Celichowski Jan, Bichler Edyta
Department of Neurobiology, University School of Physical Education, 55 Grunwaldzka St., 60-352 Poznań, Poland.
Acta Neurobiol Exp (Wars). 2002;62(1):7-17. doi: 10.55782/ane-2002-1413.
The time course of the contraction and the relaxation of individual contractions during incompletely fused tetani of motor units were analyzed. Investigations were performed on fast fatigable (FF), fast resistant (FR) and slow (S) motor units of the rat medial gastrocnemius muscle. Stimulation of a motor unit with a series of nine trains of stimuli at a frequency from 10 to 150 Hz was used and tetani fused to a variable degree were recorded. For fast motor units the procedure was repeated twice and observations were made on potentiated tetani in the second series of stimulation. For each tetanus, the amplitude of the tension increase, the peak amplitude of the contraction, the contraction time and the half-relaxation time were measured in the last contraction of the tension recording. It was observed in all three types of motor units that the last contraction was prolonged in parallel with the increase of fusion of a tetanus. In this contraction, the contraction time slightly decreased whereas the half-relaxation time strongly prolonged. The prolongation of the half-relaxation time was the strongest in tetani of slow units. Moreover, for the last contraction in a tetanus, the rate of changes in tension were studied. The rate of increase in tension during the contraction decreased in parallel with the increase of fusion of a tetanus, whereas the maximal rate of the tension decrease during the relaxation was found in tetani with fusion indices of 0.79, 0.98 and 0.95 for FF, FR and S motor units, respectively. Changes in the time course of contractions in tetani fused to a variable degree can shed light on processes of summation of contractions in unfused tetani at the level of individual motor units.
分析了运动单位不完全融合强直收缩期间单个收缩的收缩和舒张的时间进程。对大鼠腓肠肌内侧的快速易疲劳（FF）、快速抗疲劳（FR）和慢速（S）运动单位进行了研究。采用一系列九组刺激，频率从10至150Hz刺激运动单位，并记录不同程度融合的强直收缩。对于快速运动单位，该过程重复两次，并在第二系列刺激中对增强的强直收缩进行观察。对于每次强直收缩，在张力记录的最后一次收缩中测量张力增加的幅度、收缩的峰值幅度、收缩时间和半舒张时间。在所有三种类型的运动单位中均观察到，最后一次收缩随着强直收缩融合程度的增加而延长。在这次收缩中，收缩时间略有缩短，而半舒张时间则显著延长。半舒张时间的延长在慢速运动单位的强直收缩中最为明显。此外，对于强直收缩中的最后一次收缩，研究了张力的变化率。收缩期间张力增加的速率随着强直收缩融合程度的增加而降低，而在FF、FR和S运动单位中，融合指数分别为0.79、0.98和0.95的强直收缩中，发现舒张期间张力降低的最大速率。不同程度融合的强直收缩中收缩时间进程的变化可以揭示单个运动单位水平上未融合强直收缩中收缩总和的过程。
