Prediction by 31P-NMR of the irreversibility of ischemic injury in rat skeletal muscle after ligation of the femoral artery

Rat leg muscles, rendered ischaemic 1 hour previously by ligation of the femoral artery, were submitted to 20 minutes exercise by electrical stimulation of the sciatic nerve. 31P-NMR spectroscopy was used to monitor the changes in high-energy phosphate content of the muscles before, during, and after exercise. Fifteen of the 35 studied muscles evolved toward total necrosis, whereas the others showed signs of recovery over a 2-5-hour postexercise period. Those muscles which did not subsequently recover contained significantly more inorganic phosphate (Pi) at rest (before exercise) than those which recovered. It is suggested that under acute ischaemic conditions the Pi level at rest is correlated with the extent of blood flow restriction and can be used to predict the severity of the ischemia.     

Metabolic and nonmetabolic components of fatigue monitored with 31P-NMR

The goal of this study was to determine the roles of metabolic and nonmetabolic factors in muscle fatigue. Rat gastrocnemius muscles were fatigued by stimulation of the nerve (n = 6) or muscle (n = 4, after 2 days of denervation). ³¹Phosphorus nuclear magnetic resonance spectroscopy was used to measure levels of intracellular inorganic phosphate (Pi) and hydrogen ions (H⁺) (which are thought to inhibit contraction) and the high-energy phosphates, phosphocreatine (PCr), and ATP. For both indirect and direct stimulation, with fatigue to ≈60% initial tetanic force, [Pi] increased from ≈3.5 mmol/L to ≈20 mmol/L and [PCr] decreased from ≈27 mmol/L to ≈9 mmol/L. However, with continued fatigue to 25–35% initial tetanic force, neither [Pi] or [PCr] changed further. [ATP] and pH changed only slightly during fatigue. The results are consistent with early fatigue arising from metabolic inhibition of contraction; but later fatigue arising independent of metabolites, due to impaired activation beyond the neuromuscular junction. © 1994 John Wiley & Sons, Inc.     

Isolation of two populations of myoblasts from porcine skeletal muscle

Studies on the effects of time and passage on porcine primary muscle cell cultures and methods to purify myoblasts were conducted using flow cytometry and fluorescence‐activated cell sorting (FACS). Primary muscle cells cultured on single plates revealed a small cell (<10 mm diameter) population consisting of 90% desmin‐positive myoblasts and a large cell (≥10 mm diameter) population containing desmin‐positive myoblasts and nonmyoblasts. The small myoblasts were detectable up to 28 days but after cell sorting and passage, they became indistinguishable from the large myoblast population. This indicates that pig muscle contains small self‐renewing myoblasts similar to humans, that become larger when induced to proliferate. A human myoblast‐specific monoclonal antibody allows FACS of both large and small myoblasts from primary cells within 2 days of culture and independent of passage. These characteristics of porcine myoblasts indicate that the pig may be a suitable large animal model for myoblast‐mediated gene transfer. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 43–50, 1999     

Muscle fatigue unrelated to phosphocreatine and pH: an "in vivo" 31-P NMR spectroscopy study

Metabolic events were followed by 31-P NMR spectroscopy during mechanical exhaustion of directly stimulated rat gastrocnemius. During mechanical fatigue, phosphocreatine (PCr) and pH first declined but although stimulation continued high values were recovered without mechanical recovery. Total recovery was only observed after cessation of stimulation. Partial mechanical recovery was elicited by lowering stimulation rhythm; it was accompanied by decrease in PCr to a steady-state level without pH alteration. When exhaustive exercise was induced immediately after nonexhaustive exercise, failure of mechanical function occurred without decrease in pH. Major findings were: first, during exhaustive stimulations, the greater the muscle fatigue, and the higher the PCr level at the end of stimulation. Secondly, PCr and force levels did not depend on preceding levels of PCr and pH. Thirdly, acidosis was observed transiently during the first minutes of the first exercise period. These findings strongly suggested that electrical events and/or excitation-contraction (EC) coupling play a crucial role in this type of fatigue.     

