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Efthymiou S, Scala M, Nagaraj V, Ochenkowska K, Komdeur FL, Liang RA, Abdel-Hamid MS, Sultan T, Barøy T, Van Ghelue M, Vona B, Maroofian R, Zafar F, Alkuraya FS, Zaki MS, Severino M, Duru KC, Tryon RC, Brauteset LV, Ansari M, Hamilton M, van Haelst MM, van Haaften G, Zara F, Houlden H, Samarut É, Nichols CG, Smeland MF, McClenaghan C. Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome. Brain 2024; 147:1822-1836. [PMID: 38217872 PMCID: PMC11068106 DOI: 10.1093/brain/awae010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2023] [Revised: 11/22/2023] [Accepted: 12/30/2023] [Indexed: 01/15/2024] Open
Abstract
Loss-of-function mutation of ABCC9, the gene encoding the SUR2 subunit of ATP sensitive-potassium (KATP) channels, was recently associated with autosomal recessive ABCC9-related intellectual disability and myopathy syndrome (AIMS). Here we identify nine additional subjects, from seven unrelated families, harbouring different homozygous loss-of-function variants in ABCC9 and presenting with a conserved range of clinical features. All variants are predicted to result in severe truncations or in-frame deletions within SUR2, leading to the generation of non-functional SUR2-dependent KATP channels. Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness. Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death, which were also observed in an eighth family included in this study. In vivo studies of abcc9 loss-of-function in zebrafish revealed an exacerbated motor response to pentylenetetrazole, a pro-convulsive drug, consistent with impaired neurodevelopment associated with an increased seizure susceptibility. Our findings define an ABCC9 loss-of-function-related phenotype, expanding the genotypic and phenotypic spectrum of AIMS and reveal novel human pathologies arising from KATP channel dysfunction.
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Affiliation(s)
- Stephanie Efthymiou
- Department of Neuromuscular Disorders, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Marcello Scala
- Department of Neuromuscular Disorders, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
- Department of Neurosciences, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health, University of Genoa, 16147 Genoa, Italy
- U.O.C. Genetica Medica, IRCCS Istituto Giannina Gaslini, 16147 Genoa, Italy
| | - Vini Nagaraj
- Center for Advanced Biotechnology and Medicine, and Departments of Pharmacology and Medicine, Robert Wood Johnson Medical School, Rutgers the State University of New Jersey, Piscatway, NJ 08854, USA
| | - Katarzyna Ochenkowska
- Centre de Recherche du Centre Hospitalier de l’Université de Montréal (CRCHUM), and Department of Neuroscience, Université de Montréal, Montreal H2X 0A9, Quebec, Canada
| | - Fenne L Komdeur
- Section Clinical Genetics, Department of Human Genetics and Amsterdam Reproduction and Development, Amsterdam University Medical Centers, 1105 AZ, Amsterdam, The Netherlands
| | - Robin A Liang
- Department of Medical Genetics, Division of Child and Adolescent Health, University Hospital of North Norway, 9019 Tromsø, Norway
| | - Mohamed S Abdel-Hamid
- Medical Molecular Genetics Department, Human Genetics and Genome Research Institute, National Research Centre, Cairo 12622, Egypt
| | - Tipu Sultan
- Department of Pediatric Neurology, Children Hospital, University of Child Health Sciences, Lahore, Punjab 54000, Pakistan
| | - Tuva Barøy
- Department of Medical Genetics, Oslo University Hospital, 0450 Oslo, Norway
| | - Marijke Van Ghelue
- Department of Medical Genetics, Division of Child and Adolescent Health, University Hospital of North Norway, 9019 Tromsø, Norway
| | - Barbara Vona
- Institute of Human Genetics and Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, 37073 Göttingen, Germany
| | - Reza Maroofian
- Department of Neuromuscular Disorders, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Faisal Zafar
- Department of Paediatric Neurology, Children’s Hospital and Institute of Child Health, Multan, Punjab 60000, Pakistan
| | - Fowzan S Alkuraya
- Department of Translational Genomics, Center for Genomic Medicine, King Faisal Specialist Hospital and Research Center, Riyadh 12713, Saudi Arabia
| | - Maha S Zaki
- Clinical Genetics Department, Human Genetics and Genome Research Institute, National Research Centre, Cairo 12622, Egypt
