The nature of the proteins lost from isolated rat skeletal muscle during experimental damage

Blueberry fruit polyphenolics suppress oxidative stress-induced skeletal muscle cell damage in vitro

Skeletal muscle damage can result from disease and unaccustomed or excessive exercise. Muscle dysfunction occurs via an increased level of reactive oxygen species and hence there is potential in antioxidants as amelioration strategies. We explored the putative benefit of fruit polyphenolic extracts in reducing the susceptibility of skeletal muscle cells to oxidative stress. Muscle myotubes were simultaneously challenged with fruit extracts (1-50 microg/mL) and calcium ionophore (A23187), hydrogen peroxide, or 2,4-dinitrophenol and damage monitored by release of cytosolic enzymes. A blueberry fruit extract displayed a potent and significant dose-dependent protective capacity. Evaluation of the protective capacity of anthocyanin sub-extracts of blueberry fruit and pure individual glycosides, with identification of extract polyphenolic components using MS, suggested that malvidin galactoside and/or glucoside were the active compounds. These in vitro data support the concept that blueberry fruits or derived foods rich in malvidin glycosides may be beneficial in alleviating muscle damage caused by oxidative stress. More research on the benefits of blueberry fruit consumption in human intervention studies is warranted.

Damage to developing mouse skeletal muscle myotubes in culture: protective effect of heat shock proteins

Damage to skeletal muscle occurs following excessive exercise, upon reperfusion following ischaemia and in disease states, such as muscular dystrophy. Key mechanisms by which damage is thought to occur include a loss of intracellular calcium homeostasis, loss of energy supply to the cell, increased activity of oxidising free radical-mediated reactions and activation of apoptosis pathways. An increased cellular content of heat shock proteins (HSPs) has been shown to protect skeletal muscle against some forms of damage, although the mechanistic basis of this protection is not clearly understood. The aim of this study was to establish a cell culture-based model of damage to C2C12 skeletal muscle cells using the calcium ionophore, A23187 and the mitochondrial uncoupler, 2,4-dinitrophenol (DNP) as damaging agents. Treatment of cells with 1 mM DNP for 60 min resulted in the release of 63.5 % of intracellular creatine kinase (CK) activity over the 3 h experimental period. Treatment of cells with 10 microM A23187 for 30 min resulted in the release of 47.9 % of CK activity. Exposure of myotubes to a period of hyperthermia resulted in a significant increase in their content of HSP25, HSP60, HSC70 (heat shock cognate) and HSP70. This increase in HSPs was associated with significant protection against both DNP-induced and A23187-induced damage to the myotubes. These results indicate that an increased content of HSPs may provide protection against the muscle damage that occurs by a pathological increase in intracellular calcium or uncoupling of the mitochondrial respiratory chain.

Exercise-induced muscle damage and inflammation: fact or fiction?

Physical exercise is necessary for maintaining normal function of skeletal muscle. The mechanisms governing normal muscle function and maintenance are vastly unknown but synergistic function of hormones, neurosignalling, growth factors, cytokines and other factors, is undoubtedly important. Because of the complex interaction among these systems the lack of complete understanding of muscle function is not surprising. The purpose of exercise-induced changes in muscle cell function is to adapt the tissue to a demand of increased physical work capacity. Some of the approaches used to investigate changes in skeletal muscle cell function are exercise and electrical stimulation in animals and human models and isolated animal muscle. From these models, it has been concluded that during physical exercise, in an intensity and duration dependent manner, skeletal muscle is damaged and subsequently inflamed. The purpose of the inflammation would be to repair the exercise-induced damage. Because of the design and methods used in a majority of these studies, concerns must be raised, and the question asked whether the paradigm of exercise-induced muscle inflammation in fact is fiction. In a majority of conducted studies, a non-exercising control group is lacking and because of the invasive nature of the sampling methods used to study inflammation it does not appear impossible that observed inflammatory events in human skeletal muscle after physical exercise are methodological artefacts.

Weakness in mouse masticatory muscles by repetitive contractions with forced lengthening

The etiology of myofascial tenderness and pain of masticatory muscles in humans is difficult to understand. Parafunctional oral habits such as tooth grinding or vigorous chewing are thought to be factors. The objective of this study was to determine if masticatory muscles are susceptible to weakness and injury induced by repetitive, dynamic, forced-lengthening contractions. Results would support the hypothesis that contraction-induced injuries could occur in hyperactive masticatory muscles of humans in response to parafunctional oral habits. Mice were anesthetized and randomly assigned to three groups: non-treated controls, treated by repetitive passive jaw opening, or treated by repetitive isometric tetanic contractions with lengthening by jaw opening. In each treatment group, masticatory muscle injury was evaluated by contractile tension, plasma creatine kinase, and muscle glycogen. Contractile tension was determined at different stimulation frequencies and was significantly decreased 5 min, 4 h, and 72 h after repetitive contraction/lengthening. Plasma creatine kinase was significantly elevated at 4 but not at 72 h post-treatment in mice subjected to repetitive contraction/lengthening. Masticatory muscle glycogen was not significantly different in any groups at 4 or 72 h post-treatment. These results indicate that contraction injuries can be induced in masticatory muscle of mice by forced lengthening contractions which simulate eccentric contractions.