Stochastic Simulation Of Excitation-contraction Coupling

工作总结2D现象学模型已被广泛运用，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，从而使时钟与膜电流一起调节心率。 这些模拟结果已发表在《生物物理学杂志》上。完整的蒙特-卡罗耦合模型与一个单一的细胞溶质室已更新，包括在个别钙释放终端的交界SR的钙的局部消耗的影响。模拟的并行模型上运行Biowulf证实，局部消耗钙火花终止的关键贡献，它足以作为唯一的终止机制。 然而，在这种情况下，SR钙的腔内扩散速率和RyR的门控动力学之间存在关键关系，必须满足该关系以防止火花延迟终止的不稳定性。 这种现象，现在更名为“火花亚稳性”已被广泛研究的Monte Carlo模拟，并通过分析计算的一个简化的连续模型的耦合。 研究结果发表在《普通生理学杂志》上。在钙超载的情况下，单细胞溶质耦合子模型不会振荡。 一个新的3D算法，结合了完整的耦合模型与空间分辨的胞质空间，使用算子分裂方法，现在已经完成。 它表明，只有当有紧密的桥接RyR簇进行激活时，才会发生在窦房结细胞（SANC）中实验观察到的局部钙释放的传播。 免疫荧光标记的SANC的3D共聚焦切片的检查揭示了这种网络存在于这些细胞的表面上，不像心室细胞。 通过模拟网络，3D模型再现了传播的局部钙释放，其耦合到膜电流并驱动跳动速率，正如本实验室开发的“耦合时钟”理论中所假设的那样。 该模型通过调节钙循环系统中各种蛋白质的功能来再现速率的调节，这是由于响应于自主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果，因为它提供了耦合驱动膜电压，但本身，抑制局部钙波的传播。 因此，NCX表达的影响对速率具有双相影响，澄清了其他人的NCX敲低实验的实验结果。 一篇论文正在为大约一个月后提交的《普通生理学杂志》做准备，

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,