Tamura Y, Hatta I, Sugi H
Department of Physics, Suzuka College of Technology.
Adv Exp Med Biol. 1988;226:541-51.
We have developed a technique with which muscle stiffness changes during isometric contraction can be continuously recorded by measuring the propagation velocity of ultrasonic waves with negligibly small perturbations to the contractile system, and obtained an unexpected result that, during isometric contraction, muscle stiffness decreased in the transverse direction while it increased in the longitudinal direction. In the present study, we measured the stiffness of frog skeletal muscle with ultrasonic waves at various sarcomere lengths from 2.2 to more than 3.6 microns, and found that (1) the resting muscle stiffness is insensitive to the resting force development in both the longitudinal and the transverse directions, and (2) the absolute amount of both the longitudinal and the transverse stiffness changes during isometric tetanus decreased linearly with increasing sarcomere length, approaching zero at 3.6-3.8 microns sarcomere lengths. These results indicate that the stiffness changes measured with ultrasonic waves reflect the changes in the number of cross-links between the myofilaments.
我们开发了一种技术，通过测量超声波的传播速度，可以在对收缩系统的扰动可忽略不计的情况下，连续记录等长收缩过程中肌肉硬度的变化，并得到了一个意想不到的结果：在等长收缩过程中，肌肉在横向方向上的硬度降低，而在纵向方向上增加。在本研究中，我们在2.2至3.6微米以上的各种肌节长度下，用超声波测量了青蛙骨骼肌的硬度，发现：（1）静息肌肉硬度在纵向和横向方向上对静息力的发展均不敏感；（2）等长强直收缩过程中，纵向和横向硬度变化的绝对量均随肌节长度增加而线性下降，在肌节长度为3.6 - 3.8微米时接近零。这些结果表明，用超声波测量的硬度变化反映了肌丝之间交联数量的变化。
