1
|
Malak B, Celichowski J, Drzymała-Celichowska H. The temperature sensitivity of motor units in rat soleus. Sci Rep 2024; 14:3070. [PMID: 38321022 PMCID: PMC10847422 DOI: 10.1038/s41598-024-53208-8] [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: 09/28/2023] [Accepted: 01/29/2024] [Indexed: 02/08/2024] Open
Abstract
Temperature has a significant impact on the performance of the neuromuscular system and motor control processes. The smallest functional components of these systems are motor units (MUs), which may differ significantly between different muscles. The influence of temperature on the contractile properties of slow-twitch (S) MUs from soleus (SOL) muscles in rats was investigated under hypothermia (25 °C), normothermia (37 °C), and hyperthermia (41 °C). Hypothermia prolonged the twitch time parameters, decreased the rate of force development, increased the twitch-to-tetanus ratio, enhanced twitch force, and abolished post-tetanic depression. In contrast, hyperthermia did not alter twitch time parameters. Moreover, there was no effect on force despite the noted increase in post-tetanic depression and the twitch-to-tetanus ratio. Therefore, hypothermia induced more profound changes in S MUs compared with hyperthermia. The temperature effects in SOL MUs were compared to the effects previously reported for S MUs in the medial gastrocnemius (MG). The major differences between the S MUs of both muscles were the effects of temperature on twitch force, post-tetanic force modulation, twitch-to-tetanus ratio, and the slope of the force-frequency curve under hypothermia. Hyperthermia shortened twitch time parameters solely in the MG. In contrast, post-tetanic depression, twitch-to-tetanus ratio, and the slope of the force-frequency curve were influenced by hyperthermia only in SOL MUs. The different temperature effects of S MUs probably corresponded to differences in muscle architecture and their diverse functional tasks and enzyme activity. In summary, S MUs in SOL are more thermal-sensitive than their counterparts in MG.
Collapse
Affiliation(s)
- Bartosz Malak
- Department of Neurobiology, Poznan University of Physical Education, 27/39 Królowej Jadwigi St., 61-871, Poznań, Poland.
| | - Jan Celichowski
- Department of Neurobiology, Poznan University of Physical Education, 27/39 Królowej Jadwigi St., 61-871, Poznań, Poland
| | - Hanna Drzymała-Celichowska
- Department of Neurobiology, Poznan University of Physical Education, 27/39 Królowej Jadwigi St., 61-871, Poznań, Poland
- Department of Physiology and Biochemistry, Poznan University of Physical Education, 27/39 Królowej Jadwigi St., 61-871, Poznań, Poland
| |
Collapse
|
2
|
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.
Collapse
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
| |
Collapse
|
3
|
Ma Z, Paudel U, Foskett JK. Effects of temperature on action potentials and ion conductances in type II taste-bud cells. Am J Physiol Cell Physiol 2023; 325:C155-C171. [PMID: 37273235 PMCID: PMC10312327 DOI: 10.1152/ajpcell.00413.2022] [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: 09/06/2022] [Revised: 05/30/2023] [Accepted: 05/31/2023] [Indexed: 06/06/2023]
Abstract
Temperature strongly influences the intensity of taste, but it remains understudied despite its physiological, hedonic, and commercial implications. The relative roles of the peripheral gustatory and somatosensory systems innervating the oral cavity in mediating thermal effects on taste sensation and perception are poorly understood. Type II taste-bud cells, responsible for sensing sweet, bitter umami, and appetitive NaCl, release neurotransmitters to gustatory neurons by the generation of action potentials, but the effects of temperature on action potentials and the underlying voltage-gated conductances are unknown. Here, we used patch-clamp electrophysiology to explore the effects of temperature on acutely isolated type II taste-bud cell electrical excitability and whole cell conductances. Our data reveal that temperature strongly affects action potential generation, properties, and frequency and suggest that thermal sensitivities of underlying voltage-gated Na+ and K+ channel conductances provide a mechanism for how and whether voltage-gated Na+ and K+ channels in the peripheral gustatory system contribute to the influence of temperature on taste sensitivity and perception.NEW & NOTEWORTHY The temperature of food affects how it tastes. Nevertheless, the mechanisms involved are not well understood, particularly whether the physiology of taste-bud cells in the mouth is involved. Here we show that the electrical activity of type II taste-bud cells that sense sweet, bitter, and umami substances is strongly influenced by temperature. These results suggest a mechanism for the influence of temperature on the intensity of taste perception that resides in taste buds themselves.
Collapse
Affiliation(s)
- Zhongming Ma
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States
| | - Usha Paudel
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States
| | - J Kevin Foskett
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States
- Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States
| |
Collapse
|
4
|
The influence of temperature on contractile properties of motor units in rat medial gastrocnemius. J Electromyogr Kinesiol 2023; 68:102738. [PMID: 36535115 DOI: 10.1016/j.jelekin.2022.102738] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 12/05/2022] [Accepted: 12/08/2022] [Indexed: 12/23/2022] Open
Abstract
The effects of hypothermia and hyperthermia on mammalian skeletal muscle function have previously been reported. However, their effects on the contractile properties of different motor unit (MU) types were not described. This study aimed to explore the effect of temperature on contractile properties of MUs in rat medial gastrocnemius kept at 25 °C (hypothermia), 37 °C (normothermia), and 41 °C (hyperthermia). Hypothermia prolonged the twitch time parameters of all MU types, shifting the steep part of the force-frequency curve towards lower frequencies and increasing its steepness. In addition, it reduced the rate of force development but not the twitch and tetanus forces of slow-twitch (S) MUs. Moreover, it reduced the tetanic force of fast-twitch fatigable (FF) MUs and increased the twitch force of fast-twitch fatigue-resistant (FR) MUs. In contrast, hyperthermia had opposite effects on twitch time properties and the force-frequency relationship. The twitch-to-tetanus ratio decreased for FF and FR MUs, and the steep part of the force-frequency curve shifted towards higher frequencies and decreased in steepness. Our findings indicate that FF MUs are the most sensitive and S MUs are the least sensitive to temperature. Furthermore, force control processes involving changes in motoneuronal firing frequency were radically modified for fast MUs, especially FF MUs.
Collapse
|
5
|
Wang X, Nawaz M, DuPont C, Myers JH, Burke SR, Bannister RA, Foy BD, Voss AA, Rich MM. The role of action potential changes in depolarization-induced failure of excitation contraction coupling in mouse skeletal muscle. eLife 2022; 11:71588. [PMID: 34985413 PMCID: PMC8730720 DOI: 10.7554/elife.71588] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Accepted: 12/24/2021] [Indexed: 12/24/2022] Open
Abstract
Excitation-contraction coupling (ECC) is the process by which electrical excitation of muscle is converted into force generation. Depolarization of skeletal muscle resting potential contributes to failure of ECC in diseases such as periodic paralysis, intensive care unit acquired weakness and possibly fatigue of muscle during vigorous exercise. When extracellular K+ is raised to depolarize the resting potential, failure of ECC occurs suddenly, over a narrow range of resting potentials. Simultaneous imaging of Ca2+ transients and recording of action potentials (APs) demonstrated failure to generate Ca2+ transients when APs peaked at potentials more negative than -30mV. An AP property that closely correlated with failure of the Ca2+ transient was the integral of AP voltage with respect to time. Simultaneous recording of Ca2+ transients and APs with electrodes separated by 1.6mm revealed AP conduction fails when APs peak below -21mV. We hypothesize propagation of APs and generation of Ca2+ transients are governed by distinct AP properties: AP conduction is governed by AP peak, whereas Ca2+ release from the sarcoplasmic reticulum is governed by AP integral. The reason distinct AP properties may govern distinct steps of ECC is the kinetics of the ion channels involved. Na channels, which govern propagation, have rapid kinetics and are insensitive to AP width (and thus AP integral) whereas Ca2+ release is governed by gating charge movement of Cav1.1 channels, which have slower kinetics such that Ca2+ release is sensitive to AP integral. The quantitative relationships established between resting potential, AP properties, AP conduction and Ca2+ transients provide the foundation for future studies of failure of ECC induced by depolarization of the resting potential.
Collapse
Affiliation(s)
- Xueyong Wang
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| | - Murad Nawaz
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| | - Chris DuPont
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| | - Jessica H Myers
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| | - Steve Ra Burke
- Wright State University, Department of Biological Sciences, Dayton, United States
| | - Roger A Bannister
- University of Maryland School of Medicine, Departments of Pathology/Biochemistry & Molecular Biology, Baltimore, United States
| | - Brent D Foy
- Wright State University, Department of Physics, Dayton, United States
| | - Andrew A Voss
- Wright State University, Department of Biological Sciences, Dayton, United States
| | - Mark M Rich
- Wright State University, Department of Neuroscience, Cell Biology, and Physiology, Dayton, United States
| |
Collapse
|
6
|
Olesen JH, Herskind J, Pedersen KK, Overgaard K. Potassium-induced potentiation of subtetanic force in rat skeletal muscles: influences of β 2-activation, lactic acid, and temperature. Am J Physiol Cell Physiol 2021; 321:C884-C896. [PMID: 34613841 DOI: 10.1152/ajpcell.00120.2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Accepted: 09/28/2021] [Indexed: 02/04/2023]
Abstract
Moderate elevations of extracellular K+ concentration ([K+]o) occur during exercise and have been shown to potentiate force during contractions elicited with subtetanic frequencies. Here, we investigated whether lactic acid (reduced chloride conductance), β2-adrenoceptor activation, and increased temperature would influence the potentiating effect of potassium in slow- and fast-twitch muscles. Isometric contractions were elicited by electrical stimulation at various frequencies in isolated rat soleus and extensor digitorum longus (EDL) muscles incubated at normal (4 mM) or elevated K+, in combination with salbutamol (5 μM), lactic acid (18.1 mM), 9-anthracene-carboxylic acid (9-AC; 25 μM), or increased temperature (30-35°C). Elevating [K+]o from 4 mM to 7 mM (soleus) and 10 mM (EDL) potentiated isometric twitch and subtetanic force while slightly reducing tetanic force. In EDL, salbutamol further augmented twitch force (+27 ± 3%, P < 0.001) and subtetanic force (+22 ± 4%, P < 0.001). In contrast, salbutamol reduced subtetanic force (-28 ± 6%, P < 0.001) in soleus muscles. Lactic acid and 9-AC had no significant effects on isometric force of muscles already exposed to moderate elevations of [K+]o. The potentiating effect of elevated [K+]o was still well maintained at 35°C. Addition of salbutamol exerts a further force-potentiating effect in fast-twitch but not in slow-twitch muscles already potentiated by moderately elevated [K+]o, whereas lactic acid, 9-AC, or increased temperature does not exert any further augmentation. However, the potentiating effect of elevated [K+]o was still maintained in the presence of these, thus emphasizing the positive influence of moderately elevated [K+]o for contractile performance during exercise.
