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Smith IC, Adam H, Herzog W. A brief contraction has complex effects on summation of twitch pairs in human adductor pollicis. Exp Physiol 2020; 105:676-689. [PMID: 32052487 DOI: 10.1113/ep088401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 02/10/2020] [Indexed: 11/08/2022]
Abstract
NEW FINDINGS What is the central question of this study? How do contraction-induced reductions in twitch duration, without changes in twitch force, affect summation of twitch pairs into higher force contractions in skeletal muscle? What is the main finding and its importance? Abbreviating twitch duration with a brief contraction resulted in enhanced summation of fully fused twitch pairs, but impaired summation in partially fused twitch pairs even after accounting for the differences in relaxation of the first twitch. An inherent mechanism which enhances relaxation without sacrificing force generation in forceful contractions would benefit cyclic muscle activities, such as locomotion. ABSTRACT During electrically evoked contractions of skeletal muscle, the interplay between twitch duration and the time between electrical stimuli (inter-pulse interval, IPI) determines how effectively twitch forces summate into high force contractions. A brief muscle contraction can impair summation by abbreviating twitch duration, though it is not clear if these impairments occur at all physiologically relevant IPI. This study was designed to test how a brief contraction affects summation of nominally isometric twitch pairs with IPIs lasting 10-5000 ms. Left adductor pollicis muscles of human participants (n = 9) were electrically activated using stimulus pairs applied both before (Pre) and after (Post) a 10 Hz, 1.0 s contraction. Force-time records were mathematically separated into Pulse 1 (single twitch) and Pulse 2 (summated twitch) components. The ratio of Pulse 2 peak force to Pulse 1 peak force was used as our measure of summation effectiveness. Consistent with the observed decline of Pulse 1 duration at Post relative to Pre (4.7 ± 0.6%; P < 0.001; duration was defined as the time from stimulation to the time required for active force to decline by 50%), summation effectiveness was higher at Pre than at Post at IPIs of 100-333 ms. Summation effectiveness was not different between Pre and Post at IPIs of 50-83 ms or 500-5000 ms. Intriguingly, summation effectiveness was higher at Post than at Pre at IPIs of 10-25 ms. In summary, a brief contraction has complex effects on the relationship between inter-pulse interval and summation effectiveness. Future experiments are needed to reveal the mechanisms behind this novel observation.
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Affiliation(s)
- Ian C Smith
- Human Performance Lab, Faculty of Kinesiology, University of Calgary 2500 University Drive NW, Calgary, Alberta, Canada, T2N 1N4
| | - Helen Adam
- Human Performance Lab, Faculty of Kinesiology, University of Calgary 2500 University Drive NW, Calgary, Alberta, Canada, T2N 1N4
| | - Walter Herzog
- Human Performance Lab, Faculty of Kinesiology, University of Calgary 2500 University Drive NW, Calgary, Alberta, Canada, T2N 1N4
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2
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Bunda J, Gittings W, Vandenboom R. Myosin phosphorylation improves contractile economy of mouse fast skeletal muscle during staircase potentiation. ACTA ACUST UNITED AC 2018; 221:jeb.167718. [PMID: 29361581 DOI: 10.1242/jeb.167718] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 12/31/2017] [Indexed: 01/12/2023]
Abstract
Phosphorylation of the myosin regulatory light chain (RLC) by skeletal myosin light chain kinase (skMLCK) potentiates rodent fast twitch muscle but is an ATP-requiring process. Our objective was to investigate the effect of skMLCK-catalyzed RLC phosphorylation on the energetic cost of contraction and the contractile economy (ratio of mechanical output to metabolic input) of mouse fast twitch muscle in vitro (25°C). To this end, extensor digitorum longus (EDL) muscles from wild-type (WT) and from skMLCK-devoid (skMLCK-/-) mice were subjected to repetitive low-frequency stimulation (10 Hz for 15 s) to produce staircase potentiation of isometric twitch force, after which muscles were quick frozen for determination of high-energy phosphate consumption (HEPC). During stimulation, WT muscles displayed significant potentiation of isometric twitch force while skMLCK-/- muscles did not (i.e. 23% versus 5% change, respectively). Consistent with this, RLC phosphorylation was increased ∼3.5-fold from the unstimulated control value in WT but not in skMLCK-/- muscles. Despite these differences, the HEPC of WT muscles was not greater than that of skMLCK-/- muscles. As a result of the increased contractile output relative to HEPC, the calculated contractile economy of WT muscles was greater than that of skMLCK-/- muscles. Thus, our results suggest that skMLCK-catalyzed phosphorylation of the myosin RLC increases the contractile economy of WT mouse EDL muscle compared with skMLCK-/- muscles without RLC phosphorylation.
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Affiliation(s)
- Jordan Bunda
- Centre for Bone and Muscle Health, Faculty of Applied Health Sciences, Brock University, St Catharines, ON L2S 3A1, Canada
| | - William Gittings
- Centre for Bone and Muscle Health, Faculty of Applied Health Sciences, Brock University, St Catharines, ON L2S 3A1, Canada
| | - Rene Vandenboom
- Centre for Bone and Muscle Health, Faculty of Applied Health Sciences, Brock University, St Catharines, ON L2S 3A1, Canada
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Yamamoto D, Imai T, Tsuda E, Hozuki T, Yamauchi R, Hisahara S, Kawamata J, Shimohama S. Effect of local cooling on excitation-contraction coupling in myasthenic muscle: Another mechanism of ice-pack test in myasthenia gravis. Clin Neurophysiol 2017; 128:2309-2317. [DOI: 10.1016/j.clinph.2017.08.030] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Revised: 08/17/2017] [Accepted: 08/28/2017] [Indexed: 10/18/2022]
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Smith IC, Vandenboom R, Tupling AR. Contraction-induced enhancement of relaxation during high force contractions of mouse lumbrical muscle at 37°C. J Exp Biol 2017; 220:2870-2873. [PMID: 28576821 DOI: 10.1242/jeb.158998] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 05/28/2017] [Indexed: 11/20/2022]
Abstract
Repeated stimulation of unfatigued rodent fast-twitch skeletal muscle accelerates the kinetics of tension relaxation through an unknown mechanism. This effect varies with muscle type and stimulation parameters, and has been observed at physiological temperatures for submaximal but not maximal contractions. The purpose of this study was to compare relaxation kinetics of C57BL/6 mouse lumbrical muscles ex vivo from maximal isometric force (500 Hz for 20 ms) when evoked before (pre) and after (post) an intervening tetanic contraction at 37°C. During post contractions, we noted significant increases in the rate of tension decline during both the slow linear phase and the fast exponential phase of relaxation, as well as a reduced duration of the slow phase of relaxation compared with pre contractions (all P<0.05). This is the first demonstration of enhanced slow and fast relaxation phases from maximal isometric tension induced by prior stimulation in intact muscle at a physiological temperature.
