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Dupont C, Blake B, Voss AA, Rich MM. BK channels promote action potential repolarization in skeletal muscle but contribute little to myotonia. Pflugers Arch 2024:10.1007/s00424-024-03005-z. [PMID: 39150500 DOI: 10.1007/s00424-024-03005-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2024] [Revised: 07/31/2024] [Accepted: 08/06/2024] [Indexed: 08/17/2024]
Abstract
Patients with myotonia congenita suffer from slowed relaxation of muscle (myotonia), due to hyperexcitability caused by loss-of-function mutations in the ClC-1 chloride channel. A recent study suggested that block of large-conductance voltage- and Ca2+- activated K+ channels (BK) may be effective as therapy. The mechanism underlying efficacy was suggested to be lessening of the depolarizing effect of build-up of K+ in t-tubules of muscle during repetitive firing. BK channels are widely expressed in the nervous system and have been shown to play a central role in regulation of excitability, but their contribution to muscle excitability has not been determined. We performed intracellular recordings as well as force measurements in both wild type and BK-/- mouse extensor digitorum longus muscles. Action potential width was increased in BK-/- muscle due to slowing of repolarization, consistent with the possibility K+ build-up in t-tubules is lessened by block of BK channels in myotonic muscle. However, there was no difference in the severity of myotonia triggered by block of muscle Cl- channels with 9-anthracenecarboxylic acid (9AC) in wild type and BK-/- muscle fibers. Further study revealed no difference in the interspike membrane potential during repetitive firing suggesting there was no reduction in K+ build-up in t-tubules of BK-/- muscle. Force recordings following block of muscle Cl- channels demonstrated little reduction in myotonia in BK-/- muscle. In contrast, the current standard of care, mexiletine, significantly reduced myotonia. Our data suggest BK channels regulate muscle excitability, but are not an attractive target for therapy of myotonia.
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Affiliation(s)
- Chris Dupont
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, 45435, USA
| | - Brianna Blake
- Department of Biological Sciences, Wright State University, Dayton, OH, 45435, USA
| | - Andrew A Voss
- Department of Biological Sciences, Wright State University, Dayton, OH, 45435, USA
| | - Mark M Rich
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, 45435, USA.
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2
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Wang X, Dupont C, Grant D, Voss AA, Rich MM. Plateau potentials contribute to myotonia in mouse models of myotonia congenita. Exp Neurol 2023; 361:114303. [PMID: 36563835 PMCID: PMC9892346 DOI: 10.1016/j.expneurol.2022.114303] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Revised: 12/12/2022] [Accepted: 12/17/2022] [Indexed: 12/24/2022]
Abstract
It has long been accepted that myotonia (muscle stiffness) in patients with muscle channelopathies is due to myotonic discharges (involuntary firing of action potentials). In a previous study, we identified a novel phenomenon in myotonic muscle: development of plateau potentials, transient depolarizations to near -35 mV lasting for seconds to minutes. In the current study we examined whether plateau potentials contribute to myotonia. A recessive genetic model (ClCadr mice) with complete loss of muscle chloride channel (ClC-1) function was used to model severe myotonia congenita with complete loss of ClC-1 function and a pharmacologic model using anthracene-9-carboxylic acid (9 AC) was used to model milder myotonia congenita with incomplete loss of ClC-1 function. Simultaneous measurements of action potentials and myoplasmic Ca2+ from individual muscle fibers were compared to recordings of whole muscle force generation. In ClCadr muscle both myotonia and plateau potentials lasted 10s of seconds to minutes. During plateau potentials lasting 1-2 min, there was a gradual transition from high to low intracellular Ca2+, suggesting a transition in individual fibers from myotonia to flaccid paralysis in severe myotonia congenita. In 9 AC-treated muscles, both myotonia and plateau potentials lasted only a few seconds and Ca2+ remained elevated during the plateau potentials, suggesting plateau potentials contribute to myotonia without causing weakness. We propose, that in myotonic muscle, there is a novel state in which there is contraction in the absence of action potentials. This discovery provides a mechanism to explain reports of patients with myotonia who suffer from electrically silent muscle contraction lasting minutes.
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Affiliation(s)
- Xueyong Wang
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH 45435, USA
| | - Chris Dupont
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH 45435, USA
| | - Delaney Grant
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH 45435, USA
| | - Andrew A Voss
- Department of Biology, Wright State University, Dayton, OH 45435, USA
| | - Mark M Rich
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH 45435, USA.
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3
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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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4
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Montagnese F. Current Treatment Options for Patients with Myotonic Dystrophy Type 2. Curr Treat Options Neurol 2021. [DOI: 10.1007/s11940-021-00686-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Abstract
Purpose of the review
Myotonic dystrophy types 1 and 2 are frequent forms of muscular dystrophies in adulthood. Their clinical differences need to be taken into account for the most appropriate treatment of patients. The aim of this article is to provide an overview on the current and upcoming therapeutic options for patients with myotonic dystrophy type 2 (DM2).