Collapse
Affiliation(s)
- Jonas H Olesen
- Exercise Biology, Department of Public Health, Aarhus University, Aarhus, Denmark
| | - Jon Herskind
- Exercise Biology, Department of Public Health, Aarhus University, Aarhus, Denmark
| | - Katja K Pedersen
- Exercise Biology, Department of Public Health, Aarhus University, Aarhus, Denmark
| | - Kristian Overgaard
- Exercise Biology, Department of Public Health, Aarhus University, Aarhus, Denmark
| |
Collapse
|
7
|
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.
Collapse
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
| |
Collapse
|
8
|
Péterfi Z, Szilvásy-Szabó A, Farkas E, Ruska Y, Pyke C, Knudsen LB, Fekete C. Glucagon-Like Peptide-1 Regulates the Proopiomelanocortin Neurons of the Arcuate Nucleus both Directly and Indirectly via Presynaptic Action. Neuroendocrinology 2021; 111:986-997. [PMID: 33152734 DOI: 10.1159/000512806] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2020] [Accepted: 11/02/2020] [Indexed: 11/19/2022]
Abstract
Glucagon-like peptide-1 (GLP-1) exerts its anorexigenic effect at least partly via the proopiomelanocortin (POMC) neurons of the arcuate (ARC) nucleus. These neurons are known to express GLP-1 receptor (GLP-1R). The aim of the study was to determine whether in addition to its direct effect, GLP-1 also modulates how neuronal inputs can regulate the POMC neurons by acting on presynaptic terminals, ultrastructural and electrophysiological studies were performed on tissues of adult male mice. GLP-1R-immunoreactivity was associated with the cell membrane of POMC neurons and with axon terminals forming synapses on these cells. The GLP-1 analog exendin 4 (Ex4) markedly increased the firing rate of all examined POMC neurons and depolarized these cells. These effects of Ex4 were prevented by intracellular administration of the G-protein blocker guanosine 5'-[β-thio]diphosphate trilithium salt (GDP-β-S). Ex4 also influenced the miniature postsynaptic currents (mPSCs) and evoked PSCs of POMC neurons. Ex4 increased the frequency of miniature excitatory PSCs (EPSCs) and the amplitude of the evoked EPSCs in half of the POMC neurons. Ex4 increased the frequency of miniature inhibitory PSCs (IPSCs) and the amplitudes of the evoked IPSCs in one-third of neurons. These effects of Ex4 were not influenced by intracellular GDP-β-S, indicating that GLP-1 signaling directly stimulates a population of axon terminals innervating the POMC neurons. The different Ex4 responsiveness of their mPSCs indicates the heterogeneity of the POMC neurons of the ARC. In summary, our data demonstrate that in addition to its direct excitatory effect on the POMC neurons, GLP-1 signaling also facilitates the presynaptic input of these cells by acting on presynaptically localized GLP-1R.
Collapse
Affiliation(s)
- Zoltán Péterfi
- Laboratory of Integrative Neuroendocrinology, Department of Endocrine Neurobiology, Institute of Experimental Medicine, Budapest, Hungary
| | - Anett Szilvásy-Szabó
- Laboratory of Integrative Neuroendocrinology, Department of Endocrine Neurobiology, Institute of Experimental Medicine, Budapest, Hungary
| | - Erzsébet Farkas
- Laboratory of Integrative Neuroendocrinology, Department of Endocrine Neurobiology, Institute of Experimental Medicine, Budapest, Hungary
| | - Yvette Ruska
- Laboratory of Integrative Neuroendocrinology, Department of Endocrine Neurobiology, Institute of Experimental Medicine, Budapest, Hungary
| | - Charles Pyke
- Global Research, Novo Nordisk A/S, Malov, Denmark
| | | | - Csaba Fekete
- Laboratory of Integrative Neuroendocrinology, Department of Endocrine Neurobiology, Institute of Experimental Medicine, Budapest, Hungary,
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Tupper Research Institute, Tufts Medical Center, Boston, Massachusetts, USA,
| |
Collapse
|
9
|
Fienieg B, Hassing GJ, van der Wall HEC, van Westen GJP, Kemme MJB, Adiyaman A, Elvan A, Burggraaf J, Gal P. The association between body temperature and electrocardiographic parameters in normothermic healthy volunteers. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2020; 44:44-53. [PMID: 33179782 PMCID: PMC7894493 DOI: 10.1111/pace.14120] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Revised: 10/14/2020] [Accepted: 11/01/2020] [Indexed: 12/19/2022]
Abstract
Background Previous studies reported that hypo‐ and hyperthermia are associated with several atrial and ventricular electrocardiographical parameters, including corrected QT (QTc) interval. Enhanced characterization of variations in QTc interval and normothermic body temperature aids in better understanding the underlying mechanism behind drug induced QTc interval effects. The analysis’ objective was to investigate associations between body temperature and electrocardiographical parameters in normothermic healthy volunteers. Methods Data from 3023 volunteers collected at our center were retrospectively analyzed. Subjects were considered healthy after review of collected data by a physician, including a normal tympanic body temperature (35.5‐37.5°C) and in sinus rhythm. A linear multivariate model with body temperature as a continuous was performed. Another multivariate analysis was performed with only the QT subintervals as independent variables and body temperature as dependent variable. Results Mean age was 33.8 ± 17.5 years and mean body temperature was 36.6 ± 0.4°C. Body temperature was independently associated with age (standardized coefficient [SC] = −0.255, P < .001), female gender (SC = +0.209, P < .001), heart rate (SC = +0.231, P < .001), P‐wave axis (SC = −0.051, P < .001), J‐point elevation in lead V4 (SC = −0.121, P < .001), and QTcF duration (SC = −0.061, P = .002). In contrast, other atrial and atrioventricular (AV) nodal parameters were not independently associated with body temperature. QT subinterval analysis revealed that only QRS duration (SC = −0.121, P < .001) was independently associated with body temperature. Conclusion Body temperature in normothermic healthy volunteers was associated with heart rate, P‐wave axis, J‐point amplitude in lead V4, and ventricular conductivity, the latter primarily through prolongation of the QRS duration.
Collapse
Affiliation(s)
| | | | - Hein E C van der Wall
- Centre for Human Drug Research, Leiden, The Netherlands.,Leiden Academic Centre for Drug Research, Leiden, The Netherlands
| | | | - Michiel J B Kemme
- Department of Cardiology, Amsterdam UMC, Vrije Universiteit Amsterdam, Amsterdam Cardiovascular Sciences, Amsterdam, The Netherlands
| | - Ahmet Adiyaman
- Department of Cardiology, Isala Hospital, Zwolle, The Netherlands
| | - Arif Elvan
- Department of Cardiology, Isala Hospital, Zwolle, The Netherlands
| | - Jacobus Burggraaf
- Centre for Human Drug Research, Leiden, The Netherlands.,Leiden Academic Centre for Drug Research, Leiden, The Netherlands.,Leiden University Medical Center, Leiden, The Netherlands
| | - Pim Gal
- Centre for Human Drug Research, Leiden, The Netherlands.,Leiden University Medical Center, Leiden, The Netherlands
| |
Collapse
|
10
|
Dipeptidyl peptidase 4 inhibitor sitagliptin protected against dextran sulfate sodium-induced experimental colitis by potentiating the action of GLP-2. Acta Pharmacol Sin 2020; 41:1446-1456. [PMID: 32398684 DOI: 10.1038/s41401-020-0413-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2020] [Accepted: 03/30/2020] [Indexed: 02/07/2023] Open
Abstract
Dipeptidyl peptidase 4 (DPP4), a ubiquitously expressed protease that cleaves off the N-terminal dipeptide from proline and alanine on the penultimate position, has important roles in many physiological processes. In the present study, experimental colitis was induced in mice receiving 3% dextran sulfate sodium (DSS) in drinking water. We found that mice with DSS-induced colitis had significantly increased intestinal DPP activity and decreased serum DPP activity, suggesting a probable correlation of DPP4 with experimental colitis. Then, we investigated whether sitagliptin, a specific DPP4 inhibitor could protect against DSS-induced colitis. We showed that oral administration of single dose of sitagliptin (30 mg/kg) on D7 remarkably inhibited DPP enzyme activity in both serum and intestine of DSS-induced colitic mice. Repeated administration of sitagliptin (10, 30 mg/kg, bid, from D0 to D8) significantly ameliorated DSS-induced colitis, including reduction of disease activity index (DAI) and body weight loss, improvement of histological score and colon length. Sitagliptin administration dose-dependently increased plasma concentrations of active form of GLP-1 and colonic expression of GLP-2R. Co-administration of GLP-2R antagonist GLP-23-33 (500 μg/kg, bid, sc) abolished the protective effects of sitagliptin in DSS-induced colitic mice. Moreover, sitagliptin administration significantly decreased the ratio of apoptotic cells and increased the ratio of proliferative cells in colon epithelium of DSS-induced colitic mice, and this effect was also blocked by GLP-23-33. Taken together, our results demonstrate that sitagliptin could attenuate DSS-induced experimental colitis and the effects can be attributed to the enhancement of GLP-2 action and the subsequent protective effects on intestinal barrier by inhibiting epithelial cells apoptosis and promoting their proliferation. These findings suggest sitagliptin as a novel therapeutic approach for the treatment of ulcerative colitis.
Collapse
|
11
|
Alonso LM, Marder E. Temperature compensation in a small rhythmic circuit. eLife 2020; 9:e55470. [PMID: 32484437 PMCID: PMC7332291 DOI: 10.7554/elife.55470] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 05/31/2020] [Indexed: 12/28/2022] Open
Abstract
Temperature affects the conductances and kinetics of the ionic channels that underlie neuronal activity. Each membrane conductance has a different characteristic temperature sensitivity, which raises the question of how neurons and neuronal circuits can operate robustly over wide temperature ranges. To address this, we employed computational models of the pyloric network of crabs and lobsters. We produced multiple different models that exhibit a triphasic pyloric rhythm over a range of temperatures and explored the dynamics of their currents and how they change with temperature. Temperature can produce smooth changes in the relative contributions of the currents to neural activity so that neurons and networks undergo graceful transitions in the mechanisms that give rise to their activity patterns. Moreover, responses of the models to deletions of a current can be different at high and low temperatures, indicating that even a well-defined genetic or pharmacological manipulation may produce qualitatively distinct effects depending on the temperature.