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Affiliation(s)
- Ian C Smith
- Human Performance Lab, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada, T2N 1N4 .,Department of Kinesiology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada, N2L 3G1
| | - Rene Vandenboom
- Department of Kinesiology, Faculty of Applied Health Sciences, Brock University, St. Catharines, Ontario, Canada, L2S 3A1
| | - A Russell Tupling
- Department of Kinesiology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada, N2L 3G1
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5
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Vandenboom R. Modulation of Skeletal Muscle Contraction by Myosin Phosphorylation. Compr Physiol 2016; 7:171-212. [PMID: 28135003 DOI: 10.1002/cphy.c150044] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The striated muscle sarcomere is a highly organized and complex enzymatic and structural organelle. Evolutionary pressures have played a vital role in determining the structure-function relationship of each protein within the sarcomere. A key part of this multimeric assembly is the light chain-binding domain (LCBD) of the myosin II motor molecule. This elongated "beam" functions as a biological lever, amplifying small interdomain movements within the myosin head into piconewton forces and nanometer displacements against the thin filament during the cross-bridge cycle. The LCBD contains two subunits known as the essential and regulatory myosin light chains (ELC and RLC, respectively). Isoformic differences in these respective species provide molecular diversity and, in addition, sites for phosphorylation of serine residues, a highly conserved feature of striated muscle systems. Work on permeabilized skeletal fibers and thick filament systems shows that the skeletal myosin light chain kinase catalyzed phosphorylation of the RLC alters the "interacting head motif" of myosin motor heads on the thick filament surface, with myriad consequences for muscle biology. At rest, structure-function changes may upregulate actomyosin ATPase activity of phosphorylated cross-bridges. During activation, these same changes may increase the Ca2+ sensitivity of force development to enhance force, work, and power output, outcomes known as "potentiation." Thus, although other mechanisms may contribute, RLC phosphorylation may represent a form of thick filament activation that provides a "molecular memory" of contraction. The clinical significance of these RLC phosphorylation mediated alterations to contractile performance of various striated muscle systems are just beginning to be understood. © 2017 American Physiological Society. Compr Physiol 7:171-212, 2017.
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Affiliation(s)
- Rene Vandenboom
- Department of Kinesiology, Faculty of Applied Health Sciences, Brock University, Ontario, Canada
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Smith IC, Bellissimo C, Herzog W, Tupling AR. Can inorganic phosphate explain sag during unfused tetanic contractions of skeletal muscle? Physiol Rep 2016; 4:4/22/e13043. [PMID: 27884960 PMCID: PMC5358005 DOI: 10.14814/phy2.13043] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 10/31/2016] [Indexed: 12/31/2022] Open
Abstract
We test the hypothesis that cytosolic inorganic phosphate (Pi) can account for the contraction‐induced reductions in twitch duration which impair summation and cause force to decline (sag) during unfused tetanic contractions of fast‐twitch muscle. A five‐state model of crossbridge cycling was used to simulate twitch and unfused tetanic contractions. As Pi concentration ([Pi]) was increased from 0 to 30 mmol·L−1, twitch duration decreased, with progressive reductions in sensitivity to Pi as [Pi] was increased. When unfused tetani were simulated with rising [Pi], sag was most pronounced when initial [Pi] was low, and when the magnitude of [Pi] increase was large. Fast‐twitch extensor digitorum longus (EDL) muscles (sag‐prone, typically low basal [Pi]) and slow‐twitch soleus muscles (sag‐resistant, typically high basal [Pi]) were isolated from 14 female C57BL/6 mice. Muscles were sequentially incubated in solutions containing either glucose or pyruvate to create typical and low Pi environments, respectively. Twitch duration was greater (P < 0.05) in pyruvate than glucose in both muscles. Stimuli applied at intervals approximately three times the time to peak twitch tension resulted in sag of 35.0 ± 3.7% in glucose and 50.5 ± 1.4% in pyruvate in the EDL (pyruvate > glucose; P < 0.05), and 3.9 ± 0.3% in glucose and 37.8 ± 2.7% in pyruvate in the soleus (pyruvate > glucose; P < 0.05). The influence of Pi on crossbridge cycling provides a tenable mechanism for sag. Moreover, the low basal [Pi] in fast‐twitch relative to slow‐twitch muscle has promise as an explanation for the fiber‐type dependency of sag.
