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Lindinger MI, Cairns SP, Sejersted OM. Resting membrane potential and intracellular [Na +] at rest, during fatigue and during recovery in rat soleus muscle fibres in situ. J Physiol 2024; 602:3469-3487. [PMID: 38877870 DOI: 10.1113/jp285870] [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: 11/14/2023] [Accepted: 05/28/2024] [Indexed: 07/17/2024] Open
Abstract
Large trans-sarcolemmal ionic shifts occur with fatiguing exercise or stimulation of isolated muscles. However, it is unknown how resting membrane potential (EM) and intracellular sodium concentration ([Na+]i) change with repeated contractions in living mammals. We investigated (i) whether [Na+]i (peak, kinetics) can reveal changes of Na+-K+ pump activity during brief or fatiguing stimulation and (ii) how resting EM and [Na+]i change during fatigue and recovery of rat soleus muscle in situ. Muscles of anaesthetised rats were stimulated with brief (10 s) or repeated tetani (60 Hz for 200 ms, every 2 s, for 30 s or 300 s) with isometric force measured. Double-barrelled ion-sensitive microelectrodes were used to quantify resting EM and [Na+]i. Post-stimulation data were fitted using polynomials and back-extrapolated to time zero recovery. Mean pre-stimulation resting EM (layer 2-7 fibres) was -71 mV (surface fibres were more depolarised), and [Na+]i was 14 mM. With deeper fibres, 10 s stimulation (2-150 Hz) increased [Na+]i to 38-46 mM whilst simultaneously causing hyperpolarisations (7.3 mV for 2-90 Hz). Fatiguing stimulation for 30 s or 300 s led to end-stimulation resting EM of -61 to -53 mV, which recovered rapidly (T1/2, 8-22 s). Mean end-stimulation [Na+]i increased to 86-101 mM with both fatigue protocols and the [Na+]i recovery time-course (T1/2, 21-35 s) showed no difference between protocols. These combined findings suggest that brief stimulation hyperpolarises the resting EM, likely via maximum Na+-induced stimulation of the Na+-K+ pump. Repeated tetani caused massive depolarisation and elevations of [Na+]i that together lower force, although they likely interact with other factors to cause fatigue. [Na+]i recovery kinetics provided no evidence of impaired Na+-K+ pump activity with fatigue. KEY POINTS: It is uncertain how resting membrane potential, intracellular sodium concentration ([Na+]i), and sodium-potassium (Na+-K+) pump activity change during repeated muscle contractions in living mammals. For rat soleus muscle fibres in situ, brief tetanic stimulation for 10 s led to raised [Na+]i, anticipated to evoke maximal Na+-induced stimulation of the Na+-K+ pump causing an immediate hyperpolarisation of the sarcolemma. More prolonged stimulation with repeated tetanic contractions causes massive elevations of [Na+]i, which together with large depolarisations (via K+ disturbances) likely reduce force production. These effects occurred without impairment of Na+-K+ pump function. Together these findings suggest that rapid activation of the Na+-K+ pump occurs with brief stimulation to maintain excitability, whereas more prolonged stimulation causes rundown of the trans-sarcolemmal K+ gradient (hence depolarisation) and Na+ gradient, which in combination can impair contraction to contribute to fatigue in living mammals.
