Sarcoplasmic reticulum calcium leak and calcium instability in cardiac myocytes

描述（由申请人提供）：每次心跳时，少量钙通过膜通道进入细胞，触发细胞内储存的大量钙的释放。由此产生的细胞内钙的增加具有双重作用：1)使收缩和2)影响形成动作电位的离子电流。因此，心肌细胞钙转运不当可导致心室功能受损和心衰等疾病状态下致命性心律失常。研究表明，不稳定的钙调节和心律失常与细胞内储存到细胞质的“泄漏”增加有关。特别是，遗传性疾病儿茶酚胺能多形性室性心动过速（CPVT）导致泄漏增加和由钙的自发释放引发的危险室性心律失常。因此，这种疾病是心脏细胞中离子传输和电信号之间密切联系的一个明显例子。然而，钙连接增加心律失常风险的机制尚不清楚。我们假设，由于钙信号的内在复杂性和心肌细胞内的竞争效应，泄漏仅在某些条件下是有害的。创新实验和计算模型的结合将定量地确定控制钙泄漏的因素，并确定泄漏何时是危险的，何时是保护的界限。综上所述，这些研究将对影响CPVT和心力衰竭患者心律失常风险的因素产生重要的见解。该项目可细分为以下具体目标：目标1：确定健康细胞中控制钙泄漏的因素。目的2：确定心力衰竭中泄漏增加的机制。目的3：确定在肌浆网钙含量降低的情况下，ryanodine受体门控改变可增加心律失常风险的机制。这项工作将为健康心脏细胞中Ca2+的正常调节和病理中发生的缺陷提供基本的新信息。通过建立理解正常和缺陷钙释放的定量框架，这些研究可以帮助确定心脏治疗的周到目标

DESCRIPTION (provided by applicant): With each heartbeat, a small amount of calcium entering the cell through membrane channels triggers the release of a larger amount of calcium from intracellular stores. The resulting increase in intracellular calcium has the dual effects of both: 1) enabling contraction and 2) influencing the ionic currents that shape of the action potential. Improper transport of calcium in cardiac myocytes can therefore contribute to both impaired ventricular function and lethal cardiac arrhythmias in disease states such as heart failure. Studies suggest that unstable calcium regulation and arrhythmias are associated with increased "leak" from intracellular stores to the cytosol. In particular, the inherited disorder catecholaminergic polymorphic ventricular tachycardia (CPVT) results in both increased leak and dangerous ventricular arrhythmias triggered by spontaneous release of calcium. This disease therefore represents an obvious example of the close links between ion transport and electrical signaling in heart cells. However, the mechanisms by which calcium link can increase arrhythmia risk remain unclear. We hypothesize that, because of the inherent complexity of calcium signaling and competing effects within cardiac myocytes, leak is only deleterious under certain conditions. A combination of innovative experiments and computational modeling will quantitatively determine the factors that control calcium leak and define the boundaries of when leak is dangerous and when it is protective. Together the studies proposed will yield significant insight into the factors that influence arrhythmia risk in CPVT and in heart failure. The project can be sub-divided into the following Specific Aims: Aim 1: Determine, in healthy cells, the factors that control calcium leak. Aim 2: Determine the mechanisms underlying increased leak in heart failure. Aim 3: Determine the mechanisms by which altered gating of ryanodine receptors can increase the risk of arrhythmia despite reduced sarcoplasmic reticulum calcium content. The work will provide fundamental new information concerning both the normal regulation of Ca2+ in healthy heart cells and the defects that occur in pathology. By developing a quantitative framework for understanding normal and defective calcium release, these studies can help identify thoughtful targets for cardiac therapies PUBLIC HEALTH RELEVANCE: Improper regulation of calcium in heart cells has been identified as an important factor contributing to instability and potentially lethal heart rhythms. This project is aimed at developing a quantitative understanding of how changes in calcium regulation can lead to either improved heart function and greater stability, or to potentially dangerous instability. The studies will provide new insight into therapies that are likely to be effective at preventing instability and dangerous heart rhythms.