Tsuchiya T, Sugi H
Department of Physiology, School of Medicine, Teikyo University, Tokyo, Japan.
Adv Exp Med Biol. 1988;226:503-11.
The mechanism of the enhancement and the deficit of isometric force in response to slow length changes in tetanized frog muscle fibers was studied by recording the stiffness changes with sinusoidal vibrations (0.5-1.9 kHz, peak-to-peak amplitude 0.1% of L0). When a tetanized fiber was slowly stretched, the fiber stiffness first rose abruptly and then decreased linearly while the stretch went on; after the completion of stretch, the stiffness decreased towards a steady value which was equal to that during the ordinary isometric tetanus at the same fiber length, though the force decayed towards a steady level higher than that of the ordinary isometric tetanus at the same fiber length. This indicates that the enhancement of isometric force after stretch is associated with decreased stiffness. If, on the other hand, a tetanized fiber was slowly released, the force and the stiffness changed in parallel with each other. Recordings of the segmental length changes along the fiber with a high-speed video system (200 frames/s) indicated that all the segments lengthened in response to slow stretch, while the segmental length changes in response to slow release was markedly nonuniform. These results are discussed in connection with the cross-bridge performance and the filament-lattice structures.
通过记录正弦振动（0.5 - 1.9千赫兹，峰峰值振幅为L0的0.1%）时的刚度变化，研究了强直收缩的青蛙肌肉纤维在缓慢长度变化时等长力增强和减弱的机制。当一个强直收缩的纤维被缓慢拉伸时，纤维刚度首先急剧上升，然后在拉伸持续时线性下降；拉伸完成后，刚度朝着一个稳定值下降，该稳定值与相同纤维长度下普通等长强直收缩时的刚度相等，尽管力朝着一个高于相同纤维长度下普通等长强直收缩时的稳定水平衰减。这表明拉伸后等长力的增强与刚度降低有关。另一方面，如果一个强直收缩的纤维被缓慢释放，力和刚度相互平行变化。用高速视频系统（200帧/秒）记录沿纤维的节段长度变化表明，所有节段在缓慢拉伸时都会伸长，而在缓慢释放时节段长度变化明显不均匀。结合横桥性能和细丝晶格结构对这些结果进行了讨论。
