scholarly journals Extensive eccentric contractions in intact cardiac trabeculae: revealing compelling differences in contractile behaviour compared to skeletal muscles

2019 ◽  
Vol 286 (1903) ◽  
pp. 20190719 ◽  
Author(s):  
André Tomalka ◽  
Oliver Röhrle ◽  
June-Chiew Han ◽  
Toan Pham ◽  
Andrew J. Taberner ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Muscle ◽  
Skeletal Muscles ◽  
Muscle Force ◽  
Isometric Force ◽  
Muscle Length ◽  
Eccentric Contractions ◽  
Shortening Velocity ◽  
Linear Rise ◽  
Total Muscle

Force enhancement (FE) is a phenomenon that is present in skeletal muscle. It is characterized by progressive forces upon active stretching—distinguished by a linear rise in force—and enhanced isometric force following stretching (residual FE (RFE)). In skeletal muscle, non-cross-bridge (XB) structures may account for this behaviour. So far, it is unknown whether differences between non-XB structures within the heart and skeletal muscle result in deviating contractile behaviour during and after eccentric contractions. Thus, we investigated the force response of intact cardiac trabeculae during and after isokinetic eccentric muscle contractions (10% of maximum shortening velocity) with extensive magnitudes of stretch (25% of optimum muscle length). The different contributions of XB and non-XB structures to the total muscle force were revealed by using an actomyosin inhibitor. For cardiac trabeculae, we found that the force–length dynamics during long stretch were similar to the total isometric force–length relation. This indicates that no (R)FE is present in cardiac muscle while stretching the muscle from 0.75 to 1.0 optimum muscle length. This finding is in contrast with the results obtained for skeletal muscle, in which (R)FE is present. Our data support the hypothesis that titin stiffness does not increase with activation in cardiac muscle.

MUSCLE BULGING REDUCES MUSCLE FORCE AND LIMITS THE MAXIMAL EFFECTIVE MUSCLE SIZE

2006 ◽  
Vol 06 (03) ◽  
pp. 229-239 ◽  
Author(s):  
KARL DAGGFELDT
Keyword(s):  
Muscle Force ◽  
Muscle Length ◽  
Biomechanical Model ◽  
Muscle Performance ◽  
Muscle Size ◽  
Intramuscular Pressure ◽  
Shortening Velocity ◽  
Muscle Shortening ◽  
Force Reduction ◽  
Total Muscle

A biomechanical model was generated in order to investigate the possible mechanisms behind reductions in muscle performance due to muscle bulging. It was shown that the proportion of fiber force contributing to the total muscle force is reduced with fiber bulging and that the cause of this reduction is due to the intramuscular pressure (IMP) created by the bulging fibers. Moreover, it was established that the amount of IMP generated muscle force reduction is determined by the extent to which muscle thickening restricts muscle fibers from shortening, thereby limiting their power contribution. It was shown that bulging can set a limit to the maximal size a muscle can take without losing force and power producing capability. Possible effects, due to bulging, on maximal muscle force in relation to both muscle length and muscle shortening velocity were also demonstrated by the model.

Effects of altitude acclimatization on rat myoglobin. Changes in myoglobin content of skeletal and cardiac muscle

1959 ◽  
Vol 196 (3) ◽  
pp. 512-516 ◽  
Author(s):  
Adam Anthony ◽  
Eugene Ackerman ◽  
G. K. Strother
Keyword(s):  
Skeletal Muscle ◽  
Body Weight ◽  
Cardiac Muscle ◽  
Water Content ◽  
Skeletal Muscles ◽  
The Body ◽  
Continuous Exposure ◽  
Weight Changes ◽  
Body Weight Changes ◽  
Muscle Weight

Analyses were made of myoglobin content of rat skeletal and cardiac muscle following continuous exposure to simulated altitudes of 18,000 feet for a 2–10-week period. About five dozen rats were used. Acclimatization was associated with an increase in the myoglobin concentration of thigh, diaphragm, gastrocnemius and heart muscles. Total myoglobin content, however, increased during acclimatization in cardiac muscle but not in the three skeletal muscles. This finding together with the body weight changes and muscle weight changes suggested that the increases in myoglobin concentration of skeletal muscle may be merely a reflection of a decreased water content of muscles.

