MacIntosh B R, Roberge M C, Gardiner P F
Department of Exercise Science, Concordia University, Montréal, Qué., Canada.
Can J Physiol Pharmacol. 1988 Jun;66(6):707-13. doi: 10.1139/y88-113.
Repetitive stimulation of mammalian fast-twitch skeletal muscles will normally result in a positive staircase response. This phenomenon was investigated in the rat gastrocnemius muscle following a 2-week period of tetrodotoxin-induced disuse. Muscle inactivity was imposed by superfusing tetrodotoxin in saline over the left sciatic nerve via an implanted osmotic pump. In situ isometric contractile responses to double pulse stimulation and repetitive stimulation at 10 Hz were determined the day after removal of the pump. Two weeks of disuse resulted in 40% muscle weight loss. A twitch contraction gave the same force when expressed per gram of wet muscle weight in control muscles, 317 +/- 24.6 (means +/- SE) g/g, as compared with tetrodotoxin-treated muscles, 328 +/- 24.2 g/g. Both contraction time and half-relaxation time were prolonged following treatment with tetrodotoxin. Repetitive stimulation at 10 Hz resulted in a positive staircase response in the control muscles, but not in muscles of the tetrodotoxin-treated rats. The observed changes in the time course of the twitch contraction with repetitive stimulation following tetrodotoxin-induced disuse are consistent with alterations in sarcoplasmic reticulum handling of calcium. It is not certain if there is a change following disuse in the mechanism normally associated with staircase or if this mechanism is merely opposed by an early fatigue.
对哺乳动物快肌骨骼肌进行重复刺激通常会产生正向阶梯反应。在河豚毒素诱导废用2周后的大鼠腓肠肌中研究了这一现象。通过植入的渗透泵将含河豚毒素的盐水灌注到左侧坐骨神经上，从而使肌肉失活。在移除泵后的第二天，测定了原位等长收缩对双脉冲刺激和10 Hz重复刺激的反应。两周的废用导致肌肉重量减轻40%。以每克湿肌肉重量表示时，对照肌肉的单收缩产生的力量为317±24.6（平均值±标准误）g/g，与河豚毒素处理的肌肉（328±24.2 g/g）相同。用河豚毒素处理后，收缩时间和半松弛时间均延长。10 Hz的重复刺激在对照肌肉中产生了正向阶梯反应，但在河豚毒素处理的大鼠肌肉中未产生。河豚毒素诱导废用后，单收缩时间过程随重复刺激的变化与肌浆网对钙的处理改变一致。尚不确定废用后通常与阶梯现象相关的机制是否发生了变化，或者该机制是否仅仅被早期疲劳所抵消。