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Affiliation(s)
- Ian C Smith
- Human Performance Lab, University of Calgary, Calgary, Alberta, Canada
| | | | - Walter Herzog
- Human Performance Lab, University of Calgary, Calgary, Alberta, Canada
| | - A Russell Tupling
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada
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Yamaguchi M, Kimura M, Li ZB, Ohno T, Takemori S, Hoh JFY, Yagi N. X-ray diffraction analysis of the effects of myosin regulatory light chain phosphorylation and butanedione monoxime on skinned skeletal muscle fibers. Am J Physiol Cell Physiol 2016; 310:C692-700. [PMID: 26911280 DOI: 10.1152/ajpcell.00318.2015] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 02/16/2016] [Indexed: 01/04/2023]
Abstract
The phosphorylation of the myosin regulatory light chain (RLC) is an important modulator of skeletal muscle performance and plays a key role in posttetanic potentiation and staircase potentiation of twitch contractions. The structural basis for these phenomena within the filament lattice has not been thoroughly investigated. Using a synchrotron radiation source at SPring8, we obtained X-ray diffraction patterns from skinned rabbit psoas muscle fibers before and after phosphorylation of myosin RLC in the presence of myosin light chain kinase, calmodulin, and calcium at a concentration below the threshold for tension development ([Ca(2+)] = 10(-6.8)M). After phosphorylation, the first myosin layer line slightly decreased in intensity at ∼0.05 nm(-1)along the equatorial axis, indicating a partial loss of the helical order of myosin heads along the thick filament. Concomitantly, the (1,1/1,0) intensity ratio of the equatorial reflections increased. These results provide a firm structural basis for the hypothesis that phosphorylation of myosin RLC caused the myosin heads to move away from the thick filaments towards the thin filaments, thereby enhancing the probability of interaction with actin. In contrast, 2,3-butanedione monoxime (BDM), known to inhibit contraction by impeding phosphate release from myosin, had exactly the opposite effects on meridional and equatorial reflections to those of phosphorylation. We hypothesize that these antagonistic effects are due to the acceleration of phosphate release from myosin by phosphorylation and its inhibition by BDM, the consequent shifts in crossbridge equilibria leading to opposite changes in abundance of the myosin-ADP-inorganic phosphate complex state associated with helical order of thick filaments.
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Affiliation(s)
- Maki Yamaguchi
- Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan;
| | - Masako Kimura
- Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan
| | - Zhao-Bo Li
- Ludwig Center for Cancer Genetic and Therapeutics, The Johns Hopkins University, Baltimore, Maryland
| | - Tetsuo Ohno
- Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan
| | - Shigeru Takemori
- Department of Molecular Physiology, The Jikei University School of Medicine, Tokyo, Japan
| | - Joseph F Y Hoh
- Discipline of Physiology and the Bosch Institute, School of Medical Sciences, Sydney Medical School, The University of Sydney, New South Wales, Australia; and
| | - Naoto Yagi
- Japan Synchrotron Radiation Research Institute, Hyogo, Japan
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8
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Gittings W, Aggarwal H, Stull JT, Vandenboom R. The force dependence of isometric and concentric potentiation in mouse muscle with and without skeletal myosin light chain kinase. Can J Physiol Pharmacol 2015; 93:23-32. [DOI: 10.1139/cjpp-2014-0118] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The isometric potentiation associated with myosin phosphorylation is force dependent. The purpose of this study was to assess the influence of a pre-existing period of isometric force on the concentric force potentiation displayed by mouse muscles with and without the ability to phosphorylate myosin. We tested isometric (ISO) and concentric (CON) potentiation, as well as concentric potentiation after isometric force (ISO-CON), in muscles from wild-type (WT) and skeletal myosin light chain kinase-deficient (skMLCK−/−) mice. A conditioning stimulus increased (i.e., potentiated) mean concentric force in the ISO-CON and CON conditions to 1.31 ± 0.02 and 1.35 ± 0.02 (WT) and to 1.19 ± 0.02 and 1.21 ± 0.01 (skMLCK−/−) of prestimulus levels, respectively (data n = 6–8, p < 0.05). No potentiation of mean isometric force was observed in either genotype. The potentiation of mean concentric force was inversely related to relative tetanic force level (P/Po) in both genotypes. Moreover, concentric potentiation varied greatly within each contraction type and was negatively correlated with unpotentiated force in both genotypes. Thus, although no effect of pre-existing force was observed, strong and inverse relationships between concentric force potentiation and unpotentiated concentric force may suggest an influence of attached and force-generating crossbridges on potentiation magnitude in both WT and skMLCK−/− muscles.
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Affiliation(s)
- William Gittings
- Department of Kinesiology, Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON L2S 3A1, Canada
| | - Harish Aggarwal
- Department of Kinesiology, Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON L2S 3A1, Canada
| | - James T. Stull
- Department of Physiology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Rene Vandenboom
- Department of Kinesiology, Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON L2S 3A1, Canada
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9
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Smith IC, Vandenboom R, Tupling AR. Juxtaposition of the changes in intracellular calcium and force during staircase potentiation at 30 and 37°C. J Gen Physiol 2014; 144:561-70. [PMID: 25422504 PMCID: PMC4242813 DOI: 10.1085/jgp.201411257] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Temperature-dependent changes in basal calcium and in the calcium transient contribute to force potentiation during repetitive stimulation. Ca2+ entry during the action potential stimulates muscle contraction. During repetitive low frequency stimulation, skeletal muscle undergoes staircase potentiation (SP), a progressive increase in the peak twitch force induced by each successive stimulus. Multiple mechanisms, including myosin regulatory light chain phosphorylation, likely contribute to SP, a temperature-dependent process. Here, we used the Ca2+-sensitive fluorescence indicators acetoxymethyl (AM)-furaptra and AM-fura-2 to examine the intracellular Ca2+ transient (ICT) and the baseline Ca2+ level at the onset of each ICT during SP at 30 and 37°C in mouse lumbrical muscle. The stimulation protocol, 8 Hz for 8 s, resulted in a 27 ± 3% increase in twitch force at 37°C and a 7 ± 2% decrease in twitch force at 30°C (P < 0.05). Regardless of temperature, the peak rate of force production (+df/dt) was higher in all twitches relative to the first twitch (P < 0.05). Consistent with the differential effects of stimulation on twitch force at the two temperatures, raw ICT amplitude decreased during repetitive stimulation at 30°C (P < 0.05) but not at 37°C. Cytosolic Ca2+ accumulated during SP such that baseline Ca2+ at the onset of ICTs occurring late in the train was higher (P < 0.05) than that of those occurring early in the train. ICT duration increased progressively at both temperatures. This effect was not entirely proportional to the changes in twitch duration, as twitch duration characteristically decreased before increasing late in the protocol. This is the first study identifying a changing ICT as an important, and temperature-sensitive, modulator of muscle force during repetitive stimulation. Moreover, we extend previous observations by demonstrating that contraction-induced increases in baseline Ca2+ coincide with greater +df/dt but not necessarily with higher twitch force.
