Ca2+ -Induced Ca2+ Release in Heart

在成人心肌中，去极化激活了少量的钙离子内流，从而触发细胞内钙离子释放，导致收缩。这种细胞内钙的释放是由肌浆网中的2型兰尼定受体(RyR2)通道介导的。RyR2通道聚集在不连续的SR钙释放部位(1)。在这里，我们的重点是确定RyR2介导的钙信号在成年大鼠心肌细胞释放部位内和释放部位之间的局部控制。 局部RyR2介导的钙释放事件，称为钙火花，自发地发生在心肌中。人们认为，这些元素事件在时间和空间上的总和产生了更具全球性的钙释放现象，从而控制着心脏的收缩能力。有几个基本的未知因素限制了我们对心脏局部细胞内钙信号的理解。例如，目前尚不清楚钙火花是来自单个RyR2通道的开放，还是多个通道的协同开放。调节钙离子火花特性的机制(如其幅度、频率、传播等)也是定义模糊的。 为了解决这些(和其他)未知的问题，将结合单通道记录、激光闪光光解、扫描共聚焦成像、随机单通道理论和时空钙扩散模型来检验以下假设(或特定目标)。 假设1：单个RyR2通道的功能受微观的钙波动控制，这种波动在宏观的钙信号环境中并不明显。具体地说，提出了两个新的机制概念(如随机和/或反馈钙调节)，并在一个新的概念框架中进行了实验验证和解释。 假设2：RyR2通道间钙离子通讯定义了SR钙释放部位内和之间局部钙信号的时空性质。这里将在单通道和整个细胞水平上定义控制RyR2通道内和释放位点之间的钙离子通讯的机制。实验结果将使用一个独特的局部钙信号时空模型进行解释。

In adult cardiac muscle, depolarization activates a small Ca 2+ influx that triggers intracellular Ca 2+ release resulting in contraction. This intracellular Ca 2+ release is mediated by type-2 ryanodine receptor (RyR2) channels in the sarcoplasmic reticulum (SR). The RyR2 channels are clustered at discrete SR Ca 2+ release sites (1). Here, our focus is on defining the local control of RyR2-mediated Ca 2+ signaling within and between release sites in adult rat myocytes. Local elemental RyR2-mediated Ca 2+ release events, called Ca 2+ sparks, occur spontaneously in heart muscle. It is thought that these elemental events temporally and spatially sum to generate the more global Ca 2+ release phenomena that governs cardiac contractility. There are several fundamental unknowns that limit our understanding of local intracellular Ca 2+ signaling in heart. For example, it is still not clear if Ca 2+ sparks arise from the opening of an individual RyR2 channel or the concerted opening of several channels. The mechanisms that modulate Ca 2+ spark properties (e.g. their amplitude, frequency, propagation, etc.) are also poorly defined. To address these (and other) unknowns a combination of single channel recording, laser flash photolysis, scanning confocal imaging, stochastic single channel theory and spatiotemporal Ca 2+ diffusion modeling will be directed to test the following hypotheses (or specific aims). Hypothesis #1: Single RyR2 channel function is governed by microscopic Ca 2+ fluctuations that are not evident in the macroscopic Ca 2+ signaling environment. Specifically, two new mechanistic concepts (e.g. stochastic and/or feed-through Ca 2+ regulation) are proposed, experimentally tested, and interpreted in a novel conceptual framework. Hypothesis #2: Inter-RyR2 channel Ca 2+ communication defines the spatiotemporal nature of local Ca 2+ signaling within and between SR Ca 2+ release sites. The mechanisms that control inter-RyR2 channel Ca2+ communication within and between release sites will be defined here at both the single channel and whole cell levels. Experimental results will be interpreted using a unique spatiotemporal model of local Ca 2+ signaling.