Collapse
Affiliation(s)
- Leandro M Alonso
- Volen Center and Biology Department, Brandeis UniversityWalthamUnited States
| | - Eve Marder
- Volen Center and Biology Department, Brandeis UniversityWalthamUnited States
| |
Collapse
|
12
|
Physiological mechanisms determining eccrine sweat composition. Eur J Appl Physiol 2020; 120:719-752. [PMID: 32124007 PMCID: PMC7125257 DOI: 10.1007/s00421-020-04323-7] [Citation(s) in RCA: 111] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2019] [Accepted: 02/11/2020] [Indexed: 02/08/2023]
Abstract
Purpose The purpose of this paper is to review the physiological mechanisms determining eccrine sweat composition to assess the utility of sweat as a proxy for blood or as a potential biomarker of human health or nutritional/physiological status. Methods This narrative review includes the major sweat electrolytes (sodium, chloride, and potassium), other micronutrients (e.g., calcium, magnesium, iron, copper, zinc, vitamins), metabolites (e.g., glucose, lactate, ammonia, urea, bicarbonate, amino acids, ethanol), and other compounds (e.g., cytokines and cortisol). Results Ion membrane transport mechanisms for sodium and chloride are well established, but the mechanisms of secretion and/or reabsorption for most other sweat solutes are still equivocal. Correlations between sweat and blood have not been established for most constituents, with perhaps the exception of ethanol. With respect to sweat diagnostics, it is well accepted that elevated sweat sodium and chloride is a useful screening tool for cystic fibrosis. However, sweat electrolyte concentrations are not predictive of hydration status or sweating rate. Sweat metabolite concentrations are not a reliable biomarker for exercise intensity or other physiological stressors. To date, glucose, cytokine, and cortisol research is too limited to suggest that sweat is a useful surrogate for blood. Conclusion Final sweat composition is not only influenced by extracellular solute concentrations, but also mechanisms of secretion and/or reabsorption, sweat flow rate, byproducts of sweat gland metabolism, skin surface contamination, and sebum secretions, among other factors related to methodology. Future research that accounts for these confounding factors is needed to address the existing gaps in the literature. Electronic supplementary material The online version of this article (10.1007/s00421-020-04323-7) contains supplementary material, which is available to authorized users.
Collapse
|
13
|
The influence of local skin temperature on the sweat glands maximum ion reabsorption rate. Eur J Appl Physiol 2019; 119:685-695. [DOI: 10.1007/s00421-018-04059-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2018] [Accepted: 12/18/2018] [Indexed: 10/27/2022]
|
14
|
Abdelsayed M, Ruprai M, Ruben PC. The efficacy of Ranolazine on E1784K is altered by temperature and calcium. Sci Rep 2018; 8:3643. [PMID: 29483621 PMCID: PMC5827758 DOI: 10.1038/s41598-018-22033-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Accepted: 02/15/2018] [Indexed: 12/19/2022] Open
Abstract
E1784K is the most common mixed syndrome SCN5a mutation underpinning both Brugada syndrome type 1 (BrS1) and Long-QT syndrome type 3 (LQT3). The charge reversal mutant enhances the late sodium current (INa) passed by the cardiac voltage-gated sodium channel (NaV1.5), delaying cardiac repolarization. Exercise-induced triggers, like elevated temperature and cytosolic calcium, exacerbate E1784K late INa. In this study, we tested the effects of Ranolazine, the late INa blocker, on voltage-dependent and kinetic properties of E1784K at elevated temperature and cytosolic calcium. We used whole-cell patch clamp to measure INa from wild type and E1784K channels expressed in HEK293 cells. At elevated temperature, Ranolazine attenuated gain-of-function in E1784K by decreasing late INa, hyperpolarizing steady-state fast inactivation, and increasing use-dependent inactivation. Both elevated temperature and cytosolic calcium hampered the capacity of Ranolazine to suppress E1784K late INa. In-silico action potential (AP) simulations were done using a modified O'Hara Rudy (ORd) cardiac model. Simulations showed that Ranolazine failed to shorten AP duration, an effect augmented at febrile temperatures. The drug-channel interaction is clearly affected by external triggers, as reported previously with ischemia. Determining drug efficacy under various physiological states in SCN5a cohorts is crucial for accurate management of arrhythmias.
Collapse
Affiliation(s)
- Mena Abdelsayed
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada
| | - Manpreet Ruprai
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada
| | - Peter C Ruben
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
| |
Collapse
|
15
|
Ye M, Yang J, Tian C, Zhu Q, Yin L, Jiang S, Yang M, Shu Y. Differential roles of Na V1.2 and Na V1.6 in regulating neuronal excitability at febrile temperature and distinct contributions to febrile seizures. Sci Rep 2018; 8:753. [PMID: 29335582 PMCID: PMC5768682 DOI: 10.1038/s41598-017-17344-8] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 11/20/2017] [Indexed: 01/25/2023] Open
Abstract
Dysregulation of voltage-gated sodium channels (VGSCs) is associated with multiple clinical disorders, including febrile seizures (FS). The contribution of different sodium channel subtypes to environmentally triggered seizures is not well understood. Here we demonstrate that somatic and axonal sodium channels primarily mediated through NaV1.2 and NaV1.6 subtypes, respectively, behave differentially at FT, and might play distinct roles in FS generation. In contrast to sodium channels on the main axonal trunk, somatic ones are more resistant to inactivation and display significantly augmented currents, faster gating rates and kinetics of recovery from inactivation at FT, features that promote neuronal excitabilities. Pharmacological inhibition of NaV1.2 by Phrixotoxin-3 (PTx3) suppressed FT-induced neuronal hyperexcitability in brain slice, while up-regulation of NaV1.2 as in NaV1.6 knockout mice showed an opposite effect. Consistently, NaV1.6 knockout mice were more susceptible to FS, exhibiting much lower temperature threshold and shorter onset latency than wildtype mice. Neuron modeling further suggests that NaV1.2 is the major subtype mediating FT-induced neuronal hyperexcitability, and predicts potential outcomes of alterations in sodium channel subtype composition. Together, these data reveal a role of native NaV1.2 on neuronal excitability at FT and its important contribution to FS pathogenesis.
Collapse
Affiliation(s)
- Mingyu Ye
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
| | - Jun Yang
- State Key Laboratory of Cognitive Neuroscience and Learning, School of Brain and Cognitive Sciences, the Collaborative Innovation Center for Brain Science, Beijing Normal University, Beijing, China
| | - Cuiping Tian
- iHuman Institute, ShanghaiTech University, Shanghai, China
| | - Qiyu Zhu
- Brain Institute, College of Pharmaceutical Sciences, Capital Medical University, Beijing, China
| | - Luping Yin
- State Key Laboratory of Cognitive Neuroscience and Learning, School of Brain and Cognitive Sciences, the Collaborative Innovation Center for Brain Science, Beijing Normal University, Beijing, China
| | - Shan Jiang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Mingpo Yang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Yousheng Shu
- State Key Laboratory of Cognitive Neuroscience and Learning, School of Brain and Cognitive Sciences, the Collaborative Innovation Center for Brain Science, Beijing Normal University, Beijing, China.
| |
Collapse
|
16
|
Said H, Akiba Y, Narimatsu K, Maruta K, Kuri A, Iwamoto KI, Kuwahara A, Kaunitz JD. FFA3 Activation Stimulates Duodenal Bicarbonate Secretion and Prevents NSAID-Induced Enteropathy via the GLP-2 Pathway in Rats. Dig Dis Sci 2017; 62:1944-1952. [PMID: 28523577 PMCID: PMC5511769 DOI: 10.1007/s10620-017-4600-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Accepted: 04/29/2017] [Indexed: 02/08/2023]
Abstract
BACKGROUND Therapy with nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with enteropathy in humans and experimental animals, a cause of considerable morbidity. Unlike foregut NSAID-associated mucosal lesions, most treatments for this condition are of little efficacy. We propose that the endogenously released intestinotrophic hormone glucagon-like peptide-2 (GLP-2) prevents the development of NSAID-induced enteropathy. Since the short-chain fatty acid receptor FFA3 is expressed on enteroendocrine L cells and on enteric nerves in the gastrointestinal tract, we further hypothesized that activation of FFA3 on L cells protects the mucosa from injury via GLP-2 release with enhanced duodenal HCO3- secretion. We thus investigated the effects of synthetic selective FFA3 agonists with consequent GLP-2 release on NSAID-induced enteropathy. METHODS We measured duodenal HCO3- secretion in isoflurane-anesthetized rats in a duodenal loop perfused with the selective FFA3 agonists MQC or AR420626 (AR) while measuring released GLP-2 in the portal vein (PV). Intestinal injury was produced by indomethacin (IND, 10 mg/kg, sc) with or without MQC (1-10 mg/kg, ig) or AR (0.01-0.1 mg/kg, ig or ip) treatment. RESULTS Luminal perfusion with MQC or AR (0.1-10 µM) dose-dependently augmented duodenal HCO3- secretion accompanied by increased GLP-2 concentrations in the PV. The effect of FFA3 agonists was inhibited by co-perfusion of the selective FFA3 antagonist CF3-MQC (30 µM). AR-induced augmented HCO3- secretion was reduced by iv injection of the GLP-2 receptor antagonist GLP-2(3-33) (3 nmol/kg), or by pretreatment with the cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor CFTRinh-172 (1 mg/kg, ip). IND-induced small intestinal ulcers were dose-dependently inhibited by intragastric administration of MQC or AR. GLP-2(3-33) (1 mg/kg, ip) or CF3-MQC (1 mg/kg, ig) reversed AR-associated reduction in IND-induced enteropathy. In contrast, ip injection of AR had no effect on enteropathy. CONCLUSION These results suggest that luminal FFA3 activation enhances mucosal defenses and prevents NSAID-induced enteropathy via the GLP-2 pathway. The selective FFA3 agonist may be a potential therapeutic candidate for NSAID-induced enteropathy.
