Yamaguchi H, Takaki M, Matsubara H, Yasuhara S, Suga H
Department of Physiology II, Okayama University Medical School, Japan.
Am J Physiol. 1996 Apr;270(4 Pt 2):H1501-8. doi: 10.1152/ajpheart.1996.270.4.H1501.
We simulated myocardial Ca2+ (Ca) and cross-bridge (CB) kinetics to get insight into the experimentally observed constancy and variability of cardiac contractile efficiency in generating total mechanical energy under various inotropic and pathological conditions. The simulation consisted of a Ca transient, Ca association and dissociation rate constants of troponin C, and CB on and off rate constants. We evaluated sarcomere isometric twitch contractions at a constant muscle length. We assumed that each CB cycle hydrolyzes one ATP and that the force-length area (FLA) quantifies the total mechanical energy generated by CB cycles in a twitch contraction. FLA is a linear version of pressure-volume area, which quantifies the total mechanical energy of cardiac twitch contraction and correlates linearly with cardiac oxygen consumption (H. Suga, Physiol. Rev. 70: 247-277, 1990). The simulation shows that the contractile efficiency varies with changes in the Ca transient and Ca and CB kinetics except when they simultaneously speed up or slow down proportionally. These results point to possible mechanisms underlying the constancy and variability of cardiac contractile efficiency.
我们模拟了心肌钙离子（Ca）和横桥（CB）动力学，以深入了解在各种变力性和病理条件下，心脏收缩效率在产生总机械能时实验观察到的恒定性和变异性。模拟包括一个钙瞬变、肌钙蛋白C的钙结合和解离速率常数，以及横桥的开启和关闭速率常数。我们在恒定肌肉长度下评估肌节等长收缩。我们假设每个横桥循环水解一个ATP，并且力-长度面积（FLA）量化了一次收缩中横桥循环产生的总机械能。FLA是压力-容积面积的线性形式，它量化了心脏收缩的总机械能，并与心脏耗氧量呈线性相关（H. Suga，《生理学评论》70: 247 - 277，1990）。模拟结果表明，除了钙离子瞬变、钙离子和横桥动力学同时按比例加速或减速外，收缩效率会随着它们的变化而变化。这些结果指出了心脏收缩效率恒定性和变异性背后可能的机制。
