Williams J H
Muscular Function Laboratory, Virginia Polytechnic Institute and State University, Blacksburg.
Muscle Nerve. 1990 Dec;13(12):1118-24. doi: 10.1002/mus.880131206.
The purpose of this investigation was to determine the effects of low extracellular calcium and calcium antagonists on skeletal muscle staircase and fatigue. Initial experiments revealed that, brief exposure (10 minutes) of single frog sartorius muscle to diltiazem, D-600 (5 and 30 microM) and low calcium Ringer's solution (LCR, calcium replaced by magnesium and EGTA) had little effect on isometric twitches evoked every 30 seconds. However, when stimulated at 1 per second for 15 minutes, the calcium antagonists significantly decreased the magnitude and time course of the staircase, whereas LCR decreased only the time course. Each experimental condition significantly increased the rate of fatigue while diltiazem and D-600 both increased the magnitude of fatigue. Following the stimulation period, caffeine (10 mM) elicited contractures from all muscles whereas high potassium (180 mM) elicited contractures from control muscles only. These results indicate that calcium channel antagonists depress the skeletal muscle staircase response. They also indicate that these compounds as well as LCR enhance the fatigue process. Extracellular calcium influx may therefore have some influence on skeletal muscle twitches during prolonged repetitive activity.
本研究的目的是确定低细胞外钙和钙拮抗剂对骨骼肌阶梯现象和疲劳的影响。初步实验表明，将单个青蛙缝匠肌短暂暴露（10分钟）于地尔硫䓬、D - 600（5和30微摩尔）以及低钙林格氏液（LCR，钙被镁和乙二醇双四乙酸取代），对每30秒诱发的等长收缩几乎没有影响。然而，当以每秒1次的频率刺激15分钟时，钙拮抗剂显著降低了阶梯现象的幅度和时程，而LCR仅降低了时程。每种实验条件都显著增加了疲劳速率，而地尔硫䓬和D - 600都增加了疲劳幅度。在刺激期后，咖啡因（10毫摩尔）能使所有肌肉产生挛缩，而高钾（180毫摩尔）仅能使对照肌肉产生挛缩。这些结果表明，钙通道拮抗剂会抑制骨骼肌阶梯反应。它们还表明，这些化合物以及LCR会增强疲劳过程。因此，在长时间重复活动期间，细胞外钙内流可能对骨骼肌收缩有一定影响。