Collapse
Affiliation(s)
- Hyder Said
- College of Arts and Sciences, University of California, Los Angeles, CA, USA
| | - Yasutada Akiba
- Greater Los Angeles Veterans Affairs Healthcare System, 11301 Wilshire Boulevard, Bldg 115, Suite 217, Los Angeles, CA, 90073, USA
- Department of Medicine, University of California Los Angeles, School of Medicine, Los Angeles, CA, USA
- Brentwood Biomedical Research Institute, Los Angeles, CA, USA
| | - Kazuyuki Narimatsu
- Department of Medicine, University of California Los Angeles, School of Medicine, Los Angeles, CA, USA
| | - Koji Maruta
- Department of Medicine, University of California Los Angeles, School of Medicine, Los Angeles, CA, USA
| | - Ayaka Kuri
- Graduate School of Integrated Pharmaceutical and Nutritional Sciences, University of Shizuoka, Shizuoka, Japan
| | - Ken-Ichi Iwamoto
- Graduate School of Integrated Pharmaceutical and Nutritional Sciences, University of Shizuoka, Shizuoka, Japan
| | - Atsukazu Kuwahara
- Graduate School of Integrated Pharmaceutical and Nutritional Sciences, University of Shizuoka, Shizuoka, Japan
| | - Jonathan D Kaunitz
- Greater Los Angeles Veterans Affairs Healthcare System, 11301 Wilshire Boulevard, Bldg 115, Suite 217, Los Angeles, CA, 90073, USA.
- Department of Medicine, University of California Los Angeles, School of Medicine, Los Angeles, CA, USA.
- Brentwood Biomedical Research Institute, Los Angeles, CA, USA.
- Department of Surgery, University of California Los Angeles, School of Medicine, Los Angeles, CA, USA.
| |
Collapse
|
17
|
Immune recognition and response to the intestinal microbiome in type 1 diabetes. J Autoimmun 2016; 71:10-8. [DOI: 10.1016/j.jaut.2016.02.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Revised: 02/03/2016] [Accepted: 02/04/2016] [Indexed: 12/19/2022]
|
18
|
Wiśniewski K, Sueiras-Diaz J, Jiang G, Galyean R, Lu M, Thompson D, Wang YC, Croston G, Posch A, Hargrove DM, Wiśniewska H, Laporte R, Dwyer JJ, Qi S, Srinivasan K, Hartwig J, Ferdyan N, Mares M, Kraus J, Alagarsamy S, Rivière PJM, Schteingart CD. Synthesis and Pharmacological Characterization of Novel Glucagon-like Peptide-2 (GLP-2) Analogues with Low Systemic Clearance. J Med Chem 2016; 59:3129-39. [DOI: 10.1021/acs.jmedchem.5b01909] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Kazimierz Wiśniewski
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Javier Sueiras-Diaz
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Guangcheng Jiang
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Robert Galyean
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Mark Lu
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Dorain Thompson
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Yung-Chih Wang
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Glenn Croston
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Alexander Posch
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Diane M. Hargrove
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Halina Wiśniewska
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Régent Laporte
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - John J. Dwyer
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Steve Qi
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Karthik Srinivasan
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Jennifer Hartwig
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Nicky Ferdyan
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Monica Mares
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - John Kraus
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Sudarkodi Alagarsamy
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Pierre J. M. Rivière
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| | - Claudio D. Schteingart
- Ferring
Research Institute Inc., 4245 Sorrento
Valley Boulevard, San Diego, California 92121, United States
| |
Collapse
|
19
|
Abdelsayed M, Peters CH, Ruben PC. Differential thermosensitivity in mixed syndrome cardiac sodium channel mutants. J Physiol 2015; 593:4201-23. [PMID: 26131924 DOI: 10.1113/jp270139] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2015] [Accepted: 06/16/2015] [Indexed: 12/20/2022] Open
Abstract
Cardiac arrhythmias are often associated with mutations in SCN5A the gene that encodes the cardiac paralogue of the voltage-gated sodium channel, NaV 1.5. The NaV 1.5 mutants R1193Q and E1784K give rise to both long QT and Brugada syndromes. Various environmental factors, including temperature, may unmask arrhythmia. We sought to determine whether temperature might be an arrhythmogenic trigger in these two mixed syndrome mutants. Whole-cell patch clamp was used to measure the biophysical properties of NaV 1.5 WT, E1784K and R1193Q mutants. Recordings were performed using Chinese hamster ovary (CHOk1) cells transiently transfected with the NaV 1.5 α subunit (WT, E1784K, or R1193Q), β1 subunit, and eGFP. The channels' voltage-dependent and kinetic properties were measured at three different temperatures: 10ºC, 22ºC, and 34ºC. The E1784K mutant is more thermosensitive than either WT or R1193Q channels. When temperature is elevated from 22°C to 34°C, there is a greater increase in late INa and use-dependent inactivation in E1784K than in WT or R1193Q. However, when temperature is lowered to 10°C, the two mutants show a decrease in channel availability. Action potential modelling using Q10 fit values, extrapolated to physiological and febrile temperatures, show a larger transmural voltage gradient in E1784K compared to R1193Q and WT with hyperthermia. The E1784K mutant is more thermosensitive than WT or R1193Q channels. This enhanced thermosensitivity may be a mechanism for arrhythmogenesis in patients with E1784K sodium channels.
Collapse
Affiliation(s)
- Mena Abdelsayed
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada, V5A 1S6
| | - Colin H Peters
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada, V5A 1S6
| | - Peter C Ruben
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada, V5A 1S6
| |
Collapse
|
20
|
Novak KR, Norman J, Mitchell JR, Pinter MJ, Rich MM. Sodium channel slow inactivation as a therapeutic target for myotonia congenita. Ann Neurol 2015; 77:320-32. [PMID: 25515836 DOI: 10.1002/ana.24331] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2014] [Revised: 12/01/2014] [Accepted: 12/07/2014] [Indexed: 01/21/2023]
Abstract
OBJECTIVE Patients with myotonia congenita have muscle hyperexcitability due to loss-of-function mutations in the chloride channel in skeletal muscle, which causes spontaneous firing of muscle action potentials (myotonia), producing muscle stiffness. In patients, muscle stiffness lessens with exercise, a change known as the warmup phenomenon. Our goal was to identify the mechanism underlying warmup and to use this information to guide development of novel therapy. METHODS To determine the mechanism underlying warmup, we used a recently discovered drug to eliminate muscle contraction, thus allowing prolonged intracellular recording from individual muscle fibers during induction of warmup in a mouse model of myotonia congenita. RESULTS Changes in action potentials suggested slow inactivation of sodium channels as an important contributor to warmup. These data suggested that enhancing slow inactivation of sodium channels might offer effective therapy for myotonia. Lacosamide and ranolazine enhance slow inactivation of sodium channels and are approved by the US Food and Drug Administration for other uses in patients. We compared the efficacy of both drugs to mexiletine, a sodium channel blocker currently used to treat myotonia. In vitro studies suggested that both lacosamide and ranolazine were superior to mexiletine. However, in vivo studies in a mouse model of myotonia congenita suggested that side effects could limit the efficacy of lacosamide. Ranolazine produced fewer side effects and was as effective as mexiletine at a dose that produced none of mexiletine's hypoexcitability side effects. INTERPRETATION We conclude that ranolazine has excellent therapeutic potential for treatment of patients with myotonia congenita.
Collapse
Affiliation(s)
- Kevin R Novak
- Department of Neuroscience, Cell Biology, and Physiology, Wright State University, Dayton, OH
| | | | | | | | | |
Collapse
|
21
|
Inoue T, Higashiyama M, Kaji I, Rudenkyy S, Higuchi K, Guth PH, Engel E, Kaunitz JD, Akiba Y. Dipeptidyl peptidase IV inhibition prevents the formation and promotes the healing of indomethacin-induced intestinal ulcers in rats. Dig Dis Sci 2014; 59:1286-95. [PMID: 24379150 PMCID: PMC4196264 DOI: 10.1007/s10620-013-3001-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 12/11/2013] [Indexed: 02/07/2023]
Abstract
BACKGROUNDS AND AIMS We studied the intestinotrophic hormone glucagon-like peptide-2 (GLP-2) as a possible therapy for non-steroidal anti-inflammatory drug (NSAID)-induced intestinal ulcers. Luminal nutrients release endogenous GLP-2 from enteroendocrine L cells. Since GLP-2 is degraded by dipeptidyl peptidase IV (DPPIV), we hypothesized that DPPIV inhibition combined with luminal administration of nutrients potentiates the effects of endogenous GLP-2 on intestinal injury. METHODS Intestinal injury was induced by indomethacin (10 mg/kg, sc) in fed rats. The long-acting DPPIV inhibitor K579 was given intragastrically (ig) or intraperitoneally (ip) before or after indomethacin treatment. L-Alanine (L-Ala) and inosine 5'-monophosphate (IMP) were co-administered ig after the treatment. RESULTS Indomethacin treatment induced intestinal ulcers that gradually healed after treatment. Pretreatment with ig or ip K579 given at 1 mg/kg reduced total ulcer length, whereas K579 at 3 mg/kg had no effect. Exogenous GLP-2 also reduced intestinal ulcers. The preventive effect of K579 was dose-dependently inhibited by a GLP-2 receptor antagonist. Daily treatment with K579 (1 mg/kg), GLP-2, or L-Ala + IMP after indomethacin treatment reduced total ulcer length. Co-administration (ig) of K579 and L-Ala + IMP further accelerated intestinal ulcer healing. CONCLUSION DPPIV inhibition and exogenous GLP-2 prevented the formation and promoted the healing of indomethacin-induced intestinal ulcers, although high-dose DPPIV inhibition reversed the preventive effect. Umami receptor agonists also enhanced the healing effects of the DPPIV inhibitor. The combination of DPPIV inhibition and luminal nutrient-induced GLP-2 release may be a useful therapeutic tool for the treatment of NSAIDs-induced intestinal ulcers.