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Affiliation(s)
- Michael I Lindinger
- Research and Development, The Nutraceutical Alliance Inc., Guelph, Ontario, Canada
| | - Simeon P Cairns
- Sports Performance Research Institute New Zealand, School of Sport and Recreation, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand
- Health and Rehabilitation Research Institute, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand
| | - Ole M Sejersted
- Institute for Experimental Medical Research, University of Oslo and Oslo University Hospital, Oslo, Norway
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Tarasova E, Bogacheva P, Chernyshev K, Balezina O. Quantal size increase induced by the endocannabinoid 2-arachidonoylglycerol requires activation of CGRP receptors in mouse motor synapses. Synapse 2024; 78:e22281. [PMID: 37694983 DOI: 10.1002/syn.22281] [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: 05/06/2023] [Revised: 08/22/2023] [Accepted: 08/24/2023] [Indexed: 09/12/2023]
Abstract
In mouse motor synapses, the exogenous application of the endocannabinoid (EC) 2-arachidonoylglycerol (2-AG) increases acetylcholine (ACh) quantal size due to the activation of CB1 receptors and the stimulation of ACh vesicular uptake. In the present study, microelectrode recordings of miniature endplate potentials (MEPP) revealed that this effect of 2-AG is independent of brain-derived neurotrophic factor (BDNF) signaling but involves the activation of calcitonin gene-related peptide (CGRP) receptors along with CB1 receptors. Potentiation of MEPP amplitude in the presence of 2-AG was prevented by blockers of CGRP receptors and ryanodine receptors (RyR) and by inhibitors of phospholipase C (PLC) and Ca2+ /calmodulin-dependent protein kinase II (CaMKII). Therefore, we suggest a hypothetical chain of events, which starts from the activation of presynaptic CB1 receptors, involves PLC, RyR, and CaMKII, and results in CGRP release with the subsequent activation of presynaptic CGRP receptors. Activation of CGRP receptors is probably a part of a complex molecular cascade leading to the 2-AG-induced increase in ACh quantal size and MEPP amplitude. We propose that the same chain of events may also take place if 2-AG is endogenously produced in mouse motor synapses, because the increase in MEPP amplitude that follows after prolonged tetanic muscle contractions (30 Hz, 2 min) was prevented by the blocking of CB1 receptors. This work may help to unveil the previously unknown aspects of the functional interaction between ECs and peptide modulators aimed at the regulation of quantal size and synaptic transmission.
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Affiliation(s)
- Ekaterina Tarasova
- Department of Human and Animal Physiology, Biological Faculty, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Polina Bogacheva
- Department of Human and Animal Physiology, Biological Faculty, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Kirill Chernyshev
- Department of Human and Animal Physiology, Biological Faculty, Lomonosov Moscow State University, Moscow, Russian Federation
| | - Olga Balezina
- Department of Human and Animal Physiology, Biological Faculty, Lomonosov Moscow State University, Moscow, Russian Federation
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Aracil-Marco A, Sarabia JM, Pastor D, Guillén S, López-Grueso R, Gallar J, Moya-Ramón M. Acute Increase in Blood αCGRP at Maximal Exercise and Its Association to Cardiorespiratory Fitness, Carbohydrate Oxidation and Work Performed: An Exploratory Study in Young Men. BIOLOGY 2021; 10:biology10080783. [PMID: 34440015 PMCID: PMC8389686 DOI: 10.3390/biology10080783] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 08/04/2021] [Accepted: 08/11/2021] [Indexed: 11/16/2022]
Abstract
Simple Summary αCGRP is a neuropeptide that increases in blood during high-intensity exercise in humans. However, the physiological meaning of this molecular response is unknown. Previous experimental works in rodents have related this neuropeptide to several biological processes in the skeletal muscle tissue and cardiorespiratory physiology. Based on the data from these animal studies we hypothesized that in humans αCGRP release during exercise could be similarly associated to metabolic and cardiorespiratory responses. To test this hypothesis, we subjected a sample of physically active young men to an exercise test up to exhaustion while their oxygen uptake (VO2max), CO2 production (VCO2), carbohydrate oxidation and performed work were measured. Blood samples were taken before the exercise test, at maximal intensity and after the volunteers have recovered, and the blood concentration of αCGRP was measured. We found that 2/3 of the volunteers responded to maximal exercise with an increase of their blood αCGRP concentration (responders), while the resting 1/3 did not (non-responders). We also found that VO2max, VCO2, carbohydrate oxidation and performed work were higher in the responders when compared to the non-responders. Therefore, our observations support that αCGRP release during exercise may be associated to physiological responses related to physical performance. Abstract This study aimed to explore if the acute variations in plasma concentration of α-calcitonin gene-related peptide (αCGRP) induced by a single maximal exercise bout may be associated to cardiorespiratory fitness and carbohydrate oxidation in humans. Twelve young adult Caucasian men (24.3 ± 0.9 years-old; 179.2 ± 1.9 cm of height; 23.9 ± 0.6 kg·m−2 body mass index) performed a graded exercise test. A venous catheter was placed before testing, and blood samples were taken at baseline, maximal effort and recovery. αCGRP was measured in plasma using a commercial double-sandwich enzyme-linked-immunoassay. A two-way repeated measurements ANOVA was used to compare the values obtained at baseline, maximal effort and recovery. In the whole sample, αCGRP increased at maximal effort and its concentration correlated directly, albeit non-significantly, with the muscle mass normalised VO2, VCO2, carbohydrate oxidation and relative power. Two thirds of the participants showed an increase in αCGRP concentration at maximal effort. Post hoc analysis showed that in these individuals, the muscle mass normalised VO2, VCO2, carbohydrate oxidation rate and relative power were higher than in the participants lacking this molecular response. Therefore, our data suggest that (a) a majority of young men respond to exercise with an increase in blood αCGRP concentration; and (b) individuals exhibiting this response also show a higher cardiorespiratory fitness, carbohydrate oxidation and work performed. These findings suggest that this neuropeptide could act as an exerkine with potential effects on physical performance.