Low grade spinal malignant triton tumor with mature skeletal muscle differentiation

Malignant peripheral nerve sheath tumor (MPNST) is an uncommon sarcoma which arises from pluripotent stem cells of the neural crest and differentiates predominantly towards Schwann cells. Low grade spinal MPNST with skeletal muscle differentiation (malignant triton tumor) is vanishingly rare. In this study, we report a case of a 53-year-old female with a homogenously enhancing C2-C4 extradural lesion. The lesion demonstrated a biphasic histologic pattern with a diffusely infiltrating, atypical spindle cell component strongly positive for vimentin and focally positive for S-100. The second component consisted of diffusely scattered clusters of mature skeletal muscle cells which were positive for desmin, fast myosin and muscle specific actin but negative for Myogenin and MyoD-1. The Ki-67 labeling index was low (< 1%) and no necrosis was identified. The present case is remarkable because of its rare location, low grade histology and unusual immunophenotype of the skeletal muscle component, which were not previously described.     

Slow calcium current is not reduced in malignant hyperthermic porcine myotubes

Malignant hyperthermia-susceptible (MHS) pigs express a sarcoplasmic reticulum (SR) Ca²⁺-release channel mutation that results in lower than normal contractile thresholds in skeletal muscles. In adult MHS pig muscles the L-type calcium current (I_s) is also reduced. We tested the hypothesis that there is a causal relationship between I_s and the lower contractile threshold by recording I_s from MHs and normal porcine myotubes using the whole cell patch-clamp technique. Current voltage relationships for both MHS and normal myotubes were similar, with peak I_s between +20 and +30 mV. Maximum I_s amplitudes were not different (normal: 4976 ± 566 pA; MHS: 6516 ± 1088 pA) nor was I_s specific density (normal: 9.0 ± 0.8; MHS: 8.8 ± 1.1 pA/pF). In both MHS and normal myotubes, both the dihydropyridine antagonist PN200 –110 (200 nmol/L) and holding the membrane potential at −10 mV for 5 min decreased I_s significantly (by more than 50%). There was no apparent direct relationship between the mutation in the SR Ca²⁺-release channel and lowered I_s. We concluded that reduced I_s in adult MHS pig muscles may be a secondary effect of the SR Ca²⁺-release channel mutation on muscle development. © 1996 John Wiley & Sons, Inc.     

Localization of protein kinase C in human skeletal muscle.

The immunolocalization of protein kinase C (PKC) isozymes alpha, beta I and beta II, was investigated in human skeletal muscle. All three isozymes were present on the muscle fiber surface membrane and within the muscle fibers. The alpha-isozyme was most clearly delineated on the surface membrane of the muscle fiber and on small blood vessels in the connective tissue. The axons of myelinated intramuscular nerves stained intensely for the beta I isozyme, whereas the endoneurial connective tissue reacted more strongly for the alpha- and beta II-isozymes. PKC isozymes may regulate intracellular signal transduction in human skeletal muscle, as in the other tissues, but their exact role in muscle remains unknown.     

Estimation of skeletal muscle energy metabolism in Machado‐Joseph disease using 31P‐MR spectroscopy

The aim of this study was to determine if muscle energy metabolism, as measured by ³¹P‐magnetic resonance spectroscopy (MRS), is a metabolic marker for the efficacy of treatment of Machado‐Joseph disease (MJD). We obtained ³¹P‐MRS in the calf muscle of 8 male patients with MJD and 11 healthy men before, during, and after a 4 minute plantar flexion exercise in a supine position. The data showed that there was a significant difference between the groups in terms of the PCr/(Pi + PCr) ratio at rest (P = 0.03) and the maximum rate of mitochondrial ATP production (V_max) (P < 0.01). In addition, V_max was inversely correlated with the scale for the assessment and rating of ataxia score (r = ?0.34, P = 0.04). The MJD group also showed a reduction in V_max over the course of 2 years (P < 0.05). These data suggest that this noninvasive measurement of muscle energy metabolism may represent a surrogate marker for MJD. © 2010 Movement Disorder Society     

Mass-dependent decline of skeletal muscle function in cancer cachexia

CD2F1 mice were inoculated with C26 adenocarcinoma cells, followed by assessment of ex vivo muscular function. Muscles from tumor-bearing mice had a significantly lower force output during a single maximal contraction and during repeated contractions than control muscles. The relative force output, however, did not differ when corrected for muscle mass. Thus, cachexia significantly reduces absolute skeletal muscle function, but muscle "quality" appears unaltered.     

