In a contracting muscle, myosin cross-bridges extending from thick filaments pull the interdigitating thin (actin-containing) filaments during cyclical ATP-driven interactions toward the center of the sarcomere, the structural unit of striated muscle. Cross-bridge attachments in the sarcomere have been reported to exhibit a similar stiffness under both positive and negative forces. However, in vitro measurements on filaments with a sparse complement of heads detected a decrease of the cross-bridge stiffness at negative forces attributed to the buckling of the subfragment 2 tail portion. Here, we review some old and new data that confirm that cross-bridge stiffness is nearly linear in the muscle filament lattice. The implications of high myosin stiffness at positive and negative strains are considered in muscle fibers and in nonmuscle intracellular cargo transport.

中文翻译：

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理顺肌球蛋白跨桥的弹性

在收缩的肌肉中，在 ATP 驱动的周期性相互作用中，从粗肌丝延伸出来的肌球蛋白跨桥将叉指状的细肌丝（含有肌动蛋白）拉向肌节（横纹肌的结构单位）的中心。据报道，肌节中的跨桥附件在正力和负力下都表现出相似的刚度。然而，对具有稀疏头部的细丝的体外测量发现，由于子片段 2 尾部的屈曲，在负力下跨桥刚度降低。在这里，我们回顾了一些新旧数据，这些数据证实了横桥刚度在肌肉丝晶格中几乎是线性的。在肌纤维和非肌肉细胞内货物运输中考虑了正应变和负应变下高肌球蛋白硬度的影响。