| | | | - Kingsley C Duru
- Center for Advanced Biotechnology and Medicine, and Departments of Pharmacology and Medicine, Robert Wood Johnson Medical School, Rutgers the State University of New Jersey, Piscatway, NJ 08854, USA
| | - Robert C Tryon
- Department of Cell Biology and Physiology, and Center for the Investigation of Membrane Excitability Diseases (CIMED), Washington University, St Louis, MO 63110, USA
| | - Lin Vigdis Brauteset
- Division of Habilitation for Children, Innlandet Hospital Sanderud, Hamar 2312, Norway
| | - Morad Ansari
- South East Scotland Genetic Service, Western General Hospital, Edinburgh EH4 2XU, UK
| | - Mark Hamilton
- West of Scotland Clinical Genetics Service, Queen Elizabeth University Hospital, Glasgow G51 4TF, UK
| | - Mieke M van Haelst
- Section Clinical Genetics, Department of Human Genetics and Amsterdam Reproduction and Development, Amsterdam University Medical Centers, 1105 AZ, Amsterdam, The Netherlands
| | - Gijs van Haaften
- Department of Genetics, University Medical Center, Utrecht, 3584 CX, The Netherlands
| | - Federico Zara
- U.O.C. Genetica Medica, IRCCS Istituto Giannina Gaslini, 16147 Genoa, Italy
| | - Henry Houlden
- Department of Neuromuscular Disorders, UCL Queen Square Institute of Neurology, University College London, London WC1N 3BG, UK
| | - Éric Samarut
- Centre de Recherche du Centre Hospitalier de l’Université de Montréal (CRCHUM), and Department of Neuroscience, Université de Montréal, Montreal H2X 0A9, Quebec, Canada
| | - Colin G Nichols
- Department of Cell Biology and Physiology, and Center for the Investigation of Membrane Excitability Diseases (CIMED), Washington University, St Louis, MO 63110, USA
| | - Marie F Smeland
- Department of Pediatric Rehabilitation, University Hospital of North Norway, 9019 Tromsø, Norway
- Institute of Clinical Medicine, UiT The Arctic University of Norway, 9019, Tromsø, Norway
| | - Conor McClenaghan
- Center for Advanced Biotechnology and Medicine, and Departments of Pharmacology and Medicine, Robert Wood Johnson Medical School, Rutgers the State University of New Jersey, Piscatway, NJ 08854, USA
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Renaud JM, Ørtenblad N, McKenna MJ, Overgaard K. Exercise and fatigue: integrating the role of K +, Na + and Cl - in the regulation of sarcolemmal excitability of skeletal muscle. Eur J Appl Physiol 2023; 123:2345-2378. [PMID: 37584745 PMCID: PMC10615939 DOI: 10.1007/s00421-023-05270-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 06/29/2023] [Indexed: 08/17/2023]
Abstract
Perturbations in K+ have long been considered a key factor in skeletal muscle fatigue. However, the exercise-induced changes in K+ intra-to-extracellular gradient is by itself insufficiently large to be a major cause for the force decrease during fatigue unless combined to other ion gradient changes such as for Na+. Whilst several studies described K+-induced force depression at high extracellular [K+] ([K+]e), others reported that small increases in [K+]e induced potentiation during submaximal activation frequencies, a finding that has mostly been ignored. There is evidence for decreased Cl- ClC-1 channel activity at muscle activity onset, which may limit K+-induced force depression, and large increases in ClC-1 channel activity during metabolic stress that may enhance K+ induced force depression. The ATP-sensitive K+ channel (KATP channel) is also activated during metabolic stress to lower sarcolemmal excitability. Taking into account all these findings, we propose a revised concept in which K+ has two physiological roles: (1) K+-induced potentiation and (2) K+-induced force depression. During low-moderate intensity muscle contractions, the K+-induced force depression associated with increased [K+]e is prevented by concomitant decreased ClC-1 channel activity, allowing K+-induced potentiation of sub-maximal tetanic contractions to dominate, thereby optimizing muscle performance. When ATP demand exceeds supply, creating metabolic stress, both KATP and ClC-1 channels are activated. KATP channels contribute to force reductions by lowering sarcolemmal generation of action potentials, whilst ClC-1 channel enhances the force-depressing effects of K+, thereby triggering fatigue. The ultimate function of these changes is to preserve the remaining ATP to prevent damaging ATP depletion.