Isotonic relaxation in cardiac muscle

1975 ◽  
Vol 229 (3) ◽  
pp. 646-651 ◽  
Author(s):  
JE Strobeck ◽  
AS Bahler ◽  
EH Sonnenblick
Keyword(s):  
Cardiac Muscle ◽  
Isometric Force ◽  
Muscle Length ◽  
Constant Load ◽  
Papillary Muscles ◽  
Initial Length ◽  
Total Load ◽  
Relaxation Velocity ◽  
Force Velocity ◽  
Maximum Isometric Force

The force-velocity-length determinants of isotonic relaxation were studied in 12 cat papillary muscles. Isotonic relaxation velocity (VL) was found to be a function of total load (preload + afterload), with peak VL increasing to a maximum at loads approximately .3 to .4 Po(L') (Po(L') defined as maximum isometric force developed during a twitch at the experimental length) and falling with increasing loads. Initial muscle length (ML) had no effect on the peak VL with constant load. Increasing the initial length at which isotonic relaxation occurred (LL) decreased peak VL but did not alter the unique length-velocity trajectory at constant load. This unique length-velocity trajectory occurred, despite a wide variation in time during the contraction when peak VL was measured. Increasing Ca++ from 2.5 to 7.5 mM increased peak VL (1.73 +/- .16 to 2.32 +/- .20 ML/s) and shifted the entire length-velocity trajectory toward higher velocities of lengthening. The addition of 10 mM caffeine increased peak VL also (1.67 +/- .18 to 2.54 +/- .20 ML/s) and had a similar effect on the length-velocity trajectory during lengthening as Ca++. Both increased Ca++ and caffeine (10 mM) augmented the maximum VL measured on addition of load.

Inverse alterations of BCKA dehydrogenase activity in cardiac and skeletal muscles of diabetic rats

1999 ◽  
Vol 277 (4) ◽  
pp. E685-E692 ◽  
Author(s):  
Yolanda B. Lombardo ◽  
Cynthia Serdikoff ◽  
Manikkavasagar Thamotharan ◽  
Harbhajan S. Paul ◽  
Siamak A. Adibi
Keyword(s):  
Gene Expression ◽  
Skeletal Muscle ◽  
Protein Expression ◽  
Cardiac Muscle ◽  
Dehydrogenase Activity ◽  
Skeletal Muscles ◽  
Diabetic Rats ◽  
Gene Expressions ◽  
The Difference ◽  
Activity State

Rat cardiac and skeletal muscles, which have been used as model tissues for studies of regulation of branched-chain α-keto acid (BCKA) oxidation, vary greatly in the activity state of their BCKA dehydrogenase. In the present experiment, we have investigated whether they also vary in response of their BCKA dehydrogenase to a metabolic alteration such as diabetes and, if so, to investigate the mechanism that underlies the difference. Diabetes was produced by depriving streptozotocin-treated rats of insulin administration for 96 h. The investigation of BCKA dehydrogenase in the skeletal muscle (gastrocnemius) showed that diabetes 1) increased its activity, 2) increased the protein and gene expressions of all of its subunits (E1α, E1β, E2), 3) increased its activity state, 4) decreased the rate of its inactivation, and 5) decreased the protein expression of its associated kinase (BCKAD kinase) without affecting its gene expression. In sharp contrast, the investigation of BCKA dehydrogenase in the cardiac muscle showed that diabetes 1) decreased its activity, 2) had no effect on either protein or gene expression of any of its subunits, 3) decreased its activity state, 4) increased its rate of inactivation, and 5) increased both the protein and gene expressions of its associated kinase. In conclusion, our data suggest that, in diabetes, the protein expression of BCKAD kinase is downregulated posttranscriptionally in the skeletal muscle, whereas it is upregulated pretranslationally in the cardiac muscle, causing inverse alterations of BCKA dehydrogenase activity in these muscles.