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Affiliation(s)
- Adolfo Aracil-Marco
- Instituto de Neurociencias, UMH-CSIC, Department of Sports Sciences, UMH, 03202 Elche, Spain
- Correspondence: (A.A.-M.); (M.M.-R.); Tel.: +34-966-658-877 (A.A.-M.); +34-965-222-046 (M.M.-R.)
| | - José Manuel Sarabia
- Department of Sports Sciences, Centro de Investigación del Deporte, UMH, 03202 Elche, Spain; (J.M.S.); (D.P.)
| | - Diego Pastor
- Department of Sports Sciences, Centro de Investigación del Deporte, UMH, 03202 Elche, Spain; (J.M.S.); (D.P.)
| | - Silvia Guillén
- Centro de Investigación del Deporte, UMH, Hospital Universitario de Elda, 03600 Elda, Spain;
| | | | - Juana Gallar
- Instituto de Neurociencias, UMH-CSIC, Alicante Institute for Health and Biomedical Research (ISABIAL), 03550 San Juan de Alicante, Spain;
| | - Manuel Moya-Ramón
- Department of Sports Sciences, Centro de Investigación del Deporte, UMH, Alicante Institute for Health and Biomedical Research (ISABIAL), 03202 Elche, Spain
- Correspondence: (A.A.-M.); (M.M.-R.); Tel.: +34-966-658-877 (A.A.-M.); +34-965-222-046 (M.M.-R.)
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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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Pedersen KK, Nielsen OB, Overgaard K. Contractile benefits of doublet-initiated low-frequency stimulation in rat extensor digitorum longus muscle exposed to high extracellular [K +] or fatiguing contractions. Am J Physiol Cell Physiol 2019; 317:C39-C47. [PMID: 30969780 DOI: 10.1152/ajpcell.00519.2018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
During dynamic contractions, high-frequency muscle activation is needed to achieve optimal power. This must be balanced against an increased excitation-induced accumulation of extracellular K+, which can reduce excitability and ultimately may prevent adequate responses to high-frequency activation. Mean activation frequencies in vivo are often low (subtetanic), but activation patterns contain bursts of high (supratetanic) frequencies known as doublets, which enhance dynamic contraction in rested muscles at normal extracellular K+ concentration ([K+]o). Here, we examine how dynamic contractions in fast-twitch fibers stimulated by high frequency/doublets are affected during exposure to 11 mM [K+]o and during fatigue. Dynamic contractions were elicited by electrical stimulation in isolated rat extensor digitorum longus muscles incubated at 4 or 11 mM K+. When stimulation frequency was maintained constant, an increase from 150 to 300 Hz enhanced maximal power (Pmax), maximal velocity (Vmax), and rate of force development (RFD) at 4 mM K+ but only Vmax at 11 mM K+. With the use of subtetanic frequency trains (50 Hz) with or without an initiating doublet (300 Hz), the addition of a doublet increased maximal force, Pmax, Vmax, and RFD at both 4 and 11 mM K+. Furthermore, a work-matched fatiguing protocol was performed comparing a doublet-initiated subtetanic train (DT) of 60 Hz with a constant-frequency train (CFT) of 71 Hz during 100 dynamic contractions. We found that DT produced higher power, velocity, and RFD than CFT throughout the fatiguing protocol. The results indicate that doublets enhance dynamic contraction in fast-twitch muscles stimulated at subtetanic frequency during both normal and fatiguing conditions.