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Affiliation(s)
- Jean-Marc Renaud
- Faculty of Medicine, Department of Cellular and Molecular Medicine, University of Ottawa, 451 Smyth Rd., Ottawa, ON, K1H 8M5, Canada.
| | - Niels Ørtenblad
- Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark
| | - Michael J McKenna
- Institute for Health and Sport, Victoria University, Melbourne, VIC, 8001, Australia
- College of Physical Education, Southwest University, Chongqing, China
- College of Sport Science, Zhuhai College of Science and Technology, Zhuhai, China
| | - Kristian Overgaard
- Exercise Biology, Department of Public Health, Aarhus University, Aarhus, Denmark
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McClenaghan C, Mukadam MA, Roeglin J, Tryon RC, Grabner M, Dayal A, Meyer GA, Nichols CG. Skeletal muscle delimited myopathy and verapamil toxicity in SUR2 mutant mouse models of AIMS. EMBO Mol Med 2023; 15:e16883. [PMID: 37154692 PMCID: PMC10245035 DOI: 10.15252/emmm.202216883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 04/10/2023] [Accepted: 04/17/2023] [Indexed: 05/10/2023] Open
Abstract
ABCC9-related intellectual disability and myopathy syndrome (AIMS) arises from loss-of-function (LoF) mutations in the ABCC9 gene, which encodes the SUR2 subunit of ATP-sensitive potassium (KATP ) channels. KATP channels are found throughout the cardiovascular system and skeletal muscle and couple cellular metabolism to excitability. AIMS individuals show fatigability, muscle spasms, and cardiac dysfunction. We found reduced exercise performance in mouse models of AIMS harboring premature stop codons in ABCC9. Given the roles of KATP channels in all muscles, we sought to determine how myopathy arises using tissue-selective suppression of KATP and found that LoF in skeletal muscle, specifically, underlies myopathy. In isolated muscle, SUR2 LoF results in abnormal generation of unstimulated forces, potentially explaining painful spasms in AIMS. We sought to determine whether excessive Ca2+ influx through CaV 1.1 channels was responsible for myopathology but found that the Ca2+ channel blocker verapamil unexpectedly resulted in premature death of AIMS mice and that rendering CaV 1.1 channels nonpermeable by mutation failed to reverse pathology; results which caution against the use of calcium channel blockers in AIMS.