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Affiliation(s)
- Ian C Smith
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
| | - Rene Vandenboom
- Department of Kinesiology, Brock University, St. Catharines, Ontario L2S 3A1, Canada
| | - A Russell Tupling
- Department of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada
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10
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Myosin phosphorylation and force potentiation in skeletal muscle: evidence from animal models. J Muscle Res Cell Motil 2013; 34:317-32. [PMID: 24162313 DOI: 10.1007/s10974-013-9363-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 10/04/2013] [Indexed: 01/21/2023]
Abstract
The contractile performance of mammalian fast twitch skeletal muscle is history dependent. The effect of previous or ongoing contractile activity to potentiate force, i.e. increase isometric twitch force, is a fundamental property of fast skeletal muscle. The precise manifestation of force potentiation is dependent upon a variety of factors with two general types being identified; staircase potentiation referring to the progressive increase in isometric twitch force observed during low frequency stimulation while posttetanic potentiation refers to the step-like increase in isometric twitch force observed following a brief higher frequency (i.e. tetanic) stimulation. Classic studies established that the magnitude and duration of potentiation depends on a number of factors including muscle fiber type, species, temperature, sarcomere length and stimulation paradigm. In addition to isometric twitch force, more recent work has shown that potentiation also influences dynamic (i.e. concentric and/or isotonic) force, work and power at a range of stimulus frequencies in situ or in vitro, an effect that may translate to enhanced physiological function in vivo. Early studies performed on both intact and permeabilized models established that the primary mechanism for this modulation of performance was phosphorylation of myosin, a modification that increased the Ca(2+) sensitivity of contraction. More recent work from a variety of muscle models indicates, however, the presence of a secondary mechanism for potentiation that may involve altered Ca(2+) handling. The primary purpose of this review is to highlight these recent findings relative to the physiological utility of force potentiation in vivo.
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Caterini D, Gittings W, Huang J, Vandenboom R. The effect of work cycle frequency on the potentiation of dynamic force in mouse fast twitch skeletal muscle. J Exp Biol 2011; 214:3915-23. [DOI: 10.1242/jeb.061150] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
The purpose of this study was to test the hypothesis that the potentiation of concentric twitch force during work cycles is dependent upon both the speed and direction of length change. Concentric and eccentric forces were elicited by stimulating muscles during the shortening and lengthening phases, respectively, of work cycles. Work cycle frequency was varied in order to vary the speed of muscle shortening and/or lengthening; all forces were measured as the muscle passed though optimal length (Lo). Both concentric and eccentric force were assessed before (unpotentiated control) and after (potentiated) the application of a tetanic conditioning protocol known to potentiate twitch force output. The influence of the conditioning protocol on relative concentric force was speed dependent, with forces increased to 1.19±0.01, 1.25±0.01 and 1.30±0.01 of controls at 1.5, 3.3 and 6.9 Hz, respectively (all data N=9–10 with P<0.05). In contrast, the conditioning protocol had only a limited effect on eccentric force at these frequencies (range: 1.06±0.01 to 0.96±0.03). The effect of the conditioning protocol on concentric work (force × distance) was also speed dependent, being decreased at 1.5 Hz (0.84±0.01) and increased at 3.3 and 6.9 Hz (1.05±0.01 and 1.39±0.01, respectively). In contrast, eccentric work was not increased at any frequency (range: 0.88±0.02 to 0.99±0.01). Thus, our results reveal a hysteresis-like influence of activity-dependent potentiation such that concentric force and/or work were increased but eccentric force and/or work were not. These outcomes may have implications for skeletal muscle locomotor function in vivo.
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Affiliation(s)
- Daniel Caterini
- Center for Muscle Metabolism and Biophysics, Faculty of Applied Health Sciences, Brock University, St Catharine's, ON, Canada, L2S 3A1
| | - William Gittings
- Center for Muscle Metabolism and Biophysics, Faculty of Applied Health Sciences, Brock University, St Catharine's, ON, Canada, L2S 3A1
| | - Jian Huang
- University of Texas Southwestern Medical Center at Dallas, Department of Physiology, 5323 Harry Hines Boulevard, Dallas, TX 75390, USA
| | - Rene Vandenboom
- Center for Muscle Metabolism and Biophysics, Faculty of Applied Health Sciences, Brock University, St Catharine's, ON, Canada, L2S 3A1
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Cellular and whole muscle studies of activity dependent potentiation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 682:315-42. [PMID: 20824534 DOI: 10.1007/978-1-4419-6366-6_18] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
With a single activation, a skeletal muscle fiber, motor unit or whole muscle will yield a twitch contraction. The twitch is not an "all-or-none" response, but a submaximal response that can vary from one time to another. Prior activation causes myosin regulatory light chain (RLC) phosphorylation, by an enzyme called myosin light chain kinase. This phosphorylation dissipates slowly over the next several minutes due to a slow activity of light chain phosphatase. Phosphorylation of the RLC increases the mobility of the S1 head of myosin, bringing the S1 head in closer proximity to the myosin binding sites on actin. This increased mobility increases the rate of engagement of cross-bridges and increases the rate of force development and contraction magnitude on subsequent twitch or other submaximal contractions. We call this increased contractile response "activity dependent potentiation". With sequential twitches or incompletely fused tetanic contractions, the term staircase is used to describe the progressive increase in amplitude of contraction. If a twitch is elicited after a tetanic contraction, we call the enhanced response posttetanic potentiation. Stretching a muscle fiber to a longer length will also bring the actin filaments close to the myosin heads. This increases the Ca²(+) sensitivity, independent of RLC phosphorylation. At long sarcomere lengths, the impact of RLC phosphorylation is diminished, because Ca²(+) sensitivity is already increased. Similarly, lowering the temperature at which the muscle is tested increases Ca²(+) sensitivity. At low temperatures, staircase and posttetanic potentiation are diminished, but RLC phosphorylation still occurs. Activity dependent potentiation is an important functional modulator of contractile response.
