Herzog Walter
Faculty of Kinesiology, The University of Calgary, Calgary, AB, Canada.
Front Physiol. 2022 Apr 27;13:837611. doi: 10.3389/fphys.2022.837611. eCollection 2022.
Sarcomeres are the smallest functional contractile unit of muscle, and myofibrils are striated muscle organelles that are comprised of sarcomeres that are strictly aligned in series. Furthermore, passive forces in sarcomeres and myofibrils are almost exclusively produced by the structural protein titin, and all contractile, regulatory, and structural proteins are in their natural configuration. For these mechanical and structural reasons single sarcomere and myofibril preparations are arguably the most powerful to answer questions on the mechanisms of striated muscle contraction. We developed and optimized single myofibril research over the past 20 years and were the first to mechanically isolate and test single sarcomeres. The results from this research led to the uncovering of the crucial role of titin in muscle contraction, first molecular explanations for the origins of the passive and the residual force enhancement properties of skeletal and cardiac muscles, the discovery of sarcomere length stability on the descending limb of the force-length relationship, and culminating in the formulation of the three-filament theory of muscle contraction that, aside from actin and myosin, proposes a crucial role of titin in active force production. Aside from all the advantages and possibilities that single sarcomere and myofibril preparations offer, there are also disadvantages. These include the fragility of the preparation, the time-consuming training to master these preparations, the limited spatial resolution for length and force measurements, and the unavailability of commercial systems for single sarcomere/myofibril research. Ignoring the mechanics that govern serially linked systems, not considering the spatial resolution and associated accuracies of myofibril systems, and neglecting the fragility of myofibril preparations, has led to erroneous interpretations of results and misleading conclusions. Here, we will attempt to describe the methods and possible applications of single sarcomere/myofibril research and discuss the advantages and disadvantages by focusing on specific applications. It is hoped that this discussion may contribute to identifying the enormous potential of single sarcomere/myofibril research in discovering the secrets of muscle contraction.
肌节是肌肉最小的功能性收缩单位，肌原纤维是横纹肌细胞器，由一系列严格对齐的肌节组成。此外，肌节和肌原纤维中的被动力几乎完全由结构蛋白肌联蛋白产生，并且所有收缩、调节和结构蛋白均处于其自然构型。由于这些力学和结构方面的原因，单个肌节和肌原纤维制剂对于解答横纹肌收缩机制的问题而言，无疑是最强大的工具。在过去20年里，我们开发并优化了单个肌原纤维研究方法，并且是首个对单个肌节进行机械分离和测试的团队。这项研究的结果揭示了肌联蛋白在肌肉收缩中的关键作用，首次从分子层面解释了骨骼肌和心肌被动及残余力增强特性的起源，发现了力-长度关系下降支上肌节长度的稳定性，并最终形成了肌肉收缩的三丝理论，该理论除了肌动蛋白和肌球蛋白外，还提出了肌联蛋白在主动力产生中的关键作用。除了单个肌节和肌原纤维制剂所具备的所有优势和可能性外，也存在一些劣势。这些劣势包括制剂的脆弱性、掌握这些制剂所需的耗时训练、长度和力测量的空间分辨率有限，以及缺乏用于单个肌节/肌原纤维研究的商业系统。忽视控制串联系统的力学原理、不考虑肌原纤维系统的空间分辨率及相关精度，以及忽略肌原纤维制剂的脆弱性，已导致对结果的错误解读和误导性结论。在此，我们将尝试描述单个肌节/肌原纤维研究的方法和可能的应用，并通过关注特定应用来讨论其优缺点。希望这一讨论有助于认清单个肌节/肌原纤维研究在揭示肌肉收缩奥秘方面的巨大潜力。
