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Beech J, Fletcher JE, Tripolitis L, Lindborgh S. Effects of phenytoin in two myotonic horses with hyperkalemic periodic paralysis. Muscle Nerve 1992; 15:932-6. [PMID: 1495509 DOI: 10.1002/mus.880150811] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The effects of phenytoin treatment were evaluated in 2 myotonic horses with hyperkalemic periodic paralysis (HPP). Phenytoin treatment abolished the clinical signs of muscle fasciculations following oral potassium challenge and decreased or abolished repetitive firing and myotonic discharges found on electromyographic examination. In both horses, an abnormally low threshold for calcium-induced calcium release was measured in heavy sarcoplasmic reticulum fractions from skeletal muscle, and this threshold increased with phenytoin treatment. Results suggest phenytoin is useful in modifying disordered ion regulation in the sarcolemma and sarcoplasmic reticulum of skeletal muscle in equine hyperkalemic periodic paralysis.
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Affiliation(s)
- J Beech
- Department of Clinical Studies, University of Pennsylvania, School of Veterinary Medicine, Kennett Square 19348
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George AL, Komisarof J, Kallen RG, Barchi RL. Primary structure of the adult human skeletal muscle voltage-dependent sodium channel. Ann Neurol 1992; 31:131-7. [PMID: 1315496 DOI: 10.1002/ana.410310203] [Citation(s) in RCA: 142] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The gene encoding the principal voltage-dependent sodium channel expressed in adult human skeletal muscle (SCN4A) has recently been linked to the pathogenesis of human hyperkalemic periodic paralysis and paramyotonia congenita. We report the cloning and nucleotide sequence determination of the normal product of this gene. The 7,823 nucleotide complementary DNA, designated hSkM1, encodes a 1,836 amino acid protein that exhibits 92% identity with the tetrodotoxin-sensitive rat skeletal muscle sodium channel alpha subunit, but lower homology with either the human heart sodium channel or with other sodium channels from immature rat muscle or rat brain. Specific hSkM1 RNA transcripts are expressed in adult human skeletal muscle but not in heart, brain, or uterus. The SCN4A gene product, hSkM1, is the human homologue of rSkM1, the tetrodotoxin-sensitive sodium channel characteristic of adult rat skeletal muscle. This structural information should provide the necessary backdrop for identifying and evaluating mutations affecting the function of this channel in the periodic paralyses.
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Affiliation(s)
- A L George
- David Mahoney Institute of Neurological Sciences, University of Pennsylvania, Philadelphia
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Affiliation(s)
- A R Wintzen
- Department of Neurology, University Hospital, Leiden, The Netherlands
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Ebers GC, George AL, Barchi RL, Ting-Passador SS, Kallen RG, Lathrop GM, Beckmann JS, Hahn AF, Brown WF, Campbell RD. Paramyotonia congenita and hyperkalemic periodic paralysis are linked to the adult muscle sodium channel gene. Ann Neurol 1991; 30:810-6. [PMID: 1686388 DOI: 10.1002/ana.410300610] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The hyperkalemic periodic paralyses are a clinically heterogeneous group of autosomal dominant syndromes characterized by episodic paralysis associated with an elevated serum potassium level. Affected individuals in the same family tend to have homogeneous symptom complexes, although phenotypic variation is present among different families. For example, myotonia is absent in some pedigrees, present in others, and, in a third variant, paramyotonia congenita, myotonia coexists with cold-induced paralysis. Electrophysiological studies have demonstrated variant-specific abnormalities in skeletal muscle membrane sodium conductance. We tested the hypothesis that hyperkalemic periodic paralysis (without myotonia) and paramyotonia congenita are tightly linked to the tetrodotoxin-sensitive adult skeletal muscle sodium channel gene on chromosome 17q23-25 in two large pedigrees. The DNA polymorphisms detected in the growth hormone skeletal muscle sodium channel complex (GH1-SCN4A) and by flanking polymorphic markers (D17S74 and D17S40) demonstrated no recombinants between the disease phenotypes and this complex. Phenotypic variation in the hereditary hyperkalemic periodic paralyses may result from allelic heterogeneity at the tetrodotoxin-sensitive adult skeletal muscle sodium channel locus.
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Affiliation(s)
- G C Ebers
- Richard Ivey Centre for Molecular Biology, University Hospital, London, Ontario, Canada
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Koch MC, Ricker K, Otto M, Grimm T, Bender K, Zoll B, Harper PS, Lehmann-Horn F, Rüdel R, Hoffman EP. Linkage data suggesting allelic heterogeneity for paramyotonia congenita and hyperkalemic periodic paralysis on chromosome 17. Hum Genet 1991; 88:71-4. [PMID: 1660029 DOI: 10.1007/bf00204932] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Paramyotonia congenita (PC), an autosomal dominant non-progressive muscle disorder, is characterised by cold-induced stiffness followed by muscle weakness. The weakness is caused by a dysfunction of the sodium channel in muscle fibre. Parts of the gene coding for the alpha-subunit of the sodium channel of the adult human skeletal muscle (SCN4A) have been localised on chromosome 17. To investigate the role of this gene in the etiology of PC, a linkage analysis in 17 well-defined families was carried out. The results (zeta = 20.61, theta = 0.001) show that the mutant gene responsible for the disorder is indeed tightly linked to the SCN4A gene. The mutation causing hyperkalemic periodic paralysis (HyperPP) with myotonia has previously been mapped to this gene locus by the same candidate gene approach. Thus, our data suggest that PC and HyperPP are caused by allelic mutations at a single locus on chromosome 17.
