Vergara J L, Rapoprot S I, Nassar-Gentina V
Am J Physiol. 1977 May;232(5):C185-90. doi: 10.1152/ajpcell.1977.232.5.C185.
At 15 degrees C, direct stimulation of frog single muscle fibers at a frequency of 20 Hz produced a tetanic tension that remained constant for 20 s and then declined. The decline was reversed during 1-s interruptions of the stimulus train in the first 50 s of stimulation, but not with longer stimulation. Posttetanic potentiation (PTP), characterized by prolonged twitch relaxation and contraction times and elevation of twitch height, remained for 10-40 min after a 10-s tetanus and for at least 90 min after a 50- to 150-s tetanus. Posttetanic fatigue appeared only after at least 50s of tetanic stimulation. Fatigue was manifested invariably by a reduction in the height of a 200-ms tetanic contraction and usually by a reduction in twitch height after PTP. Fatigued fibers recovered normal contractile responses in 40-160 min. Hypertonic solutions, which blocked contraction in response to tetanic stimulation, prevented posttetanic fatigue but not PTP. The observations suggest that fatigue is caused by a failure in excitation-contraction coupling, probably in relation to consumption of metabolic substrates. Even 10-s tetani which do not produce fatigue can affect muscle contractile function for up to 40 min.
在15摄氏度时，以20赫兹的频率直接刺激青蛙单根肌纤维会产生强直张力，该张力在20秒内保持恒定，然后下降。在刺激的前50秒内，当刺激序列中断1秒时，这种下降会逆转，但刺激时间更长时则不会。强直后增强（PTP）表现为抽搐舒张和收缩时间延长以及抽搐高度升高，在10秒强直刺激后持续10 - 40分钟，在50至150秒强直刺激后至少持续90分钟。强直后疲劳仅在至少50秒的强直刺激后出现。疲劳总是表现为200毫秒强直收缩高度降低，通常在PTP后抽搐高度也降低。疲劳的纤维在40 - 160分钟内恢复正常收缩反应。高渗溶液可阻断对强直刺激的收缩反应，能预防强直后疲劳，但不能预防PTP。这些观察结果表明，疲劳是由兴奋 - 收缩偶联失败引起的，可能与代谢底物的消耗有关。即使是不产生疲劳的10秒强直刺激也能在长达40分钟内影响肌肉收缩功能。