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Affiliation(s)
| | - Ole Bækgaard Nielsen
- Department of Public Health, Aarhus University , Aarhus , Denmark.,Department of Biomedicine, Aarhus University , Aarhus , Denmark
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Gaydukov AE, Balezina OP. Ryanodine- and CaMKII-dependent release of endogenous CGRP induces an increase in acetylcholine quantal size in neuromuscular junctions of mice. Brain Behav 2018; 8:e01058. [PMID: 29978952 PMCID: PMC6085904 DOI: 10.1002/brb3.1058] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 05/29/2018] [Accepted: 06/11/2018] [Indexed: 01/11/2023] Open
Abstract
OBJECTIVE The aim of this study was to identify the mechanism responsible for an increase in miniature endplate potentials (MEPPs) amplitude, induced by ryanodine as an agonist of ryanodine receptors in mouse motor nerve terminals. METHODS Using intracellular microelectrode recordings of MEPPs and evoked endplate potentials (EPPs), the changes in spontaneous and evoked acetylcholine release in motor synapses of mouse diaphragm neuromuscular preparations were studied. RESULTS Ryanodine (0.1 μM) increased both the amplitudes of MEPPs and EPPs to a similar extent (up to 130% compared to control). The ryanodine effect was prevented by blockage of receptors of calcitonin gene-related peptide (CGRP) by a truncated peptide CGRP8-37 . Endogenous CGRP is stored in large dense-core vesicles in motor nerve terminals and may be released as a co-transmitter. The ryanodine-induced increase in MEPPs amplitude may be fully prevented by inhibition of vesicular acetylcholine transporter by vesamicol or by blocking the activity of protein kinase A with H-89, suggesting that endogenous CGRP is released in response to the activation of ryanodine receptors. Activation of CGRP receptors can, in turn, upregulate the loading of acetylcholine into synaptic vesicles, which will increase the quantal size. This new feature of endogenous CGRP activity looks similar to recently described action of exogenous CGRP in motor synapses of mice. The ryanodine effect was prevented by inhibitors of Ca/Calmodulin-dependent kinase II (CaMKII) KN-62 or KN-93. Inhibition of CaMKII did not prevent the increase in MEPPs amplitude, which was caused by exogenous CGRP. CONCLUSIONS We propose that the activity of presynaptic CaMKII is necessary for the ryanodine-stimulated release of endogenous CGRP from motor nerve terminals, but CaMKII does not participate in signaling downstream the activation of CGRP-receptors followed by quantal size increase.
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Affiliation(s)
- Alexander E Gaydukov
- Department of Human and Animal Physiology, Biological Faculty, Lomonosov Moscow State University, Moscow, Russia.,Department of Physiology, Russian National Research Medical University, Moscow, Russia
| | - Olga P Balezina
- Department of Human and Animal Physiology, Biological Faculty, Lomonosov Moscow State University, Moscow, Russia
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Lima WG, Marques-Oliveira GH, da Silva TM, Chaves VE. Role of calcitonin gene-related peptide in energy metabolism. Endocrine 2017; 58:3-13. [PMID: 28884411 DOI: 10.1007/s12020-017-1404-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/23/2017] [Accepted: 08/22/2017] [Indexed: 12/14/2022]
Abstract
PURPOSE Calcitonin gene-related peptide (CGRP) is a neuropeptide produced by alternative tissue-specific splicing of the primary transcript of the CALC genes. CGRP is widely distributed in the central and peripheral nervous system, as well as in several organs and tissues. The presence of CGRP in the liver and brown and white adipose tissue suggests an effect of this neuropeptide on regulation of energy homeostasis. METHODS In this review, we summarize the current knowledge of the effect of CGRP on the control of energy metabolism, primarily focusing on food intake, thermoregulation and lipid metabolism in adipose tissue, liver and muscle. RESULTS CGRP induces anorexia, stimulating anorexigenic neuropeptide and/or inhibiting orexigenic neuropeptide expression, through cAMP/PKA pathway activation. CGRP also induces energy expenditure, increasing the skin temperature and brown adipose tissue thermogenesis. It has been also suggested that information related to peripheral lipid stores may be conveyed to the brain via CGRP-sensory innervation from adipose tissue. More recently, it was demonstrated that mice lacking αCGRP are protected from obesity induced by high-fat diet and that CGRP regulates the content of lipid in liver, muscle and adipose tissue. CONCLUSIONS It is unclear the receptor responsible by CGRP effects, as well as whether this neuropeptide acts directly or indirectly in liver, muscle and adipose tissue.