scholarly journals Overexpression of Galgt2 in skeletal muscle prevents injury resulting from eccentric contractions in both mdx and wild-type mice

2009 ◽  
Vol 296 (3) ◽  
pp. C476-C488 ◽  
Author(s):  
Paul T. Martin ◽  
Rui Xu ◽  
Louise R. Rodino-Klapac ◽  
Elaine Oglesbay ◽  
Marybeth Camboni ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscular Dystrophy ◽  
Transgenic Mice ◽  
Skeletal Muscles ◽  
Eccentric Contractions ◽  
Cytotoxic T Cell ◽  
Muscle Pathology ◽  
Mdx Mice ◽  
Specific Force ◽  
Wild Type

The cytotoxic T cell (CT) GalNAc transferase, or Galgt2, is a UDP-GalNAc:β1,4- N-acetylgalactosaminyltransferase that is localized to the neuromuscular synapse in adult skeletal muscle, where it creates the synaptic CT carbohydrate antigen {GalNAcβ1,4[NeuAc(orGc)α2, 3]Galβ1,4GlcNAcβ-}. Overexpression of Galgt2 in the skeletal muscles of transgenic mice inhibits the development of muscular dystrophy in mdx mice, a model for Duchenne muscular dystrophy. Here, we provide physiological evidence as to how Galgt2 may inhibit the development of muscle pathology in mdx animals. Both Galgt2 transgenic wild-type and mdx skeletal muscles showed a marked improvement in normalized isometric force during repetitive eccentric contractions relative to nontransgenic littermates, even using a paradigm where nontransgenic muscles had force reductions of 95% or more. Muscles from Galgt2 transgenic mice, however, showed a significant decrement in normalized specific force and in hindlimb and forelimb grip strength at some ages. Overexpression of Galgt2 in muscles of young adult mdx mice, where Galgt2 has no effect on muscle size, also caused a significant decrease in force drop during eccentric contractions and increased normalized specific force. A comparison of Galgt2 and microdystrophin overexpression using a therapeutically relevant intravascular gene delivery protocol showed Galgt2 was as effective as microdystrophin at preventing loss of force during eccentric contractions. These experiments provide a mechanism to explain why Galgt2 overexpression inhibits muscular dystrophy in mdx muscles. That overexpression also prevents loss of force in nondystrophic muscles suggests that Galgt2 is a therapeutic target with broad potential applications.

Aminophylline increases submaximum power but not intrinsic velocity of shortening of frog muscle

1992 ◽  
Vol 73 (1) ◽  
pp. 71-74 ◽  
Author(s):  
B. M. Block ◽  
S. R. Barry ◽  
J. A. Faulkner
Keyword(s):  
Skeletal Muscles ◽  
Isometric Force ◽  
Frog Muscle ◽  
Measured Parameter ◽  
Shortening Velocity ◽  
Force Development ◽  
Velocity Of Shortening ◽  
Force Velocity ◽  
Maximum Isometric Force ◽  
Frequency Of Stimulation

We hypothesized that methylxanthines, such as aminophylline, increase the power developed by submaximally activated frog skeletal muscles by increasing the force developed at any given velocity of shortening. Frog semitendinosus muscles were excised and tested at 20 degrees C in oxygenated control and aminophylline Ringer solutions. Force-velocity relationships were determined and power was calculated from muscles stimulated at frequencies of 80 and 300 Hz. The 300-Hz frequency of stimulation produced a maximum rate of force development. In 50 and 500 microM aminophylline, twitch force increased by 25 +/- 12 and 75 +/- 13%, respectively. Aminophylline did not affect maximum isometric force generation or the shortening velocity at any relative load. At 80-Hz stimulation and in the presence of 500 microM aminophylline, power increased by an average of 11% at 10 of 14 relative loads. At maximum frequencies of stimulation, aminophylline had no effect on any measured parameter. We conclude that aminophylline increases the power developed by submaximally activated frog muscles through an increase in the force generated particularly at the lower velocities of shortening.

