Lorenzini C A, Colomo F, Lombardi V
Adv Exp Med Biol. 1984;170:757-64. doi: 10.1007/978-1-4684-4703-3_73.
The force-velocity (T-V) relation and the force-extension (T1) relation are determined at present times and at increasing isometric tensions during a tetanic contraction in frog single muscle fibres in which the passive compliance in series with the sarcomeres was made very small. The slope of the instantaneous T1 relation, the fibre stiffness, increases roughly in proportion to the level of the rising isometric tension at which the measurements were made. The value of V0 (the velocity of shortening under zero load) is time-independent, whereas the force T exerted during shortening at any velocity V lower than V0 increases gradually with time after the beginning of the tetanus volley and attains its steady state level before the isometric tension has attained the tetanus plateau and the fibre stiffness its final value. It is concluded that the delay of the development of the isometric tension and of the fibre stiffness with respect to the development of the T-V relation is determined by a specific factor of the contractile process. It is interesting to note that in a cross-bridge model of contraction, in which the value of the rate constant for cross-bridge formation is moderate, the recruitment of actin sites which is measured by the characteristics of the instantaneous T-V relation, is expected to lead significantly the actual cross-bridge formation, which is measured both by the instantaneous isometric tension and by the instantaneous stiffness.
在蛙单肌纤维强直收缩过程中，当与肌节串联的被动顺应性变得非常小时，目前确定了力 - 速度（T - V）关系和力 - 伸长（T1）关系，且等长张力不断增加。瞬时T1关系的斜率，即纤维刚度，大致与进行测量时上升的等长张力水平成比例增加。V0（零负荷下的缩短速度）的值与时间无关，而在任何低于V0的速度V下缩短过程中施加的力T，在强直脉冲开始后的时间里逐渐增加，并在等长张力达到强直平台之前以及纤维刚度达到其最终值之前达到其稳态水平。得出的结论是，等长张力和纤维刚度相对于T - V关系发展的延迟是由收缩过程的一个特定因素决定的。有趣的是，在一个收缩的横桥模型中，其中横桥形成的速率常数的值适中，通过瞬时T - V关系的特征测量的肌动蛋白位点的募集，预计会显著领先于通过瞬时等长张力和瞬时刚度测量的实际横桥形成。
