心肌细胞同步化节律的实验观察及其动力学研究

【作者】 袁岚；

【导师】 古华光；

【作者基本信息】 陕西师范大学 ， 生物物理学， 2010， 硕士

【摘要】 生命活动的正常进行依赖于心脏有节律的搏动。但是心脏的搏动节律不是均匀的,而是复杂的、非线性的。目前,人们认识到心脏节律复杂性表现在三个层次上。整体心脏中,神经、体液调节下的心脏节律的波动是内源性的,并具有混沌的性质；在心脏内兴奋的传导过程中,各级单元的失匹配会导致节律紊乱,如异位节律和折返性心率失常。在起搏节律上,窦房结中的细胞具有异质性,它们耦合而成的同步化的心脏起搏节律也具有复杂性。心脏起搏节律的复杂性是心脏节律复杂性的重要原因。因此,研究同步化的起搏节律的形成是很必要的。心肌单细胞的搏动节律极不稳定,节律变异系数大,较难从中发现可辨识的、统一的规律。同步化收缩的心肌细胞片在正常灌流液中呈现多种模式的搏动节律,周期节律(周期1、周期2、周期3)、阵发节律、整数倍节律和非周期节律等。以前,人们研究从单细胞到细胞团的同步化形成过程都是在大的网络中观察几个细胞从不同步搏动到同步化搏动的。但是这种对同步化形成过程的研究方法不能够反映同步化形成过程的细节现象。本文将选取相邻的两个或三个细胞所在的小网络,通过两个或三个细胞从不同步到同步化搏动的同步化过程的观察来说明同步化形成的具体过程。此外,通过网络的数学模型,仿真了在培养心肌细胞网络中观察到的已经达到同步化的周期1节律,用以解释心脏正常起步节律的形成机制。本文通过活细胞工作站,采用光密度记录手段,定位记录两个或三个细胞从不同步博动到同步搏动的过程。本研究还采用钙荧光记录手段,观察到心肌细胞小网络形成的同步化节律是多样的,其中包括同步化程度高的周期一节律,但不是完全同步化的,有较小的平均相位差。为了研究心脏正常起搏节律的产生机制,我们运用非线性动力学理论与方法。研究结果如下：1.两个或三个独立搏动的细胞随着培养时间的增加,也就是耦合强度的增加,会形成同步化的搏动节律。2.同步初期的同步化节律是复杂多样的。3.搏动节律从不同步到同步化的过程是复杂多样的。例如,在一些两个细胞网络中,部分搏动先达到同步,然后所有搏动达到同步。在三个细胞的网络中,两个细胞会先到达同步,然后三个细胞都达到同步。4.随着培养时间的增加和心肌细胞网络中细胞个数的增加可以稳定网络的同步化节律为类似周期节律。5.选用不同参数配置的Morris-Lecar(ML)模型模拟心肌细胞的异质性,在邻近耦合的异质振子构成的心肌细胞网络,振子参数远离Hopf分岔点时,可以仿真与实验相似的同步化周期一节律。6.耦合强度越大,不同细胞的相位差就会越小但不为零；噪声作用下的细胞节律间的相位差略有增大。本研究结果不仅揭示了同步化节律形成过程中的节律变化特征,还提供生物系统的节律同步的实验例证。仿真结果提示耦合强度是节律同步的原因,而振子的异质性和噪声是产生相位差的原因。研究结果给出了心肌细胞网络同步化周期一节律形成的动力学解释。这就从理论上解释了同步化周期节律的产生机制,有助于认识正常心脏的起搏节律。更多还原

【Abstract】 The normal activity of life depends on rhythmic beating of the heart. However, the beating of heart is not of the uniformity but complex and nonlinear. People know that cardiac beating rhythms exhibit complex characteristics in multiple levels. In the whole heart, the fluctuation of rhythm which is adjusted by nerve and body fluid is endogenesis, and exhibits the characteristics of chaos. When units of conduction of heart’s excitement mismatch, the rhythm will be turbulenced, such as the ectopic rhythm and arrhythmia. For the pace-making rhythm, the synchronized rhythms of cells in sinoatrial node are diverse, because they are heterogeneity. The diversity of pacemaker rhythm is the essential reason for the complex rhythm in the whole heart. In a word, it’s necessary to study the synchronized pace-making rhythm. That the beating rhythm of single cardiac myocyte was unstable and exhibited bigger coefficient of variation was discovered in the previous experiment. It’s difficult to find the recognizable and general rules. In normal solution, the synchronized beating rhythms of cultured cardiac cells exhibit periodic rhythms including period 1, period 2 and period 3, periodic rhythm with intermittency, integer multiple rhythms and non-periodic rhythms and so on. The procedure of the formation of synchronized process from single cells to network were studied in several cells whose behaviors were changed from non-synchronized rhythms to synchronized rhythms in a large scale network in previous studies. But the research method could not acquire the details in procedure to form synchronization. In this study, the network composed of two or three interfacing cells are employed to study the procedure of synchronized rhythms through the observation of the procedure from non-synchronized rhythm to synchronized rhythm in the cells. In addition, the dynamics of synchronized period 1 rhythm observed in the network composed of cultured cardiac cells are simulated in a mathematical network, and employed to interpret the periodic pace-making rhythms of heart.The beating rhythms of two or three cultured single cardiac myocytes were recorded by light density on workstation of living cells. The synchronized rhythms of networks exhibited diversity including synchronous period 1 rhythms, using calcic fluorescence recording method. Synchronous period 1 rhythms exhibited non-complete synchronization and weak phase difference. The results are as follow:1. With the increases of cultured time as well as coupling strength, independent rhythms of two or three myocytes became synchronous rhythms. 2. The synchronized rhythms are diversity in starting synchronization.3. The changes of beating rhythm from independence to synchronization are complex and of diversity. For example, in network composed of two myocytes, some of beatings became synchronization while others were independent firstly, and then all beatings became synchronous. In networks composed of three myocytes, beating rhythms of two myocytes achieved synchronization firstly, and then rhythms of three cells acquired synchronization.4. The synchronized rhythms were stabilized in period rhythm almostly with increasing of cultured time and the number of cells in networks.5. Similar synchronized rhythms can be simulated in a network composed of heterogeneous cells, which is described by Morris-Lecar model with different parameters and with neighboring coupling manner when the parameters are far from the bifurcation Hopf points.6. If the coupling strength is much stronger, the phase difference between different cells is much lower, but the value is not zero. Noise can slightly increase the phase difference, but the synchronous behavior is influenced little. The phase difference increases slightly when noise density is increased.The results not only gave changing characteristics during the procedure of forming synchronous rhythm, but also provided experimental demonstration of rhythm synchronization in life system. The simulation results imply that coupling strength leads to synchronization and heterogeneity of cells and noise lead to phase difference. The results provided theoretical interpretation of the synchronized period 1 rhythm, helpful to recognize the normal pace-making rhythm of heart.更多还原