Study for the Abnormality of Intracellular Calcium Regulation in Myocardial Ischemia

1999：钙通过肌层Na/Ca交换（NCX）内流在洋地黄和缺血/再灌注诱导损伤中的作用。钠钙交换（Na/Ca exchange， NCX）是心肌细胞内主要的钙挤出系统，但也可以介导钙内流并触发SR钙释放。在洋地黄中毒或缺血/再灌注等情况下，[Na] i升高可通过NCX导致[Ca] i升高，引起Ca超载，诱发心律失常。我们使用了一种据报道可选择性阻断NCX钙内流的药物，KB-R7943 (KBR)，并评估了载有indo-1的大鼠心室肌细胞和豚鼠（GP）乳头肌的抽搐收缩和钙瞬态。在大鼠中，KBR （5μM）没有减少控制稳态抽搐收缩或Ca瞬态。当细胞通过灌注strophanthidin加载na时，KBR的加入降低了舒张[Ca] i，并消除了发生的自发Ca振荡。在GP暴露于无底物缺氧介质60分钟后，KBR减少了再氧诱导的心律失常的发生率和持续时间。KBR还能促进再氧化后张力的恢复。我们得出结论，通过NCX的钙内流可能是引起心肌钙超载和由心糖苷或再氧化引起的触发活动的关键。2000：细胞内酸中毒对抽动收缩和Ca短暂性的影响酸中毒通过降低肌原纤维Ca反应扰乱收缩性能，但在长时间酸中毒后收缩恢复。我们研究了离体大鼠心室肌细胞酸中毒时收缩性恢复的机制。通过增加碳酸氢盐缓冲液中二氧化碳的百分比，可以获得稳定的酸中毒。在酸中毒初期，抽搐细胞缩短减少，但随后收缩恢复。在初始下降过程中，舒张[Ca] i和瞬态Ca （CaT）振幅均升高，CaT下降时间延长。随后的恢复伴随着CaT振幅的进一步增加和下降的加速。阻断SR功能或选择性抑制Ca-calmodulin kinase II （CaMKII）完全消除了CaT下降的再加速，几乎消除了收缩恢复。我们得出结论，在长期酸中毒过程中，camkii依赖性SR Ca摄取的再激活可以增加SR Ca含量和CaT振幅。在未来的项目中，我们计划建立一个通过抑制线粒体氧化磷酸化来模拟缺血/再灌注的环境，然后研究对Ca电流、Ca瞬态和SR Ca含量的影响，并利用激光共聚焦显微镜观察Ca火花来估计SR Ca释放通道的活性。此外，我们希望研究KBR和线粒体保护药物（如二氮氧化物）对抗缺血/再灌注损伤的可能性。少

1999 : The role of Ca influx via sarcolemmal Na/Ca exchange (NCX) in digitalis- and ischemia/reperfusion-induced injuries.Na/Ca exchange (NCX) is a major Ca extrusion system in cardiac myocytes, but can also mediate Ca influx and can trigger SR Ca release. Under conditions such as digitalis toxicity or ischemia/reperfusion, increased [Na] i may lead to a rise in [Ca] i through NCX, causing Ca overload and triggered arrhythmias. We used an agent reported to selectively block Ca influx by NCX, KB-R7943 (KBR) and assessed twitch contractions and Ca transients in rat ventricular myocytes loaded with indo-1, and in guinea pig (GP) papillary muscles. In rat, KBR (5μM) did not decrease control steady-state twitch contractions or Ca transients. When cells were Na-loaded by perfusion of strophanthidin, the addition of KBR reduced diastolic [Ca] i and abolished spontaneous Ca oscillations which occured. In GP exposed to substrate-free hypoxic medium for 60 min, KBR reduced reoxygenation-induced … More arrhythmias both in incidence and in duration. KBR also enhanced the recovery of developed tension after reoxygenation. We conclude that Ca influx via NCX may be critical in causing myocardial Ca overload and triggered activity induced by cardiac glycoside or by reoxygenation.2000 : Effects of intracellular acidosis on twitch contraction and Ca transientsAcidosis disturbs contractile performance by decreasing myofibrillar Ca response, but the contraction recovers at prolonged acidosis. We examined the mechanism of the contractile recovery during acidosis in isolated rat ventricular myocytes. Stable acidosis was obtained by increasing the percentage of CO2 in a bicarbonate buffer. During initial min of acidosis, the twitch cell shortening decreased, but these cells appeared subsequent contractile recovery. During the initial decline, both the diastolic [Ca] i and amplitude of Ca transient (CaT) increased, and decline of CaT prolonged. The following recovery was accompanied by a further increase in amplitude and an acceleration of decline of CaT.A blockade of SR function or selective inhibition of Ca-calmodulin kinase II (CaMKII) completely abolished the reacceleration in the decline of CaT and almost eliminated the contractile recovery. We concluded that during prolonged acidosis, the CaMKII-dependent reactivation of SR Ca uptake can increase SR Ca content and CaT amplitude. This recovery can compensate for the decreased myofibrillar Ca response, but may also cause Ca overload after returning to physiological pH.In future projects, we plan to build a setup for simulated ischemia/reperfusion with inhibition of mitochondrial oxidative phosphorylation, then to study the effects on Ca currents, Ca transients and SR Ca contents, and also to estimate the activity of SR Ca release channel with Ca sparks which can be visualized using laser confocal microscopy. In addtion, we would like to examine the possibility of KBR and drugs protective for mitochondria (e.g. diazoxide) against ischemic/reperfused injuries. Less