Evaluation of a novel model of skeletal muscle fatigue

骨骼肌疲劳新模型的评估

• 批准号: RGPIN-2014-06654
• 负责人: MacIntosh, Brian
• 金额: $ 1.89万
• 依托单位: University of Calgary
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=567954
• 关键词: Evaluation; novel; model; skeletal; muscle

Skeletal muscle fatigue has fascinated physiologists for centuries, yet the cellular processes impacting contractile properties during and following repeated activations are not well understood. Most current theories of fatigue consider build-up of metabolic products and their assumed ability to inhibit or impair the contractile response as the likely mechanism of fatigue. Yet, this is not consistent with the known primary mechanism of fatigue; inhibition of excitation-contraction coupling (E-CC). It is time to advance an understanding of how E-CC is impaired to truly comprehend how muscle behaves as a tissue when exposed to a metabolic stress. It is postulated that: fatigue is cellular regulation of E-CC to preserve ATP in the muscle. Essentially, this theory represents a realistic model of catastrophe avoidance. ATP use by both myosin ATPase and Ca2+ ATPase must also be regulated. A series of experiments are proposed to test this theory and to provide details for how this regulation contributes to fatigue. This work will use a recently developed structurally accurate 3-dimensional computer model of a sarcomere to simulate E-CC, contractile response and energetics at the myofibrillar level. In addition, experiments using various levels of organization are proposed. The sarcomere model will permit nanoscale evaluation of free and bound [Ca2+] as well as distribution of [ATP], taking us well beyond the scale that can otherwise be visualized. Single fibre and whole muscle experiments will supplement this computer simulation approach. All simulations and proposed experiments will be conducted at or close to physiological temperature for mammals because it has been demonstrated that mechanisms contributing to fatigue at room temperature are not relevant at mammalian physiological temperature. It is proposed to undertake several projects: 1) Computer modeling of muscle energetics, to gain an understanding of subcellular distribution of metabolites including: ATP, ADP, AMP, creatine, and creatine phosphate; 2) Whole muscle study of changes in [ATP] and the impact on fatigue; 3) Single fibre measurement of Ca2+ sensitivity and altered Ca2+ release to probe specific mechanisms. The computer simulation will use our current structurally accurate 3-dimensional model of the half sarcomere and monitor regional differences in [ATP] and other metabolites, based on known rates and locations of ATP use and regeneration. This will reveal the [ATP] around the ryanodine receptor, and how it changes during repeated contractions. The whole muscle studies will be undertaken to demonstrate rapid (contraction to contraction) regulation of E-CC, as manifest in rapid changes in EMG and muscle force with no change in the intermittent stimulation, but altered energy requirements by rapid adjustment of length. It is anticipated that a brief decrease in ATP requirement will result in enhanced activation and therefore greater force. When length is decreased from near optimal, active force and therefore ATP use decreases. Similar work with single fibres will evaluate the current theory that changes in Ca2+ sensitivity contribute to fatigue, and drug interventions to evaluate rapid adjustments in Ca2+ release following changes in energy cost of muscle contractions. 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 is primed for some novel thinking. The proposed work represents a new direction for the study of muscle fatigue and should be remarkably revealing in support of the proposed model of this common yet intriguing property of skeletal muscle.

几个世纪以来，骨骼肌疲劳一直吸引着生理学家，但在重复激活期间和之后影响收缩特性的细胞过程还没有得到很好的理解。目前大多数疲劳理论认为代谢产物的积累及其抑制或损害收缩反应的假定能力是疲劳的可能机制。然而，这与已知的疲劳的主要机制不一致;兴奋-收缩偶联（E-CC）的抑制。现在是时候进一步了解E-CC是如何受损的，以真正理解肌肉在暴露于代谢应激时作为组织的行为。推测疲劳是E-CC的细胞调节，以保存肌肉中的ATP。从本质上讲，这一理论代表了一个现实的灾难避免模型。肌球蛋白ATP酶和Ca 2 + ATP酶对ATP的利用也必须受到调节。提出了一系列的实验来测试这一理论，并提供细节，这种调节如何有助于疲劳。这项工作将使用最近开发的结构上精确的三维计算机模型的肌节模拟E-CC，收缩反应和能量在肌原纤维水平。此外，实验使用不同层次的组织提出。肌节模型将允许对游离和结合的[Ca 2 +]以及[ATP]的分布进行纳米级评估，使我们远远超出了可以可视化的规模。单纤维和整个肌肉实验将补充这种计算机模拟方法。所有模拟和拟定实验将在哺乳动物的生理温度或接近生理温度下进行，因为已证明室温下导致疲劳的机制与哺乳动物的生理温度无关。建议开展几个项目：1）肌肉能量学的计算机建模，以了解代谢物的亚细胞分布，包括：ATP，ADP，AMP，肌酸和磷酸肌酸; 2）[ATP]变化的全肌肉研究和对疲劳的影响; 3）Ca 2+敏感性的单纤维测量和改变的Ca 2+释放，以探测特定机制。计算机模拟将使用我们目前结构准确的半肌节三维模型，并根据已知的ATP使用和再生速率和位置，监测[ATP]和其他代谢物的区域差异。这将揭示ryanodine受体周围的ATP，以及它在重复收缩中的变化。将进行整个肌肉研究以证明E-CC的快速（收缩到收缩）调节，如EMG和肌肉力量的快速变化所示，间歇性刺激没有变化，但通过快速调整长度改变了能量需求。预计ATP需求的短暂减少将导致激活增强，从而导致更大的力量。当长度从接近最佳的位置减少时，主动力和ATP的使用就会减少。对单纤维的类似工作将评估目前的理论，即Ca 2+敏感性的变化有助于疲劳，以及药物干预，以评估肌肉收缩能量消耗变化后Ca 2+释放的快速调整。拟议的实验将为E-CC的调节如何导致疲劳提供证据，推进我们在一个为一些新思维做好准备的研究领域的知识。拟议的工作代表了肌肉疲劳研究的新方向，并应显着揭示支持骨骼肌这种常见但有趣的特性的拟议模型。