Collapse
Affiliation(s)
- Takuya Inoue
- Department of Medicine, School of Medicine, University of California, Los Angeles
- The Second Department of Internal Medicine, Osaka Medical College, Osaka, Japan
| | - Masaaki Higashiyama
- Department of Medicine, School of Medicine, University of California, Los Angeles
| | - Izumi Kaji
- Department of Medicine, School of Medicine, University of California, Los Angeles
| | - Sergiy Rudenkyy
- Greater Los Angles Veterans Affairs Healthcare System, University of California, Los Angeles
| | - Kazuhide Higuchi
- The Second Department of Internal Medicine, Osaka Medical College, Osaka, Japan
| | - Paul H. Guth
- Greater Los Angles Veterans Affairs Healthcare System, University of California, Los Angeles
| | - Eli Engel
- Department of Biomathematics, University of California, Los Angeles
| | - Jonathan D Kaunitz
- Greater Los Angles Veterans Affairs Healthcare System, University of California, Los Angeles
- Department of Medicine, School of Medicine, University of California, Los Angeles
- Brentwood Biomedical Research Institute, Los Angeles, CA 90073, USA
| | - Yasutada Akiba
- Greater Los Angles Veterans Affairs Healthcare System, University of California, Los Angeles
- Department of Medicine, School of Medicine, University of California, Los Angeles
- Brentwood Biomedical Research Institute, Los Angeles, CA 90073, USA
| |
Collapse
|
22
|
Diclofenac toxicity in human intestine ex vivo is not related to the formation of intestinal metabolites. Arch Toxicol 2014; 89:107-19. [PMID: 24770551 DOI: 10.1007/s00204-014-1242-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Accepted: 04/10/2014] [Indexed: 12/22/2022]
Abstract
The use of diclofenac (DCF), a nonsteroidal anti-inflammatory drug, is associated with a high prevalence of gastrointestinal side effects. In vivo studies in rodents suggested that reactive metabolites of DCF produced by the liver or the intestine might be responsible for this toxicity. In the present study, precision-cut intestinal slices (PCIS) prepared from the jejunum of 18 human donors were used as an ex vivo model to investigate whether DCF intestinal metabolites are responsible for its intestinal toxicity in man. PCIS were incubated with a concentration range of DCF (0-600 µM) up to 24 h. DCF (≥400 µM) caused direct toxicity to the intestine as demonstrated by ATP depletion, morphological damage, caspase 3 activation, and lactate dehydrogenase leakage. Three main metabolites produced by PCIS (4'-hydroxy DCF, 5-hydroxy DCF, and DCF acyl glucuronide) were detected by HPLC. Protein adducts were detected by immunohistochemical staining and showed correlation with the intestinal metabolites. DCF induced similar toxicity to each of the samples regardless of the variation in metabolism among them. Less metabolites were produced by slices incubated with 400 µM DCF than with 100 µM DCF. The addition of the metabolic inhibitors such as ketoconazole, cimetidine, or borneol decreased the metabolite formation but increased the toxicity. The results suggest that DCF can induce intestinal toxicity in human PCIS directly at therapeutically relevant concentrations, independent of the reactive metabolites 4'-OH DCF, 5-OH DCF, or diclofenac acylglucuronide produced by the liver or formed in the intestine.
Collapse
|
23
|
Thermal mechanisms of millimeter wave stimulation of excitable cells. Biophys J 2014; 104:2622-8. [PMID: 23790370 DOI: 10.1016/j.bpj.2013.05.014] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Revised: 04/30/2013] [Accepted: 05/07/2013] [Indexed: 11/22/2022] Open
Abstract
Interactions between millimeter waves (MMWs) and biological systems have received increasing attention due to the growing use of MMW radiation in technologies ranging from experimental medical devices to telecommunications and airport security. Studies have shown that MMW exposure alters cellular function, especially in neurons and muscles. However, the biophysical mechanisms underlying such effects are still poorly understood. Due to the high aqueous absorbance of MMW, thermal mechanisms are likely. However, nonthermal mechanisms based on resonance effects have also been postulated. We studied MMW stimulation in a simplified preparation comprising Xenopus laevis oocytes expressing proteins that underlie membrane excitability. Using electrophysiological recordings simultaneously with 60 GHz stimulation, we observed changes in the kinetics and activity levels of voltage-gated potassium and sodium channels and a sodium-potassium pump that are consistent with a thermal mechanism. Furthermore, we showed that MMW stimulation significantly increased the action potential firing rate in oocytes coexpressing voltage-gated sodium and potassium channels, as predicted by thermal terms in the Hodgkin-Huxley model of neurons. Our results suggest that MMW stimulation produces significant thermally mediated effects on excitable cells via basic thermodynamic mechanisms that must be taken into account in the study and use of MMW radiation in biological systems.
Collapse
|
24
|
Mechanisms of a human skeletal myotonia produced by mutation in the C-terminus of NaV1.4: is Ca2+ regulation defective? PLoS One 2013; 8:e81063. [PMID: 24324661 PMCID: PMC3855693 DOI: 10.1371/journal.pone.0081063] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Accepted: 10/08/2013] [Indexed: 12/24/2022] Open
Abstract
Mutations in the cytoplasmic tail (CT) of voltage gated sodium channels cause a spectrum of inherited diseases of cellular excitability, yet to date only one mutation in the CT of the human skeletal muscle voltage gated sodium channel (hNaV1.4F1705I) has been linked to cold aggravated myotonia. The functional effects of altered regulation of hNaV1.4F1705I are incompletely understood. The location of the hNaV1.4F1705I in the CT prompted us to examine the role of Ca2+ and calmodulin (CaM) regulation in the manifestations of myotonia. To study Na channel related mechanisms of myotonia we exploited the differences in rat and human NaV1.4 channel regulation by Ca2+ and CaM. hNaV1.4F1705I inactivation gating is Ca2+-sensitive compared to wild type hNaV1.4 which is Ca2+ insensitive and the mutant channel exhibits a depolarizing shift of the V1/2 of inactivation with CaM over expression. In contrast the same mutation in the rNaV1.4 channel background (rNaV1.4F1698I) eliminates Ca2+ sensitivity of gating without affecting the CaM over expression induced hyperpolarizing shift in steady-state inactivation. The differences in the Ca2+ sensitivity of gating between wild type and mutant human and rat NaV1.4 channels are in part mediated by a divergence in the amino acid sequence in the EF hand like (EFL) region of the CT. Thus the composition of the EFL region contributes to the species differences in Ca2+/CaM regulation of the mutant channels that produce myotonia. The myotonia mutation F1705I slows INa decay in a Ca2+-sensitive fashion. The combination of the altered voltage dependence and kinetics of INa decay contribute to the myotonic phenotype and may involve the Ca2+-sensing apparatus in the CT of NaV1.4.
Collapse
|
25
|
Franssen H, Straver DCG. Pathophysiology of immune-mediated demyelinating neuropathies--Part II: Neurology. Muscle Nerve 2013; 49:4-20. [PMID: 24037667 DOI: 10.1002/mus.24068] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2013] [Indexed: 12/13/2022]
Abstract
In the second part of this review we deal with the clinical aspects of immune-mediated demyelinating neuropathies. We describe the relationship between pathophysiology and symptoms and discuss the pathophysiology of specific disease entities, including Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy, multifocal motor neuropathy, anti-myelin-associated glycoprotein neuropathy, and POEMS syndrome.
Collapse
Affiliation(s)
- Hessel Franssen
- Department of Neurology and Neurosurgery, Brain Center Rudolf Magnus, University Medical Center Utrecht, Heidelberglaan 100, 3584, CX Utrecht, The Netherlands
| | | |
Collapse
|
26
|
Franssen H, Straver DC. Pathophysiology of immune-mediated demyelinating neuropathies-part I: Neuroscience. Muscle Nerve 2013; 48:851-64. [DOI: 10.1002/mus.24070] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2013] [Indexed: 11/09/2022]
Affiliation(s)
- Hessel Franssen
- Department of Neurology, Section Neuromuscular Disorders, F02.230, Rudolf Magnus Institute for Neuroscience; University Medical Center Utrecht; Heidelberglaan 100, 3584 CX Utrecht The Netherlands
| | - Dirk C.G. Straver
- Department of Neurology, Section Neuromuscular Disorders, F02.230, Rudolf Magnus Institute for Neuroscience; University Medical Center Utrecht; Heidelberglaan 100, 3584 CX Utrecht The Netherlands
| |
Collapse
|
27
|
Radicke S, Riedel T, Cotella D, Turnow K, Ravens U, Schaefer M, Wettwer E. Accessory subunits alter the temperature sensitivity of Kv4.3 channel complexes. J Mol Cell Cardiol 2013; 56:8-18. [PMID: 23291429 DOI: 10.1016/j.yjmcc.2012.12.017] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Revised: 12/19/2012] [Accepted: 12/20/2012] [Indexed: 01/11/2023]
Abstract
In human atrial myocytes the transient outward current I(to) develops a conspicuous faster inactivation with increasing temperatures. Since β-subunits are known to modulate I(to) current kinetics, we hypothesized that the temperature sensitivity of I(to) is not only determined by the property of the ion-passing α-subunit Kv4.3 but also by its interaction with accessory β-subunits. We therefore studied the influence of the transmembrane β-subunits KCNE1, KCNE2 and DPP6 on Kv4.3/KChIP2 channels in CHO cells at room temperature and at physiological temperature. Exposure to 37°C caused a significant acceleration of the channel kinetics, whereas current densities and voltage dependences remained unaltered at 37°C compared to 23°C. However, Kv4.3/KChIP2 channels without transmembrane β-subunits showed the strongest temperature sensitivity with considerably increased rates of activation and inactivation at 37°C. KCNE2 significantly slowed the current kinetics at 37°C compared to Kv4.3/KChIP2 channels, whereas KCNE1 did not influence the channel properties at both temperatures. Interestingly, the accelerating effects of DPP6 on current kinetics described at 23°C were diminished at physiological temperature, thus at 37°C current kinetics became remarkably similar for channel complexes Kv4.3/KChIP2 with and without DPP6 isoforms. A Markov state model was developed on the basis of experimental measurements to simulate the influence of β-subunits on Kv4.3 channel complex at both temperatures. In conclusion, the remarkably fast kinetics of the native I(to) at 37°C could be reproduced by co-expressing Kv4.3, KChIP2, KCNE2 and DPP6 in CHO cells, whereas the high temperature sensitivity of human I(to) could be not mimicked.
Collapse
Affiliation(s)
- S Radicke
- Rudolf-Boehm-Institute of Pharmacology and Toxicology, University of Leipzig, Härtelstr.16-18, 04107 Leipzig, Germany.
| | | | | | | | | | | | | |
Collapse
|
28
|
Bostock H, Baumann C, Humm AM, Z'Graggen WJ. Temperature dependency of human muscle velocity recovery cycles. Muscle Nerve 2012; 46:264-6. [DOI: 10.1002/mus.23429] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
29
|
Egri C, Ruben PC. A hot topic: temperature sensitive sodium channelopathies. Channels (Austin) 2012; 6:75-85. [PMID: 22643347 DOI: 10.4161/chan.19827] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Perturbations to body temperature affect almost all cellular processes and, within certain limits, results in minimal effects on overall physiology. Genetic mutations to ion channels, or channelopathies, can shift the fine homeostatic balance resulting in a decreased threshold to temperature induced disturbances. This review summarizes the functional consequences of currently identified voltage-gated sodium (NaV) channelopathies that lead to disorders with a temperature sensitive phenotype. A comprehensive knowledge of the relationships between genotype and environment is not only important for understanding the etiology of disease, but also for developing safe and effective treatment paradigms.
