失速条件下肌肉稳定的一种合理机制
A plausible mechanism of muscle stabilization in stall conditions
摘要：
我们解决了Huxley和Simmons 1971（HS）模型的众所周知的局限性。这是一个声明，在肌动球蛋白复合体中的刚度的生理值下，肌球蛋白马达的分布在从失速（等长收缩）条件的无限小位移后变得微观上均匀（所有马达处于动力冲程前或动力冲程后的构象）。在纤维水平上的这种均匀行为将在$T_2-δ$关系中产生负斜率（在HS论文的命名中），这在实验中没有观察到。这种负斜率意味着宏观肌节构型的不均匀性，这也没有观察到。为了解决这一有争议的预测HS理论，我们探讨的可能性，即$T_2-δ$曲线的斜率，事实上，由于相邻的跨桥之间的相互作用是积极的。我们表明，这种相互作用可以潜在地不稳定的均匀配置（所有前或所有后），使非均匀的配置大力优选。我们认为，尽管存在其他因素，原则上也可以确保微观不均匀性的跨桥配置，隐含的相互作用是肌肉力学的一个重要角色。
英文摘要：
We address the well-known limitation of the Huxley and Simmons 1971 (HS) model. It is a statement that at physiological value of stiffness in the actomyosin complex, the distribution of the myosin motors becomes microscopically uniform (all the motors are either in pre- or post-power stroke conformation) after an infinitesimal displacement from the stall (isometric contractions) conditions. Such uniform behavior at the fiber level would generate a negative slope in the $T_2-δ$ relationship (in the nomenclature of the HS paper), not observed experimentally. This negative slope means inhomogeneity of the macroscopic sarcomere configuration, which is also not observed. To address this controversial prediction of the HS theory, we explore the possibility that the slope of the $T_2-δ$ curve is, in fact, positive due to an interaction between neighboring cross-bridges. We show that such interaction can potentially destabilize the uniform configurations (all pre or all post) by making the non-uniform configurations energetically preferable. We argue that, despite the presence of other factors, which can in principle also ensure the microscopic inhomogeneity of cross-bridge configurations, the implied interaction is an important player in muscle mechanics.
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