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Affiliation(s)
- Conor McClenaghan
- Center for the Investigation of Membrane Excitability Diseases, and Department of Cell Biology and PhysiologyWashington University School of MedicineSt. LouisMOUSA
- Center for Advanced Biotechnology and Medicine, and Departments of Pharmacology and Medicine, Robert Wood Johnson Medical SchoolRutgers UniversityPiscatawayNJUSA
| | - Maya A Mukadam
- Center for the Investigation of Membrane Excitability Diseases, and Department of Cell Biology and PhysiologyWashington University School of MedicineSt. LouisMOUSA
| | - Jacob Roeglin
- Center for the Investigation of Membrane Excitability Diseases, and Department of Cell Biology and PhysiologyWashington University School of MedicineSt. LouisMOUSA
| | - Robert C Tryon
- Center for the Investigation of Membrane Excitability Diseases, and Department of Cell Biology and PhysiologyWashington University School of MedicineSt. LouisMOUSA
| | - Manfred Grabner
- Department of PharmacologyMedical University of InnsbruckInnsbruckAustria
| | - Anamika Dayal
- Department of PharmacologyMedical University of InnsbruckInnsbruckAustria
| | - Gretchen A Meyer
- Program in Physical Therapy, Departments of Orthopaedic Surgery, Neurology and Biomedical EngineeringWashington University School of MedicineSt. LouisMOUSA
| | - Colin G Nichols
- Center for the Investigation of Membrane Excitability Diseases, and Department of Cell Biology and PhysiologyWashington University School of MedicineSt. LouisMOUSA
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Gerwin RD. A New Unified Theory of Trigger Point Formation: Failure of Pre- and Post-Synaptic Feedback Control Mechanisms. Int J Mol Sci 2023; 24:ijms24098142. [PMID: 37175845 PMCID: PMC10179372 DOI: 10.3390/ijms24098142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 04/27/2023] [Indexed: 05/15/2023] Open
Abstract
The origin of the myofascial trigger point (TrP), an anomalous locus in muscle, has never been well-described. A new trigger point hypothesis (the new hypothesis) presented here addresses this lack. The new hypothesis is based on the concept that existing myoprotective feedback mechanisms that respond to muscle overactivity, low levels of adenosine triphosphate, (ATP) or a low pH, fail to protect muscle in certain circumstances, such as intense muscle activity, resulting in an abnormal accumulation of intracellular Ca2+, persistent actin-myosin cross bridging, and then activation of the nociceptive system, resulting in the formation of a trigger point. The relevant protective feedback mechanisms include pre- and postsynaptic sympathetic nervous system modulation, modulators of acetylcholine release at the neuromuscular junction, and mutations/variants or post-translational functional alterations in either of two ion channelopathies, the ryanodine receptor and the potassium-ATP ion channel, both of which exist in multiple mutation states that up- or downregulate ion channel function. The concepts that are central to the origin of at least some TrPs are the failure of protective feedback mechanisms and/or of certain ion channelopathies that are new concepts in relation to myofascial trigger points.
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Affiliation(s)
- Robert D Gerwin
- Department of Neurology, The Johns Hopkins School of Medicine, Baltimore, MD 21287, USA
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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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Sánchez-Duarte E, Trujillo X, Cortés-Rojo C, Saavedra-Molina A, Camargo G, Hernández L, Huerta M, Montoya-Pérez R. Nicorandil improves post-fatigue tension in slow skeletal muscle fibers by modulating glutathione redox state. J Bioenerg Biomembr 2017; 49:159-170. [DOI: 10.1007/s10863-016-9692-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Accepted: 12/20/2016] [Indexed: 11/30/2022]
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Cè E, Rampichini S, Monti E, Venturelli M, Limonta E, Esposito F. Changes in the electromechanical delay components during a fatiguing stimulation in human skeletal muscle: an EMG, MMG and force combined approach. Eur J Appl Physiol 2016; 117:95-107. [PMID: 27858153 DOI: 10.1007/s00421-016-3502-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Accepted: 11/09/2016] [Indexed: 11/29/2022]
Abstract
PURPOSE Peripheral fatigue involves electrochemical and mechanical mechanisms. An electromyographic, mechanomyographic and force combined approach may permit a kinetic evaluation of the changes at the synaptic, skeletal muscle fiber, and muscle-tendon unit level during a fatiguing stimulation. METHODS Surface electromyogram, mechanomyogram, force and stimulation current were detected from the gastrocnemius medialis muscle in twenty male participants during a fatiguing stimulation (twelve blocks of 35 Hz stimulations, duty cycle 9 s on/1 s off, duration 120 s). The total electromechanical delay and its three components (between stimulation current and electromyogram, synaptic component; between electromyogram and mechanomyogram signal onset, muscle fiber electrochemical component, and between mechanomyogram and force signal onset, mechanical component) were calculated. Interday reliability and sensitivity were determined. RESULTS After fatigue, peak force decreased by 48% (P < 0.05) and the total electromechanical delay and its synaptic, electrochemical and mechanical components lengthened from 25.8 ± 0.9, 1.47 ± 0.04, 11.2 ± 0.6, and 13.1 ± 1.3 ms to 29.0 ± 1.6, 1.56 ± 0.05, 12.4 ± 0.9, and 17.2 ± 0.6 ms, respectively (P < 0.05). During fatigue, the total electromechanical delay and the mechanical component increased significantly after the 40th second, and then remained stable. The synaptic and electrochemical components lengthened significantly after the 20th and 30th second, respectively. Interday reliability was high to very high, with an adequate level of sensitivity. CONCLUSIONS The kinetic evaluation of the delays during the fatiguing stimulation highlighted different onsets and kinetics, with the events at synaptic level being the first to reveal a significant elongation, followed by those at the intra-fiber level. The mechanical events, which were the most affected by fatigue, were the last to lengthen.