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Affiliation(s)
- M C Koch
- Abteilung Allgemeine Humangenetik, Philipps Universität, Marburg, Federal Republic of Germany
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Koch MC, Ricker K, Otto M, Grimm T, Hoffman EP, Rüdel R, Bender K, Zoll B, Harper PS, Lehmann-Horn F. Confirmation of linkage of hyperkalaemic periodic paralysis to chromosome 17. J Med Genet 1991; 28:583-6. [PMID: 1683408 PMCID: PMC1015786 DOI: 10.1136/jmg.28.9.583] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Linkage studies were performed in six European families with hyperkalaemic periodic paralysis (PPII) with myotonia, an autosomal dominantly inherited disorder characterised by episodic weakness. The weakness is caused by non-inactivating sodium channels of reduced single channel conductance of the muscle fibre membrane. Recently, portions of the gene coding for the alpha subunit of the sodium channel of the adult human skeletal muscle (h-Na2) have been cloned and localised on chromosome 17q with no recombinants to the human growth hormone locus (GH1). Linkage between these two chromosome 17 markers and the disease was shown in our families (Z = 7.14, 0 = 0.00). These results, combined with the linkage data of a single large American family, suggest that the disease is caused by dominant mutations of the adult sodium channel, and that it is probably a genetically homogeneous disorder. Hyperkalaemic periodic paralysis is the first non-progressive myotonic disorder to be localised on the human genome.
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Affiliation(s)
- M C Koch
- Abteilung Allgemeine Humangenetik, Phillips Universität Marburg, Germany
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Pickar JG, Spier SJ, Snyder JR, Carlsen RC. Altered ionic permeability in skeletal muscle from horses with hyperkalemic periodic paralysis. THE AMERICAN JOURNAL OF PHYSIOLOGY 1991; 260:C926-33. [PMID: 2035619 DOI: 10.1152/ajpcell.1991.260.5.c926] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A recently described disorder in certain registered Quarter horses bears many clinical similarities to the muscle disease identified as hyperkalemic periodic paralysis (HPP) in humans. Pathological changes in membrane permeability or Na(+)-K+ pump activity have been proposed to produce the muscle depolarization and inexcitability that characterize the condition in humans. Biopsies of external intercostal muscle from normal and affected horses were used to determine whether alterations in either permeability and/or pump activity could be linked to the pathology in horses. Affected horse muscle is approximately 16 mV more depolarized than normal muscle at rest, and the muscle membrane potential of HPP horses is less responsive to changes in extracellular K+. Calculation of the relative membrane permeabilities of Na+ and K+ (PNa/PK) indicates that this ratio is significantly increased in HPP muscle. The increase is probably due to an increase in PNa rather than to a decrease in PK, since addition of 10(-6) M tetrodotoxin produces an approximately 14-mV membrane hyperpolarization in HPP fibers but is without effect in normal fibers. The clinical similarities between HPP in horses and humans suggest a common genetic defect in the two species.
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Affiliation(s)
- J G Pickar
- Department of Human Physiology, University of California, Davis 95616
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Cannon SC, Brown RH, Corey DP. A sodium channel defect in hyperkalemic periodic paralysis: potassium-induced failure of inactivation. Neuron 1991; 6:619-26. [PMID: 1849724 DOI: 10.1016/0896-6273(91)90064-7] [Citation(s) in RCA: 161] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Hyperkalemic periodic analysis (HPP) is an autosomal dominant disorder characterized by episodic weakness lasting minutes to days in association with a mild elevation in serum K+. In vitro measurements of whole-cell currents in HPP muscle have demonstrated a persistent, tetrodotoxin-sensitive Na+ current, and we have recently shown by linkage analysis that the Na+ channel alpha subunit gene may contain the HPP mutation. In this study, we have made patch-clamp recordings from cultured HPP myotubes and found a defect in the normal voltage-dependent inactivation of Na+ channels. Moderate elevation of extracellular K+ favors an aberrant gating mode in a small fraction of the channels that is characterized by persistent reopenings and prolonged dwell times in the open state. The Na+ current, through noninactivating channels, may cause the skeletal muscle weakness in HPP by depolarizing the cell, thereby inactivating normal Na+ channels, which are then unable to generate an action potential. Thus the dominant expression of HPP is manifest by inactivation of the wild-type Na+ channel through the influence of the mutant gene product on membrane voltage.
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Affiliation(s)
- S C Cannon
- Department of Neurology, Massachusetts General Hospital, Boston
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