Post-reextension force decay of relaxing cardiac muscle

1987 ◽  
Vol 253 (2) ◽  
pp. H256-H261 ◽  
Author(s):  
S. U. Sys ◽  
W. J. Paulus ◽  
V. A. Claes ◽  
D. L. Brutsaert
Keyword(s):  
Cardiac Muscle ◽  
Isometric Force ◽  
Muscle Length ◽  
Wall Stress ◽  
Left Ventricular ◽  
Segment Length ◽  
Force Decay ◽  
Ventricular Compliance ◽  
Left Ventricular Compliance ◽  
Ventricular Filling

Residual active cardiac muscle force during ventricular filling causes deviations of the pressure-volume and pressure-segment length relations from passive left ventricular compliance curves. A possible interaction at the myocardial level between muscle reextension and subsequent active force decay has not yet been investigated. We therefore studied the relation between isolated cat papillary muscle reextension, load during reextension, and isometric force decay after isotonic reextension. Both timing and extent of the isotonic muscle reextension phase were altered while load during reextension was lowered, subsequent residual isometric force was decreased. The extent of reextension or the final muscle length did not alter residual active isometric force after isotonic reextension at an identical load. Moreover, irrespective of the loading history of the shortening phase of the contraction, equal loads during reextension resulted in superimposable subsequent isometric force decay traces. From these results it therefore appears that residual isometric force after isotonic reextension is determined by the load during reextension. Extrapolation of these results to the filling ventricle implies the existence of a dynamic interaction between instantaneous extent of filling, wall stress, and residual force development.

scholarly journals Chemical and immunochemical characteristics of tropomyosins from striated and smooth muscle

1974 ◽  
Vol 141 (1) ◽  
pp. 43-49 ◽  
Author(s):  
Peter Cummins ◽  
S. Victor Perry
Keyword(s):  
Skeletal Muscle ◽  
Smooth Muscle ◽  
Cardiac Muscle ◽  
Skeletal Muscles ◽  
Striated Muscle ◽  
Β Subunit ◽  
Muscle Type ◽  
Amphibian Species ◽  
Species Specific ◽  
Immunochemical Characteristics

1. On electrophoresis in dissociating conditions the tropomyosins isolated from skeletal muscles of mammalian, avian and amphibian species migrated as two components. These were comparable with the α and β subunits of tropomyosin present in rabbit skeletal muscle. 2. The α and β components of all skeletal-muscle tropomyosins contained 1 and 2 residues of cysteine per 34000g respectively. 3. The ratio of the amounts of α and β subunit present in skeletal muscle tropomyosins was characteristic for the muscle type. Muscle consisting of slow red fibres contained a greater proportion of β-tropomyosin than muscles consisting predominantly of white fast fibres. 4. Mammalian and avian cardiac muscle tropomyosins consisted of α-tropomyosin only. 5. Mammalian and avian smooth-muscle tropomyosins differed both chemically and immunologically from striated-muscle tropomyosins. 6. Antibody raised against rabbit skeletal α-tropomyosin was species non-specific, reacting with all other striated muscle α-tropomyosin subunits tested. 7. Antibody raised against rabbit skeletal β-tropomyosin subunit was species-specific.

scholarly journals Active shortening protects against stretch-induced force deficits in human skeletal muscle

2017 ◽  
Vol 122 (5) ◽  
pp. 1218-1226 ◽  
Author(s):  
Anjali L. Saripalli ◽  
Kristoffer B. Sugg ◽  
Christopher L. Mendias ◽  
Susan V. Brooks ◽  
Dennis R. Claflin
Keyword(s):  
Skeletal Muscle ◽  
High Velocity ◽  
Isometric Force ◽  
Human Subjects ◽  
Causative Factor ◽  
Negative Consequences ◽  
Shortening Velocity ◽  
Contracting Muscle ◽  
Working Hypothesis ◽  
Force Maintenance

