The mechanisms of force enhancement during constant velocity lengthening in tetanized single fibres of frog muscle.
The mechanisms of force enhancement during constant velocity lengthening in tetanized single fibres of frog muscle.
复制标题
蛙肌强直单纤维等速拉长过程中力增强的机制。
DOI：
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发表时间：
1988
影响因子：
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通讯作者：
G. Piazzesi
中科院分区：
文献类型：
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作者：
F. Colomo;V. Lombardi;G. Piazzesi
本文讨论了响应于等长强直收缩平台上施加的等速延长而导致力增强的机制。实验在 3.5-5.6 摄氏度下对从青蛙胫骨前肌分离的单纤维进行。静止肌节长度约为2.15微米。在力对延长的响应特征中观察到的大变化以及因此在力-延长速度关系的形状中观察到的大变化主要由肌纤维的纵向不均匀程度决定。沿着它们选择的“同质”纤维和单个“无腱段”表现出可叠加的力-延长速度关系，且形状变化可忽略不计。刚度和力随着延长而增加，达到近似稳定值，分别比等长破伤风平台时大 10-15% 和 60-70%，速度约为每半肌节 (hs) 0.1 微米/秒。在较高的延长速度下，刚度实际上保持不变，而力响应的稳定分量继续增加，渐进地达到最大值，比等长破伤风平台时的值大约 100%，速度在约 0.5 至 1 微米/秒/小时之间。达到峰值所需的伸长量对于刚度（10 nm/hs）小于力（12-14 nm/hs）。根据A. F. Huxley 1957年的模型，结果表明，延长（i）通过增加附着的横桥的数量和延伸程度来增强肌肉的机械输出，（ii）提高横桥附着和分离的速度。
The present paper deals with the mechanism responsible for the force enhancement in response to constant velocity lengthenings imposed at the plateau of isometric tetanic contractions. Experiments were performed at 3.5-5.6 degrees C on single fibres isolated from the tibialis anterior muscle of the frog. The resting sarcomere length was about 2.15 microns. The large variation observed in the characteristics of the force responses to lengthening and therefore in the shape of the force-lengthening velocity relations is mainly determined by the degree of longitudinal dishomogenities of muscle fibres. "Homogeneous" fibres and individual "tendon-free segments" selected along them exhibited superimposable force-lengthening velocity relations with negligible shape variation. Stiffness and force increased with lengthening, reaching, approximately steady values, respectively 10-15% and 60-70% greater than at the isometric tetanus plateau, at velocities of about 0.1 micron/s per half-sarcomere (hs). At higher lengthening velocities stiffness remained practically unvaried, whereas the steady component of the force responses continued to increase, reaching asymptotically a maximum value, about 100% greater than at the isometric tetanus plateau, at velocities between about 0.5 and 1 micron/s per hs. The amount of lengthening required to attain the peak value was smaller for stiffness (10 nm per hs) than for force (12-14 nm per hs). In terms of 1957 model of A. F. Huxley, the results indicate that lengthening (i) potentiates the mechanical output of muscle by increasing the number and the degree of extension of attached cross-bridges, (ii) enhances the speed of cross-bridge attachment and detachment.