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Affiliation(s)
- William Gustavo Lima
- Laboratory of Physiology, Federal University of São João del-Rei, Divinópolis, Minas Gerais, Brazil
| | | | - Thaís Marques da Silva
- Laboratory of Physiology, Federal University of São João del-Rei, Divinópolis, Minas Gerais, Brazil
| | - Valéria Ernestânia Chaves
- Laboratory of Physiology, Federal University of São João del-Rei, Divinópolis, Minas Gerais, Brazil.
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Pirkmajer S, Chibalin AV. Na,K-ATPase regulation in skeletal muscle. Am J Physiol Endocrinol Metab 2016; 311:E1-E31. [PMID: 27166285 DOI: 10.1152/ajpendo.00539.2015] [Citation(s) in RCA: 70] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/31/2015] [Accepted: 05/02/2016] [Indexed: 12/17/2022]
Abstract
Skeletal muscle contains one of the largest and the most dynamic pools of Na,K-ATPase (NKA) in the body. Under resting conditions, NKA in skeletal muscle operates at only a fraction of maximal pumping capacity, but it can be markedly activated when demands for ion transport increase, such as during exercise or following food intake. Given the size, capacity, and dynamic range of the NKA pool in skeletal muscle, its tight regulation is essential to maintain whole body homeostasis as well as muscle function. To reconcile functional needs of systemic homeostasis with those of skeletal muscle, NKA is regulated in a coordinated manner by extrinsic stimuli, such as hormones and nerve-derived factors, as well as by local stimuli arising in skeletal muscle fibers, such as contractions and muscle energy status. These stimuli regulate NKA acutely by controlling its enzymatic activity and/or its distribution between the plasma membrane and the intracellular storage compartment. They also regulate NKA chronically by controlling NKA gene expression, thus determining total NKA content in skeletal muscle and its maximal pumping capacity. This review focuses on molecular mechanisms that underlie regulation of NKA in skeletal muscle by major extrinsic and local stimuli. Special emphasis is given to stimuli and mechanisms linking regulation of NKA and energy metabolism in skeletal muscle, such as insulin and the energy-sensing AMP-activated protein kinase. Finally, the recently uncovered roles for glutathionylation, nitric oxide, and extracellular K(+) in the regulation of NKA in skeletal muscle are highlighted.
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Affiliation(s)
- Sergej Pirkmajer
- Institute of Pathophysiology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia; and
| | - Alexander V Chibalin
- Department of Molecular Medicine and Surgery, Karolinska Institutet, Stockholm, Sweden
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Machado J, Manfredi LH, Silveira WA, Gonçalves DAP, Lustrino D, Zanon NM, Kettelhut IC, Navegantes LC. Calcitonin gene-related peptide inhibits autophagic-lysosomal proteolysis through cAMP/PKA signaling in rat skeletal muscles. Int J Biochem Cell Biol 2015; 72:40-50. [PMID: 26718975 DOI: 10.1016/j.biocel.2015.12.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2015] [Revised: 12/04/2015] [Accepted: 12/18/2015] [Indexed: 12/29/2022]
Abstract
Calcitonin gene-related peptide (CGRP) is a neuropeptide released by motor neuron in skeletal muscle and modulates the neuromuscular transmission by induction of synthesis and insertion of acetylcholine receptor on postsynaptic muscle membrane; however, its role in skeletal muscle protein metabolism remains unclear. We examined the in vitro and in vivo effects of CGRP on protein breakdown and signaling pathways in control skeletal muscles and muscles following denervation (DEN) in rats. In isolated muscles, CGRP (10(-10) to 10(-6)M) reduced basal and DEN-induced activation of overall proteolysis in a concentration-dependent manner. The in vitro anti-proteolytic effect of CGRP was completely abolished by CGRP8-37, a CGRP receptor antagonist. CGRP down-regulated the lysosomal proteolysis, the mRNA levels of LC3b, Gabarapl1 and cathepsin L and the protein content of LC3-II in control and denervated muscles. In parallel, CGRP elevated cAMP levels, stimulated PKA/CREB signaling and increased Foxo1 phosphorylation in both conditions. In denervated muscles and starved C2C12 cells, Rp-8-Br-cAMPs or PKI, two PKA inhibitors, completely abolished the inhibitory effect of CGRP on Foxo1, 3 and 4 and LC3 lipidation. A single injection of CGRP (100 μg kg(-1)) in denervated rats increased the phosphorylation levels of CREB and Akt, inhibited Foxo transcriptional activity, the LC3 lipidation as well as the mRNA levels of LC3b and cathepsin L, two bona fide targets of Foxo. This study shows for the first time that CGRP exerts a direct inhibitory action on autophagic-lysosomal proteolysis in control and denervated skeletal muscle by recruiting cAMP/PKA signaling, effects that are related to inhibition of Foxo activity and LC3 lipidation.