Recent findings
At the moment, no disease-modifying therapies are available for DM2; next-generation therapies may however be available in the near future. In the meanwhile, the symptomatic management of patients has greatly improved, thank to the production of consensus-based standards of care and the growing evidence of efficacy of anti-myotonic drugs, promising employment of cannabinoids for symptom’s relief, regular monitoring, and early detection of treatable extra-muscular manifestations.
Summary
The treatment of DM2 is currently symptomatic and relies on the coordinated intervention of a multidisciplinary team. It remains to be determined whether upcoming causal therapies for myotonic dystrophy type 1 will be applicable also in DM2.
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5
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Padilla CJ, Harrigan ME, Harris H, Schwab JM, Rutkove SB, Rich MM, Clark BC, Arnold WD. Profiling age-related muscle weakness and wasting: neuromuscular junction transmission as a driver of age-related physical decline. GeroScience 2021; 43:1265-1281. [PMID: 33895959 PMCID: PMC8190265 DOI: 10.1007/s11357-021-00369-3] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Accepted: 04/19/2021] [Indexed: 12/22/2022] Open
Abstract
Pathological age-related loss of skeletal muscle strength and mass contribute to impaired physical function in older adults. Factors that promote the development of these conditions remain incompletely understood, impeding development of effective and specific diagnostic and therapeutic approaches. Inconclusive evidence across species suggests disruption of action potential signal transmission at the neuromuscular junction (NMJ), the crucial connection between the nervous and muscular systems, as a possible contributor to age-related muscle dysfunction. Here we investigated age-related loss of NMJ function using clinically relevant, electrophysiological measures (single-fiber electromyography (SFEMG) and repetitive nerve stimulation (RNS)) in aged (26 months) versus young (6 months) F344 rats. Measures of muscle function (e.g., grip strength, peak plantarflexion contractility torque) and mass were assessed for correlations with physiological measures (e.g., indices of NMJ transmission). Other outcomes also included plantarflexion muscle contractility tetanic torque fade during 1-s trains of stimulation as well as gastrocnemius motor unit size and number. Profiling NMJ function in aged rats identified significant declines in NMJ transmission stability and reliability. Further, NMJ deficits were tightly correlated with hindlimb grip strength, gastrocnemius muscle weight, loss of peak contractility torque, degree of tetanic fade, and motor unit loss. Thus, these findings provide direct evidence for NMJ dysfunction as a potential mechanism of age-related muscle dysfunction pathogenesis and severity. These findings also suggest that NMJ transmission modulation may serve as a target for therapeutic development for age-related loss of physical function.
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Affiliation(s)
- Carlos J Padilla
- Division of Neuromuscular Diseases, Department of Neurology, The Ohio State University Wexner Medical Center, 1060 Carmack Road, Room 207, Columbus, OH, 43210, USA
| | - Markus E Harrigan
- Division of Neuromuscular Diseases, Department of Neurology, The Ohio State University Wexner Medical Center, 1060 Carmack Road, Room 207, Columbus, OH, 43210, USA
| | - Hallie Harris
- Division of Neuromuscular Diseases, Department of Neurology, The Ohio State University Wexner Medical Center, 1060 Carmack Road, Room 207, Columbus, OH, 43210, USA
| | - Jan M Schwab
- Division of Neuromuscular Diseases, Department of Neurology, The Ohio State University Wexner Medical Center, 1060 Carmack Road, Room 207, Columbus, OH, 43210, USA
- Belford Center for Spinal Cord Injury, The Ohio State University Wexner Medical Center, Columbus, OH, USA
- Department of Physical Medicine and Rehabilitation, The Ohio State University Wexner Medical Center, Columbus, OH, USA
- Center for Brain and Spinal Cord Repair, The Ohio State University Wexner Medical Center, Columbus, OH, USA
- The Neurological Institute, The Ohio State University Wexner Medical Center, Columbus, OH, USA
- Department of Neuroscience, The Ohio State University Wexner Medical Center, Columbus, OH, USA
| | - Seward B Rutkove
- Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
| | - Mark M Rich
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, 45435, USA
| | - Brian C Clark
- Department of Biomedical Sciences, Ohio Musculoskeletal and Neurological Institute, Athens, OH, 45701, USA
| | - W David Arnold
- Division of Neuromuscular Diseases, Department of Neurology, The Ohio State University Wexner Medical Center, 1060 Carmack Road, Room 207, Columbus, OH, 43210, USA.
- Department of Physical Medicine and Rehabilitation, The Ohio State University Wexner Medical Center, Columbus, OH, USA.
