钙火花终结的亚细胞动力学研究

Calcium spark is the elementary event of calcium induced calcium release in cardiac myocytes, which plays an important role in cardiac muscle excitation-contraction coupling processes. However, to date, no reasonable mechanism can adequately account for spark termination. The calcium spark is the local elevations of the calcium ions concentration in cardiac cytosol caused by the calcium ions release through the opening of the ryanodine receptor on the junctional sarcoplasmic reticulum cisterna (jSR). Calcium blink is a depletion signal in the jSR as the calcium spark arises. Calcium blinks mirror calcium sparks. They are signal pairs. So, calcium blinks can reveal the mechanisms of calcium spark termination in a sense. In the proposal,we will examine the sub-cellular calcium signals in sarcoplasmic reticulum (SR) in order to uncover dynamical mechanism of the spark termination. Firstly, based on the anomalous diffusion law and considering the boundary effects of calcium ions release from ryanodine receptor and refilling from free sarcoplasmic reticulum (fSR), we will develop a reaction-diffusion model for calcium blink and discuss the time-space dynamical characters. Secondly, we'll use fSR-targeted calcium biosensor and fluorescence resonance energy transfer method to record the dynamical process of calcium signals in fSR in real-time. Finally, considering the effects of boundary oscillation and deformation, nano-scale of fSR and slip flow, we will develop a dynamical mathematical model for the rapid transport of calcium signals in fSR. We will uncover why calcium ions can rapidly transport in fSR and its relations with spark termination. Our work will promote the biomechanics research on calcium spark from cellular level to sub-cellular level. It will be of importance for the development of sub-cellular mechanics.

钙火花是心肌细胞钙致钙释放的基本单位，在心肌兴奋收缩耦联过程中发挥着重要作用，但是，至今还没有一个合理的理论来解释钙火花是如何终结的。本项目从钙火花的姊妹事件钙空穴入手，在亚细胞水平研究钙火花终结的动力学机制。首先，基于反常扩散理论，考虑雷诺丁受体释放钙离子和自由肌浆网输运钙离子的边界效应，建立钙空穴模型，定量分析肌浆网终池内钙空穴的时空动力学特征；其次，利用荧光蛋白定位表达技术和荧光共振能量转移成像方法，实时记录自由肌浆网内钙离子浓度变化的动力学特征，利用图像处理技术综合分析实验数据；最后，考虑边界振动变形效应、纳米尺度效应和滑移边界效应，建立钙离子在自由肌浆网内输运的动力学模型，数值分析钙离子在自由肌浆网内快速输运的微观机理。实验研究和理论分析相结合，在亚细胞水平揭示钙火花终结的动力学机制。这一工作将钙火花的生物力学研究从细胞水平推进到亚细胞水平，对亚细胞力学的发展和完善具有科学意义。

钙火花终结是钙火花时空动力学过程中的基本事件，在心肌兴奋收缩耦联过程中发挥着重要作用。本项目首次考虑了肌浆网终池膜表面游离随机分布的雷诺丁受体的存在，理论计算与实验数据相结合，建立了钙空穴反应扩散的新模型，定量分析了钙空穴的时空动力学特征及自由肌浆网对钙空穴的影响。结果发现，游离随机分布的雷诺丁受体的开放可以引起附近成串雷诺丁受体的开放，诱发钙空穴的发生，雷诺丁受体开放的时间、钙离子释放的强度决定钙空穴的大小，肌浆网终池与自由肌浆网连接的条数决定钙空穴的填充时间。游离随机分布的雷诺丁受体的开放可以诱导钙火花、钙波的发生，增加钙火花、钙波发生的频率。利用荧光蛋白定位表达技术和荧光共振能量转移成像方法，实验记录了钙空穴的动力学特征,得到了钙空穴的实验数据。另外，基于钙火花的空间反常扩散机制，建立了钙波模型，研究发现，当雷诺丁受体的钙离子释放电流达到4pA时，钙波就可能被诱发，这与以前基于钙离子Fick扩散模型得到的20pA大不相同，这一结果与实际生理背景更为接近。雷诺丁受体钙离子的释放强度比其开放时间更能影响钙波的动力学特性。本项目对在细胞水平理解心衰的生物力学机理具有重要的科学意义。