Collapse
Affiliation(s)
- Csilla Egri
- Department of Biomedical Physiology and Kinesiology; Simon Fraser University; Burnaby, BC, Canada
| | | |
Collapse
|
30
|
Egri C, Vilin YY, Ruben PC. A thermoprotective role of the sodium channel β1 subunit is lost with the β1 (C121W) mutation. Epilepsia 2012; 53:494-505. [PMID: 22292491 DOI: 10.1111/j.1528-1167.2011.03389.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
PURPOSE A mutation in the β(1) subunit of the voltage-gated sodium (Na(V)) channel, β(1) (C121W), causes genetic epilepsy with febrile seizures plus (GEFS+), a pediatric syndrome in which febrile seizures are the predominant phenotype. Previous studies of molecular mechanisms underlying neuronal hyperexcitability caused by this mutation were conducted at room temperature. The prevalence of seizures during febrile states in patients with GEFS+, however, suggests that the phenotypic consequence of β(1) (C121W) may be exacerbated by elevated temperature. We investigated the putative mechanism underlying seizure generation by the β(1) (C121W) mutation with elevated temperature. METHODS Whole-cell voltage clamp experiments were performed at 22 and 34°C using Chinese Hamster Ovary (CHO) cells expressing the α subunit of neuronal Na(V) channel isoform, Na(V) 1.2. Voltage-dependent properties were recorded from CHO cells expressing either Na(V) 1.2 alone, Na(V) 1.2 plus wild-type (WT) β(1) subunit, or Na(V) 1.2 plus β(1) (C121W). KEY FINDINGS Our results suggest WT β(1) is protective against increased channel excitability induced by elevated temperature; protection is lost in the absence of WT β(1) or with expression of β(1) (C121W). At 34°C, Na(V) 1.2 + β(1) (C121W) channel excitability increased compared to NaV1.2 + WT β(1) by the following mechanisms: decreased use-dependent inactivation, increased persistent current and window current, and delayed onset of, and accelerated recovery from, fast inactivation. SIGNIFICANCE Temperature-dependent changes found in our study are consistent with increased neuronal excitability of GEFS+ patients harboring C121W. These results suggest a novel seizure-causing mechanism for β(1) (C121W): increased channel excitability at elevated temperature.
Collapse
Affiliation(s)
- Csilla Egri
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
| | | | | |
Collapse
|
31
|
Vipperla K, O'Keefe SJ. Teduglutide for the treatment of short bowel syndrome. Expert Rev Gastroenterol Hepatol 2011; 5:665-78. [PMID: 22017694 DOI: 10.1586/egh.11.82] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Extensive resection of the intestine impairs its absorptive capacity and results in short bowel syndrome when the nutritional equilibrium is compromised. The remnant intestine adapts structurally to compensate, but nutritional autonomy cannot be achieved in patients with intestinal failure, requiring intravenous fluids and parenteral nutrition (PN) for sustenance of life. PN is expensive and associated with serious complications. Efforts to minimize or eliminate the need for PN heralded research focusing on the therapeutic utility of intrinsic gut factors involved in the postresection adaptation process. With the breakthrough recognition of the intestinotrophic properties of glucagon-like peptide-2, teduglutide, a recombinant analogue of glucagon-like peptide-2, is being investigated as a promising hope to mitigate the requirement of PN. Clinical studies to date have demonstrated a desirable benefit-to-risk profile in regards to its safety and efficacy. If approved for marketing, it will be the first of its class in short bowel syndrome management, offering an innovative therapeutic modality for this debilitating condition.
Collapse
Affiliation(s)
- Kishore Vipperla
- Division of General Internal Medicine, University of Pittsburgh Medical Center, 200 Lothrop Street, 933W MUH, Pittsburgh, PA 15213, USA
| | | |
Collapse
|
32
|
Iaia FM, Bangsbo J. Speed endurance training is a powerful stimulus for physiological adaptations and performance improvements of athletes. Scand J Med Sci Sports 2011; 20 Suppl 2:11-23. [PMID: 20840558 DOI: 10.1111/j.1600-0838.2010.01193.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The present article reviews the physiological and performance effects of speed endurance training consisting of exercise bouts at near maximal intensities in already trained subjects. Despite a reduction in training volume, speed endurance training of endurance-trained athletes can maintain the oxidative capacity and improve intense short-duration/repeated high-intensity exercise performance lasting 30 s to 4 min, as it occurs in a number of sports. When combined with a basic volume of training including some aerobic high-intensity sessions, speed endurance training is also useful in enhancing performance during longer events, e.g. 40 K cycling and 10 K running. Athletes in team sports involving intense exercise actions and endurance aspects can also benefit from performing speed endurance training. These improvements don't appear to depend on changes in maximum oxygen uptake (VO2max), muscle substrate levels, glycolytic and oxidative enzymes activity, and membrane transport proteins involved in pH regulation. Instead they appear to be related to a reduced energy expenditure during submaximal exercise and a higher expression of muscle Na(+) ,K(+) pump α-subunits, which via a higher Na(+) ,K(+) pump activity during exercise may delay fatigue development during intense exercise. In conclusion, athletes from disciplines involving periods of intense exercise can benefit from the inclusion of speed endurance sessions in their training programs.
Collapse
Affiliation(s)
- F M Iaia
- Department of Exercise and Sport Sciences, Section of Human Physiology, Copenhagen Muscle Research Centre, University of Copenhagen, Copenhagen, Denmark
| | | |
Collapse
|
33
|
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]
|
34
|
Piitulainen H, Botter A, Merletti R, Avela J. Muscle fiber conduction velocity is more affected after eccentric than concentric exercise. Eur J Appl Physiol 2010; 111:261-73. [PMID: 20865423 DOI: 10.1007/s00421-010-1652-y] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/08/2010] [Indexed: 11/30/2022]
Affiliation(s)
- Harri Piitulainen
- Department of Biology of Physical Activity, Neuromuscular Research Center, University of Jyväskylä, P.O. Box 35, 40014, Jyväskylä, Finland.
| | | | | | | |
Collapse
|
35
|
Puwanant A, Ruff RL. INa and IKir are reduced in Type 1 hypokalemic and thyrotoxic periodic paralysis. Muscle Nerve 2010; 42:315-27. [PMID: 20589886 DOI: 10.1002/mus.21693] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
We evaluated voltage-gated Na(+) (I(Na)) and inward rectifier K(+) (I(Kir)) currents and Na(+) conductance (G(Na)) in patients with Type 1 hypokalemic (HOPP) and thyrotoxic periodic paralysis (TPP). We studied intercostal muscle fibers from five subjects with HOPP and one with TPP. TPP was studied when the patient was thyrotoxic (T-toxic) and euthyroid. We measured: (1) I(Kir), (2) action potential thresholds, (3) I(Na), (4) G(Na), (5) intracellular [Ca(2+)], and (6) histochemical fiber type. HOPP fibers had lower I(Na), G(Na), and I(Kir) and increased action potential thresholds. Paralytic attack frequency correlated with the action potential threshold, G(Na) and I(Na), but not with I(Kir). G(Na), I(Na), and [Ca(2+)] varied with fiber type. HOPP fibers had increased [Ca(2+)]. The subject with TPP had values for G(Na), I(Na), action potential threshold, I(Kir), and [Ca(2+)] that were similar to HOPP when T-toxic and to controls when euthyroid. HOPP T-toxic TPP fibers had altered G(Na), I(Na), and I(Kir) associated with elevation in [Ca(2+)].
Collapse
Affiliation(s)
- Araya Puwanant
- Louis Stokes Cleveland Veterans Administration Medical Center, University Hospitals of Cleveland, Case Western Reserve University, Cleveland, Ohio 44106, USA
| | | |
Collapse
|
36
|
Buchman AL, Katz S, Fang JC, Bernstein CN, Abou-Assi SG. Teduglutide, a novel mucosally active analog of glucagon-like peptide-2 (GLP-2) for the treatment of moderate to severe Crohn's disease. Inflamm Bowel Dis 2010; 16:962-73. [PMID: 19821509 DOI: 10.1002/ibd.21117] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
BACKGROUND Teduglutide, an analog of glucagon-like peptide-2 (GLP-2), is associated with trophic effects on gut mucosa. Its role in the treatment of active Crohn's disease (CD) was assessed in a pilot, randomized, placebo-controlled, double-blinded, dose-ranging study. METHODS Subjects with moderate-to-severe CD were randomized 1:1:1:1 to placebo or 1 of 3 doses of teduglutide (0.05, 0.10, or 0.20 mg/kg daily) delivered as a daily subcutaneous injection for 8 weeks. The primary outcome measure was the percentage of subjects in each group that responded to treatment, defined as a decrease in Crohn's Disease Activity Index (CDAI) score to <150 or a decrease of > 100 points. At week 8 there was an optional 12-week open-label period of treatment with teduglutide 0.10 mg/kg/d. RESULTS One hundred subjects were enrolled and 71 completed the study. The mean baseline CDAI score was 290.8 +/- 57.6 and was similar across groups. There were numerically higher response and remission rates in all teduglutide-treated groups as compared with placebo, although the percentage of subjects who achieved a clinical response or remission was more substantial, and seen as early as week 2 of treatment in the highest dose (0.2 mg/kg/d) group (44% response and 32% remission versus 32% response and 20% remission in the placebo group). Of subjects who had not achieved remission during the 8-week placebo-controlled phase in the higher-dose group, 50% achieved remission during the more prolonged, open-label treatment phase. Plasma citrulline was similar across groups at baseline, but increased substantially over time in all teduglutide groups when compared with placebo at week 8. Adverse events were not different between placebo and active treatment groups. CONCLUSIONS Teduglutide is a novel and potentially effective therapy for inducing remission and mucosal healing in patients with active moderate-to-severe CD. Further clinical investigation of this growth factor is warranted.
Collapse
Affiliation(s)
- Alan L Buchman
- Division of Gastroenterology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA.
| | | | | | | | | | | |
Collapse
|
37
|
Jurkat-Rott K, Lerche H, Weber Y, Lehmann-Horn F. Hereditary channelopathies in neurology. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 686:305-34. [PMID: 20824453 DOI: 10.1007/978-90-481-9485-8_18] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Ion channelopathies are caused by malfunction or altered regulation of ion channel proteins due to hereditary or acquired protein changes. In neurology, main phenotypes include certain forms of epilepsy, ataxia, migraine, neuropathic pain, myotonia, and muscle weakness including myasthenia and periodic paralyses. The total prevalence of monogenic channelopathies in neurology is about 35:100,000. Susceptibility-related mutations further increase the relevance of channel genes in medicine considerably. As many disease mechanisms have been elucidated by functional characterization on the molecular level, the channelopathies are regarded as model disorders for pathogenesis and treatment of non-monogenic forms of epilepsy and migraine. As more than 35% of marketed drugs target ion channels, there is a high chance to identify compounds that counteract the effects of the mutations.
