Bozler E
J Gen Physiol. 1972 Sep;60(3):239-47. doi: 10.1085/jgp.60.3.239.
Shortening causes a transient decrease, extension an increase, in activity during contractures of the frog ventricle induced by high Ca or by isosmotic K solution. This is shown by the fact that, after the immediate passive shortening, the muscle is extended under isotonic conditions when the load is diminished, and that under isometric conditions quick release causes first a rapid drop, then a further, much slower, fall of tension. Increasing the load or stretching induce the opposite effects. At low temperatures all rapid changes in length produce oscillations of low frequency. These responses are due to a sensitive feedback mechanism similar to that previously demonstrated for insect fibrillar muscle. That this mechanism comes into play in the heart under normal conditions and controls the time-course of the twitch is demonstrated by the observation that relaxation begins earlier the greater the shortening. Thus, during afterloaded isotonic twitches the onset of relaxation is advanced as the load is diminished.
在高钙或等渗钾溶液诱导的青蛙心室挛缩过程中，缩短会导致活性短暂降低，伸展则会使其增加。这表现为以下事实：在立即被动缩短后，当负荷减小时，肌肉在等张条件下被伸展；而在等长条件下，快速释放首先会导致张力迅速下降，随后张力进一步缓慢下降。增加负荷或拉伸会产生相反的效果。在低温下，所有长度的快速变化都会产生低频振荡。这些反应归因于一种敏感的反馈机制，类似于先前在昆虫纤维状肌肉中所证明的机制。正常情况下，这种机制在心脏中起作用并控制抽搐的时间进程，这一点可通过以下观察得到证明：缩短程度越大，松弛开始得越早。因此，在有后负荷的等张抽搐过程中，随着负荷减小，松弛的开始会提前。
