Stretch-Dependent Calcium Signaling in Heart

描述（由申请人提供）：在心脏舒张期和收缩期的生理条件下，PI显示心脏中的Ca2+火花。它们不仅是正常的[Ca2+]i短暂的基础，而且在介导细胞对压力和疾病的反应中也被发现是至关重要的，在从钙超载到肌营养不良的心肌病的条件下，它们有助于收缩和心律失常功能障碍。最近，PI的工作表明，生理性拉伸，如心肌细胞在舒张充盈期间所经历的拉伸，会短暂地显著改变正常心室肌细胞中Ca2+火花的发生。这种行为取决于影响肌浆网（SR）释放机制的微管。尽管一年前这一新发现很重要，但我们现在才开发出额外的工具来研究动态长度变化如何影响不同条件下Ca2+火花的触发。使用这些新工具，我们观察到（在初步调查中）Ca2+火花的拉伸依赖性变化甚至比以前观察到的更大，并且似乎是由ryanodine受体（RyR2s）敏感性的短暂增加引起的。额外的初步研究表明，令人惊讶的是，在对照小鼠的心脏细胞中，这种短暂的Ca2+火花的增加是诱发心律失常的Ca2+波激活的基础，其激活率非常低，但在mdx小鼠（杜氏肌营养不良小鼠模型）的肌细胞中，其激活率要高得多。由PI和他的同事开发的工具将使一项创新的最先进的研究成为可能，即心脏Ca2+信号是如何被生理拉伸调节的。提出的工作旨在研究拉伸依赖性Ca2+火花和Ca2+波在1。对照心室肌细胞；2. RyR2特性发生改变的心室肌细胞；3. 微管被调节时的心室肌细胞；4. 抗肌营养不良蛋白缺失（mdx）小鼠心室肌细胞。计划中的研究应首次揭示拉伸在心室肌细胞正常和病理Ca2+信号传导中的重要性。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，而且还将提供心律失常发生机制的新信息。此外，它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。

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.