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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Skeletal muscle has an inherent biochemical phenotypic plasticity that provides the possibility for it to be remodeled into a "heart-like" muscle for use in cardiac-assist devices. The purpose of this study was to chronically stimulate skeletal muscle electrically to transform the biochemical capacities of the three major subcellular systems (i.e., metabolic, calcium regulating, and contractile) to resemble those of heart muscle. The latissimus dorsi muscle (LDM) of mongrel dogs weighing 22-27 kg was stimulated via the thoracodorsal nerve at 2 Hz for 6-8 wk. This stimulation protocol reduced the phosphorylase (glycogenolytic) and phosphofructokinase (glycolytic) activities by 70%. The aerobic (citrate synthase activity) and fatty acid oxidative (3-hydroxyacyl-CoA dehydrogenase activity) capacities were not significantly increased by chronic stimulation and remained at about one-fourth those in the canine heart. The calcium-dependent sarcoplasmic reticulum adenosinetriphosphatase (ATPase) activity in the microsomal fraction, which was sixfold greater in the nonstimulated LDM than in the heart, was reduced by electrical stimulation to a level similar to that of the dog heart. The contractile capacity was evaluated by determining the percentage of types I and II fibers, the myofibrillar ATPase activity, and the proportion of myosin isoforms. The transformed muscle was comprised of 93 +/- 2% type I fibers, a myofibrillar ATPase activity similar to that in heart with primarily a slow-twitch muscle myosin isoform. In conclusion, electrical stimulation of canine LDM at 2 Hz for 6-8 wk resulted in two of the three biochemical systems, which confer physiological expression and fatigue resistance to muscle being transformed to resemble those of the myocardium.
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PMID:Biochemical transformation of canine skeletal muscle for use in cardiac-assist devices. 214 Aug 28

This study was designed to determine the effects of reduced neuromuscular activity on the expression of proteins associated with contractile and metabolic functions and the size of single muscle fibers in the cat soleus. Adult cats were spinalized (Sp) at T12-T13 and maintained in a healthy condition for 6 months. Some of the cats were trained to weight-support (Sp-WS) for 30 minutes per day beginning one month posttransection. Cross-sectional area (CSA), succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (GPD), and myofibrillar adenosine triphosphatase (ATPase) activities were determined in a population of single fibers identified in frozen serial cross-sections. Each fiber was categorized as either light or dark based on its staining density for qualitative myosin ATPase, alkaline preincubation (pH 8.75). The Sp (45%) and Sp-WS (31%) groups had significantly higher percentages of dark ATPase fibers than control (less than 1%). All dark ATPase fibers were shown to react positively for a fast myosin heavy chain monoclonal antibody, while some of these fibers showed a reaction to both fast and slow myosin heavy chain antibodies. Overall mean fiber CSA were significantly smaller (approximately 25%) than control in both Sp groups. In the Sp-WS, but not the Sp cats, the dark fibers were larger than the light fibers (P less than 0.05), suggesting a preferential effect of postural training on the ATPase converted fibers. There were no significant differences among the three groups in any of the mean enzyme activities for either ATPase type fiber. However, there was a general tendency for the Sp cats to have elevated GPD and ATP activities per muscle; this appeared to be directly related to the percentage of fibers staining darkly for myosin ATPase. These data indicate that 6 months after spinalization some of the fibers of the slow muscle developed fast myosin staining patterns and oxidative and glycolytic enzyme profiles that are normally exhibited in fast fatigue-resistant motor units. Periods of daily weight-support appear to ameliorate some of these adaptations to spinalization. Further, the observation that SDH activities are maintained at control values in spinalized adult cats as well as in spinalized kittens (unpublished observations) suggest that, at least in the soleus, skeletal muscle fibers can maintain their oxidative potential even though there is a marked reduction in neuromuscular activity for 6 months.
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PMID:Expression of a fast fiber enzyme profile in the cat soleus after spinalization. 214 97