Matrix metalloproteinases and skeletal muscle: a brief review

Matrix metalloproteinases (MMPs) are a family of zinc- dependent proteolytic enzymes that function mainly in the extracellular matrix, where they contribute to the development, functioning, and pathology of a wide range of tissues. This mini-review describes the MMPs and tissue inhibitors of MMPs (TIMPs) in skeletal muscle, and considers their involvement in muscle development, ischemia, myonecrosis, angiogenesis, denervation, exercise-induced injuries, disuse atrophy, muscle repair and regeneration, and inflammatory myopathies and dystrophies. Despite the very limited information currently available on MMPs and their inhibitors in skeletal muscle, it is becoming increasingly clear that they have important physiological functions in maintenance of the integrity and homeostasis of muscle fibers and of the extracellular matrix. Understanding the roles of MMPs and TIMPs may lead to the development of new drug-related treatments for various muscle disorders based on suppression or upregulation of their expression.     

Improvement of muscular oxidative capacity by training is associated with slight acidosis and ATP depletion in exercising muscles

Metabolic and mechanical properties of female rat skeletal muscles, submitted to endurance training on a treadmill, were studied by a 60-min in vivo multistep fatigue test. ³¹P-NMR was used to follow energy metabolism and pH. Mechanical performance was greatly improved in trained muscles. The oxidative capacity of the skeletal muscles was evaluated from the relationship between ADP calculated from the creatine kinase equilibrium and work and from the measure of the rate of phosphocreatine (PCr) resynthesis following exercise. In trained muscles, ADP production was lower per unit of mechanical performance, showing an improvement of oxidative metabolism. However, the PCr resynthesis rate was not modified. Slight acidosis and ATP depletion were observed from the beginning of the fatigue test. These modifications suggest changes of the creatine kinase equilibrium favoring mitochondrial ATP production. Our results indicate that muscle status improvement could be accompanied by ATP depletion and minimal acidosis during contraction; this would be of particular importance for objective evaluation of muscle regeneration processes and of gene therapy in muscle diseases. © 1996 John Wiley & Sons, Inc.     

Myasthenia gravis: the specificities of skeletal muscle and thymus antibodies

Antibodies against skeletal muscle antigens and against thymic myoid cells were examined in sera from 40 patients with myasthenia gravis (MG). Using an indirect immunofluorescence technique, antibodies against the surface of muscle cells were found in 23 sera, and antibodies against muscle cell cross-striations in 28 sera. Antibodies against thymic myoid cells were found in 27 sera, stained cells also occurring in fetal thymus from 14 weeks of gestation and in hyperplastic thymus from MG patients. Sera which stained myoid cells also stained muscle cell cross-striations. Sera from all the 20 patients with thymoma contained antibodies to a citric acid extract of skeletal muscle (CAE) as detected by indirect haemagglutination, whereas sera from 20 comparable patients without thymoma did not contain CAE antibodies. The myoid cell antibodies could be absorbed by homogenized muscle, but not by CAE-coated sheep erythrocytes. Different antibody patterns are seen among different MG patients; close associations were found between cross-striational and myoid cell antibodies, and between CAE-antibodies and a thymoma.     

Regeneration of mouse peripheral nerves in degenerating skeletal muscle: guidance by residual muscle fibre basement membrane

The part played by basement membrane in the guidance of peripheral nerve growth in vivo has been assessed by examining the capacity of degenerating mouse muscle to support the regeneration of the cut sciatic and saphenous nerves. Ethanol and formaldehydefixed gluteus maximus muscles were implanted around the contralateral cut nerves. The subsequent nerve growth into the degenerating muscle was assessed by silver staining after 3, 4 and 10 days. By 4 days, linear axonal growth was seen, parallel to the length of the muscle fibers, and coinciding with the onset of degeneration of the sarcoplasm. Transverse sections of the 10 day preparations showed that over 90% of linearly growing axons were located inside the remaining sheaths of muscle fibre basement membrane. This relationship was confirmed by electron microscopy of ruthenium red-stained preparations. Both motor and sensory axons were able to grow in this manner, for electrophysiological testing revealed the presence of motor axons from the sciatic nerve, while the saphenous nerve contains only sensory axons. Identical growth was seen at 10 days in muscles caused to degenerate by incubation in distilled water. However, linear growth did not occur in live-innervated and glutaraldehyde-fixed muscles, in which muscle fibre architecture was preserved.It is concluded that basement membrane derived from muscle can promote peripheral nerve regeneration. Furthermore, both motor and sensory axons show a strong preference for growth along its inner surface, the basal lamina.     

