Stretch-Dependent Calcium Signaling in Heart

描述(由申请人提供)：PI显示心脏中的CA2火花发生在舒张期和收缩期的生理条件下。它们不仅是正常的[钙]i瞬变的基础，而且被发现在调节细胞对应激和疾病的反应方面至关重要，在从钙超载到肌营养不良的心肌病等情况下，它们会导致收缩和心律失常。最近，PI的研究表明，生理性拉伸，如心肌细胞在舒张期充盈时所经历的拉伸，显著改变正常心肌细胞瞬间发生的钙火花。这种行为依赖于影响肌浆网(SR)释放机制的微管。尽管一年前的这一新发现很重要，但我们现在才开发出必要的额外工具来研究动态长度变化如何在不同条件下影响钙火花的触发。使用这些新工具，我们(在初步调查中)观察到，钙火花中的拉伸依赖变化甚至比之前观察到的更大，似乎是由于兰诺定受体(RyR2)敏感性的一过性增加引起的。另外的前期工作表明，令人惊讶的是，这种短暂的钙火花激活在对照组小鼠的心肌细胞中以非常低的速度激活致心律失常的钙波，但在MDX小鼠、Duchenne肌营养不良的小鼠模型或SR中钙过量的对照组小鼠的心肌细胞中激活的频率要高得多。PI和他的同事开发的工具将使一种创新的最先进的研究成为可能，即心脏钙信号是如何通过生理性拉伸来调节的。这项拟议的工作试图研究1.对照心室肌细胞；2.RyR2特性已改变的心室肌细胞；3.微管调节时的心室肌细胞；4.来自dystrophin缺失(MDX)小鼠的心室肌细胞中的拉伸依赖性钙火花和钙波。这项计划中的研究将首次揭示Stretch在正常和病理性心肌细胞钙信号中的重要性。因此，这项工作不仅将提供有关正常细胞行为的基本新信息，还将提供有关心律失常发生机制的新信息。此外，它还将为包括杜氏肌营养不良症在内的各种心脏病的新疗法奠定基础。 与公众健康相关：收缩和心律由心脏细胞内的钙调节。现在已知这种钙水平部分是由细胞长度的变化(这些变化也被称为“拉伸”)决定的，这是致力于这一提议的科学家最近发现的一个令人惊讶的结果。这项计划中的工作将检查这种依赖拉伸的细胞钙和功能的变化，并确定拉伸是如何影响正常和有缺陷的心脏功能的。

DESCRIPTION (provided by applicant): Ca2+ sparks in heart have been shown by the PI to occur under physiological conditions during diastole and systole. They not only underlie the normal [Ca2+]i transient but have been found to be critically important in mediating the cellular response to stress and disease, contributing to contractile and arrhythmic dysfunction in conditions ranging from calcium overload to the cardiomyopathy of muscular dystrophy. Recently, work by the PI shows that physiologic stretch, such as that experienced by a myocyte during diastolic filling, dramatically alters Ca2+ spark occurrence transiently in normal cardiac ventricular myocytes. This behavior depends on microtubules affecting the release mechanisms of the sarcoplasmic reticulum (SR). Despite the importance of this new discovery one year ago, we have only now developed the additional tools needed to investigate how dynamic length changes can affect the triggering of Ca2+ sparks under diverse conditions. Using these new tools, we observe (in preliminary investigations) that stretch-dependent changes in Ca2+ sparks are even larger than previously observed and appear to arise from a transient increase in the sensitivity of ryanodine receptors (RyR2s). Additional preliminary work shows that, surprisingly, this transient increase in Ca2+ sparks underlies the activation of arrhythmogenic Ca2+ waves at a very low rate in heart cells from control mice, but at a much higher rate in myocytes from mdx mice, the murine model of Duchenne muscular dystrophy, or from control mice with excessive calcium in the SR. The tools developed by the PI and his colleagues will enable an innovative state-of-the-art investigation into how cardiac Ca2+ signaling is modulated by physiological stretch. The proposed work seeks to investigate stretch-dependent Ca2+ sparks and Ca2+ waves in 1. control ventricular myocytes; 2. ventricular myocytes in which RyR2 properties have been altered; 3. ventricular myocytes when microtubules are modulated; 4. ventricular myocytes from dystrophin null (mdx) mice. The planned research should reveal for the first time the importance of stretch in normal and pathological Ca2+ signaling of cardiac ventricular myocytes. The work will therefore provide not only fundamental new information on normal cellular behavior but also on mechanisms of arrhythmogenesis. Furthermore it will lay the foundation for novel therapies for diverse heart diseases including Duchenne muscular dystrophy. PUBLIC HEALTH RELEVANCE: Contraction and the heart rhythm are regulated by calcium inside of heart cells. This calcium level is now known to be set in part by changes in the cell length (these changes are also called "stretch"), a surprising result that was discovered recently by the scientists working on this proposal. The planned work will examine such stretch-dependent changes in cellular calcium and function and determine how stretch underlies normal and defective heart function.