- The Neurological Institute, The Ohio State University Wexner Medical Center, Columbus, OH, USA.
- Department of Neuroscience, The Ohio State University Wexner Medical Center, Columbus, OH, USA.
- Department of Physiology and Cell Biology, The Ohio State University Wexner Medical Center, Columbus, OH, USA.
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Myers JH, Denman K, DuPont C, Hawash AA, Novak KR, Koesters A, Grabner M, Dayal A, Voss AA, Rich MM. The mechanism underlying transient weakness in myotonia congenita. eLife 2021; 10:e65691. [PMID: 33904400 PMCID: PMC8079152 DOI: 10.7554/elife.65691] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2020] [Accepted: 03/24/2021] [Indexed: 12/23/2022] Open
Abstract
In addition to the hallmark muscle stiffness, patients with recessive myotonia congenita (Becker disease) experience debilitating bouts of transient weakness that remain poorly understood despite years of study. We performed intracellular recordings from muscle of both genetic and pharmacologic mouse models of Becker disease to identify the mechanism underlying transient weakness. Our recordings reveal transient depolarizations (plateau potentials) of the membrane potential to -25 to -35 mV in the genetic and pharmacologic models of Becker disease. Both Na+ and Ca2+ currents contribute to plateau potentials. Na+ persistent inward current (NaPIC) through NaV1.4 channels is the key trigger of plateau potentials and current through CaV1.1 Ca2+ channels contributes to the duration of the plateau. Inhibiting NaPIC with ranolazine prevents the development of plateau potentials and eliminates transient weakness in vivo. These data suggest that targeting NaPIC may be an effective treatment to prevent transient weakness in myotonia congenita.
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Affiliation(s)
- Jessica H Myers
- Department of Neuroscience, Cell Biology and Physiology, Wright State UniversityDaytonUnited States
| | - Kirsten Denman
- Department of Neuroscience, Cell Biology and Physiology, Wright State UniversityDaytonUnited States
| | - Chris DuPont
- Department of Neuroscience, Cell Biology and Physiology, Wright State UniversityDaytonUnited States
| | - Ahmed A Hawash
- Department of Dermatology & Cutaneous Surgery, University of MiamiMiamiUnited States
| | | | - Andrew Koesters
- Naval Medical Research Unit, Wright Patterson Air Force BaseDaytonUnited States
| | - Manfred Grabner
- Department of Pharmacology, Medical University of InnsbruckInnsbruckAustria
| | - Anamika Dayal
- Department of Pharmacology, Medical University of InnsbruckInnsbruckAustria
| | - Andrew A Voss
- Department of Biology, Wright State UniversityDaytonUnited States
| | - Mark M Rich
- Department of Neuroscience, Cell Biology and Physiology, Wright State UniversityDaytonUnited States
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Triplett JD, Shelly S, Livne G, Milone M, Kassardjian CD, Liewluck T, Kelly C, Naddaf E, Laughlin RS, Lamb CJ, Rubin D, Dimberg EL, Dubey D, Mills JR, Mandrekar J, Klein CJ. Diagnostic modelling and therapeutic monitoring of immune-mediated necrotizing myopathy: role of electrical myotonia. Brain Commun 2020; 2:fcaa191. [PMID: 33364599 PMCID: PMC7749792 DOI: 10.1093/braincomms/fcaa191] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2020] [Revised: 09/19/2020] [Accepted: 09/28/2020] [Indexed: 12/11/2022] Open
Abstract
Delayed diagnosis of immune-mediated necrotizing myopathy leads to increased morbidity. Patients with the chronic course without 3-hydroxy-3-methylglutaryl-coenzyme-A reductase-IgG or signal recognition particle-IgG are often challenging to diagnose. Immunotherapy response can also be difficult to assess. We created a statistical model to assist immune-mediated necrotizing myopathy diagnosis. Electrical myotonia versus fibrillations were reviewed as biomarkers for immunotherapy treatment response. Identified were 119 immune-mediated necrotizing myopathy cases and 938 other myopathy patients. Inclusion criteria included all having electrophysiological evaluations, muscle biopsies showing inflammatory/necrotizing myopathies, comprehensively recorded neurological examinations, and creatine kinase values. Electrical myotonia was recorded in 56% (67/119) of retrospective and 67% (20/30) of our validation immune-mediated necrotizing myopathy cohorts, and significantly (P < 0.001) favoured immune-mediated necrotizing myopathy over other myopathies: sporadic inclusion body myositis (odds ratio = 4.78); dermatomyositis (odds ratio = 10.61); non-specific inflammatory myopathies (odds ratio = 8.46); limb-girdle muscular dystrophies (odds ratio = 5.34) or mitochondrial myopathies (odds ratio = 14.17). Electrical myotonia occurred in immune-mediated necrotizing myopathy seropositive (3-hydroxy-3-methylglutaryl-coenzyme-A reductase-IgG 70%, 37/53; signal recognition particle-IgG 29%, 5/17) and seronegative (51%, 25/49). Multivariate regression analysis of 20 variables identified 8 (including electrical myotonia) in combination accurately predicted immune-mediated necrotizing myopathy (97.1% area-under-curve). The model was validated in a separate cohort of 30 immune-mediated necrotizing myopathy cases. Delayed diagnosis of cases with electrical myotonia occurred in 24% (16/67, mean 8 months; range 0–194). Half (8/19) had a chronic course and were seronegative, with high model prediction (>86%) at the first visit. Inherited myopathies were commonly first suspected in them. Follow-up evaluation in patients with electrical myotonia on immunotherapy was available in 19 (median 21 months, range 2–124) which reduced from 36% (58/162) of muscles to 7% (8/121; P < 0.001). Reduced myotonia correlated with immunotherapy response in 64% (9/14) as well as with median creatine kinase reduction of 1779 U/l (range 401–9238, P < 0.001). Modelling clinical features with electrical myotonia is especially helpful in immune-mediated necrotizing myopathy diagnostic suspicion among chronic indolent and seronegative cases. Electrical myotonia favours immune-mediated necrotizing myopathy diagnosis and can serve as an adjuvant immunotherapy biomarker.
