Ca2+ -Induced Ca2+ Release in Heart

在成人心肌中，去极化激活少量Ca 2+内流，触发细胞内Ca 2+释放，导致收缩。这种细胞内Ca 2+释放是由肌浆网（SR）中的RyR 2通道介导的。RyR 2通道聚集在离散的SR Ca 2+释放位点（1）。在这里，我们的重点是定义本地控制RyR 2介导的Ca 2+信号内和之间的释放网站在成年大鼠心肌细胞。 RyR 2介导的局部钙释放事件，称为钙火花，在心肌中自发发生.据认为，这些基本事件的时间和空间的总和，以产生更多的全球钙2+释放现象，支配心肌收缩力。有几个基本的未知因素限制了我们对心脏局部细胞内Ca 2+信号的理解。例如，目前尚不清楚Ca 2+火花是由单个RyR 2通道的开放还是几个通道的协同开放引起的。研究了钙离子电火花特性（如电火花的振幅、频率、传播等）的调节机制。也很难定义。 为了解决这些（和其他）未知数的单通道记录，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的组合将直接测试以下假设（或具体目标）。 假设#1：单个RyR 2通道的功能受微观Ca 2+波动的控制，而在宏观Ca 2+信号环境中这种波动并不明显。具体而言，两个新的机制的概念（如随机和/或馈通钙调节）提出，实验测试，并解释一个新的概念框架。 假设#2：RyR 2通道间的Ca 2+通讯定义了SR Ca 2+释放位点内和之间局部Ca 2+信号传导的时空性质。控制释放位点内和之间的RyR 2通道间Ca 2+通信的机制将在单通道和全细胞水平上定义。实验结果将被解释使用一个独特的时空模型的本地钙2+信号。

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.