Arrhythmogenic [Ca^<2+>]_i dynamics of the pefused heart revealed by confocal microscopy

细胞内钙离子的异常处理被认为是快速性心律失常的重要底物。在钙超载的情况下，细胞内钙离子的异常处理可导致心脏缺血再灌注损伤。然而，目前尚不清楚受损心脏的[Ca^&lt；2&gt；]i动力学改变是否以及如何促进快速性心律失常的发生。为了解决这个问题，我们使用实时共聚焦显微镜研究了在冷冻损伤和非冷冻损伤情况下，在Fluo-3/AM负载的大鼠心脏外膜区域[Ca^&lt；2&gt；]_i的时空变化。实验结果如下：1)在静息状态下，完整的心脏区域以4波/分/细胞的速度出现零星的钙波，并被短暂的钙超载所完全消除。钙超载区的波(钙超载波)通常传播到周围的心肌细胞，而…严重损伤区的E波频率较高，未见细胞间传播，也未被一过性钙波消灭。3)液氮冷冻心脏损伤后，交界区出现较多的钙波，与未损伤区形成鲜明对比，前者仅出现均匀的钙瞬变波，而无钙瞬变波。边界带表现出两种不同类型的钙波：频率较高的钙波(210/min/cell)，不受周围瞬变的影响，发生在紧邻冷冻坏死区的地方，频率较低的波(79/min/cell)，被瞬变完全减弱。相邻部位的波与心脏固有节律或高频(2-3赫兹)的兴奋不同步，而邻近部位的频率较低的波则随着心脏受到高频刺激而更频繁和普遍地出现。这些观察结果可能代表了急性心肌损伤时[Ca^&lt；2&gt；]_i的异常处理。损伤区域的钙波可能成为触发心律失常和收缩衰竭的底物。较少

Abnormal intracellular Ca^<2+> ([Ca^<2+>]_i) handling, which deyelops under Ca^<2+> overloaded conditions of the heart by e.g., ischemia-reperfusion injury, has been considered to be an important substrate for tachyarrhythmias. However, it is unknown whether and how altered [Ca^<2+>]_i dynamics of the injured heart contributes to the development of tachyarrhythmias. To address this question, we studied spatiotemporal changes in [Ca^<2+>]_i at the epicardial regions of the fluo-3/AM-loaded rat heart with and without cryo-injury using real-time confocal microscopy. The following results were obtained.1) Under quiescent conditions, the intact regions of the heart exhibited Ca^<2+> waves sporadically at 4 waves/min/cell, which were totally abolished by Ca^<2+> transients.2) The Ca^<2+> waves occurred more frequently as the heart was more highly Ca^<2+>-overloaded. The waves at the Ca^<2+>-overloaded regions (Ca^<2+>-overloaded waves) often propagated to the surrounding myocytes, whereas th … More e waves at highly damaged regions showed extremely high-frequency with neither cell-to-cell propagation nor abolition by Ca^<2+> transients.3) When cryo-injury was applied to the heart via liquid nitrogen, the border zones exhibited prevalent Ca^<2+> waves, in sharp contrast to the intact zones, where only homogeneous Ca^<2+> transients but no Ca^<2+> waves occurred. The border zones exhibited two different types of Ca^<2+> waves : the highly frequent Ca^<2+> waves (210/min/cell), which were unaffected by the surrounding Ca^<2+> transients, occurred at just adjacent to the cryo-necrosed regions, and the less frequent waves (79/min/cell), totally diminished by the transients, occurred at the vicinities.4) The frequent Ca^<2+> waves at the adjacent regions occurred asynchronously to either the intrinsic heart rhythm or high-frequency (2-3 Hz) excitation, whereas the less-frequent waves at the vicinities occurred more frequently and prevalently as the heart was stimulated at higher frequencies.These observations may represent abnormal [Ca^<2+>]_i handling during acute myocardial injury. The Ca^<2+> waves at the injured regions may become a substrate for triggered arrhythmias and contractile failure. Less