Collapse
|
38
|
Thomas EA, Hawkins RJ, Richards KL, Xu R, Gazina EV, Petrou S. Heat opens axon initial segment sodium channels: A febrile seizure mechanism? Ann Neurol 2009; 66:219-26. [DOI: 10.1002/ana.21712] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
|
39
|
Peripheral nerve at extreme low temperatures 2: Pharmacologic modulation of temperature effects. Cryobiology 2009; 59:12-8. [DOI: 10.1016/j.cryobiol.2009.01.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2008] [Revised: 12/09/2008] [Accepted: 01/21/2009] [Indexed: 11/20/2022]
|
40
|
Filatov GN, Pinter MJ, Rich MM. Role of Ca(2+) in injury-induced changes in sodium current in rat skeletal muscle. Am J Physiol Cell Physiol 2009; 297:C352-9. [PMID: 19494240 DOI: 10.1152/ajpcell.00021.2009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Characteristics of voltage-dependent sodium current recorded from adult rat muscle fibers in loose patch mode were rapidly altered following nearby impalement with a microelectrode. Hyperpolarized shifts in the voltage dependence of activation and fast inactivation occurred within minutes. In addition, the amplitude of the maximal sodium current decreased within 30 min of impalement. Impalement triggered a sustained elevation of intracellular Ca(2+). However, buffering Ca(2+) by loading fibers with AM-BAPTA did not affect the hyperpolarized shifts in activation and inactivation, although it did prevent the reduction in current amplitude. Surprisingly, the rise in intracellular Ca(2+) occurred even in the absence of extracellular Ca(2+). This result indicated that the injury-induced Ca(2+) increase came from an intracellular source, but it was not blocked by an inhibitor of release from the sarcoplasmic reticulum, which suggested involvement of mitochondria. Ca(2+) release from mitochondria triggered by carbonyl cyanide 3-chlorophenylhydrazone was sufficient to cause a reduction in sodium current amplitude but had little effect of the voltage dependence of activation and fast inactivation. Our data suggest the effects of muscle injury can be separated into a Ca(2+)-dependent reduction in amplitude and a largely Ca(2+)-independent shift in activation and fast inactivation. Together, the impalement-induced changes in sodium current reduce the number of sodium channels available to open at the resting potential and may limit further depolarization and thus promote survival of muscle fibers following injury.
Collapse
Affiliation(s)
- Gregory N Filatov
- Department of Cell Biology and Neuroscience, University of California, Riverside, CA, USA
| | | | | |
Collapse
|
41
|
Carle T, Fournier E, Sternberg D, Fontaine B, Tabti N. Cold-induced disruption of Na+ channel slow inactivation underlies paralysis in highly thermosensitive paramyotonia. J Physiol 2009; 587:1705-14. [PMID: 19221125 DOI: 10.1113/jphysiol.2008.165787] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The Q270K mutation of the skeletal muscle Na(+) channel alpha subunit (Nav1.4) causes atypical paramyotonia with a striking sensitivity to cold. Attacks of paralysis and a drop in the compound muscle action potential (CMAP) are exclusively observed at cold. To understand the pathogenic process, we studied the consequences of this mutation on channel gating at different temperatures. WT or Q270K recombinant Nav1.4 channels fused at their C-terminal end to the enhanced green fluorescent protein (EGFP) were expressed in HEK-293 cells. Whole-cell Na(+) currents were recorded using the patch clamp technique to examine channel gating at 30 degrees C and after cooling the bathing solution to 20 degrees C. Mutant channel fast inactivation was impaired at both temperatures. Cooling slowed the kinetics and enhanced steady-state fast inactivation of both mutant and WT channels. Mutant channel slow inactivation was fairly comparable to that of the WT at 30 degrees C, but became clearly abnormal at 20 degrees C. Cooling enhanced slow inactivation in the WT by shifting the voltage dependence toward hyperpolarization, but induced the opposite effect in the mutant. Destabilization of mutant channel slow inactivation in combination with defective fast inactivation is expected to increase the susceptibility to prolonged membrane depolarization, and can ultimately lead to membrane inexcitability and paralysis at cold. Thus, abnormal temperature sensitivity of slow inactivation can be a determinant pathogenic factor, and should therefore be more widely considered in thermosensitive Na(+) channelopathies.
Collapse
|
42
|
Macdonald WA, Nielsen OB, Clausen T. Effects of calcitonin gene-related peptide on rat soleus muscle excitability: mechanisms and physiological significance. Am J Physiol Regul Integr Comp Physiol 2008; 295:R1214-23. [DOI: 10.1152/ajpregu.00893.2007] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Intense exercise causes a large loss of K+ from contracting muscles. The ensuing elevation of extracellular K+ ([K+]o) has been suggested to cause fatigue by depressing muscle fiber excitability. In isolated muscles, however, repeated contractions confer some protection against this effect of elevated K+. We hypothesize that this excitation-induced force-recovery is related to the release of the neuropeptide calcitonin gene-related peptide (CGRP), which stimulates the muscular Na+-K+ pumps. Using the specific CGRP antagonist CGRP-(8-37), we evaluated the role of CGRP in the excitation-induced force recovery and examined possible mechanisms. Intact rat soleus muscles were stimulated to evoke short tetani at regular intervals. Increasing extracellular K+ ([K+]o) from 4 to 11 mM decreased force to ∼20% of initial force ( P < 0.001). Addition of exogenous CGRP (10−9 M), release of endogenous CGRP with capsaicin, or repeated electrical stimulation recovered force to 50–70% of initial force ( P < 0.001). In all cases, force recovery could be almost completely suppressed by CGRP-(8-37). At 11 mM [K+]o, CGRP (10−8 M) did not alter resting membrane potential or conductance but significantly improved action potentials ( P < 0.001) and increased the proportion of excitable fibers from 32 to 70% ( P < 0.001). CGRP was shown to induce substantial force recovery with only modest Na+-K+ pump stimulation. We conclude that the excitation-induced force recovery is caused by a recovery of excitability, induced by local release of CGRP. The data suggest that the recovery of excitability partly was induced by Na+-K+ pump stimulation and partly by altering Na+ channel function.
Collapse
|
43
|
The dominant cold-sensitive Out-cold mutants of Drosophila melanogaster have novel missense mutations in the voltage-gated sodium channel gene paralytic. Genetics 2008; 180:873-84. [PMID: 18723887 DOI: 10.1534/genetics.108.090951] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Here we report the molecular characterization of Out-cold (Ocd) mutants of Drosophila melanogaster, which produce a dominant, X-linked, cold-sensitive paralytic phenotype. From its initial 1.5-Mb cytological location within 13F1-16A2, P-element and SNP mapping reduced the Ocd critical region to <100 kb and to six candidate genes: hangover, CG9947, CG4420, eIF2a, Rbp2, and paralytic (para). Complementation testing with para null mutations strongly suggests Ocd and para are allelic, as does gene rescue of Ocd semilethality with a wild-type para transgene. Pesticide resistance and electrophysiological phenotypes of Ocd mutants support this conclusion. The para gene encodes a voltage-gated sodium channel. Sequencing the Ocd lines revealed mutations within highly conserved regions of the para coding sequence, in the transmembrane segment S6 of domain III (I1545M and T1551I), and in the linker between domains III and IV (G1571R), the location of the channel inactivation gate. The G1571R mutation is of particular interest as mutations of the orthologous residue (G1306) in the human skeletal muscle sodium channel gene SCN4A are associated with cases of periodic paralysis and myotonia, including the human cold-sensitive disorder paramyotonia congenita. The mechanisms by which sodium channel mutations cause cold sensitivity are not well understood. Therefore, in the absence of suitable vertebrate models, Ocd provides a system in which genetic, molecular, physiological, and behavioral tools can be exploited to determine mechanisms underlying sodium channel periodic paralyses.
Collapse
|
44
|
Piitulainen H, Komi P, Linnamo V, Avela J. Sarcolemmal excitability as investigated with M-waves after eccentric exercise in humans. J Electromyogr Kinesiol 2008; 18:672-81. [PMID: 17331740 DOI: 10.1016/j.jelekin.2007.01.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2006] [Revised: 01/09/2007] [Accepted: 01/09/2007] [Indexed: 11/17/2022] Open
Abstract
It has been shown that intensive eccentric muscle actions lead to prolonged loss of muscle force and sarcolemmal damage. This may lead to a reduction in the excitability of the sarcolemma and contribute to the functional deficit. Experiments were carried out to test sarcolemmal excitability after eccentric elbow flexor exercise in humans. Electrically elicited surface compound muscle action potential (M-wave) properties from 30s stimulation trains (20Hz) were analyzed in biceps brachii muscle immediately after, 1h and 48h after the exercise. M-wave area, amplitude, root mean square and duration were reduced immediately after the eccentric exercise. However, no such reduction could be observed 48h after the exercise, although the maximal voluntary isometric and eccentric torques were still depressed by 12.2+/-9% (P<0.001) and 17.7+/-9% (P<0.001), respectively. Acute increase in plasma concentrations of K(+) and Ca(2+) were also observed after the eccentric exercise. These findings suggest that eccentric exercise may acutely decrease sarcolemmal excitability, which seems to be partially related to increased extracellular ion concentrations. However, disturbance of sarcolemmal excitability is not the major factor determining eccentric exercise induced prolonged loss of muscle strength, because no prolonged impairment was observed in any of the studied M-wave parameters.