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Abstract
Fatigue of skeletal muscle involves many systems beginning with the central nervous system and ending with the contractile machinery. This review concentrates on those factors that directly affect the actomyosin interaction: the build-up of metabolites; myosin phosphorylation; and oxidation of the myofibrillar proteins by free radicals. The decrease in [ATP] and increase in [ADP] appear to play little role in modulating function. The increase in phosphate inhibits tension. The decrease in pH, long thought to be a major factor, is now known to play a more minor role. Myosin phosphorylation potentiates the force achieved in a twitch, and a further role in inhibiting velocity is proposed. Protein oxidation can both potentiate and inhibit the actomyosin interaction. It is concluded that these factors, taken together, do not fully explain the inhibition of the actomyosin interaction observed in living fibers, and thus additional modulators of this interaction remain to be discovered.
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Affiliation(s)
- Roger Cooke
- Department of Biochemistry and Biophysics and Cardiovascular Research Institute, University of California, San Francisco, California 94158-2517, USA.
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14
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Karatzaferi C, Franks-Skiba K, Cooke R. Inhibition of shortening velocity of skinned skeletal muscle fibers in conditions that mimic fatigue. Am J Physiol Regul Integr Comp Physiol 2007; 294:R948-55. [PMID: 18077511 DOI: 10.1152/ajpregu.00541.2007] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The mechanisms responsible for the inhibition of shortening velocity that occurs during muscle fatigue have not been completely elucidated. Phosphorylation of the myosin regulatory light chain (RLC) occurs during heavy use; however, previous reports on its role in affecting velocity have been equivocal. To further understand the process of fatigue, we varied the levels of myosin RLC phosphorylation (from 10 to >50%) and the concentrations of protons (from pH 7 to 6.2) and phosphate (from 5 to 30 mM), all of which change during fatigue. We measured the mechanics of permeable rabbit psoas fibers at a temperature closer to physiological (30 degrees C), using a temperature jump protocol to briefly activate the fibers at the higher temperature to preserve sarcomere homogeneity. Although lowered pH alone had an effect on velocity, it was the three factors together, i.e., high phosphorylation, low pH, and high phosphate, that acted synergistically to inhibit fiber velocity by approximately 40%. Our data demonstrate that in conditions that simulate physiological muscle fatigue, myosin phosphorylation does contribute to the inhibition of contraction velocity of fully activated fast muscle fibers.
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Affiliation(s)
- Christina Karatzaferi
- Institute of Human Performance and Rehabilitation, Center for Research and Technology Thessaly, University of Thessaly, Trikala, Greece
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15
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Franks-Skiba K, Lardelli R, Goh G, Cooke R. Myosin light chain phosphorylation inhibits muscle fiber shortening velocity in the presence of vanadate. Am J Physiol Regul Integr Comp Physiol 2006; 292:R1603-12. [PMID: 17158267 DOI: 10.1152/ajpregu.00499.2006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have shown that myosin light chain phosphorylation inhibits fiber shortening velocity at high temperatures, 30 degrees C, in the presence of the phosphate analog vanadate. Vanadate inhibits tension by reversing the transition to force-generating states, thus mimicking a prepower stroke state. We have previously shown that at low temperatures vanadate also inhibits velocity, but at high temperatures it does not, with an abrupt transition in inhibition occurring near 25 degrees C (E. Pate, G. Wilson, M. Bhimani, and R. Cooke. Biophys J 66: 1554-1562, 1994). Here we show that for fibers activated in the presence of 0.5 mM vanadate, at 30 degrees C, shortening velocity is not inhibited in dephosphorylated fibers but is inhibited by 37 +/- 10% in fibers with phosphorylated myosin light chains. There is no effect of phosphorylation on fiber velocity in the presence of vanadate at 10 degrees C. The K(m) for ATP, defined by the maximum velocity of fibers partially inhibited by vanadate at 30 degrees C, is 20 +/- 4 microM for phosphorylated fibers and 192 +/- 40 microM for dephosphorylated fibers, showing that phosphorylation also affects the binding of ATP. Fiber stiffness is not affected by phosphorylation. Inhibition of velocity by phosphorylation at 30 degrees C depends on the phosphate analog, with approximately 12% inhibition in fibers activated in the presence of 5 mM BeF(3) and no inhibition in the presence of 0.25 mM AlF(4). Our results show that myosin phosphorylation can inhibit shortening velocity in fibers with large populations of myosin heads trapped in prepower stroke states, such as occurs during muscle fatigue.
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Affiliation(s)
- Kathleen Franks-Skiba
- Department of Biochemistry and Biophysics and Cardiovascular Research Institute, University of California, San Francisco, CA 94158, USA
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16
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Zhi G, Ryder JW, Huang J, Ding P, Chen Y, Zhao Y, Kamm KE, Stull JT. Myosin light chain kinase and myosin phosphorylation effect frequency-dependent potentiation of skeletal muscle contraction. Proc Natl Acad Sci U S A 2005; 102:17519-24. [PMID: 16299103 PMCID: PMC1297671 DOI: 10.1073/pnas.0506846102] [Citation(s) in RCA: 151] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Repetitive stimulation potentiates contractile tension of fast-twitch skeletal muscle. We examined the role of myosin regulatory light chain (RLC) phosphorylation in this physiological response by ablating Ca(2+)/calmodulin-dependent skeletal muscle myosin light chain kinase (MLCK) gene expression. Western blot and quantitative-PCR showed that MLCK is expressed predominantly in fast-twitch skeletal muscle fibers with insignificant amounts in heart and smooth muscle. In contrast, smooth muscle MLCK had a more ubiquitous tissue distribution, with the greatest expression observed in smooth muscle tissue. Ablation of the MYLK2 gene in mice resulted in loss of skeletal muscle MLCK expression, with no change in smooth muscle MLCK expression. In isolated fast-twitch skeletal muscles from these knockout mice, there was no significant increase in RLC phosphorylation in response to repetitive electrical stimulation. Furthermore, isometric twitch-tension potentiation after a brief tetanus (posttetanic twitch potentiation) or low-frequency twitch potentiation (staircase) was attenuated relative to responses in muscles from wild-type mice. Interestingly, the site of phosphorylation of the small amount of monophosphorylated RLC in the knockout mice was the same site phosphorylated by MLCK, indicating a potential alternative signaling pathway affecting contractile potentiation. Loss of skeletal muscle MLCK expression had no effect on cardiac RLC phosphorylation. These results identify myosin light chain phosphorylation by the dedicated skeletal muscle Ca(2+)/calmodulin-dependent MLCK as a primary biochemical mechanism for tension potentiation due to repetitive stimulation in fast-twitch skeletal muscle.
