LOCAL CONTROL OF CARDIAC EXCITATION/CONTRACTION COUPLING

肌浆网钙离子释放的调控 (SR)是正常心脏功能的基础， 激素神经递质和电刺激 的总体目标 本研究旨在验证两个关于SR钙释放的假设：1）“局部” “对照”：SR释放通道的空间离散组或“簇” 首先被Ca 2+通过共同缔合的L型进入而激活。 Ca 2+通道 在本地控制中，发生群集激活 独立于任何其它这样的簇的激活。 2)损失 “局部控制”导致某些心脏功能异常， Ca 2+波和触发性心律失常。 失去本地控制意味着 团簇最初不再被附近的Ca 2+内流激活，但可能 被来自其他簇的Ca 2+激活。 据推测 此外，局部控制的丧失可以被细胞内的 镁离子（Mg 2+）。 局部控制被认为是由于 单个L-型Ca 2+通道和一个 SR释放通道在SR和横向连接处的“簇” 小管 据推测，诱发Ca 2+释放的可能性 由L-型Ca 2+通道第一次开放的潜伏期决定， 并且由单位L型电流的大小（而不是由 全细胞Ca ~（2+）电流、Na ~+/Ca ~（2+）交换或已释放的Ca ~（2+） 其他集群）。 根据当地控制，“耦合剂”（[Ca 2 +]） 在RyR的局部亚细胞区域， 这可以从常规的全细胞Ca 2+测量来预测。 电流和空间平均Ca 2+瞬变。 因此，共焦激光器 扫描显微镜，它提供了更高的空间分辨率，将 用于观察电压钳诱发的局部[Ca 2 +]i瞬变（LCT） 豚鼠和大鼠单个心室肌细胞的去极化 内部灌注荧光Ca 2+指示剂。 图像处理 将用于确定诱发局部的（空间）特征 [Ca2+] i-瞬变和自发Ca 2 +-火花，根据需要评估 严格的局部控制假设。 全细胞膜片钳 记录将用于确定局部[Ca 2 +] i-瞬变是否 诱发的方式与L型Ca 2 + - 渠道 SR负载和细胞内Mg 2+对大小的影响， 诱发局部[Ca 2 +] i-瞬变的发生概率和位置， 自发钙火花，和钙波将进行研究。 研究 将提供关于正常兴奋-收缩（E-C）的新信息 耦合，并将测试的假设，异常E-C耦合出现 由于SR Ca 2+释放的正常局部控制的丧失。

Control of the release o calcium ions (Ca2+) from sarcoplasmic reticulum (SR) is fundamental to normal cardiac function and its modulation by hormones, neurotransmitters, and electrical excitation. The overall aim of this research is to test two hypotheses on SR calcium release; 1) 'Local control': Spatially discrete groups or 'clusters" of SR release channels are first activated exclusively by Ca2+ entering via co-associated L-type. Ca2+ channels. In local control activation of a cluster occurs independently of the activation of any other such clusters. 2) Loss of 'local control" leads to certain abnormalities of cardiac function such as Ca2+ waves and triggered arrhythmias. Loss of local control means that clusters are no longer activated initially by nearby Ca2+ influx, but may be activated by Ca2+ reaching them from other clusters. It is hypothesized also that loss of local control can be antagonized by intracellular magnesium ions (Mg 2+). Local control is thought to result from a microscopic 'coupling' between individual L-type Ca2+-channels and a 'cluster' of SR release channels at the junction between SR and transverse tubule. It is hypothesized that the probability of evoking Ca2+ release there is determined by latency to first opening of the L-type Ca2+ channel, and by the magnitude of the unitary L-type current (rather than by the whole-cell Ca2+-current, Na+/Ca2+_ exchange, or by Ca2+ already released from other clusters). According to local control, the 'coupler' ([Ca2+]) in the local subcellular region of the RyR is very different from that which would be predicted from conventional measurements of whole-cell Ca2+- current and spatial-average Ca2+ transient. Accordingly, confocal laser scanning microscopy, which provides increased spatial resolution, will be used to observe local [Ca2+]i transients (LCTs) evoked by voltage clamp depolarization in single guinea-pig and rat cardiac ventricular cells perfused internally with fluorescent Ca2+ indicators. Image processing will be used to determine (spatial) characteristics of evoked local [Ca2+]i-transients and spontaneous Ca2+-sparks, as required to evaluate the hypothesis of local control rigorously. Whole-cell and patch clamp recording will be used to determine whether local [Ca2+]i-transients are evoked in a manner consistent with gating properties of L-type Ca2+ - channels. The effect of SR loading and intracellular Mg2+ on the size, probability, and location of occurrence of evoked local [Ca2+]i-transients, spontaneous Ca2+-sparks, and Ca2+ -waves will be studied. The research will provide new information on normal excitation-contraction (E-C) coupling, and it will test the hypothesis that abnormal E-C coupling arises from loss of the normal 'local control of SR Ca2+ release.