银杏苦内酯B对缺血豚鼠心室肌动作电位、L-型钙电流和延迟整流钾电流的作用

目的:研究银杏苦内酯B对正常和缺血心室肌细胞动作电位(action potential,AP),L-型钙电流(L-type calcium current,ICa-L)、延迟整流钾电流(Delayed Rectifier Currennt,IK)的影响.方法:用常规细胞内微电极方法记录豚鼠心室肌细胞动作电位,用全细胞膜片钳技术记录游离心室肌细胞离子流.结果:①在生理条件下,银杏苦内酯B可缩短心室肌细胞动作电位时程 (action potential duration,APD),但对AP其他参数无影响,银杏苦内酯B可增大IK,呈浓度依赖性,但对ICa-L无显著作用;②在缺血条件下,APD50、APD90明显缩短,RP、APA减小,Vmax减慢,而银杏苦内酯B则可延缓和减轻缺血所引起上述参数的变化;3.在缺血条件下,IK和ICa-L均受到抑制,但加入银杏苦内酯B后可逆转缺血所造成这两种离子流的减小.结论:银杏苦内酯B可对抗心肌缺血所引起的心肌电生理的变化,提示银杏苦内酯B可预防心律失常的发生.     

酸中毒后室性心律失常仿真研究

本文旨在分析酸中毒对心脏电生理活动的影响,探讨其诱发室性心律失常的机制.首先建立了具有pH和钙/钙调素依赖蛋白激酶Ⅱ(calcium/calmodulin dependent protein kinaseⅡ,Ca MKⅡ)调控作用的人体心室酸中毒计算模型,然后模拟了酸中毒过程中细胞和组织电活动的变化,并定量分析了心电图的改变情况.实验结果表明:在酸中毒期间,细胞动作电位时程的缩短和复极离散度的降低导致心电图QT间期缩短、T波幅值和宽度减小.同时,细胞静息电位的抬高和最大去极化速率的降低也促进了组织电兴奋的缓慢传导和传导阻滞.另外,酸中毒后的初期,肌浆网钙超载促进钙释放增多,导致细胞产生延迟后除极(delayed afterdepolarization,DADs),使心电图上表现为室性早搏.而缓慢传导、传导阻滞和室性早搏有利于折返波的产生,进而发展为室速.因此,酸中毒后细胞的触发活动是诱发室性心律失常的主要原因之一.     

人诱导多能干细胞分化的心肌细胞电生理鉴定

本文旨在研究人诱导多能干细胞分化的心肌细胞(human induced pluripotent stem cell-derived cardiomyocytes,hiPSC-CMs)的电生理特性。采用时序性短暂激活/短暂抑制Wnt信号通路的方法将未分化的IMR90-4细胞系定向诱导分化为心肌细胞。用免疫荧光染色法和流式细胞术检测心肌肌钙蛋白T(cardiac troponin T,cTnT)蛋白表达,计算hiPSC-CMs的分化率。用膜片钳技术记录hiPSC-CMs的动作电位,根据动作电位的表现对心肌细胞进行分类,并进一步分析电生理特征。结果显示,hiPSC-CMs的纯度大于95%。根据动作电位的表现,hiPSC-CMs可分为心房肌样细胞、心室肌样细胞和窦房结样细胞。其中,心室肌样细胞的动作电位时程(action potential duration,APD)、动作电位幅度(action potential amplitude,APA)和最大去极化速率(dV/dt_(max))均大于心房肌样细胞和窦房结样细胞,窦房结样细胞的d V/dt_(max)低于心室肌样细胞和心房肌样细胞。以上结果表明hiPSC-CMs纯度高,并且分化出的三种不同类型的心肌细胞具有和成熟心肌细胞相似的动作电位特征。     

室性心律失常的基因诊疗

在一些发达国家,心脏骤停已成为最主要的死亡原因.快速性室性心律失常是导致心脏骤停最主要的原因,且快速性室性心律失常会增加结构性心脏病患者发病的风险.通过药物和器械治疗方法,存在较大的局限性.心脏电活动的细胞基础是动作电位.动作电位是由于时间和电压依赖性激活各种钠、钙和钾离子通道和泵产生的.心律失常机制包括折返,自律性异常和触发活动.折返是在组织水平发生的.异常的自动性和触发活动是细胞现象,能够存在于单个心肌细胞或细胞群.心律失常的发生就是上述电冲动传播从这个局部激动由细胞间传导至更多的心肌中.故研究人员提出开展基因治疗心律失常替代现有的治疗方法.在本文中,我们讨论应用基因治疗快速性室性心律失常的基本机制并总结方法.     

