Atrial Excitation-Contraction Coupling, Calcium Signaling and Electro-Mechanical Alternans

项目总结/摘要 心房肌细胞兴奋收缩偶联（ECC）和肌浆网（SR）钙释放 具有由于横小管膜的缺乏或不规则组织而产生的独特特征 系统心房肌细胞具有两种类型的SR，连接型（j-SR）和非连接型（nj-SR）。钙从j- SR受电压门控L型Ca通道（ICa，L）的Ca内流控制，而nj-SR的释放则受电压门控L型Ca通道（ICa，L）的Ca内流控制。 发生的后续传播波样钙诱导钙释放（CICR）驱动的新确定的“火- 扩散-吸收-着火（FDUF）机理。IP 3受体诱导的Ca释放（IICR）通过以下方式促进ECC： 增强收缩力，但也导致促炎性Ca释放和交替。心脏电交替一直是 与心律失常有关，包括心房纤颤。交替被定义为心跳到心跳的交替， 动作电位（AP）持续时间（APD，电交替）、收缩强度和钙瞬变（CaT） 振幅，从而产生动态心律失常基质。双向耦合干扰 [Ca]i和膜电压（Vm）的调节（[Ca]i参与Vm偶联）是交替发生的原因。 心脏结构和电特性的性别差异与心律失常的差异有关 敏感性和确定交替诱导。以FDUF机制为重点，总体目标是 建立了心房肌ECC、Ca释放和心房电交替机制模型， 细胞、细胞对和器官水平。 具体目标1.确定房性电交替的FDUF依赖性机制。我们将决定关键的 新FDUF范例在心房交替中的作用，测试以下假设：1）j-SR和nj- SR Ca释放促进“反向”FDUF并触发交替; 2）FDUF触发信号（伊卡，L，连接性 CaT）具有Vm依赖性，3）SERCA依赖性Ca摄取; 4）线粒体Ca缓冲，能量学 和氧化还原信号传导和5）IICR调节FDUF和交替糖。 具体目标2。确定细胞对中的FDUF交替机制。Alternans是Vm或Ca驱动的。 Vm驱动的交替在空间上是均匀的，而Ca驱动的交替可以在空间上不一致， 在短距离上，区域异相交替。细胞对定义基本的结构和功能 细胞间通讯的单位。我们将测试1）CaT和APD交替的时空组织， 2）在钙驱动的交替过程中，FDUF机制、SERCA、线粒体信号传导和IICR如何改变 确定细胞对交替;以及3）Vm驱动的交替如何在相邻细胞中沉淀CaT交替。 具体目标3。确定Ca和Vm驱动的时空组织和机制 组织交替我们将在器官水平（灌注心脏，活体动物）确定机制， 1）钙驱动和2）电压驱动交替的表现和时空组织，以及测试 药物干预，以减少促肾上腺皮质激素交替风险。

PROJECT SUMMARY/ABSTRACT In atrial myocytes excitation-contraction coupling (ECC) and Ca release from the sarcoplasmic reticulum (SR) have unique features that result from the lack or the irregular organization of the transverse tubule membrane system. Atrial myocytes have two types of SR, junctional (j-SR) and non-junctional (nj-SR). Ca release from j- SR is controlled by Ca entry through voltage-gated L-type Ca channels (ICa,L) whereas release from nj-SR occurs by subsequent propagating wave-like Ca-induced Ca release (CICR) driven by the newly identified 'fire- diffuse-uptake-fire' (FDUF) mechanism. IP3 receptor-induced Ca release (IICR) contributes to ECC by enhancing inotropy, but also leads to arrhythmogenic Ca release and alternans. Cardiac alternans has been linked to cardiac arrhythmia, including atrial fibrillation. Alternans is defined as beat-to-beat alternations in action potential (AP) duration (APD, electrical alternans), contraction strength and Ca transient (CaT) amplitude, and thereby generates a dynamic arrhythmia substrate. Disturbances of the bi-directional coupling of [Ca]i and membrane voltage (Vm) regulation ([Ca]i↔Vm coupling) are responsible for alternans occurrence. Sex differences in cardiac structural and electrical properties have been linked to differences in arrhythmia susceptibility and determine alternans inducibility. Focusing on the FDUF mechanism, the overall goals are to establish a mechanistic model of atrial ECC, Ca release and atrial alternans and its sex-specific attributes at cellular, cell pair and organ level. Specific aim 1. Determine FDUF-dependent mechanisms of atrial alternans. We will determine the critical role of the novel FDUF paradigm in atrial alternans, testing the hypotheses that 1) uncoupling of j-SR and nj- SR Ca release promotes 'reverse' FDUF and triggers alternans; 2) the FDUF trigger signal (ICa,L, junctional CaT) has Vm dependence, and that 3) SERCA dependent Ca uptake; 4) mitochondrial Ca buffering, energetics and redox signaling and 5) IICR modulate FDUF and alternans. Specific aim 2. Determine FDUF alternans mechanisms in cell pairs. Alternans is either Vm- or Ca-driven. Vm-driven alternans is spatially homogeneous, while Ca-driven alternans can be spatially discordant where over short distances regions alternate out-of-phase. Cell pairs define the elementary structural and functional unit of cell-cell communication. We will test 1) the spatio-temporal organization of CaT and APD alternans in cell pairs, 2) how during Ca-driven alternans the FDUF mechanism, SERCA, mitochondrial signaling and IICR determine cell pair alternans; and 3) how Vm-driven alternans precipitates CaT alternans in adjacent cells. Specific aim 3. Determine the spatio-temporal organization and mechanisms of Ca- and Vm-driven tissue alternans. We will determine at organ level (perfused hearts, live animals) the mechanisms, manifestations and spatio-temporal organization of 1) Ca-driven and 2) voltage-driven alternans, and test pharmacological interventions to reduce pro-arrhythmic alternans risk.