STOCHASTIC SIMULATION OF EXCITATION-CONTRACTION COUPLING

在上一个项目期间，我们开发了新的，更强大的蒙特卡罗仿真算法，以模拟骨骼肌的局部控制。按照计划，这些方法现在已经适应并扩展到心脏兴奋-收缩耦合。l型钙通道（也称为二氢吡啶受体DHPR）的门控方案与钙依赖性l型电流失活和门控电荷运动的实验数据都不一致，因此有必要开发一种新的门控方案。心脏ECC随机模拟的初步结果表明，局部控制实际上可以解释SR钙释放的分级和稳定性，并可以定量模拟我们实验室使用新的俄勒冈绿色/EGTA技术测量的SR钙释放率。模拟还表明，不同dhpr之间存在几种类型的竞争以释放SR钙，这可以解释先前几个实验室发表的关于心脏EC偶联的实验数据中令人困惑的特征。然而，一个新的矛盾出现了：如果我们假设心脏ryyanodine受体存在足够强大的失活过程，以及多个钙离子对该通道的协同激活，该模型仅显示出足够的局部和全局稳定性——这些特征在脂质双分子层中分离的心脏RyR门控的研究中尚未得到令人信服的证明。这导致了一种假设，即体内RyRs的门控与体外的门控明显不同，可能是邻近通道足突之间的变构相互作用的结果。-肌浆网Ryanodine受体蒙特卡洛心脏钙信号

SUMMARY OF WORK During the last project period, we developed new, more powerful Monte Carlo simulation algorithms in order to model local control in skeletal muscle. As planned, these methods have now been adapted and extended to cardiac excitation-contraction coupling. It was necessary to develop a new gating scheme for the L-type calcium channel (also known as dihydropyridine receptor, DHPR), since none of the published gating schemes for this channel were consistent with the experimental data on both calcium-dependent inactivation of L-type current and gating charge movement. Preliminary results of stochastic simulation of cardiac ECC show that local control can, in fact, explain the gradation and stability of SR calcium release, and can model quantitatively the rate of SR calcium release measured in our laboratory using the new Oregon green/EGTA technique. The simulations also demonstrate the existence of several types of competition between different DHPRs to release SR calcium, which can explain previously puzzling features of the published experimental data on cardiac EC coupling from several laboratories. However, a new paradox has arisen: the model only demonstrates adequate local and global stability if we assume the existence of a sufficiently powerful inactivation process of the cardiac ryanodine receptor, as well as cooperative activation of this channel by more than one calcium ion--features that have not been convincingly demonstrated in studies of isolated cardiac RyR gating in lipid bilayers. This has led to the hypothesis that the gating of RyRs in vivo is significantly different from that in vitro, possibly as a result of allosteric interactions between the foot processes of neighboring channels. - Sarcoplasmic Reticulum Ryanodine Receptor Monte Carlo Heart Calcium Signaling