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Affiliation(s)
- Emiliano Cè
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy.
| | - Susanna Rampichini
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Elena Monti
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Massimo Venturelli
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Eloisa Limonta
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
| | - Fabio Esposito
- Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Via G. Colombo 71, 20133, Milan, Italy
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8
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Hostrup M, Bangsbo J. Limitations in intense exercise performance of athletes - effect of speed endurance training on ion handling and fatigue development. J Physiol 2016; 595:2897-2913. [PMID: 27673449 DOI: 10.1113/jp273218] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Accepted: 09/21/2016] [Indexed: 01/10/2023] Open
Abstract
Mechanisms underlying fatigue development and limitations for performance during intense exercise have been intensively studied during the past couple of decades. Fatigue development may involve several interacting factors and depends on type of exercise undertaken and training level of the individual. Intense exercise (½-6 min) causes major ionic perturbations (Ca2+ , Cl- , H+ , K+ , lactate- and Na+ ) that may reduce sarcolemmal excitability, Ca2+ release and force production of skeletal muscle. Maintenance of ion homeostasis is thus essential to sustain force production and power output during intense exercise. Regular speed endurance training (SET), i.e. exercise performed at intensities above that corresponding to maximum oxygen consumption (V̇O2, max ), enhances intense exercise performance. However, most of the studies that have provided mechanistic insight into the beneficial effects of SET have been conducted in untrained and recreationally active individuals, making extrapolation towards athletes' performance difficult. Nevertheless, recent studies indicate that only a few weeks of SET enhances intense exercise performance in highly trained individuals. In these studies, the enhanced performance was not associated with changes in V̇O2, max and muscle oxidative capacity, but rather with adaptations in muscle ion handling, including lowered interstitial concentrations of K+ during and in recovery from intense exercise, improved lactate- -H+ transport and H+ regulation, and enhanced Ca2+ release function. The purpose of this Topical Review is to provide an overview of the effect of SET and to discuss potential mechanisms underlying enhancements in performance induced by SET in already well-trained individuals with special emphasis on ion handling in skeletal muscle.