Magnetic stimulation excites skeletal muscle via motor nerve axons in the cat

Surface magnetic stimulation has been applied directly over skeletal muscle (triceps surae) in decerebrated cats. Recordings were made of the twitch contraction and electromyographic responses in triceps surae, and of the centripetal nerve volley in the sciatic nerve or spinal roots. Stimulus/response curves were established up to the maximum output of the magnetic stimulator. Neuromuscular blockade abolished the twitch contraction and muscle action potential leaving the nerve volley unaffected. Raising the stimulator output to its maximum increased the size of the nerve volley but failed to produce any muscle response. We conclude that magnetic stimulation applied directly to skeletal muscle excites via stimulation of motor nerve axons. The maximum output of the stimulator was incapable of exciting muscle fibers by direct depolarization. Use of magnetic stimulation in the clinical appraisal of muscle function should be interpreted in the knowledge that the stimulator elicits contraction only indirectly through nerve stimulation. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1108–1114, 1997     

Structure and function of the skeletal muscle extracellular matrix

The skeletal muscle extracellular matrix (ECM) plays an important role in muscle fiber force transmission, maintenance, and repair. In both injured and diseased states, ECM adapts dramatically, a property that has clinical manifestations and alters muscle function. Here we review the structure, composition, and mechanical properties of skeletal muscle ECM; describe the cells that contribute to the maintenance of the ECM; and, finally, overview changes that occur with pathology. New scanning electron micrographs of ECM structure are also presented with hypotheses about ECM structure–function relationships. Detailed structure–function relationships of the ECM have yet to be defined and, as a result, we propose areas for future study.     

Relation between in vivo and in vitro measurements of skeletal muscle oxidative metabolism.

The relationships between in vivo (31)P magnetic resonance spectroscopy (MRS) and in vitro markers of oxidative capacity (mitochondrial function) were determined in 27 women with varying levels of physical fitness. Following 90-s isometric plantar flexion exercises, calf muscle mitochondrial function was determined from the phosphocreatine (PCr) recovery time constant, the adenosine diphosphate (ADP) recovery time constant, the rate of change of PCr during the initial 14 s of recovery, and the apparent maximum rate of oxidative adenosine triphosphate (ATP) synthesis (Q(max)). Muscle fiber type distribution (I, IIa, IIx), citrate synthase (CS) activity, and cytochrome c oxidase (COX) activity were determined from a biopsy sample of lateral gastrocnemius. MRS markers of mitochondrial function correlated moderately (P < 0.05) with the percentage of type IIa oxidative fibers (r = 0.41 to 0.66) and CS activity (r = 0.48 to 0.64), but only weakly with COX activity (r = 0.03 to 0.26, P > 0.05). These results support the use of MRS to determine mitochondrial function in vivo.     

Effects of alcohol on skeletal and cardiac muscle

The acute and chronic toxic effects of alcohol on skeletal and cardiac muscle are clinically important. Muscle weakness and atrophy are the main manifestations of skeletal myopathy, and arrhythmias and progressive left-ventricular dysfunction are those of cardiomyopathy. Most patients remain asymptomatic from these effects for a long time. Myocyte atrophy and death are the main pathological findings. A clear dose-related effect has been established with ethanol consumption, with gender and some specific gene polymorphisms being factors of increased susceptibility to alcohol-induced muscle damage. Pathogenic mechanisms are pleiotropic, the most relevant being disturbances in carbohydrate, protein, and energy cell turnover, signal transduction, and induction of apoptosis and gene dysregulation. Ethanol abstinence is the only effective treatment, although controlled drinking is useful in patients who do not achieve abstinence. Persistent high-dose consumption results in deterioration of muscle and heart function, with a high mortality due to arrhythmias and progression of heart failure.     