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Affiliation(s)
| | - Shahar Shelly
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | | | | | - Charles D Kassardjian
- Division of Neurology, Department of Medicine, St. Michael's Hospital, University of Toronto, Canada
| | | | - Cecilia Kelly
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | - Elie Naddaf
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | | | | | - Devon Rubin
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | | | - Divanshu Dubey
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
| | - John R Mills
- Department of Laboratory Medicine and Pathology, Mayo Clinic, Rochester, MN, USA
| | - Jay Mandrekar
- Department of Neurology, Mayo Clinic, Rochester, MN, USA
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8
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Dupont C, Novak K, Denman K, Myers JH, Sullivan JM, Walker PV, Brown NL, Ladle DR, Bogdanik L, Lutz CM, A Voss A, Sumner CJ, Rich MM. TRPV4 Antagonism Prevents Mechanically Induced Myotonia. Ann Neurol 2020; 88:297-308. [PMID: 32418267 PMCID: PMC7657963 DOI: 10.1002/ana.25780] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 04/27/2020] [Accepted: 05/07/2020] [Indexed: 11/08/2022]
Abstract
OBJECTIVE Myotonia is caused by involuntary firing of skeletal muscle action potentials and causes debilitating stiffness. Current treatments are insufficiently efficacious and associated with side effects. Myotonia can be triggered by voluntary movement (electrically induced myotonia) or percussion (mechanically induced myotonia). Whether distinct molecular mechanisms underlie these triggers is unknown. Our goal was to identify ion channels involved in mechanically induced myotonia and to evaluate block of the channels involved as a novel approach to therapy. METHODS We developed a novel system to enable study of mechanically induced myotonia using both genetic and pharmacologic mouse models of myotonia congenita. We extended ex vivo studies of excitability to in vivo studies of muscle stiffness. RESULTS As previous work suggests activation of transient receptor potential vanilloid 4 (TRPV4) channels by mechanical stimuli in muscle, we examined the role of this cation channel. Mechanically induced myotonia was markedly suppressed in TRPV4-null muscles and in muscles treated with TRPV4 small molecule antagonists. The suppression of mechanically induced myotonia occurred without altering intrinsic muscle excitability, such that myotonia triggered by firing of action potentials (electrically induced myotonia) was unaffected. When injected intraperitoneally, TRPV4 antagonists lessened the severity of myotonia in vivo by approximately 80%. INTERPRETATION These data demonstrate that there are distinct molecular mechanisms triggering electrically induced and mechanically induced myotonia. Our data indicates that activation of TRPV4 during muscle contraction plays an important role in triggering myotonia in vivo. Elimination of mechanically induced myotonia by TRPV4 inhibition offers a new approach to treating myotonia. ANN NEUROL 2020;88:297-308.
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Affiliation(s)
- Chris Dupont
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | - Kevin Novak
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | - Kirsten Denman
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | - Jessica H Myers
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | - Jeremy M Sullivan
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Phillip V Walker
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | - Nicklaus L Brown
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | - David R Ladle
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
| | | | | | - Andrew A Voss
- Department of Biology, Wright State University, Dayton, OH, USA
| | - Charlotte J Sumner
- Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Mark M Rich
- Department of Neuroscience, Cell Biology and Physiology, Wright State University, Dayton, OH, USA
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9
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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: 6] [Impact Index Per Article: 1.5] [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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