Dipartimento di Scienze Fisiologiche, Università degli Studi di Firenze, Firenze, Italy.
Biophys J. 2009 Dec 2;97(11):2922-9. doi: 10.1016/j.bpj.2009.09.018.
Force generation and movement in skeletal muscle result from a cyclical interaction of overlapping myosin and actin filaments that permits the free energy of ATP hydrolysis to be converted into mechanical work. The rapid force recovery that occurs after a step release imposed on a muscle is thought to result from a synchronized tilting of myosin lever arms toward a position of lower free energy (the power stroke). We investigated the power stroke mechanism in intact muscle fibers of Rana esculenta using a fast stretch to detach forcibly cross-bridges. Stretches were applied either with or without a conditioning step release. Cross-bridge rupture tension was not significantly influenced by the release, whereas sarcomere elongation at the rupture point increased immediately after the release and returned to the prerelease condition within 15-20 ms, following a slower time course compared to the recovery of tension. These observations suggest that the rupture force of a bridge is unaltered by a conditioning release, but rupture must first be preceded by a power stroke reversal, which restores the prepower stroke state. The sarcomere extension at the rupture point indicates both the extent of this power stroke reversal and the time course of strained bridge replenishment.
骨骼肌中的力生成和运动是由肌球蛋白和肌动蛋白丝的周期性相互作用引起的，这种相互作用允许 ATP 水解的自由能转化为机械功。在对肌肉施加阶跃释放后，快速恢复力被认为是由于肌球蛋白杠杆臂向低自由能位置（力冲程）的同步倾斜引起的。我们使用快速拉伸来强行分离交联桥，研究了完整的牛蛙肌纤维中的力冲程机制。拉伸要么在有条件的释放之前施加，要么在有条件的释放之后施加。释放对交联桥断裂张力没有显著影响，而在释放点处的肌节伸长立即增加，并在 15-20ms 内恢复到释放前的状态，与张力恢复相比，时间过程较慢。这些观察结果表明，条件释放不会改变桥的断裂力，但断裂必须首先由力冲程反转来完成，力冲程反转恢复了预力冲程状态。断裂点处的肌节延伸表明了这种力冲程反转的程度和应变桥补充的时间过程。