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Affiliation(s)
- Gang Zhi
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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17
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Kornegay JN, Sharp NJ, Bogan DJ, Van Camp SD, Metcalf JR, Schueler RO. Contraction tension and kinetics of the peroneus longus muscle in golden retriever muscular dystrophy. J Neurol Sci 1994; 123:100-7. [PMID: 8064300 DOI: 10.1016/0022-510x(94)90210-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Contraction tension and kinetics of the peroneus longus muscle were studied in dogs with the Duchenne homologue, golden retriever muscular dystrophy (GRMD), in advance of evaluating localized therapies such as myoblast transplantation. Absolute and both muscle- and body-weight-corrected twitch tension in GRMD dogs were low compared to normal litter mates at 3 months of age (p < 0.0005 for all). Tetanic tension was affected similarly. However, whereas absolute values were still reduced at 6 months (p < 0.0005 for twitch and 0.005 for tetany), twitch and tetanic tension corrected for either muscle or body weight was not statistically different, suggesting that the peroneus longus may be relatively spared in GRMD. Post-tetanic potentiation was more pronounced in GRMD versus normal dogs at both 3 (p < 0.0001) and 6 (p < 0.01) months. The degree of positive staircase at 3 months of age did not differ. Twitch contraction and relaxation times were dramatically prolonged, and there was concomitant sustained electrical activity, at, or before, 6 months of age in some severely affected dogs. Relatively few carriers were evaluated at these ages, but their values were similar to those of normal dogs. Apparent sparing of the peroneus longus muscle may limit application of this technique to evaluation of therapies administered early in life or in combination with toxins. Treatment to alter changes in contraction kinetics could also be assessed.
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Affiliation(s)
- J N Kornegay
- Companion Animal and Special Species Medicine, College of Veterinary Medicine, North Carolina State University, Raleigh 27606
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18
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Engbaek J, Skovgaard LT, Friis B, Kann T, Viby-Mogensen J. Monitoring of the neuromuscular transmission by electromyography (I). Stability and temperature dependence of evoked EMG response compared to mechanical twitch recordings in the cat. Acta Anaesthesiol Scand 1992; 36:495-504. [PMID: 1325093 DOI: 10.1111/j.1399-6576.1992.tb03506.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The stability over time and the effect of muscle temperature change were evaluated for the evoked compound EMG and for the mechanomyogram of the tibialis anterior muscle of 7 anaesthetized cats. Both EMG areas and amplitudes were recorded. During stimulation for 3 h with 0.1 Hz (one leg) and train-of-four (TOF) (the other leg), the EMG was stable while the mechanomyogram initially increased 35-50% in the first 7-8 min and then decreased 19-22% and 5-8% over the first and second 1.5-h period, respectively. During subsequent mean muscle temperature reduction to 28.8 degrees C (0.1 Hz) and 29.7 degrees C (TOF) and rewarming, an inverse linear relationship was found between temperature and both the EMG and the mechanomyogram. During temperature reduction EMG increased about 6% (areas) and 2% (amplitudes) per degrees C. During rewarming, parameters decreased about 4.5% and 2% per degrees C, respectively (P less than 0.05 comparing EMG areas during cooling and rewarming). TOF ratio of the EMG was not affected by temperature. A very large interindividual variation was observed for the effect of temperature on the mechanomyogram with changes ranging up to 15% per degrees C for some cats. TOF ratio of the mechanomyogram was reduced from 1.02 to 0.94 at lowest muscle temperature. It is concluded that the evoked EMG may be preferable to the mechanomyogram in cat experiments investigating the neuromuscular transmission.
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Affiliation(s)
- J Engbaek
- Department of Anaesthesia, Herlev Hospital, Denmark
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19
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Moore RL, Palmer BM, Williams SL, Tanabe H, Grange RW, Houston ME. Effect of temperature on myosin phosphorylation in mouse skeletal muscle. THE AMERICAN JOURNAL OF PHYSIOLOGY 1990; 259:C432-8. [PMID: 2399966 DOI: 10.1152/ajpcell.1990.259.3.c432] [Citation(s) in RCA: 118] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The effect of muscle contraction on phosphorylatable myosin light chain (P-light chain) phosphate content and isometric twitch tension was examined at 25, 30, and 35 degrees C in intact mouse extensor digitorum longus muscle. Peak tetanic tension was unaffected by temperature, whereas peak unpotentiated isometric twitch tension was inversely proportional to muscle incubation temperature. The extent of phosphate incorporation into P-light chain elicited by a 20-s train of twitches (5/s) was inversely proportional to muscle incubation temperature, whereas the fractional increase in twitch tension (twitch potentiation) elicited by repetitive stimulation was directly proportional to muscle incubation temperature. After the twitch train, the rate of decline of potentiated twitch tension and of P-light chain dephosphorylation was directly proportional to muscle incubation temperature. The net result was that a significant and unique relationship between P-light chain phosphate content and contraction-induced tension potentiation existed at each temperature examined. The slope of the P-light chain phosphate vs. isometric twitch potentiation relationship varied directly as a function of muscle incubation temperature. The observations that the slope of this relationship increases and that unpotentiated twitch tension decreases when muscle incubation temperature is increased support the hypothesis that contraction-induced tension potentiation in intact mammalian skeletal muscle is the result of a sensitization of the contractile element to activation by Ca2+ that is brought about by P-light chain phosphorylation.