Breakdown of adenine nucleotide pool in fatiguing skeletal muscle in McArdle's disease: a noninvasive 31P-MRS and EMG study

Energy metabolism and electrical muscle activity were studied in the calf muscles of 19 patients with proven McArdle's disease and in 25 healthy subjects. Phosphorus magnetic resonance spectroscopy and surface electromyography (S-EMG) were performed during two isometric muscle contractions of 3 min at 30% maximum voluntary contraction, one performed during normal perfusion and the other during applied ischemia. After about 1 min of ischemic muscle contraction in diseased muscle a significant acceleration in phosphocreatine breakdown was observed, along with a significant decrease in adenosine triphosphate. During both contractions the absence of glycolysis was shown by a significant alkalinization. Furthermore, in patients we observed a greater increase in the S-EMG amplitude than in control subjects. We conclude that early on during moderate exercise, a small number of muscle fibers reach metabolic depletion, indicated by a reduction in the adenine nucleotide pool. An increasing number of motor units, which are still in a high-energy state, are continuously recruited to compensate for muscle fatigue. This functional compartmentation may contribute to the pathophysiology of exercise intolerance in McArdle's disease.     

Effect of neural activity on skeletal muscle phosphoproteins

A number of phosphoproteins were found in the soluble fraction of rat skeletal muscle by two-dimensional polyacrylamide gel electrophoresis (PAGE). The pattern of some of these phosphoproteins differed in fast (extensor digitorum longus, EDL) or slow (soleus) muscles, was dependent on normal innervation, and was altered with denervation. In order to determine if the pattern was maintained by electrical activity or trophic factors, we compared the effect of electrical block by local neural application of tetrodotoxin with the effect of complete nerve section. Both methods produced similar alterations in phosphoproteins, indicating that the pattern is dependent on nerve activity, not trophic factors. Such phosphoproteins are possible mediators of neural activity on gene expression.     

肌肉运动与骨骼肌细胞的凋亡

背景：不少医学研究表明,细胞凋亡能导致大量自由基增多、Ca2+浓度升高、线粒体膜电位下降引起运动能力的下降。因此,研究细胞凋亡与运动训练的关系意义重要。 目的：总结与探索关于肌肉运动与骨骼肌细胞凋亡的相关问题。 方法：计算机检索中国期刊全文数据(网址http://dlib.cnki.net/kns50/index.aspx)及PubMed数据库(网址http://www.ncbi.nlm.nih.gov/pubmed/ )1990-01/2009-06期间的相关文章,检索词为“肌肉运动,骨骼肌细胞凋亡,muscle exercise,apoptosis in the skeletal muscle”。纳入与肌肉运动与骨骼肌细胞的凋亡研究现状与发展密切相关。①有关骨骼肌细胞凋亡的研究。②运动与骨骼肌细胞凋亡研究。③运动诱发骨骼肌细胞凋亡的基因调控研究。④骨骼肌细胞凋亡的分子机制研究。⑤同一领域选择近期发表或在权威杂志上发表的文章。排除重复性研究。 结果与结论：运动后,正常肌肉中或是病理状态下的肌肉中骨骼肌细胞都会出现凋亡,凋亡的形态学表现与普通凋亡细胞相似,即核固缩、质膜发泡、细胞器紧缩,凋亡小体形成,其凋亡过程大致可分为3个阶段,即启始阶段、效应阶段和降解阶段。骨骼肌细胞凋亡的增加是导致运动性疲劳的重要原因。目前国内外对骨骼肌细胞凋亡的基因调控研究主要是从 凋亡调控因子Bcl-2蛋白、肿瘤坏死因子α及死亡蛋白酶半胱氨酸天冬氨酸酶着手。bcl-2基因蛋白的抗凋亡作用主要是通过阻止线粒体通透性转换孔的开放,阻止线粒体释放促凋亡蛋白、防止线粒体膜脂质过氧化以及线粒体基质Ca2+释放实现的。肿瘤坏死因子家族在启动死亡因子及其受体途径中起重要作用,此途径的启动依赖于死亡配体与死亡受体相结合,激活半胱氨酸天冬氨酸酶,导致细胞凋亡。通过研究探索运动强度与骨骼肌细胞凋亡及坏死的界限关系,有利于在运动中认识运动性疲劳产生的机制及有效消除疲劳。