Pagala M K
Biochim Biophys Acta. 1980 Jun 10;591(1):177-86. doi: 10.1016/0005-2728(80)90231-5.
In an isometric tetanus of frog sartorius muscle the total relaxation time increased linearly with change in length from 0.7 to 1.4 times rest length. Maximal rate of relaxation, measured from the time derivative (dp/dt) of tension decay, decreased with both decrease and increase from rest length in correlation with the generated tetanus tension. Stretching the muscle did not significantly affect the times to maximal rate, positive and negative inflexion points but greatly increased the time to total relaxation from the negative inflexion point. Caffeine at 2 mM, acting on muscles at rest length, also slowed the relaxation and decreased the maximal rate of tension decay. However, caffeine increased the times to maximal rate, positive and negative inflexion points without significantly affecting time to total relaxation from the negative inflexion point. These results suggest that caffeine slows an earlier step in relaxation, while stretch slows a later step. It is proposed that muscle relaxation is a two step process: an initial step that is regulated by the rate of Ca2+ uptake by sarcoplasmic reticulum, and a later step that is mostly controlled by the speed of dissociation of remaining cross-bridges.
在青蛙缝匠肌的等长强直收缩中，总舒张时间随长度从静息长度的0.7倍变化至1.4倍而呈线性增加。从张力衰减的时间导数（dp/dt）测得的最大舒张速率，随着与产生的强直收缩张力相关的静息长度的减小和增加而降低。拉伸肌肉对达到最大速率、正拐点和负拐点的时间没有显著影响，但从负拐点到总舒张的时间大幅增加。2 mM的咖啡因作用于静息长度的肌肉时，也会减慢舒张并降低张力衰减的最大速率。然而，咖啡因增加了达到最大速率、正拐点和负拐点的时间，而对从负拐点到总舒张的时间没有显著影响。这些结果表明，咖啡因减慢了舒张的较早步骤，而拉伸减慢了较晚步骤。有人提出，肌肉舒张是一个两步过程：第一步由肌浆网摄取Ca2+的速率调节，第二步主要由剩余横桥解离的速度控制。