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Affiliation(s)
- R L Moore
- Department of Medicine, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033
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20
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Barnes WS, Williams JH. Staircase potentiation in isolated frog skeletal muscle: power spectral analysis of the evoked compound muscle action potential. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. A, COMPARATIVE PHYSIOLOGY 1990; 96:387-94. [PMID: 1976480 DOI: 10.1016/0300-9629(90)90101-w] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
1. The mechanical and electrophysiological effects of repetitive, low-frequency electrical stimulation on paired sartorii muscles from small male frogs have been investigated, in vitro. 2. Stimulation for 90 sec at 5 Hz resulted in a progressive rise (staircase) than fall (fatigue) in peak twitch tension. 3. The root mean square amplitude, peak-to-peak amplitude, conduction velocity and mean power frequency of evoked compound muscle action potentials (CMAPs) decreased over the stimulation period. 4. Results suggest that alterations in the shape of the CMAP during repetitive stimulation may contribute to the staircase phenomenon.
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Affiliation(s)
- W S Barnes
- Department of Health and Kinesiology, Texas A&M University, College Station 77843
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21
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Quinlan JG, Iaizzo PA, Lambert EH, Gronert GA. Ankle dorsiflexor twitch properties in malignant hyperthermia. Muscle Nerve 1989; 12:119-25. [PMID: 2710144 DOI: 10.1002/mus.880120206] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
A noninvasive method to diagnose malignant hyperthermia (MH) was sought. To this end, in vivo isometric twitch properties of the ankle dorsiflexor muscles were studied in three groups: (1) MH-susceptible patients (n = 12), (2) relatives (n = 12) of MH-susceptible patients who were judged to be MH resistant, and (3) a group of normal volunteers (n = 42) chosen from the community. Twitch properties were studied under resting state conditions and with 1 or 2 Hz stimulation to produce the negative staircase twitch response. There was a high degree of overlap between the ranges of the measured twitch parameters of all groups. Thus, the techniques presented in this study have no value in diagnosing susceptibility to MH. Several physiological features of human isometric twitch properties were demonstrated: (1) slowing of twitch speed with advancing age, (2) strong positive correlation between body weight and twitch torque, and (3) a negative staircase response typical of that described in other mammalian twitch studies.
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Affiliation(s)
- J G Quinlan
- Department of Neurology, Mayo Clinic, Rochester, MN
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22
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Wylie SR, Ranatunga KW. Temperature dependence of contraction characteristics in developing rat muscles. Muscle Nerve 1987; 10:775-82. [PMID: 3683450 DOI: 10.1002/mus.880100902] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Contractions of rat extensor digitorum longus (EDL, a fast muscle) and soleus (SOL, a slow muscle) muscles of different ages (1-4 weeks) were recorded in vitro with direct stimulation and at different temperatures (range 35-10 degrees C). Twitch tension in 4-week-old EDL muscle increased in cooling from 35 to 20 degrees C (cooling potentiation); the tension decreased in further cooling below 20 degrees C. This pattern of temperature dependence of twitch tension was seen in fast muscles of all ages (1-4 weeks). Twitch tension in 4-week-old SOL muscle decreased monotonically in cooling from 35 to 10 degrees C (cooling depression). This pattern of cooling depression was not clearly evident in younger SOL muscles. There was a marked hysteresis in the temperature dependence of twitch tension in the 1-week-old SOL muscles. Tetanic tension was depressed by low temperature in both EDL and SOL muscles at 1 week and at 4 weeks of age. Results show that the processes concerned with contractile activation are nearly fully developed in the fast muscle fibers at an early age (1 week), whereas they develop later in the slow muscle fibers.
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Affiliation(s)
- S R Wylie
- Department of Physiology, Medical School, University of Bristol, England
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23
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Buller AJ, Kean CJ, Ranatunga KW, Smith JM. Temperature dependence of isometric contractions of cat fast and slow skeletal muscles. J Physiol 1984; 355:25-31. [PMID: 6491991 PMCID: PMC1193475 DOI: 10.1113/jphysiol.1984.sp015403] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The influence of temperature (range 38-20 degrees C) on the isometric contractions of flexor digitorum longus (fast-twitch) and soleus (slow-twitch) muscles of the cat hind leg was examined in situ and with supramaximal nerve stimulation. The maximum tetanic tension decreased by 5-7% on cooling from 38 to 27 degrees C and by about 17% on further cooling to 20 degrees C. The results were similar between the two muscles. The twitch tension increased by 100% in flexor digitorum longus and decreased by about 40% in soleus when the temperature was lowered from 38 to 20-24 degrees C. The results are compared with those reported for fast- and slow-twitch muscles of the rat.
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24
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Yeagle SP, Mayer RF, Max SR. Contractile properties of rat fast-twitch skeletal muscle during reinnervation: effects of testosterone and castration. Exp Neurol 1983; 82:344-57. [PMID: 6628622 DOI: 10.1016/0014-4886(83)90407-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The isometric contractile properties of skeletal muscle were examined after nerve crush to establish the temporal sequence of recovery during reinnervation of normal, castrated, and testosterone-treated rats. Extensor digitorum longus muscles of male rats were studied in vivo 8 to 21 days after crushing the peroneal nerve 1 cm from the muscle. The earliest signs of functional reinnervation in normal animals were observed 8 to 9 days after nerve crush when faint muscle twitches with markedly prolonged twitch contraction times were recorded. By days 10 and 11, twitch tension was 9 to 20% of control, twitch contraction time was 149 to 183% of control, and tetanic tension was 4 to 9% of control values. The optimal frequency of stimulation was 58 to 64 Hz, the twitch:tetanus ratio was three times control values, and little or no posttetanic potentiation of twitch tension was observed. During the next 9 days there was a gradual return of all experimentally measured contractile properties toward control values; the relative rate of return was twitch tension greater than twitch contraction time greater than twitch:tetanus ratio greater than tetanic tension greater than optimal frequency of stimulation greater than posttetanic potentiation. Neither testosterone nor castration significantly altered either the rate or extent of functional reinnervation 8 to 21 days after nerve crush (P greater than 0.05). During this period the twitch:tetanus ratio for any given animal was highly correlated (r = 0.83, P less than 0.001) with the extent of functional recovery of neurally evoked muscle tension and was determined to be the most reliable index of the degree of muscle reinnervation. These data provide valuable baseline information for future studies of reinnervation of skeletal muscle.