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Affiliation(s)
- Morten Hostrup
- Section of Integrated Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark.,Department of Respiratory Research, Bispebjerg University Hospital, Denmark
| | - Jens Bangsbo
- Section of Integrated Physiology, Department of Nutrition, Exercise and Sports, University of Copenhagen, Denmark
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9
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Scott K, Benkhalti M, Calvert ND, Paquette M, Zhen L, Harper ME, Al-Dirbashi OY, Renaud JM. KATP channel deficiency in mouse FDB causes an impairment of energy metabolism during fatigue. Am J Physiol Cell Physiol 2016; 311:C559-C571. [PMID: 27488667 DOI: 10.1152/ajpcell.00137.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Accepted: 07/27/2016] [Indexed: 12/25/2022]
Abstract
The skeletal muscle ATP-sensitive K+ (KATP) channel is crucial in preventing fiber damage and contractile dysfunction, possibly by preventing damaging ATP depletion. The objective of this study was to investigate changes in energy metabolism during fatigue in wild-type and inwardly rectifying K+ channel (Kir6.2)-deficient (Kir6.2-/-) flexor digitorum brevis (FDB), a muscle that lacks functional KATP channels. Fatigue was elicited with one tetanic contraction every second. Decreases in ATP and total adenylate levels were significantly greater in wild-type than Kir6.2-/- FDB during the last 2 min of the fatigue period. Glycogen depletion was greater in Kir6.2-/- FDB for the first 60 s, but not by the end of the fatigue period, while there was no difference in glucose uptake. The total amount of glucosyl units entering glycolysis was the same in wild-type and Kir6.2-/- FDB. During the first 60 s, Kir6.2-/- FDB generated less lactate and more CO2; in the last 120 s, Kir6.2-/- FDB stopped generating CO2 and produced more lactate. The ATP generated during fatigue from phosphocreatine, glycolysis (lactate), and oxidative phosphorylation (CO2) was 3.3-fold greater in Kir6.2-/- than wild-type FDB. Because ATP and total adenylate were significantly less in Kir6.2-/- FDB, it is suggested that Kir6.2-/- FDB has a greater energy deficit, despite a greater ATP production, which is further supported by greater glucose uptake and lactate and CO2 production in Kir6.2-/- FDB during the recovery period. It is thus concluded that a lack of functional KATP channels results in an impairment of energy metabolism.
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Affiliation(s)
- Kyle Scott
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Maria Benkhalti
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Nicholas D Calvert
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Mathieu Paquette
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Li Zhen
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Mary-Ellen Harper
- Department of Biochemistry, Microbiology, and Immunology, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Osama Y Al-Dirbashi
- Newborn Screening Ontario, Children's Hospital of Eastern Ontario, Ottawa, Ontario, Canada; and Faculty of Medicine and Health Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates
| | - Jean-Marc Renaud
- Department of Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada;
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10
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Selvin D, Hesse E, Renaud JM. Properties of single FDB fibers following a collagenase digestion for studying contractility, fatigue, and pCa-sarcomere shortening relationship. Am J Physiol Regul Integr Comp Physiol 2015; 308:R467-79. [PMID: 25568074 DOI: 10.1152/ajpregu.00144.2014] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The objective of this study was to optimize the approach to obtain viable single flexor digitorum brevis (FDB) fibers following a collagenase digestion. A first aim was to determine the culture medium conditions for the collagenase digestion. The MEM yielded better fibers in terms of morphology and contractility than the DMEM. The addition of FBS to culture media was crucial to prevent fiber supercontraction. The addition of FBS to the physiological solution used during an experiment was also beneficial, especially during fatigue. Optimum FBS concentration in MEM was 10% (vol/vol), and for the physiological solution, it ranged between 0.2 and 1.0%. A second aim was to document the stability of single FDB fibers. If tested the day of the preparation, most fibers (∼80%) had stable contractions for up to 3 h, normal stimulus duration strength to elicit contractions, and normal and stable resting membrane potential during prolonged microelectrode penetration. A third aim was to document their fatigue kinetics. Major differences in fatigue resistance were observed between fibers as expected from the FDB fiber-type composition. All sarcoplasmic [Ca(2+)] and sarcomere length parameters returned to their prefatigue levels after a short recovery. The pCa-sarcomere shortening relationship of unfatigued fibers is very similar to the pCa-force curve reported in other studies. The pCa-sarcomere shortening from fatigue data is complicated by large decreases in sarcomere length between contractions. It is concluded that isolation of single fibers by a collagenase digestion is a viable preparation to study contractility and fatigue kinetics.
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Affiliation(s)
- David Selvin
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
| | - Erik Hesse
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
| | - Jean-Marc Renaud
- University of Ottawa, Department of Cellular and Molecular Medicine, Ottawa, Ontario, Canada
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