Study for the Abnormality of Intracellular Calcium Regulation in Myocardial Ischemia

1999：通过肌膜Na/Ca交换(NCX)的钙内流在洋地黄和缺血/再灌注性损伤中的作用。Na/Ca交换(NCX)是心肌细胞内主要的钙排出系统，但也可以介导钙内流和触发SR钙释放。在洋地黄毒性或缺血/再灌流等条件下，[Na]i升高可能通过NCX导致[Ca]i升高，导致钙超载并触发心律失常。我们使用一种选择性阻断NCX引起的钙内流的药物KB-R7943(KBR)，观察了INDO-1对大鼠心室肌细胞和豚鼠(GP)乳头肌的收缩和钙瞬变的影响。在大鼠中，KbR(5μM)不能减少控制性稳态收缩或钙瞬变。当细胞灌流毒毛花素钠时，KBrR的加入降低了舒张期[Ca]i，并抑制了自发性钙振荡。在无底物低氧培养60min的GP中，KbR可降低复氧诱导的…心律失常的发生率和持续时间均有所增加。KBR还能促进复氧后发达张力的恢复。我们的结论是，通过NCX的钙内流可能在引起心肌钙超载和由心苷或复氧引起的触发活动中起关键作用。2000：细胞内酸中毒对抽动收缩和钙瞬变的影响酸中毒通过降低肌原纤维的钙反应来干扰收缩性能，但持续酸中毒后收缩恢复。我们研究了酸中毒时大鼠心室肌细胞收缩功能恢复的机制。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。在酸中毒的最初分钟，收缩细胞缩短减少，但这些细胞随后出现收缩恢复。在最初的下降过程中，舒张期[Ca]i和钙瞬变幅度(CAT)均升高，且CAT下降时间延长。阻断SR功能或选择性抑制钙调蛋白激酶II(CaMKII)可完全消除CAT下降的再加速作用，使收缩恢复几乎消失。结论：在长期酸中毒过程中，CaMKII依赖的肌浆网钙摄取的重新激活可增加肌浆网钙含量和CAT幅度。在未来的项目中，我们计划建立一个抑制线粒体氧化磷酸化的模拟缺血/再灌注装置，然后研究其对钙电流、钙瞬变和肌浆网钙含量的影响，并用激光共聚焦显微镜观察钙火花来估计SR钙释放通道的活性。此外，我们还想研究KBR和保护线粒体的药物(如二氮嗪)对抗缺血/再灌流损伤的可能性。较少

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