The proportions of fast and slow myosin molecules in external urethral sphincter specimens from ten urodynamically normal male bladder carcinoma patients were estimated from the contents of fast and slow myosin light chains in two-dimensional electrophoretic gels. The percentages of fast and slow myosin molecules ranged from 5.0% to 61.4% with a mean of 35.5% and from 38.6% to 95.0% with a mean of 65.5% respectively. It is therefore concluded that the human external urethral sphincter is composed of both fast and slow muscle fibers as well as other voluntary muscles. The human external urethral sphincter is considered to be a highly fatigue-resistant muscle with a very high proportion of slow muscle fibers. In the cases studied so far, there is a great diversity in the proportions of fast and slow myosin molecules; the reason for this remains unknown.
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PMID:The proportions of fiber types in human external urethral sphincter: electrophoretic analysis of myosin. 225 34

Metabolic fatigue is a characteristic muscle response to intense exercise that has outstripped the rate of ATP replacement. The accumulation of metabolic by-products, namely hydrogen ions and diprotonated phosphate, interferes with actin-myosin interaction, effectively preserving muscle ATP levels by preventing further ATP hydrolysis. Muscle force and metabolite concentrations return to normal in about 5 minutes. Less intense exercise causes a more subtle, non-metabolic fatigue due to a still-undefined disturbance of excitation-contraction coupling, which can last for several hours. In this type of fatigue, greater effort is required to generate submaximal forces. Endurance exercise is mainly limited by the size of muscle glycogen stores and how efficiently they are used. Endurance training permits an athlete to work aerobically at high rates, consuming a mixture of lipid and carbohydrate fuels. When muscle glycogen is used up, exercise can only continue at the relatively low rate supportable by lipid metabolism. Anaerobic exercise is also limited by subjective factors such as dyspnoea and muscle pain, which have objective determinants. Extremely prolonged exercise can lead to general collapse because of dehydration, hyperthermia, or hypoglycaemia. None of these factors explains the phenomenon of asthenia, a subjective sense of exhaustion that produces no objective impairment of physical performance. The metabolic myopathies are experiments of nature that promise to shed new light on the biochemical basis of muscle fatigue. This will require quantitative studies of the kind provided by topical magnetic resonance spectroscopy, correlating physiology and metabolism in vivo.
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PMID:Muscle metabolism during fatigue and work. 226 24

The gross anatomy, microscopical anatomy, morphometry, enzyme histochemistry, immunohistochemistry and electron microscopy of the tensor tympani muscle of the rat was studied. The aim of the study was to create an integrated insight into the morphology of the muscle and to discuss functional implications. The tensor tympani muscle of the rat is an atypical muscle. It is a small muscle composed of very small muscle fibres with a complex microscopical and submicroscopical architecture. Histochemically the muscle consists mainly of fast oxidative glycolytic fibres, but discrepancies are found when anti-heavy chain myosin antibodies are used for fibre typing. Different adult heavy chain myosin isotypes coexist in one single muscle fibre. The electron microscopical study shows that bundles of myofilaments branch and interconnect with other bundles of myofilaments. The findings suggest that the muscle is able to contract fast and is fatigue-resistant. Both features seem to suggest that the muscle has a function in protecting the inner ear against noise damage.
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PMID:Detailed morphology of the tensor tympani muscle of the rat. An integrated light microscopical, morphometrical, histochemical, immunohistochemical and electron microscopical study in relation to function. 253 39

