van der Heide U, Ketelaars M, Treijtel B W, de Beer E L, Blangé T
Department of Physiology, University of Amsterdam, Academic Medical Center, The Netherlands.
Biophys J. 1997 Feb;72(2 Pt 1):814-21. doi: 10.1016/s0006-3495(97)78715-0.
Stretch and release experiments carried out on skinned single fibers of frog skeletal muscle under rigor conditions indicate that the elastic properties of the fiber depend on strain. For modulation frequencies below 1000 Hz, the results show an increase in Young's modulus of 20% upon a stretch of 1 nm/half-sarcomere. Remarkably, the strain dependence of Young's modulus decreases at higher frequencies to about 10% upon a 1-nm/half-sarcomere stretch at a modulation frequency of 10 kHz. This suggests that the cause of the effect is less straightforward than originally believed: a simple slackening of the filaments would result in an equally large strain dependence at all frequencies, whereas strain-dependent properties of the actin filaments should show up most clearly at higher frequencies. We believe that the reduction of the strain dependence points to transitions of the cross-bridges between distinct force-producing states. This is consistent with the earlier observation that Young's modulus in rigor increases toward higher frequencies.
在僵直条件下对青蛙骨骼肌的去皮单纤维进行的拉伸和释放实验表明，纤维的弹性特性取决于应变。对于低于1000 Hz的调制频率，结果显示在每半个肌节拉伸1 nm时，杨氏模量增加20%。值得注意的是，在10 kHz的调制频率下，每半个肌节拉伸1 nm时，杨氏模量的应变依赖性在较高频率下降低至约10%。这表明该效应的原因比最初认为的要复杂：细丝的简单松弛将导致在所有频率下具有同样大的应变依赖性，而肌动蛋白丝的应变依赖性特性应该在较高频率下最明显地表现出来。我们认为，应变依赖性的降低表明横桥在不同的力产生状态之间发生了转变。这与早期观察到的僵直状态下杨氏模量随频率升高而增加是一致的。
