A Multi-Scale Approach to Cardiac Arrhythmia: from the Molecule to the Organ

描述（由申请人提供）：本提案的总体目标是通过应用创新技术、计算机建模和使用1型和2型长QT综合征（LQT1和LQT2）的新遗传模型来研究SCD的新机制。这种多管齐下的方法包括对睾丸切除的雄性LQT2兔和接受房室结消融（LQT1- avb）的LQT1兔的研究。在细胞水平上对这些兔的肌细胞进行研究，将用于研究性激素在调节心肌细胞钙动态的关键蛋白功能中的作用。由于钙（Ca）瞬态和动作电位动力学是通过钙诱导的钙释放和钙瞬态对钙敏感膜电流（ICa，L， INCX和IKs）的反馈双向耦合的，因此评估不稳定的钙循环和改变的复极化对触发活性的相对贡献通常是困难的。在此，我们建议首先研究没有Vm影响的亚细胞Ca循环动力学，以表征RyR的敏感性，然后用箝位动作电位波形研究Vm对Ca循环动力学的单向影响（即没有Cai对Vm的反馈），从而确定导致心律失常的全细胞Cai振荡的条件，无CaT影响的Vm动力学研究ICa重新开放促进的EADs，L在复极改变的情况下。最后双向耦合自由Cai和自由Vm动力学，研究Cai振荡和ICa重开的协同效应。迭代将由功能组成

DESCRIPTION (provided by applicant): The overall goal of this proposal is to investigate new mechanisms that underlie SCD through the application of innovative technology, computer modeling and the use of new genetic models of long QT syndrome type 1and type 2 (LQT1 and LQT2). This multi-pronged approach includes the investigation of orchiectomized male LQT2 rabbits and LQT1 rabbits that underwent ablation of the AV node (LQT1-AVB). Studies at the cellular levels with myocytes derived from these rabbits will be used to investigate the role of sex hormones in modulation of the function of key proteins that regulate calcium dynamics in cardiomyocytes. Since the calcium (Ca) transients and action potential dynamics are bi-directionally coupled through Ca-induced-Ca-release and the feedback of the Ca transient on Ca-sensitive membrane current (ICa,L, INCX, and IKs), assessing the relative contributions of unstable Ca cycling and altered repolarization to triggered activity is in general difficult. Here e propose to investigate the subcellular Ca cycling dynamics first without Vm influence to characterize RyR sensitivity, and then with a clamped action potential waveform to investigate the uni-directional effect of Vm on Ca cycling dynamics (i.e. without feedback of Cai on Vm), thereby identify conditions leading to arrhythmogenic whole cell Cai oscillations, Vm dynamics without CaT influence to study EADs facilitated by reopening of ICa,L in the presence of altered repolarization, and finally bi-directionally coupled free Cai and free Vm dynamics to investigate synergistic effects of Cai oscillations and reopening of ICa,. Iteration will consist of functional electrophysiological measurements of the specific currents and their biophysical properties, and biochemical and electrophysiological studies (as well as measured subcellular Ca dynamical properties-spark frequency and Ca wave threshold), to calibrate relevant ranges of computational model parameters to be used in the exploration of arrhythmogenic state (unsafe zone) and safe zone (no spontaneous arrhythmias or SCD). Studies at the tissue and organ levels will examine the role synchronization of the triggered activity combined with bi-stable wave conduction (bi- excitability) and tissue heterogeneities mediate the R-on-T phenomenon as well as test whether short-long-short sequence increases EAD formations and tissue heterogeneities, thus self propels until the onset of TdP and weather TdP and PVT are maintained by Ica-mediated wavefronts and chaos synchronization.