Blangé T, van der Heide U A, Treijtel B W, de Beer E L
University of Amsterdam, Department of Physiology, The Netherlands.
J Muscle Res Cell Motil. 1997 Apr;18(2):125-31. doi: 10.1023/a:1018649420778.
Recently, X-ray diffraction studies provided direct evidence for an appreciable length change in the actin filament upon activation. This finding has profound implications on the interpretation of the elastic properties of skeletal muscle fibre. In this study we determined the compliance of the actin filament during activation, using the data obtained previously from quick stretch and release experiments on skeletal muscle fibres of the frog. The effects of filament compliance are demonstrated clearly in the elastic properties of partially activated fibres. The low-frequency elasticity increases linearly with tension, reflecting an increase in the number of force-producing cross-bridges. At higher frequencies, this linearity is lost. In this study we describe the data consistently in terms of a cross-bridge stiffness increasing linearly with tension and a constant Young's modulus for the actin filament of 44 MN m-2. This corresponds to a compliance of 23 pm microns-1 per kN m-2 tension developed. Using this value for the actin filament Young's modulus, its contribution to the elastic properties of skeletal muscle fibre of the frog is considered in rigor and relaxation. The filament compliance hardly affects the overall elasticity of the muscle fibre in relaxation. In contrast, it contributes to a large extent to the overall elasticity in rigor. Taking account of the filament compliance, we find that the Young's modulus in rigor exhibits an increase from 14 MN m-2 at frequencies below 500 Hz to 55 MN m-2 above 40 kHz.
最近，X射线衍射研究为肌动蛋白丝在激活时发生明显的长度变化提供了直接证据。这一发现对骨骼肌纤维弹性特性的解释具有深远意义。在本研究中，我们利用先前从青蛙骨骼肌纤维的快速拉伸和释放实验中获得的数据，确定了激活过程中肌动蛋白丝的顺应性。在部分激活的纤维的弹性特性中，丝顺应性的影响得到了清晰的证明。低频弹性随张力呈线性增加，反映了产生力的横桥数量的增加。在较高频率下，这种线性关系消失。在本研究中，我们根据横桥刚度随张力线性增加以及肌动蛋白丝的杨氏模量恒定为44 MN m-2来一致地描述这些数据。这对应于每产生1 kN m-2张力时23 pm μm-1的顺应性。利用这个肌动蛋白丝杨氏模量值，在强直收缩和舒张状态下考虑了其对青蛙骨骼肌纤维弹性特性的贡献。在舒张状态下，丝顺应性几乎不影响肌肉纤维的整体弹性。相比之下，在强直收缩状态下，它在很大程度上对整体弹性有贡献。考虑到丝顺应性，我们发现强直收缩状态下的杨氏模量在频率低于500 Hz时从14 MN m-2增加到高于40 kHz时的55 MN m-2。
