TENSION RESPONSES TO SUDDEN LENGTH CHANGE IN STIMULATED FROG MUSCLE-FIBERS NEAR SLACK LENGTH
TENSION RESPONSES TO SUDDEN LENGTH CHANGE IN STIMULATED FROG MUSCLE-FIBERS NEAR SLACK LENGTH
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DOI：
10.1113/jphysiol.1977.sp011911
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发表时间：
1977-01-01
影响因子：
5.5
通讯作者：
SIMMONS, RM
中科院分区：
文献类型：
--
作者：
FORD, LE;HUXLEY, AF;SIMMONS, RM
描述了用于将长度的阶跃变化应用于分离的肌纤维的设备。该步骤是在约0.2毫秒内完成的。肌腱顺应性的影响被消除，通过使用一个点跟随器设备，并通过夹紧肌腱与金属夹靠近光纤端部。力传感器的固有频率> 10 kHz。在强直刺激过程中，将各种幅度和任一方向的步骤施加到约6 mm长的蛙胫前肌分离肌纤维。初始肌节长度为2.0-2.2 μ m，温度为0 - 3 ℃。C.对一个台阶的张力反应分为4个阶段。最初的反应是一个明显的弹性变化，在步骤本身（阶段1）。在步骤完成之后，存在朝向原始张力的快速部分恢复（阶段2，持续2-5 ms），随后是恢复的减慢或逆转（阶段3，10-50 ms），并且最后是慢得多的返回到原始张力（阶段4）。初始张力变化（阶段1）与施加的长度变化同步发生，表明纤维具有几乎线性且几乎无阻尼的柔顺性。它的刚度是这样的，约4纳米/半肌节的瞬时缩短带来的张力从其等距值为0。在阶段1期间没有可检测到的阻尼表明受激纤维的粘度基本上小于静止时纤维的表观粘度。瞬时力-伸长曲线以锐角接近长度轴，并且当施加非常大的步长时，在力传感器处出现负张力。负责纤维刚度的结构在不受张力时保持刚性。在步骤（阶段2）之后的几ms内，张力恢复到步骤之前存在的水平的一部分。在缩短步骤中，该恢复的时间过程由4个指数项的总和充分拟合，并且在不同幅度的步骤中相似，但时间尺度缩短，步骤越大。在伸展运动中，缓慢的成分相对大于释放。在第2阶段接近的张力水平T2仅取决于步骤的总振幅，而不取决于长度变化的时间过程，只要它在1-2 ms内完成。因此，在步骤期间达到的极端张力可能变化很大，而T2没有可检测到的变化。随着约3 nm/半肌节的伸展和释放，这一早期发现几乎完成，因此T2对阶跃幅度的曲线几乎是水平的。随着较大的释放，线向下弯曲，在约14 nm/半肌节的释放中达到0。当温度升高时，所产生的张力和刚度均增加，但张力的相对增加大于刚度的相对增加。因此，使张力达到0所需的瞬时缩短量也增加了。给出了一组经验方程，描述了响应于任何施加的缩短时间过程的张力变化的前几个ms。快速弹性和早期张力恢复类似于2个弹性组分和1个粘性组分的组合的响应。原因给出了更好的解释，在一个无阻尼的遵守与阻尼的遵守（Voigt元素），而不是一个无阻尼的弹性并联的粘性和弹性组件（麦克斯韦元素）的串联组合。快速顺应性不对应于肌肉收缩的2分量理论的系列弹性分量。
Apparatus for applying a step change of length to an isolated muscle fiber is described. The step was complete in about 0.2 ms. Effects of tendon compliance were eliminated by using a spot-follower device and by gripping the tendons with metal clips close to the fiber ends. The natural frequency of the force transducer was > 10 kHz. Steps of various amplitudes and in either direction were applied to isolated muscle fibers about 6 mm long from the anterior tibial muscle of Rana temporaria during tetanic stimulation. Initial sarcomere length was 2.0-2.2 .mu.m, and temperature was 0-3.degree. C. The tension response to a step was divided into 4 phases. The initial response was an apparently elastic change during the step itself (phase 1). After the step was completed there was a rapid partial recovery toward the original tension (phase 2, lasting 2-5 ms), followed by a slowing or reversal of recovery (phase 3, 10-50 ms) and finally a much slower return to the original tension (phase 4). The initial tension change (phase 1) occurred synchronously with the applied length change, indicating that the fibers possessed a compliance which was almost linear and almost undamped. Its stiffness was such that an instantaneous shortening of about 4 nm/half-sarcomere brought the tension to 0 from its isometric value. The absence of detectable damping during phase 1 indicated that the viscosity of a stimulated fiber was substantially less than the apparent viscosity of a fiber at rest. The instantaneous force-extension curve approached the length axis at a sharp angle and a negative tension appeared at the force transducer when a very large step was applied. The structures responsible for the stiffness of the fiber remained rigid when they were not under tension. Within few ms after the step (phase 2) the tension recovered part of the way toward the level which existed before the step. In shortening steps the time course of this recovery was adequately fitted by the sum of 4 exponential terms and was similar in steps of different amplitude but with a time scale shorting, the larger the step. In stretches the slow components were relatively larger than in releases. The tension level, T2, approached during phase 2 depended only on the total amplitude of the step and not on the time course of the length change, provided it was complete in 1-2 ms. The extreme tension reached during a step could thus vary widely without detectable change in T2. With stretches and releases of up to approximately 3 nm/half-sarcomere this early discovery was almost complete, so that the curve of T2 against step amplitude was nearly horizontal. With larger releases the line curved downwards, reaching 0 in a release of about 14 nm/half-sarcomere. When the temperature was raised both the developed tension and the stiffness increased, but the relative increase was greater for tension than for stiffness. The amount of instantaneous shortening needed to bring tension to 0 was therefore also increased. A set of empirical equations is given which described the 1st few ms of the tension change in response to any imposed time course of shortening. The rapid elasticity and early tension recovery resemble the response of a combination of 2 elastic components and 1 viscous component. Reasons are given for preferring an interpretation in terms of an undamped compliance in series with a damped compliance (Voigt element) rather than an undamped elasticity in parallel with a series combination of viscous and elastic components (Maxwell element). The rapid compliance did not correspond to the series elastic component of 2-component theories of muscle contraction.