Evaluation of a novel model of skeletal muscle fatigue

骨骼肌疲劳是一种常见的经历，几个世纪以来一直吸引着科学家，但在反复激活期间和之后影响收缩特性的细胞过程尚不清楚。大多数疲劳理论认为是代谢产物的积累和收缩反应的抑制。这与已知的疲劳的主要机制：抑制兴奋-收缩耦合（E-CC）不一致。现在是研究E-CC如何受损的时候了。对肌肉疲劳提出了一个创新的解释：疲劳是E-CC细胞调节的结果，以保持肌肉中的能量电荷。提出了实验来检验这一理论以及其他理论。拟采用单纤维、纤维束和生理温度下的全肌肉进行实验。研究表明，室温下的疲劳机制与生理温度下的疲劳机制不相关。提出的研究的第二个创新和实用方面是考虑的收缩将是次最大的，就像普通运动中的自然收缩一样。****如果理论是正确的，那么改变细胞能量电荷应该导致E-CC的改变，在收缩到收缩的基础上，并处于稳定状态。例如，拉伸肌肉以增加活动力和ATP周转量，而不改变与活化相关的跨膜离子交换，将导致随后Ca2+释放的衰减。游离[Ca2+]将在单纤维实验中测量，以检测Ca2+瞬态的任何变化。测量平均自由[Ca2+]在频率范围内的收缩揭示力- pca2 +的关系。ryanodine受体的调节被认为是通过Ca2+-钙调素结合和/或Mg2+结合的增加而发生的。一旦实现RyR抑制，Ca2+-钙调素的潜在影响可能受到限制。游离[Ca2+]的减少将导致Ca2+钙调蛋白的减少。这将通过观察肌球蛋白轻链磷酸化的生物测定在全肌肉中进行评估，允许首次评估全肌肉中的Ca2+瞬态。还将考虑轻链磷酸化减少导致Ca2+敏感性受损的可能性。***提出的实验将为E-CC的调节如何导致疲劳提供证据，在一个需要一些新颖思维的研究领域中推进我们的知识。所提出的工作代表了肌肉疲劳研究的一个新方向，并且应该非常揭示支持骨骼肌这种常见但有趣的特性的新模型。

Skeletal muscle fatigue, is a common experience that has fascinated scientists for centuries, yet the cellular processes impacting contractile properties during and following repeated activations are not understood. Most theories of fatigue considered build-up of products of metabolism and inhibition of the contractile response. This is not consistent with the known primary mechanism of fatigue: inhibition of excitation-contraction coupling (E-CC). It is time to study how E-CC is impaired. An innovative explanation for muscle fatigue is proposed: fatigue is a consequence of cellular regulation of E-CC to preserve energy charge in the muscle. Experiments are proposed to test this theory as well as alternative theories. Experiments are proposed using: single fibre, fibre bundles and whole muscle at physiological temperature. It has been demonstrated that fatigue mechanisms at room temperature are not relevant at physiological temperature. A second innovative and practical aspect of the proposed studies is contractions under consideration will be sub maximal, like natural contractions in common movements. ****If the theory is correct, then changing cellular energy charge should result in altered E-CC, on a contraction-to-contraction basis and in steady state. For example, stretching a muscle to increase active force and ATP turnover, without changing cross-membrane ion exchange associated with activation will result in attenuation of subsequent Ca2+ release.  Free [Ca2+] will be measured in single fibre experiments to detect any changes in Ca2+ transients. Measuring average free [Ca2+] during contractions over a range of frequencies reveals the force-pCa2+ relationship. Regulation of the ryanodine receptor is thought to occur by increases in Ca2+-calmodulin binding and/or binding of Mg2+. The potential impact of Ca2+-calmodulin may be limited once RyR inhibition is achieved. Decreased free [Ca2+] will result in less Ca2+-calmodulin. This will be assessed in whole muscle with a bioassay by looking at myosin light chain phosphorylation, permitting the first assessment of Ca2+ transients in whole muscle. The possibility that decreases in light chain phosphorylation contributes to impaired Ca2+ sensitivity will also be considered.  ***The proposed experiments will provide evidence for how the regulation of E-CC can result in fatigue, advancing our knowledge in a field of study that requires some novel thinking. The proposed work represents a new direction for the study of muscle fatigue and should be remarkably revealing in support of a new model of this common yet intriguing property of skeletal muscle.