Bateson D S, Parry D J
J Physiol. 1983 Dec;345:515-23. doi: 10.1113/jphysiol.1983.sp014993.
Isometric contractions of motor units, isolated functionally by ventral root splitting were recorded from extensor digitorum longus muscles of normal and dystrophic mice of the strain C57BL/6J dy2J/dy2J. Motor unit tetanic tension was significantly lower and both time to peak tension and to half-relaxation of the twitch were significantly prolonged in dystrophic mice relative to age-matched controls. In control mice, motor unit tetanic tension averaged 4.98% of whole muscle tension, corresponding to twenty motor units. Two out of fifteen dystrophic mice exhibited an apparent decrease in the number of motor units, but the data from the remaining thirteen mice indicated no change in relative motor unit size, and hence in the number of motor units. The two mice in which changes were seen were the most severely affected and it is suggested that the apparent reduction in the number of units might be due to some units becoming so small as to be unmeasurable. No evidence was obtained for a population of units with normal characteristics within the dystrophic muscles. There was no clear relationship between tetanic tension and the time to peak tension or to half-relaxation in units from control mice. In dystrophic mice, however, a significant correlation was seen. This possibly reflects two simultaneous effects of the dystrophic process, a loss of tension accompanied by slowing of the twitch.
通过腹根分离在功能上分离出运动单位，记录了C57BL/6J dy2J/dy2J品系正常和营养不良小鼠的趾长伸肌的等长收缩。与年龄匹配的对照相比，营养不良小鼠的运动单位强直张力显著降低，并且单收缩的峰值张力时间和半松弛时间均显著延长。在对照小鼠中，运动单位强直张力平均为全肌肉张力的4.98%，相当于20个运动单位。15只营养不良小鼠中有2只表现出运动单位数量明显减少，但其余13只小鼠的数据表明相对运动单位大小没有变化，因此运动单位数量也没有变化。观察到变化的这两只小鼠受影响最严重，提示单位数量的明显减少可能是由于一些单位变得太小而无法测量。在营养不良的肌肉中未获得具有正常特征的单位群体的证据。对照小鼠单位的强直张力与峰值张力时间或半松弛时间之间没有明显关系。然而，在营养不良小鼠中，观察到显著相关性。这可能反映了营养不良过程的两种同时出现的效应，即张力丧失伴随着单收缩减慢。
