Stochastic Simulation Of Excitation-contraction Coupling

工作概述新的窦房结细胞(SANC)随机钙释放三维模型已被完善和修订，以提供广泛的成像和电影输出，并允许无限长度的模拟以研究节律效应。人们试图直接基于观察到的RyR分布的免疫荧光图像来建立模型的几何结构，但发现常规光学显微镜图像中的信息不足以定义CICR在相邻偶联之间传播的局部路径。有必要获得这些细胞的超分辨率显微镜。为此，我们与NIBIB的一个显微镜小组建立了合作关系。初步的合作研究证实了该模型的结果，即钙释放事件仅限于肌膜下的一层薄层，这是标准共聚焦显微镜无法证实的。该模型已被广泛应用，并在《普通生理学杂志》上发表了一篇大型论文。进一步的研究指向通过建模发现的一种病理机制，在这种机制中，当RyR敏感性太高时，肾上腺素能系统对心率的调节作用被逆转。我们已经开始探索这一机制--在心力衰竭以及RyR和CASQ的遗传异常中可能具有临床意义--使用咖啡因来调节RyR。初步结果表明，为了理解SANC在耦合时钟状态下的心律失常跳动，有必要改进已被广泛接受的这些细胞的潜在电生理模型。我们还使用3D模型在单细胞水平上研究心率变异性的机制，这需要持续数天的模拟。

SUMMARY OF WORK The new 3D model of stochastic calcium release in sino-atrial node cells (SANC) has been elaborated and revised to provide extensive imaging and movie output, and to allow simulations of indefinite length in order to study rhythm effects. An attempt was made to base the model geometry directly on observed immunofluorescence images of RyR distribution, but it was found that the information in conventional light microscopic images has insufficient resolution to define the local pathways by which CICR spreads between neighboring couplons. It will be necessary to obtain super-resolution microscopy of these cells. For this reason we have established a collaboration with a microscopy group in NIBIB. Preliminary collaborative studies have confirmed the model result that calcium release events are confined to a thin layer beneath the sarcolemma, which would not be demonstrated with standard confocal microscopy. The model has been extensively exercised and a large paper has been published in Journal of General Physiology. Further studies have been directed to a pathological regime discovered by modeling, in which the regulatory effects of the adrenergic system on heart rate are reversed when RyR sensitivity is too high. We have begun exploring this regime -- of possible clinical significance in heart failure and genetic abnormalities of RyR and CASQ -- using caffeine to modulate the RyR. Initial results show that, in order to understand arrhythmic beating of SANC in the coupled-clock regime, it will be necessary to improve on the underlying electrophysiological model of these cells that has been widely accepted. We are also using the 3D model to study the mechanism of heart rate variability at the single-cell level, which requires simulations lasting for days.