Collapse
Affiliation(s)
- Harri Piitulainen
- Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, Finland.
| | | | | | | |
Collapse
|
45
|
Cifelli C, Boudreault L, Gong B, Bercier JP, Renaud JM. Contractile dysfunctions in ATP-dependent K+ channel-deficient mouse muscle during fatigue involve excessive depolarization and Ca2+ influx through L-type Ca2+ channels. Exp Physiol 2008; 93:1126-38. [PMID: 18586858 DOI: 10.1113/expphysiol.2008.042572] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Muscles deficient in ATP-dependent potassium (KATP) channels develop contractile dysfunctions during fatigue that may explain their apparently faster rate of fatigue compared with wild-type muscles. The objectives of this study were to determine: (1) whether the contractile dysfunctions, namely unstimulated force and depressed force recovery, result from excessive membrane depolarization and Ca2+ influx through L-type Ca2+ channels; and (2) whether reducing the magnitude of these two contractile dysfunctions reduces the rate of fatigue in KATP channel-deficient muscles. To reduce Ca2+ influx, we lowered the extracellular Ca2+ concentration ([Ca2+]o) from 2.4 to 0.6 mM or added 1 microM verapamil, an L-type Ca2+ channel blocker. Flexor digitorum brevis (FDB) muscles deficient in KATP channels were obtained by exposing wild-type muscles to 10 microM glibenclamide or by using FDB from Kir6.2-/- mice. Fatigue was elicited with one contraction per second for 3 min at 37 degrees C. In wild-type FDB, lowered [Ca2+]o or verapamil did not affect the decrease in peak tetanic force and unstimulated force during fatigue and force recovery following fatigue. In KATP channel-deficient FDB, lowered [Ca2+]o or verapamil slowed down the decrease in peak tetanic force recovery, reduced unstimulated force and improved force recovery. In Kir6.2-/- FDB, the rate of fatigue became slower than in wild-type FDB in the presence of verapamil. The cell membrane depolarized from -83 to -57 mV in normal wild-type FDB. The depolarizations in some glibenclamide-exposed fibres were similar to those of normal FDB, while in other fibres the cell membrane depolarized to -31 mV in 80 s, which was also the time when these fibres supercontracted. It is concluded that: (1) KATP channels are crucial in preventing excessive membrane depolarization and Ca2+ influx through L-type Ca2+ channels; and (2) they contribute to the decrease in force during fatigue.
Collapse
Affiliation(s)
- Carlo Cifelli
- University of Ottawa, Department of Cellular and Molecular Medicine, 451 Smyth Road, Ottawa, Ontario, Canada K1H 8M5
| | | | | | | | | |
Collapse
|
46
|
Nordsborg N, Ovesen J, Thomassen M, Zangenberg M, Jøns C, Iaia FM, Nielsen JJ, Bangsbo J. Effect of dexamethasone on skeletal muscle Na+,K+ pump subunit specific expression and K+ homeostasis during exercise in humans. J Physiol 2008; 586:1447-59. [PMID: 18174214 DOI: 10.1113/jphysiol.2007.143073] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The effect of dexamethasone on Na(+),K(+) pump subunit expression and muscle exchange of K(+) during exercise in humans was investigated. Nine healthy male subjects completed a randomized double blind placebo controlled protocol, with ingestion of dexamethasone (Dex: 2 x 2 mg per day) or placebo (Pla) for 5 days. Na(+),K(+) pump catalytic alpha1 and alpha2 subunit expression was approximately 17% higher (P < 0.05) and the structural beta1 and beta2 subunit expression was approximately 6-8% higher (P < 0.05) after Dex compared with Pla. During one-legged knee-extension for 10 min at low intensity (LI; 18.6 +/- 1.0 W), two moderate intensity (51.7 +/- 2.4 W) exercise bouts (MI(1): 5 min; 2 min recovery; MI(2): exhaustive) and two high-intensity (71.7 +/- 2.5 W) exercise bouts (HI(1): 1 min 40 s; 2 min recovery; HI(2): exhaustive), femoral venous K(+) was lower (P < 0.05) in Dex compared with Pla. Thigh K(+) release was lower (P < 0.05) in Dex compared with Pla in LI and MI, but not in HI. Time to exhaustion in MI(2) tended to improve (393 +/- 50 s versus 294 +/- 41 s; P = 0.07) in Dex compared with Pla, whereas no difference was detected in HI(2) (106 +/- 10 s versus 108 +/- 9 s). The results indicate that an increased Na(+),K(+) pump expression per se is of importance for thigh K(+) reuptake at the onset of low and moderate intensity exercise, but less important during high intensity exercise.
Collapse
Affiliation(s)
- Nikolai Nordsborg
- University of Copenhagen, Department of Exercise and Sport Sciences, Section for Human Physiology, Universitetsparken 13, 2100 Copenhagen, Denmark.
| | | | | | | | | | | | | | | |
Collapse
|
47
|
McKenna MJ, Bangsbo J, Renaud JM. Muscle K+, Na+, and Cl− disturbances and Na+-K+ pump inactivation: implications for fatigue. J Appl Physiol (1985) 2008; 104:288-95. [DOI: 10.1152/japplphysiol.01037.2007] [Citation(s) in RCA: 184] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Membrane excitability is a critical regulatory step in skeletal muscle contraction and is modulated by local ionic concentrations, conductances, ion transporter activities, temperature, and humoral factors. Intense fatiguing contractions induce cellular K+ efflux and Na+ and Cl− influx, causing pronounced perturbations in extracellular (interstitial) and intracellular K+ and Na+ concentrations. Muscle interstitial K+ concentration may increase 1- to 2-fold to 11–13 mM and intracellular K+ concentration fall by 1.3- to 1.7-fold; interstitial Na+ concentration may decline by 10 mM and intracellular Na+ concentration rise by 1.5- to 2.0-fold. Muscle Cl− concentration changes reported with muscle contractions are less consistent, with reports of both unchanged and increased intracellular Cl− concentrations, depending on contraction type and the muscles studied. When considered together, these ionic changes depolarize sarcolemmal and t-tubular membranes to depress tetanic force and are thus likely to contribute to fatigue. Interestingly, less severe local ionic changes can also augment subtetanic force, suggesting that they may potentiate muscle contractility early in exercise. Increased Na+-K+-ATPase activity during exercise stabilizes Na+ and K+ concentration gradients and membrane excitability and thus protects against fatigue. However, during intense contraction some Na+-K+ pumps are inactivated and together with further ionic disturbances, likely precipitate muscle fatigue.
Collapse
|
48
|
Blijham PJ, Drost G, Stegeman DF, Zwarts MJ. Reduced muscle-fiber conduction but normal slowing after cold exposure in paramyotonia congenita. Muscle Nerve 2008; 37:23-6. [PMID: 17823953 DOI: 10.1002/mus.20885] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
In this study we investigated a family with paramyotonia (PC) congenita caused by a Gly1306Val mutation in the voltage-gated sodium-channel gene SCN4A. A previous study showed that exposure to cold aggravates the muscle stiffness in patients with this mutation. However, the mechanism behind cold sensitivity and the sodium-channel defect remained unclear. In order to gain a better understanding of sarcolemmal propagation in these patients, we measured muscle-fiber conduction velocity (MFCV) invasively. We studied four PC patients and four healthy subjects at room temperature. After the muscle was cooled, MFCV was measured again in the two PC patients and four control subjects. MFCV was significantly lower in the PC patients at room temperature, compatible with dysfunctional sodium channels. After cooling, MFCV was significantly lower in both groups as compared with room temperature. The relative slowing was 1.4% per degrees C for PC patients and 1.5% per degrees C for healthy subjects. These results indicate that, in these PC patients, mutant and wild-type sodium channels respond equally to cold exposure. Thus, MFCV is abnormal in these patients, but the aggravation of muscle stiffness cannot be explained by an abnormal sarcolemmal response to cold.
Collapse
Affiliation(s)
- Paul J Blijham
- Department of Clinical Neurophysiology, Institute of Neurology, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
| | | | | | | |
Collapse
|
49
|
Nielsen OB, de Paoli FV. Regulation of Na+–K+ homeostasis and excitability in contracting muscles: implications for fatigue. Appl Physiol Nutr Metab 2007; 32:974-84. [DOI: 10.1139/h07-099] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The performance of skeletal muscles depends on their ability to initiate and propagate action potentials along their outer membranes in response to motor signals from the central nervous system. This excitability of muscle fibres is related to the function of Na+ and K+ and Cl– channels and to steep chemical gradients for the ions across the cell membranes, i.e., the sarcolemma and T-tubular membranes. At rest, the chemical gradients for Na+ and K+ are maintained within close limits by the action of the Na+–K+ pump. During contractile activity, however, the muscles lose K+, which causes an increase in the concentration of K+ in the extracellular compartments of the body, the magnitude of which depends on the intensity of the exercise and the size of the muscle groups involved. Since the ensuing reduction in the chemical K+ gradient can have adverse effects on muscle excitability, it has repeatedly been suggested that, during intense exercise, the loss of K+ from muscle fibres can contribute to the complex set of mechanisms that leads to the development of muscle fatigue. In this review, aspects of the regulation of Na+–K+ homeostasis and excitability in contracting muscles is discussed within this context, together with the implications for the contractile function of skeletal muscles.
Collapse
Affiliation(s)
- Ole Bækgaard Nielsen
- Institute of Physiology and Biophysics, University of Aarhus, Ole Worms Allé 160, 8000 Århus C, Denmark
| | - Frank Vincenzo de Paoli
- Institute of Physiology and Biophysics, University of Aarhus, Ole Worms Allé 160, 8000 Århus C, Denmark
| |
Collapse
|
50
|
Webb J, Cannon SC. Cold-induced defects of sodium channel gating in atypical periodic paralysis plus myotonia. Neurology 2007; 70:755-61. [PMID: 17898326 PMCID: PMC4094148 DOI: 10.1212/01.wnl.0000265397.70057.d8] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Missense mutations of the skeletal muscle voltage-gated sodium channel (NaV1.4) are an established cause of several clinically distinct forms of periodic paralysis and myotonia. The mechanistic basis for the phenotypic variability of these allelic disorders of muscle excitability remains unknown. An atypical phenotype with cold-induced hypokalemic paralysis and myotonia at warm temperatures was reported to segregate with the P1158S mutation. OBJECTIVE This study extends the functional characterization of the P1158S mutation and tests the specific hypothesis that impairment of Na channel slow inactivation is a common feature of periodic paralysis. METHODS Mutant NaV1.4 channels (P1158S) were transiently expressed in human embryonic kidney cells and characterized by voltage-clamp studies of Na currents. RESULTS Wild-type and P1158S channels displayed comparable behavior at 37 degrees C, but upon cooling to 25 degrees C, mutant channels activated at more negative potentials and slow inactivation was destabilized. CONCLUSIONS Consistent with other NaV1.4 mutations associated with a paralytic phenotype, the P1158S mutation disrupts slow inactivation. The unique temperature sensitivity of the channel defect may contribute to the unusual clinical phenotype.
Collapse
Affiliation(s)
- Jadon Webb
- Department of Neurology, UT Southwestern Medical Center, 5323 Harry Hines Blvd., Dallas, TX 75390-8813, USA
| | | |
Collapse
|