Campbell K B, Razumova M V, Kirkpatrick R D, Slinker B K
Department of VCAPP, Washington State University, Pullman 99163, USA.
Ann Biomed Eng. 2001 May;29(5):384-405. doi: 10.1114/1.1366669.
To better understand the relationship between kinetic processes of contraction and the dynamic features of an isometric twitch, studies were conducted using a mathematical model that included: (1) kinetics of cross bridge (XB) cycling; (2) kinetics of thin filament regulatory processes; (3) serial and feedback interactions between these two kinetic processes; and (4) time course of calcium activation. Isometric twitch wave forms were predicted, morphometric features of the predicted twitch wave form were evaluated, and sensitivities of wave form morphometric features to model kinetic parameters were assessed. Initially, the impulse response of the XB cycle alone was analyzed with the findings that dynamic constants of the twitch transient were much faster than turnover number of steady-state XB cycling, and, although speed and duration of the twitch wave form were sensitive to XB cycle kinetic constants. parameters of wave shape were not. When thin filament regulatory unit (RU) kinetics were added to XB cycle kinetics, the system impulse response was slowed with only little effect on wave shape. When cooperative neighbor interactions between RU and XB were added, twitch wave shape (as well as amplitude, speed and duration) proved to be sensitive to variation in cooperativity. Importantly, persistence and shape of the falling phase could be strongly modified. When kinetic coefficients of XB attachment were made to depend on sarcomere length, changes in wave shape occurred that did not occur when only sliding filament mechanisms were operative. Indeed, the force-length relationship proved to be highly sensitive to length-dependent XB attachment in combination with cooperative interactions. These model findings are the basis of hypotheses for the role of specific kinetic events of contraction in generating twitch wave form features.
为了更好地理解收缩动力学过程与等长收缩的动态特征之间的关系，研究采用了一个数学模型，该模型包括：（1）横桥（XB）循环动力学；（2）细肌丝调节过程动力学；（3）这两个动力学过程之间的串联和反馈相互作用；（4）钙激活的时间进程。预测了等长收缩波形，评估了预测收缩波形的形态特征，并评估了波形形态特征对模型动力学参数的敏感性。最初，单独分析了XB循环的脉冲响应，结果发现收缩瞬变的动态常数比稳态XB循环的周转数快得多，并且，虽然收缩波形的速度和持续时间对XB循环动力学常数敏感，但波形参数并非如此。当将细肌丝调节单位（RU）动力学添加到XB循环动力学中时，系统脉冲响应减慢，对波形的影响很小。当添加RU和XB之间的协同相邻相互作用时，收缩波形（以及幅度、速度和持续时间）被证明对协同性变化敏感。重要的是，下降阶段的持续性和形状可能会被强烈改变。当使XB附着的动力学系数取决于肌节长度时，会出现仅在滑动丝机制起作用时不会出现的波形变化。实际上，力-长度关系被证明对长度依赖性XB附着与协同相互作用的组合高度敏感。这些模型发现是关于收缩特定动力学事件在产生收缩波形特征中作用的假设的基础。
