Eisenberg B R, Brown J M, Salmons S
Cell Tissue Res. 1984;238(2):221-30. doi: 10.1007/BF00217292.
When fast-twitch skeletal muscles of the adult rabbit are subjected to continuous low-frequency activity by electrical stimulation of the corresponding motor nerves, the fibers undergo an ultrastructural transformation, so that after 6 weeks they have acquired an appearance typical of slow-twitch fibers. In the present study, stimulation was discontinued at this stage in order to follow the reverse transformation, in which the fibers recovered their original morphological characteristics under conditions of normal endogenous activity. Stereological techniques were used to assess the time course of this process over a period of 20 weeks in terms of fiber cross-sectional area, extent of T-system, thickness of the Z-band, and volume fraction of mitochondria in the fiber core. Fibers of transformed muscles were smaller than those of control muscles, but the differences were no longer evident after 9 weeks of recovery. After 2 weeks the T-system was still of limited extent, as is characteristic of slow-twitch fibers; it increased toward the amount typical of fast-twitch fibers between 2 and 4 weeks, and had reached its full extent by 12 weeks. The wide Z-bands characteristic of slow-twitch fibers were retained for 4 weeks, but the thickness had begun to decrease by 8 weeks and recovery was complete by 12 weeks. The mitochondrial volume did not increase during recovery, in contrast to the large increases which had been observed to take place between 2 and 6 weeks during the fast-to-slow transformation. Overall, the recovery of fast-twitch ultrastructural characteristics was complete, but followed a more extended time course, and involved less myofibrillar disruption at an intermediate stage, than the original fast-to-slow transformation.
当通过电刺激成年兔相应的运动神经，使其快肌骨骼肌受到持续低频活动刺激时，肌纤维会发生超微结构转变，以至于6周后它们呈现出慢肌纤维的典型外观。在本研究中，在此阶段停止刺激，以追踪逆向转变过程，在此过程中，肌纤维在正常内源性活动条件下恢复其原始形态特征。采用体视学技术，从纤维横截面积、T系统范围、Z带厚度以及纤维核心中线粒体的体积分数等方面，评估了这一过程在20周内的时间进程。转变后肌肉的纤维比对照肌肉的纤维小，但恢复9周后差异不再明显。2周后，T系统的范围仍然有限，这是慢肌纤维的特征；在2至4周之间，它朝着快肌纤维的典型数量增加，到12周时达到其最大范围。慢肌纤维特有的宽Z带保留了4周，但厚度在8周时开始减小，到12周时恢复完全。与在快向慢转变过程中2至6周期间观察到的大幅增加相比，恢复过程中线粒体体积没有增加。总体而言，快肌超微结构特征的恢复是完全的，但比最初的快向慢转变过程耗时更长，且在中间阶段涉及的肌原纤维破坏更少。
