Jung D W, Blangé T, de Graaf H, Treijtel B W
Department of Physiology, University of Amsterdam, The Netherlands.
Pflugers Arch. 1992 Apr;420(5-6):434-45. doi: 10.1007/BF00374617.
Tension transients, in response to small and rapid length changes (completed within 40 microseconds), were obtained from skinned single frog muscle fibres incubated in activating solutions with varying concentrations of Ca2+. The first 2 ms of these transients were described by a linear model in which the fibre is regarded as a rod composed of infinitesimally small, identical segments containing a mass, one undamped elastic element and in the case of relaxed fibres two damped elastic elements in series, or in the case of activated fibres three such elastic elements in series. The stiffness of activated fibres, expressed in elastic constants or apparent elastic constants, increased with increasing concentrations of Ca2+. All the damped elastic constants that were necessary to describe the tension responses of activated fibres were proportional to isometric tension. However, the undamped elastic constant did not increase linearly with increasing isometric tension. Equatorial X-ray diffraction patterns were obtained from single frog muscle fibres under similar conditions as under which the tension transients were obtained. The filament spacing (d10) of Ca(2+)-activated single frog muscle fibres decreased with increasing isometric force, whereas the intensity ratio (I11/I10) increased linearly with increasing isometric force. From experiments in which dextran (MW 200,000 Da) was added, it followed that such a change in filament spacing would modify passive stiffness. The d10 value of relaxed fibres decreased and stiffness increased with increasing concentrations of the polymer dextran, whereas I11/I10 remained constant. The relation of stiffness and filament spacing with concentration of dextran was used to eliminate the effect of decreased filament spacing on stiffness of activated fibres. After correction for changes in filament spacing the undamped complicance C1, normalized to tension, was not constant, but increased with increasing isometric tension. If we assume that isometric tension is proportional to the number of force generating cross-bridges, this means that only part of the undamped compliance of activated fibres is located in the cross-bridges.
通过在含有不同浓度Ca2+的激活溶液中孵育的去皮单根青蛙肌肉纤维，获得了对小而快速的长度变化（在40微秒内完成）的张力瞬变。这些瞬变的前2毫秒由一个线性模型描述，其中纤维被视为由无限小的、相同的段组成的杆，每个段包含一个质量、一个无阻尼弹性元件，对于松弛纤维，还有两个串联的阻尼弹性元件，对于激活纤维，则有三个这样的弹性元件串联。以弹性常数或表观弹性常数表示的激活纤维的刚度随着Ca2+浓度的增加而增加。描述激活纤维张力响应所需的所有阻尼弹性常数与等长张力成正比。然而，无阻尼弹性常数并不随等长张力的增加而线性增加。在与获得张力瞬变相似的条件下，从单根青蛙肌肉纤维获得了赤道X射线衍射图。Ca(2+)激活的单根青蛙肌肉纤维的细丝间距（d10）随着等长力的增加而减小，而强度比（I11/I10）随着等长力的增加而线性增加。从添加右旋糖酐（分子量200,000 Da）的实验中可以看出，细丝间距的这种变化会改变被动刚度。随着聚合物右旋糖酐浓度的增加，松弛纤维的d10值减小而刚度增加，而I11/I10保持不变。利用刚度和细丝间距与右旋糖酐浓度的关系来消除细丝间距减小对激活纤维刚度的影响。在对细丝间距的变化进行校正后，归一化到张力的无阻尼柔度C1不是常数，而是随着等长张力的增加而增加。如果我们假设等长张力与产生力的横桥数量成正比，这意味着激活纤维的无阻尼柔度只有一部分位于横桥中。
