Brown I E, Loeb G E
Department of Physiology. Queen's Ulniversity, Kingston, ON, Canada.
J Muscle Res Cell Motil. 2000 Jan;21(1):21-31. doi: 10.1023/a:1005619014170.
Stretch-induced force enhancement and shortening-induced force depression were examined in fast-twitch feline caudofemoralis muscle at 37 degrees C. These phenomena were induced by applying ramp length changes during the first 100--200 ms of an otherwise isometric contraction. The effects of various stimulus frequencies ranging from 30 to 120 pps were investigated over lengths ranging from 0.85 to 1.15 L0. Distributed asynchronous stimulation of bundles of ventral roots was employed to produce smooth contractions at sub-tetanic stimulus frequencies in whole muscle. Of the two components of force enhancement identified by Noble (1992) we observed only the transient component that decays with time; we did not observe residual force enhancement. The force depression that we observed was symmetrical in almost all respects to the transient force enhancement, and was unlike the shortening-induced de-activation and residual force depression identified by Edman (Edman. 1975; Edman et al., 1993). Both transient force enhancement and depression were independent of work, load and activation. Reversals in the direction of ramp length changes following either an initial stretch or initial shortening were shown to cancel the effects of both transient force enhancement and transient force depression. The distances over which these cancellations could be achieved were different for the lengthening and shortening effects. This asymmetry can be reconciled with the predictions of Huxley's original cross-bridge mechanism by incorporating the recent suggestion that myosin heads can interact with multiple actin binding sites during a single 'working' stroke. We conclude that the types of force enhancement/ depression that are most likely to be encountered under physiological conditions are the transient effects observed here, but that even these will have relatively little effect on force production during most natural behaviors.
在37摄氏度下，对快速收缩的猫科动物股后肌进行了拉伸诱导的力增强和缩短诱导的力降低实验。这些现象是在等长收缩的最初100 - 200毫秒内施加斜坡长度变化而诱发的。研究了在0.85至1.15 L0范围内，各种30至120次/秒刺激频率的影响。采用对腹侧神经根束进行分布式异步刺激，以在全肌肉的亚强直刺激频率下产生平滑收缩。在Noble（1992年）确定的力增强的两个组成部分中，我们只观察到随时间衰减的瞬态部分；我们没有观察到残余力增强。我们观察到的力降低在几乎所有方面都与瞬态力增强对称，并且与Edman（Edman，1975年；Edman等人，1993年）确定的缩短诱导的失活和残余力降低不同。瞬态力增强和降低都与功、负荷和激活无关。在初始拉伸或初始缩短后，斜坡长度变化方向的反转被证明可以消除瞬态力增强和瞬态力降低的影响。对于延长和缩短效应，实现这些抵消的距离是不同的。通过纳入最近的建议，即肌球蛋白头部在单个“工作”冲程中可以与多个肌动蛋白结合位点相互作用，这种不对称性可以与赫胥黎原始横桥机制的预测相协调。我们得出结论，在生理条件下最可能遇到的力增强/降低类型是这里观察到的瞬态效应，但即使是这些效应在大多数自然行为中对力产生的影响也相对较小。