1. Maximal calcium-activated force (Fmax) and calcium sensitivity were markedly decreased in detergent-skinned fibres from skeletal and cardiac muscle by solutions that mimicked the total milieu changes associated with fatigue and hypoxia. Further experiments determined the relative contribution of each of the individual changes in milieu. 2. Both Ca2+ sensitivity and Fmax of skeletal and cardiac fibres were decreased with increased [H+] or inorganic phosphate (Pi). These effects were greater in cardiac muscle. 3. Decreasing MgATP over the range observed with fatigue and hypoxia (6.8-4.7 mM) had no effect on Fmax or Ca2+ sensitivity of either muscle type. 4. Decreasing phosphocreatine (PCr: 15-1 mM) increased Fmax but had little effect on Ca2+ sensitivity in both muscle types. In cardiac fibres, the effect on Fmax could be mimicked by inhibition of endogenous creatine kinase. 5. ADP (0.7 mM) increased Fmax and Ca2+ sensitivity, while AMP (0.06 mM) slightly increased Fmax but had no effect on Ca2+ sensitivity of either skeletal or cardiac fibres. 6. Creatine (25 mM) had no significant effect on either Ca2+ sensitivity or Fmax of skeletal and cardiac muscle fibres. At higher levels (50 mM), however, creatine depressed Fmax and slightly altered Ca2+ sensitivity. 7. Thiophosphorylation of myosin P light chains (phosphorylatable light chains of myosin) in rabbit psoas fibres had no effect on Ca2+ sensitivity, yet slightly but significantly increased Fmax under fatigue conditions. 8. Reducing the affinity for ATP hydrolysis (by adding ADP, AMP and creatine) over the range calculated for fatigue/hypoxia (60-45 kJ/mol) produced the enhancement in Fmax expected from added ADP and AMP in cardiac but not skeletal muscle, indicating that changes in affinity influence Fmax of skeletal muscle. Reducing affinity produced little change in Ca2+ sensitivity of skeletal muscle. In contrast, the change produced in cardiac muscle was greater than that expected from addition of ADP and AMP; i.e. decreasing affinity increases calcium sensitivity of the heart. 9. Simple summation of all significant changes expected from each constituent altered by fatigue/hypoxia adequately predicted the observed changes in Fmax and Ca2+ sensitivity in both cardiac and skeletal muscle fibres with but one exception (the change in Ca2+ sensitivity of skeletal muscle at pH 7 was slightly overestimated).
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PMID:Changes of intracellular milieu with fatigue or hypoxia depress contraction of skinned rabbit skeletal and cardiac muscle. 260 Aug 30

1. The effects of phosphate and protons on the mechanics and energetics of muscle contraction have been investigated using glycerinated rabbit psoas muscle. 2. Fibres were fully activated by addition of Ca2+ (pCa 4-5) at 10 degrees C. The velocities of contraction were measured in isotonic load clamps, and the velocities of unloaded fibres were measured by applying a series of step changes in fibre length. Fibre ATPase activity was monitored using an enzyme system to couple ADP production to reduced nicotinamide-adenine dinucleotide (NADH) and measuring the depletion of NADH by optical density. 3. At pH 7.0 and 3 mM-phosphate, isometric tension (P0) was 13.2 +/- 0.9 N/cm (mean +/- S.E.M., n = 10 observations), the maximum contraction velocity (Vmax) was 1.63 +/- 0.05 lengths/s (n = 5) and the ATPase activity was 1.27 +/- 0.12 s-1 myosin head-1 (n = 35). Increasing phosphate from 3 to 20 mM at pH 7.0 does not affect Vmax, causes a small decrease in the ATPase activity (15-20%) and decreases P0 by approximately 20%. Changing pH from 7 to 6 at 3 mM-phosphate decreases P0 by 45% and both Vmax and ATPase activity by 25-30%. The effects of changing both pH and phosphate were approximately additive for all parameters measured. The inhibition of these parameters by low pH and high concentration of phosphate was reversible. 4. The force-velocity relation was fitted by the Hill equation using a non-linear least-squares method. The value of the parameter which describes the curvature, a/P0, was 0.20. The curvature of the force-velocity relation was not changed by addition of phosphate or by changes in pH. 5. These data provide information on both the kinetics of the actomyosin interaction and on the process of muscle fatigue. The data are consistent with models of cross-bridge kinetics in which phosphate is released within the powerstroke in a step involving a rapid equilibrium between states. The inhibition by protons is more complex, and may involve less specific effects on protein structure. 6. During moderate fatigue of living skeletal muscle, MgATP concentration is known to remain approximately constant at 4 mM, phosphate to increase from 3 to 20 mM, and protons from 0.1 to 1 microM. The data suggest that much of the inhibition of P0 observed during moderate fatigue can be explained by the increased levels of phosphate and protons, and that much of the inhibition of fibre Vmax and ATPase activity can be explained by the increase in protons.
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PMID:The inhibition of rabbit skeletal muscle contraction by hydrogen ions and phosphate. 284 89

