Santana L F, Cheng H, Gómez A M, Cannell M B, Lederer W J
Department of Physiology, University of Maryland at Baltimore School of Medicine 21201, USA.
Circ Res. 1996 Jan;78(1):166-71. doi: 10.1161/01.res.78.1.166.
Ca2+ sparks, the elementary events underlying excitation-contraction (E-C) coupling, occur when sarcoplasmic reticulum (SR) Ca2+ release channels open. They are activated locally by Ca2+ influx through sarcolemmal (SL) Ca2+ channels. By measuring the probability of spark occurrence under conditions in which their probability of occurrence is low, we address two important questions raised by our recent work: (1) When a Ca2+ spark is triggered, how many SL Ca2+ channels (at a minimum) contribute to its activation? (2) What is the relation between the subcellular local [Ca2+], produced by the opening of SL Ca2+ channels and the consequent SR Ca2+ release? By comparing the voltage dependence of Ca2+ sparks in rat ventricular myocytes with the Ca2+ current, we show that the opening of a single SL Ca2+ channel can trigger a Ca2+ spark. Furthermore, we deduce that the probability of SR Ca2+ release depends of the square of the local [Ca2+]i produced by SL Ca2+ channel openings. These results are discussed with respect to the properties of Ca2+-induced Ca2+-release (CICR) and the local control theory of excitation-contraction coupling.
钙火花是兴奋 - 收缩（E - C）偶联的基本事件，当肌浆网（SR）钙释放通道开放时发生。它们通过肌膜（SL）钙通道的钙内流在局部被激活。通过在钙火花发生概率较低的条件下测量其发生概率，我们解决了我们最近工作中提出的两个重要问题：（1）当触发钙火花时，至少有多少个SL钙通道对其激活有贡献？（2）SL钙通道开放产生的亚细胞局部[Ca²⁺]与随之而来的SR钙释放之间有什么关系？通过比较大鼠心室肌细胞中钙火花的电压依赖性与钙电流，我们表明单个SL钙通道的开放可以触发钙火花。此外，我们推断SR钙释放的概率取决于SL钙通道开放产生的局部[Ca²⁺]i的平方。结合钙诱导钙释放（CICR）的特性和兴奋 - 收缩偶联的局部控制理论对这些结果进行了讨论。
