Nonlinear dynamics of heart beat rhythm during ischemia / reperfusion and death of cardiac myocytes.

在缺血/再灌注损伤的动物模型以及充血性心力衰竭或急性心肌梗死患者中，心肌细胞的凋亡已被证实。然而，心肌细胞凋亡的机制在很大程度上仍不清楚。本研究旨在阐明与缺血/再灌注性心脏损伤相关的心律失常的诱发机制。本研究的主要结果如下：(1)在培养的新生大鼠分离的心肌细胞中，放线菌酮(CHX)对新生蛋白合成的抑制可引起心肌细胞特异性的类凋亡细胞死亡。细胞通透性的caspase-3特异性抑制物(CPP32)可减少CHX诱导的心肌细胞死亡。活性氧物种(ROS)似乎参与了CHX诱导的心肌细胞死亡，因为细胞通透性的超氧化物歧化酶模拟物四(苯甲酸)卟啉(MnTBAP)可以防止这种细胞死亡。我们的结果表明，心肌细胞的凋亡不需要从头合成蛋白质，而蛋白质合成抑制本身就会导致心肌细胞的凋亡。(2)在培养的新生大鼠分离的心肌细胞中，缺氧和缺糖(体外缺血)导致收缩间期延长和搏动节律波动。然而，在体外缺血期间，心肌细胞之间的同步性保持不变。这一结果提示心肌细胞间的缝隙连接在缺氧/缺血期间保持开放的可能性。(3)在成年大鼠Langendorff灌流的心脏中，全心缺血导致心脏周期延长，心脏在大约10分钟内停止跳动。然而，大多数Langendorff制剂在再灌流后心率恢复到对照节律。在某些情况下，再灌流可引起心律失常样的不规则搏动。

Cardiomyocyte apoptosis has been demonstrated in animal models of ischemia/reperfusion injury as well as patients with congestive heart failure or acute myocardial infarction. However, the mechanism responsible for cardiomyocyte apoptosis remains largely unknown. The present study aimed at elucidating the mechanisms responsible for the induction of cardiac arrhythmia associated with ischemia/reperfusion cardiac injury. The results obtained from this study are summarized as follows:(1) In the cultured dissociated myocytes from neonatal rats, inhibition of de novo protein synthesis itself by cycloheximide (CHX) evoked myocyte-specific apoptosis-like cell death. CHX-induced myocyte death was reduced by a treatment with a cell-permeable, specific inhibitor of caspase-3 (CPP32). Reactive oxygen Species (ROS) appeared to be involved in the CHX-induced myocyte death, because such cell death was prevented by co-treatment of Mn(III) tetrakis(benzoic acid) porphyrin (MnTBAP), a cell-permeable superoxide dismutase mimic. Our results suggest a possibility that cardiomyocyte apoptosis would not require de novo protein synthesis, and that protein synthesis inhibition itself would result in the myocyte apoptosis.(2) In the cultured dissociated myocytes from neonatal rats, hypoxia and glucose deprivation (in vitro ischemia) resulted in the increase of the contraction interval and of the fluctuation of the beating rhythm. However, synchronization between myocytes remained unchanged during in vitro ischemia. This result suggests a possibility that gap-junction among myocytes remained open during hypoxia/ischemla.(3) In the Langendorff-perfused heart from adult rats, global ischemia resulted in the elongation of heart periods, and the heart eventually stopped beating in about 10 min. However, heart beat rhythm recovered to the control one after reperfusion in most of the Langendorff preparations. In some cases, reperfusion induced arrhythmia-like irregular beat.