Skeletal muscle contraction results from molecular interactions of myosin “crossbridges” with adjacent actin filament binding sites. The binding of myosin to actin can be “weak” or “strong,” and only strong binding states contribute to force production. During active shortening, the number of strongly bound crossbridges declines with increasing shortening velocity. Forcibly stretching a muscle that is actively shortening at high velocity results in no apparent negative consequences, whereas stretch of an isometrically (fixed-length) contracting muscle causes ultrastructural damage and a decline in force-generating capability. Our working hypothesis is that stretch-induced damage is uniquely attributable to the population of crossbridges that are strongly bound. We tested the hypothesis that stretch-induced force deficits decline as the prevailing shortening velocity is increased. Experiments were performed on permeabilized segments of individual skeletal muscle fibers obtained from human subjects. Fibers were maximally activated and allowed either to generate maximum isometric force (Fo), or to shorten at velocities that resulted in force maintenance of ≈50% Fo or ≈2% Fo. For each test condition, a rapid stretch equivalent to 0.1 × optimal fiber length was applied. Relative to prestretch Fo, force deficits resulting from stretches applied during force maintenance of 100, ≈50, and ≈2% Fo were 23.2 ± 8.6, 7.8 ± 4.2, and 0.3 ± 3.3%, respectively (means ± SD, n = 20). We conclude that stretch-induced damage declines with increasing shortening velocity, consistent with the working hypothesis that the fraction of strongly bound crossbridges is a causative factor in the susceptibility of skeletal muscle to stretch-induced damage. NEW & NOTEWORTHY Force deficits caused by stretch of contracting muscle are most severe when the stretch is applied during an isometric contraction, but prevented if the muscle is shortening at high velocity when the stretch occurs. This study indicates that velocity-controlled modulation of the number of strongly bound crossbridges is the basis for the observed relationship between stretch-induced muscle damage and prevailing shortening velocity.

scholarly journals Causes of fatigue in slow-twitch rat skeletal muscle during dynamic activity

2009 ◽  
Vol 297 (3) ◽  
pp. R900-R910 ◽  
Author(s):  
Morten Munkvik ◽  
Per Kristian Lunde ◽  
Ole M. Sejersted
Keyword(s):  
Skeletal Muscle ◽  
Isometric Force ◽  
Force Production ◽  
Maximum Force ◽  
Stimulation Protocol ◽  
Shortening Velocity ◽  
Dynamic Activity ◽  
Initial Values ◽  
Isotonic Shortening

Skeletal muscle fatigue is most often studied in vitro at room temperature and is classically defined as a decline in maximum force production or power output, exclusively linked to repeated isometric contractions. However, most muscles shorten during normal use, and we propose that both the functional correlate of fatigue, as well as the fatigue mechanism, will be different during dynamic contractions compared with static contractions. Under isoflurane anesthesia, fatigue was induced in rat soleus muscles in situ by isotonic shortening contractions at 37°C. Muscles were stimulated repeatedly for 1 s at 30 Hz every 2 s for a total of 15 min. The muscles were allowed to shorten isotonically against a load corresponding to one-third of maximal isometric force. Maximal unloaded shortening velocity (V0), maximum force production (Fmax), and isometric relaxation rate (−dF/d t) was reduced after 100 s but returned to almost initial values at the end of the stimulation protocol. Likewise, ATP and creatine phosphate (CrP) were reduced after 100 s, but the level of CrP was partially restored to initial values after 15 min. The rate of isometric force development, the velocity of shortening, and isotonic shortening were also reduced at 100 s, but in striking contrast, did not recover during the remainder of the stimulation protocol. The regulatory myosin light chain (MLC2s) was dephosphorylated after 100 s and did not recover. Although metabolic changes may account for the changes of Fmax, −dF/d t, and V0, dephosphorylation of MLC2s may be involved in the fatigue seen as sustained slower contraction velocities and decreased muscle shortening.

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