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Affiliation(s)
- Juliano Machado
- Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Leandro H Manfredi
- Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Wilian A Silveira
- Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Dawit A P Gonçalves
- Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Danilo Lustrino
- Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Neusa M Zanon
- Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Isis C Kettelhut
- Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil; Department of Biochemistry/Immunology, Ribeirão Preto Medical School, University of São Paulo, Brazil
| | - Luiz C Navegantes
- Department of Physiology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil.
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The differential effects of a selective kappa-opioid receptor agonist, U50488, in guinea pig heart tissues. BIOMED RESEARCH INTERNATIONAL 2015; 2015:906039. [PMID: 25815340 PMCID: PMC4359854 DOI: 10.1155/2015/906039] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Revised: 11/02/2014] [Accepted: 11/04/2014] [Indexed: 01/15/2023]
Abstract
The differential effects of a selective kappa- (κ-) opioid receptor agonist, U50488, were elucidated by monitoring the contraction of isolated guinea pig atrial and ventricular muscles. In electrically driven left atria, U50488 in nanomolar concentration range decreased the contractile force. Norbinaltorphimine (norBNI), a selective κ-receptor antagonist, and pertussis toxin (PTX) abolished the negative inotropic effect of U50488. In contrast, the inhibitory effect was not affected by the pretreatment of atropine or propranolol. Even though U50488 exerted a negative inotropic effect in the left atrium, it did not affect the contractile force of the right atrium and ventricles paced at 2 Hz. Similarly, the beating rate of the spontaneously beating right atrium was also unaffected by U50488. These results indicate that the activation of κ-opioid receptors can only produce negative inotropic effect in left atria via activation of PTX-sensitive G protein in guinea pigs. The absence of negative inotropic effects in right atria and ventricles suggests that there may be a greater distribution of functional κ-opioid receptors in guinea pig left atria than in right atria and ventricles, and the distribution of the receptors may be species-specific.
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Clausen T. Quantification of Na+,K+ pumps and their transport rate in skeletal muscle: functional significance. ACTA ACUST UNITED AC 2014; 142:327-45. [PMID: 24081980 PMCID: PMC3787770 DOI: 10.1085/jgp.201310980] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
During excitation, muscle cells gain Na+ and lose K+, leading to a rise in extracellular K+ ([K+]o), depolarization, and loss of excitability. Recent studies support the idea that these events are important causes of muscle fatigue and that full use of the Na+,K+-ATPase (also known as the Na+,K+ pump) is often essential for adequate clearance of extracellular K+. As a result of their electrogenic action, Na+,K+ pumps also help reverse depolarization arising during excitation, hyperkalemia, and anoxia, or from cell damage resulting from exercise, rhabdomyolysis, or muscle diseases. The ability to evaluate Na+,K+-pump function and the capacity of the Na+,K+ pumps to fill these needs require quantification of the total content of Na+,K+ pumps in skeletal muscle. Inhibition of Na+,K+-pump activity, or a decrease in their content, reduces muscle contractility. Conversely, stimulation of the Na+,K+-pump transport rate or increasing the content of Na+,K+ pumps enhances muscle excitability and contractility. Measurements of [3H]ouabain binding to skeletal muscle in vivo or in vitro have enabled the reproducible quantification of the total content of Na+,K+ pumps in molar units in various animal species, and in both healthy people and individuals with various diseases. In contrast, measurements of 3-O-methylfluorescein phosphatase activity associated with the Na+,K+-ATPase may show inconsistent results. Measurements of Na+ and K+ fluxes in intact isolated muscles show that, after Na+ loading or intense excitation, all the Na+,K+ pumps are functional, allowing calculation of the maximum Na+,K+-pumping capacity, expressed in molar units/g muscle/min. The activity and content of Na+,K+ pumps are regulated by exercise, inactivity, K+ deficiency, fasting, age, and several hormones and pharmaceuticals. Studies on the α-subunit isoforms of the Na+,K+-ATPase have detected a relative increase in their number in response to exercise and the glucocorticoid dexamethasone but have not involved their quantification in molar units. Determination of ATPase activity in homogenates and plasma membranes obtained from muscle has shown ouabain-suppressible stimulatory effects of Na+ and K+.
