Mitsui T, Kumagai S, Chiba H, Yoshimura H, Ohshima H
Department of Physics, School of Science and Technology, Meiji University, Kawasaki, Japan.
J Theor Biol. 1998 May 7;192(1):35-41. doi: 10.1006/jtbi.1997.0614.
The model for myosin head motion along an actin filament as proposed by Mitsui & Chiba [(1996). J. theor. Biol. 182, 147-159] is here modified so that it can explain the isometric tension and isotonic velocity transients having the same parameter values as the stationary filament sliding. The modified model differs in that a myosin head forms a complex with two actin molecules in an actin filament and has two attached states in the complex instead of three. Thus an incremental step in the myosin head motion is equal to the F-actin monomer repeat (5.46 nm). Muscle properties concerning the stationary filament sliding are calculated with new parameters in a manner similar to that of Mitsui-Chiba, with the results being qualitatively similar to theirs. In studying the transient phenomena, a quantitative expression is given for the potential energy of the myosin head in the complex, and two rate constants are applied to the kinetics of the head. The time course of tension recovery after a quick length change is determined by calculating the statistical distribution of the head in the two attached states, which conforms to experimental observations by Ford et al. [(1977). J. Physiol. 269, 441-515]. The tension variations T1/T0 and T2/T0 calculated with parameters determined from the analysis of stationary filament slidings are in fairly good agreement with the experimental data by Ford et al. The model suggests that a large fluctuation exists in the relative position between the actin and myosin filaments even when the load on a muscle is kept constant. Taking this fluctuation into account explains the characteristics of the isotonic velocity transient observed by Civan & Podolsky.
三井和千叶提出的肌球蛋白头部沿肌动蛋白丝运动的模型（[(1996). J. theor. Biol. 182, 147 - 159]）在此进行了修改，以便它能够解释等长张力和等张速度瞬变，这些瞬变具有与固定丝滑动相同的参数值。修改后的模型的不同之处在于，一个肌球蛋白头部在肌动蛋白丝中与两个肌动蛋白分子形成复合物，并且在复合物中有两种附着状态而非三种。因此，肌球蛋白头部运动的一个增量步长等于F - 肌动蛋白单体重复长度（5.46纳米）。关于固定丝滑动的肌肉特性，使用新参数以类似于三井 - 千叶的方式进行计算，结果在定性上与他们的结果相似。在研究瞬变现象时，给出了复合物中肌球蛋白头部势能的定量表达式，并将两个速率常数应用于头部的动力学。快速长度变化后张力恢复的时间进程通过计算头部在两种附着状态下的统计分布来确定，这与福特等人的实验观察结果相符（[(1977). J. Physiol. 269, 441 - 515]）。用从固定丝滑动分析中确定的参数计算出的张力变化T1/T0和T2/T0与福特等人的实验数据相当吻合。该模型表明，即使肌肉上的负荷保持恒定，肌动蛋白丝和肌球蛋白丝之间的相对位置也存在很大波动。考虑到这种波动解释了西万和波多尔斯基观察到的等张速度瞬变的特征。