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25
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Krarup C. Evoked responses in normal and diseased muscle with particular reference to twitch potentiation. Acta Neurol Scand 1983; 68:269-315. [PMID: 6320576 DOI: 10.1111/j.1600-0404.1983.tb04838.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The compound muscle action potential and isometric twitch tension evoked by single and repetitive electrical stimuli are indicators of the number of motor units activated and of the contractile properties of the muscle. The action potentials and mechanical responses were recorded in proximal and distal muscles in patients with myasthenia gravis and myopathy and compared with findings in normal subjects. In normal muscle, at low rates of stimulation (2-3 s-1) the decrement was at most 5% in the action potential and 15-24% in the twitch tension. Tetanic stimuli (50 s-1) were unsuitable for diagnostic purposes because of movement artefact. In patients with myasthenia gravis, the incidence and size of the decrement of evoked responses were greater in the platysma than in the elbow flexors and the adductor pollicis (ADP) muscles. The 2-3 times greater post-tetanic facilitation (PTF) of the action potential in the platysma than in extremity muscles also indicates a more severe functional block in facial muscle. The PTF is an indicator of recruitment of blocked fibres. The maximal decrement was grossly related to the titre of antibodies against the acetylcholine receptor. To reveal failure of neuromuscular transmission in patients with myasthenia gravis without a decrement, a small dose of d-tubocurarine (0.2 mg in 30 ml of saline) was injected i.v. in the upper arm in a regional curare test. The sensitivity was greater in patients with myasthenia gravis than in controls and in patients with myopathy. Potentiation of twitch tension reflects contractile properties. In normal muscle twitch potentiation in the staircase (1-3 s-1, 100 s in duration) and after tetanus (50 s-1, 1.5 s in duration) was 2-3 times greater in the platysma than in the elbow flexors and ADP, presumably related to the greater proportion of fast-twitch fibers in facial muscle. The amplitude of the action potential and the twitch tension varied proportionally with the number of fibers activated and the difference in the decrements of the action potential and the twitch during the staircase in some patients with myasthenia gravis showed that the staircase phenomenon was diminished suggesting abnormalities in the excitation-contraction coupling. The diminution of the staircase and post-tetanic potentiation (PTP) in myopathy also indicates impairment of the excitation-contraction coupling. In rats with severe chronic myasthenia gravis, the staircase and PTP were decreased even when the failing neuromuscular transmission was circumvented by applying direct stimuli to the extensor digitorum longus muscle (EDL).
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26
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Ranatunga KW. Temperature-dependence of shortening velocity and rate of isometric tension development in rat skeletal muscle. J Physiol 1982; 329:465-83. [PMID: 7143257 PMCID: PMC1224791 DOI: 10.1113/jphysiol.1982.sp014314] [Citation(s) in RCA: 148] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
1. The temperature-dependence of the maximum velocity of shortening and of the maximum rate of isometric tension development were examined in a rat fast twitch muscle, extensor digitorum longus (e.d.l.), and a slow twitch muscle, soleus, in vitro and with direct stimulation. The temperature range was 35-20 degrees C.2. The maximum velocity of shortening and the maximum rate of tension development decreased with cooling in both muscles. The decrease was such that their logarithms were linearly related to the reciprocal of the absolute temperature over the temperature range of 35-20 degrees C in e.d.l. and 35-25 degrees C in soleus.3. The calculated Arrhenius activation energy for maximum velocity of shortening was around 40-45 kJ in both muscles. The activation energies for maximum rate of tension development were 48 kJ in e.d.l. and 56 kJ in soleus. Similar analyses made on the time to peak and time to half-relaxation of the isometric twitch showed that their activation energies were higher, between 60-80 kJ, in both muscles.4. The results are examined in relation to biochemical findings and discussed in relation to A. F. Huxley's (1957) cross-bridge theory.
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27
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Krarup C. The effect of dantrolene on the enhancement and diminution of tension evoked by staircase and by tetanus in rat muscle. J Physiol 1981; 311:389-400. [PMID: 7264974 PMCID: PMC1275416 DOI: 10.1113/jphysiol.1981.sp013591] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
1. The effect of Dantrolene on the potentiation of isometric twitch tension was examined during and after the staircase (5/sec, 250 stimuli) and after the tetanus (167/sec, 250 stimuli) in the extensor digitorum longus muscle of adult Lewis rats at 37-38 degrees C.2. The study confirmed that Dantrolene decreased the twitch tension much more than the tetanic tension. The drug shortened the contraction time of the twitch. The rate of force development of the twitch was diminished by only half that of the twitch tension. The findings may suggest that the drug both shortened and diminished the activation of the muscle during the twitch.3. Dantrolene decreased the potentiation produced by a given number of stimuli early in the staircase. At the 250th stimulus the staircase was about 25% larger after than before application of the drug. Dantrolene increased the potentiation 2 sec after the tetanus by about 60%.4. After application of Dantrolene, the decay of potentiation after the staircase indicated that the process that diminished the twitch during the staircase, present before application of the drug, was absent. The size of the process causing potentiation was the same with and without the drug. Both events of potentiation after the tetanus were increased by Dantrolene. Both after the staircase and after the tetanus, Dantrolene increased the slow phase of decay by 60-70%. The fast rate of decay after the tetanus was unchanged by the drug.5. The contraction time was prolonged less in the potentiated twitch after than before application of Dantrolene. This was presumably due to a greater relative increase in activation rather than to a prolongation of the time during which the muscle was activated.6. A model is proposed where the delay in potentiation during the staircase and the increase in potentiation after the tetanus are due to the proportion of sites in the excitation-contraction coupling occupied by Dantrolene being reduced by repetitive depolarizations of the transverse tubules during trains of repetitive stimuli.
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