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Affiliation(s)
- Torben Clausen
- Department of Biomedicine, Aarhus University, DK-8000 Aarhus C, Denmark
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Vanheel B. Calcitonin gene-related powerpeptide and its puzzling receptor. Acta Physiol (Oxf) 2014; 210:710-3. [PMID: 24495305 DOI: 10.1111/apha.12245] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- B. Vanheel
- Department of Basic Medical Sciences; Division of Physiology; Ghent University; Ghent Belgium
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Pedersen KK, Nielsen OB, Overgaard K. Effects of high-frequency stimulation and doublets on dynamic contractions in rat soleus muscle exposed to normal and high extracellular [K(+)]. Physiol Rep 2013; 1:e00026. [PMID: 24303113 PMCID: PMC3831922 DOI: 10.1002/phy2.26] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2013] [Revised: 05/28/2013] [Accepted: 06/13/2013] [Indexed: 12/04/2022] Open
Abstract
The development of maximal velocity and power in muscle depends on the ability to transmit action potentials (AP) at very high frequencies up to about 400 Hz. However, for every AP there is a small loss of K+ to the interstitium, which during intense exercise, may build up to a point where excitability is reduced, thus limiting the intensity of further exercise. It is still unknown how the muscle responds to high-frequency stimulation when exposed to high [K+]. Contractile parameters of the muscles (force [F], velocity [V], power [P], rate of force development [RFD], and work) were examined during dynamic contractions, performed in vitro using rat soleus muscles incubated in buffers containing 4 or 8 mmol/L K+ and stimulated with constant trains of tetanic or supratetanic frequency or with trains initiated by a high-frequency doublet, followed by tetanic or subtetanic trains. At 4 mmol/L K+, an increase in frequency increased Pmax when using constant train stimulation. When stimulating with trains containing high-frequency doublets an increase in 120-msec work was seen, however, no increase in Pmax was observed. At 8 mmol/L K+, no differences were seen for either Pmax or 120-msec work when increasing frequency or introducing doublets. In all experiments where the frequency was increased or doublets applied, an increase in RFD was seen in both normal and high [K+]. The results indicate that stimulation with supratetanic frequencies can improve dynamic muscle contractility, but improvements are attenuated when muscles are exposed to high extracellular [K+].
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Affiliation(s)
- Katja K Pedersen
- Department of Public Health, Section of Sport Science, Aarhus University Aarhus, Denmark
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Abstract
High-frequency tetanic stimulation is associated with an increase in extracellular and T-tubular K(+) and changes of Na(+) and Cl(-) concentrations, membrane depolarization as well as inactivation of voltage-gated Na(+) channels. These alterations are expected to lead to fiber inexcitability, which is largely prevented by mechanisms intrinsic or extrinsic to muscle fibers. They act by adapting electrical membrane properties or by accelerating the reconstitution of ionic homeostasis. The high Cl(-) conductance of muscle fibers supports the K(+) conductance in fast and complete repolarization and creates a mechanism for the fast reuptake of K(+), thereby reducing the T-tubular K(+) accumulation. Excitability is increased by a Ca(2+) and proteinkinase C dependent inhibition of the Cl(-) conductance which is efficient especially in the T-tubular system. Several mediators activate the Na(+)/K(+)-ATPase and thus enhance the restoration of ionic homeostasis. Examples are purines (ATP, ADP), calcitonin-gene related peptide and adrenaline. It is also necessary to adapt the strength of the sarcoplasmic Ca(2+) concentration to the requirements of tetanic contractions. An overwhelming Ca(2+) signal leads to enzymatically driven excitation-contraction uncoupling. This process is most likely driven by the Ca(2+) dependent protease μ-calpain and might lead to the long-lasting fatigue observed after excessive physical activity.