The influence of variations in muscle fibre composition on isometric endurance capacity was measured in 23 young healthy untrained male volunteers. After determination of the maximum voluntary force of contraction (MVC), subjects sustained to fatigue contractions at forces of 80%, 50% and 20% of MVC with a 5-min rest between each. A needle biopsy was obtained from m. vastus lateralis and used for histochemical determination of fibre composition based on myosin ATP-ase activity, and fibre are a based on succinate dehydrogenase (SDH) activity. Endurance times were 21 +/- 9 s (mean +/- SD) at 80% of MVC, 56 +/- 17 s at 50% of MVC and 203 +/- 89 s at 20% of MVC. A wide range of muscle fibre compositions was observed with Type I fibres accounting for 48.0 +/- 10.5% of the total, corresponding to 45.0 +/- 11.5% of the total muscle area. Muscle fibre composition, whether expressed as the proportions of the different fibre types present, or as the fraction of total muscle cross-sectional area occupied by each fibre type was not correlated with isometric endurance capacity at any of the three forces studied. Endurance time was also unrelated to MVC. In contrast to the results of previous studies where trained subjects were used, or where different muscle groups were compared, these results suggest that isometric endurance is not influenced by muscle fibre composition.
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PMID:The relationship between muscle myosin ATP-ase activity and isometric endurance in untrained male subjects. 293 54

The goal of this review is to summarize our knowledge of the plasticity of striated muscles in terms of contractile proteins. During development or when the working conditions are changed, the intrinsic physiological properties of both cardiac and skeletal muscles are modified. These modifications generally adapt the muscle to the new environmental requirements. One of the best examples is compensatory overload obtained in fast skeletal muscle by synergistic tenotomy and in a fast ventricle, such as in rats, by aortic banding. In both cases, after a few weeks the initial speed of shortening for the unloaded muscle drops, whereas the maximum tension developed remains unchanged. Heat measurements show that efficiency (i.e., g work/mol ATP) is improved at the fiber level. The fast skeletal muscle becomes slow, fatigue resistant, and then more adapted to endurance. For the ventricle as a whole to become slow is beneficial only if one contraction is considered; however, it is detrimental in terms of cardiac output and leads finally to failure. This adaptational process is partly explained by quantitative and qualitative changes in contractile proteins. Protein synthesis is rapidly enhanced and muscles hypertrophy, which in turn multiplies the contractile units and for the cardiac cylinder normalizes the wall stress. In the meantime the structure and, for myosin, the biological activity of several contractile proteins are modified. These modifications are very unlikely to be posttranscriptional and are in fact explained by several isoform shifts. In both tissues, for example, the expression of the gene coding for a fast myosin (MHCf in skeletal muscle, alpha-MHC in ventricles) is repressed and that of the gene coding for a slow myosin (beta-MHC in both tissues) is stimulated. This is accompanied by a coordinated increase in synthesis of other contractile proteins and, in skeletal muscle only, by isoform shifts of myosin light chains and of the TM-TN regulatory system. Other changes are less well understood. During development it has recently been discovered that three different MHCs (MHCemb, MHCneo, and MHCf) appear sequentially in fast skeletal muscle, which explains, for example, several contradictions of immunological cross-reactions. Currently, however, the functional significance of this finding is unknown, and the well-known decrease of shortening velocity observed in cardiac and skeletal muscles during fetal life is unexplained in terms of contractile proteins.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Developmental and functional adaptation of contractile proteins in cardiac and skeletal muscles. 294 54

Isomyosin analyses by biochemical, immunochemical, and histochemical investigations have been carried out in five sheep following unilateral recurrent laryngeal nerve paralysis and direct functional electrostimulation of the denervated cricoarytenoid posterior muscle. Myosin light chains were identified by two-dimensional gel electrophoresis. Myosin heavy chains were analyzed by one-dimensional SDS-polyacrylamide gel electrophoresis. Slow myosin heavy chain was identified by orthogonal peptide mapping and immunochemistry. The stimulation effect at cellular level was determined using adenosine triphosphatase (ATPase) histochemistry. A dramatic increase of the type 1 fiber area (slow, fatigue-resistant fibers) could be seen after many weeks of an increasing regime of low-frequency direct electrical stimulation. Biochemically, the amount of slow myosin was always higher than in normal muscles. Some muscles were transformed almost completely to the slow type. At the time they were studied and with the methods employed, the expression of embryonic isomyosin was not observed. In conclusion, after numerous weeks of maintained functional activity, elicited by direct electrostimulation, the denervated muscle regionally showed areas of hypertrophy or at least lack of atrophy of slow myofibers without major signs of muscle damage.
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PMID:Isomyosin changes after functional electrostimulation of denervated sheep muscle. 297 27


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