Stochastic Simulation Of Excitation-contraction Coupling

二维现象学模型已被广泛应用，以产生统计数据，显示钙时钟的周期性如何随着RyR钙释放电流的增加而出现，允许时钟随膜电流携带以调节心率。这些模拟的结果已经发表在《生物物理杂志》上。具有单个细胞质室的完整蒙特卡罗耦合模型已被更新，以包括在连接层的单个钙释放末端钙的局部耗尽的影响。在Biowulf上运行的并行模型的模拟证实，局部耗尽对钙火花终止起关键作用，并且它足以作为唯一的终止机制。然而，在这种情况下，SR钙的腔内扩散速率与RyR的门控动力学之间必须满足临界关系，以防止延迟终止的火花不稳定。这种现象，现在被重新命名为“火花亚稳态”，已经被广泛地研究了蒙特卡罗模拟，并通过对耦合的简化连续体模型的分析计算。研究结果发表在《普通生理学杂志》上。在钙超载的情况下，单细胞质偶联子模型不振荡。现在已经完成了一种新的3D算法，该算法使用算子分裂方法将全耦合子模型与空间分辨的细胞质空间结合起来。这表明，实验中观察到的窦房结细胞（SANC）局部钙释放的传播，只有在ryr的紧密桥接簇进行激活时才会发生。免疫荧光标记的SANC三维共聚焦切片显示，与心室细胞不同，这种网络存在于这些细胞的表面。通过模拟网络，3D模型再现了局部钙释放的传播，钙释放与膜电流耦合并驱动跳动速率，正如本实验室开发的“耦合时钟”理论所假设的那样。该模型通过调节钙循环系统中各种蛋白质的功能来重现速率的调节，这是由于自主神经激活的磷酸化而发生的。钠钙交换器（NCX）被发现有一个矛盾的效应，因为它提供耦合来驱动膜电压，但是，它本身，抑制局部钙波的传播。因此，NCX表达对率的影响是双相的，这澄清了其他NCX敲除实验的实验结果。一篇论文正准备在一个月后提交给《普通生理学杂志》，

SUMMARY OF WORK The 2D phenomenalogical model has been exercised extensively to generate statistics showing how periodicity of the calcium clock emerges as the RyR calcium release current is increased, allowing the clock to entrain with membrane currents to regulate the heart rate. The results of those simulations have been published in Biophysical Journal. The full Monte-Carlo couplon model with a single cytosolic compartment has been updated to include the effects of local depletion of calcium at individual calcium release terminals of the junctional SR. Simulations of the parallelized model run on Biowulf confirm that local depletion makes a critical contribution to calcium spark termination and that it suffices as the only termination mechanism. However, in that case, there is a critical relationship between the intra-lumenal diffusion rate of SR calcium and the gating kinetics of the RyR that must be satisfied to prevent instability of sparks with delayed termination. This phenomenon, now renamed "spark metastability" has been extensively studied by Monte Carlo simulation, and by analytical computations on a simplified continuum model of the couplon. The results have been published in Journal of General Physiology Under calcium overload, the single-cytosol couplon model does not oscillate. A new 3D algorithm, combining the full couplon model with a spatially resolved cytosolic space using an operator splitting method, has now been completed. It demonstrated that the propagation of local calcium releases seen experimentally in sino-atrial node cells (SANC) can only occur if there are close, bridging clusters of RyRs to conduct the activation. Examination of 3D confocal sections of immunofluorescent labeled SANC reveals that such a network is present on the surface of these cells, unlike ventricular cells. By simulating the network, the 3D model reproduced propagating local calcium release that couple to membrane currents and drive the beating rate, as posited in the "coupled clock" theory developed in this Laboratory. The model reproduces the regulation of rate by modulating the function of the various proteins in the calcium cycling system, as would occur due to phosphorylation in response to autonomic activation. The sodium-calcium exchanger (NCX) was found to have a paradoxical effect, in that it provides the coupling to drive the membrane voltage, but, itself, inhibits the propagation of local calcium waves. The effect of NCX expression therefore has a biphasic effect on rate, clarifying experimental results of NCX knock-down experiments by others. A paper is in preparation for Journal of General Physiology to be submitted in about a month,