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Clausen T, Nielsen OB, Clausen JD, Pedersen TH, Hayward LJ. Na+,K+-pump stimulation improves contractility in isolated muscles of mice with hyperkalemic periodic paralysis. ACTA ACUST UNITED AC 2011; 138:117-30. [PMID: 21708955 PMCID: PMC3135321 DOI: 10.1085/jgp.201010586] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In patients with hyperkalemic periodic paralysis (HyperKPP), attacks of muscle weakness or paralysis are triggered by K+ ingestion or rest after exercise. Force can be restored by muscle work or treatment with β2-adrenoceptor agonists. A missense substitution corresponding to a mutation in the skeletal muscle voltage-gated Na+ channel (Nav1.4, Met1592Val) causing human HyperKPP was targeted into the mouse SCN4A gene (mutants). In soleus muscles prepared from these mutant mice, twitch, tetanic force, and endurance were markedly reduced compared with soleus from wild type (WT), reflecting impaired excitability. In mutant soleus, contractility was considerably more sensitive than WT soleus to inhibition by elevated [K+]o. In resting mutant soleus, tetrodotoxin (TTX)-suppressible 22Na uptake and [Na+]i were increased by 470 and 58%, respectively, and membrane potential was depolarized (by 16 mV, P < 0.0001) and repolarized by TTX. Na+,K+ pump–mediated 86Rb uptake was 83% larger than in WT. Salbutamol stimulated 86Rb uptake and reduced [Na+]i both in mutant and WT soleus. Stimulating Na+,K+ pumps with salbutamol restored force in mutant soleus and extensor digitorum longus (EDL). Increasing [Na+]i with monensin also restored force in soleus. In soleus, EDL, and tibialis anterior muscles of mutant mice, the content of Na+,K+ pumps was 28, 62, and 33% higher than in WT, respectively, possibly reflecting the stimulating effect of elevated [Na+]i on the synthesis of Na+,K+ pumps. The results confirm that the functional disorders of skeletal muscles in HyperKPP are secondary to increased Na+ influx and show that contractility can be restored by acute stimulation of the Na+,K+ pumps. Calcitonin gene-related peptide (CGRP) restored force in mutant soleus but caused no detectable increase in 86Rb uptake. Repeated excitation and capsaicin also restored contractility, possibly because of the release of endogenous CGRP from nerve endings in the isolated muscles. These observations may explain how mild exercise helps locally to prevent severe weakness during an attack of HyperKPP.
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Affiliation(s)
- Torben Clausen
- Department of Physiology and Biophysics, Aarhus University, Denmark. tc@-fi.au.dk
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Broch-Lips M, de Paoli F, Pedersen TH, Overgaard K, Nielsen OB. Effects of 8 wk of voluntary unloaded wheel running on K+ tolerance and excitability of soleus muscles in rat. J Appl Physiol (1985) 2011; 111:212-20. [DOI: 10.1152/japplphysiol.00687.2010] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During intense exercise, efflux of K+ from working muscles increases extracellular K+ ([K+]o) to levels that can compromise muscle excitability and hence cause fatigue. In this context, the reduction in the exercise-induced elevation of [K+]o observed after training in humans is suggested to contribute to the increased performance after training. Although a similar effect could be obtained by an increase in the tolerance of muscle to elevated [K+]o, this possibility has not been investigated. To examine this, isolated soleus muscles from sedentary (sedentary) rats and from rats that had voluntarily covered 13.1 ± 0.7 km/day in an unloaded running wheel for 8 wk (active) were compared. In muscles from active rats, the loss of force induced by exposure to an elevated [K+]o of 9 mM was 42% lower than in muscles from sedentary rats ( P < 0.001). This apparent increase in K+ tolerance in active rats was associated with an increased excitability as evident from a 33% reduction in the electrical current needed to excite individual muscle fibers ( P < 0.0009). Moreover, muscles from active rats had lower Cl− conductance, higher maximal rate of rise of single-fiber action potentials (AP), and higher Na+/K+ pump content. When stimulated intermittently at 6.5 mM K+, muscles from active rats displayed better endurance than muscles from sedentary rats, whereas no difference was found when the muscles were stimulated continuously at 30 or 120 Hz. We conclude that voluntary running increases muscle excitability, leading to improved tolerance to elevated [K+]o.
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Cairns SP, Leader JP, Loiselle DS. Exacerbated potassium-induced paralysis of mouse soleus muscle at 37°C vis-à-vis 25°C: implications for fatigue. Pflugers Arch 2011; 461:469-79. [DOI: 10.1007/s00424-011-0927-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2010] [Revised: 12/21/2010] [Accepted: 01/14/2011] [Indexed: 10/18/2022]
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Clausen T. In isolated skeletal muscle, excitation may increase extracellular K+10-fold; how can contractility be maintained? Exp Physiol 2011; 96:356-68. [DOI: 10.1113/expphysiol.2010.054999] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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