面向短QT综合征的药物作用建模与仿真研究

短QT综合征(short QT syndrome,SQTS)是以心电图QT间期、心室和心房不应期明显缩短为主要显性特征,并伴有晕厥、高发心源性猝死(sudden cardiac death,SCD)和恶性心律失常风险的一类遗传性心肌离子通道病.据目前资料信息,关于SQTS致病机理的报道比较多,而对SQTS药物治疗的报道罕见.为了揭示在SQTS下的药物作用,本文通过计算机仿真构建人体心室细胞和组织的药物作用模型,利用该模型,从亚细胞、细胞、组织三个尺度,模拟SQT1、SQT2和SQT3下的普罗帕酮药物作用过程,并仿真心电图的变化情况.仿真结果表明:在SQT1下普罗帕酮延长了动作电位时程(action potential duration,APD)和心电图QT间期,并降低T波幅值;相反,在SQT2和SQT3下普罗帕酮缩短了APD和QT间期.计算使用药物前后细胞间膜电压和APD空间离散度的变化,定量分析了普罗帕酮降低T波振幅的原因.总之,对SQT1,普罗帕酮有效;对SQT2和SQT3,普罗帕酮没有改变其致心律失常的危险.仿真结果为普罗帕酮用于临床治疗SQTS提供理论参考.     

高脂饮食引起小鼠心律失常及心肌纤维化

目的不良饮食方式导致的相关疾病,如肥胖和血脂异常是心律失常的(arrhythmia)重要因素。然而,这些疾病与心律失常的确切关系尚未得到充分确认。本研究中,我们通过高脂饮食(high fatty diet,HFD)动物模型评估了HFD与小鼠心律失常与心肌纤维化的关系。方法将成年雄性C57BL/6J小鼠分为标准饮食组(STD,12%脂肪)和高脂肪饮食组(HFD;50%脂肪)两组。10周后进行在体心电图测试,随后采集心脏组织进行生化及组织学测定。结果HFD可引起小鼠室性心动过速(ventricular tachycardia),QT间期(QT interval duration)显著延长,心房传导速度(atrial conduction velocity)显著降低,右心房动作电位持续时间(action potential duration)延长。组织学和生化分析表明,HFD增加小鼠心脏组织的纤维化程度,并导致炎症。结论HFD可导致小鼠心律失常和心肌纤维化。     

Calcineurin在心衰小鼠左心室跨壁电压依赖性钾电流下调中的作用

本文旨在探讨钙调神经磷酸酶(calcineurin,Ca N)在心衰心脏左室跨壁电压依赖性钾电流下调中的作用及意义。主动脉弓部分结扎法制备小鼠压力超负荷心衰模型,采用全细胞膜片钳技术,记录应用Ca N抑制剂环孢素A(cyclosporine A,Cs A)后,假手术或心衰小鼠心室肌内膜下(subendocardial,Endo)、外膜下(subepicardial,Epi)心肌细胞电压依赖性钾电流各种成分及动作电位(action potential,AP)的变化。结果显示:各组小鼠左室游离壁心肌细胞的Ca N活性存在明显区域性差异,Endo细胞Ca N活性均高于Epi。心衰时Endo、Epi细胞Ca N活性明显升高,而使用Cs A后Ca N活性降低。在心衰模型小鼠上,Cs A可部分逆转Ito密度的下调,完全逆转Endo和Epi细胞IK,slow密度的下调,完全逆转Endo细胞Iss密度的下调。Cs A可部分逆转心衰小鼠心室肌细胞动作电位时程(action potential duration,APD)的延长,使得增高了的AP跨壁复极离散度(transmural dispersion of repolarization,TDR)明显降低,Endo、Epi细胞APD90的比值由心衰时的4.8:1恢复到2.6:1。以上结果提示,心衰时Endo、Epi细胞Ca N不同程度的激活是电压依赖性钾电流非同步下调,AP的TDR增大的重要原因,抑制Ca N可望成为防治心衰心律失常和猝死的新策略。     

缺血对心室浦肯野纤维跨膜电位和起搏离子流的影响

采用细胞内微电极和双微电极电压箝制术观察缺血对绵羊心室浦肯野纤维跨膜电位和起搏离子流（Ｉｆ）的影响。结果：模拟缺血液灌流３０ｍｉｎ,浦肯野纤维最大舒张电位（ＭＤＰ）、动作电位幅度（ＡＰＡ）明显减少;动作电位时程ＡＰＤ５０,ＡＰＤ９０明显缩短（ｎ＝１５Ｐ＜０．０１）;起搏离子流（Ｉｆ）,幅度降低,激活曲线向超极化方向移位,最大激活时间及半最大激活时间延长（ｎ＝１３Ｐ＜０．００１）。上述结果表明：心肌缺血时,心室浦肯野细胞跨膜电位及正常起搏活动不是增强,而是减弱。提示缺血性室性心律失常不是由于正常心室自律活动异常增强引起     

微电极矩阵研究小鼠胚胎心脏电生理活动

本实验采用一种新方法——微电极矩阵技术从整体水平研究小鼠胚胎离体整体心脏电生理活动。我们用微电极矩阵记录与60个电极相接触的心肌细胞的电活动(细胞外记录),称为场电位(field potentials,FPs),并与全细胞膜片钳记录的动作电位(action potentials,APs)(细胞内记录)进行比较,发现心房、心室处场电位形态类似于负向的细胞动作电位,场电位时程亦与动作电位时程类似。为研究兴奋的传导,我们比较了不同电极处场电位发生时间,发现在房室结构还未形成的胚胎发育第9．5天(E9．5)已经观察到明显的房室传导延迟(A-V delay)[(50．21±9．7)ms],而心室不同部位兴奋几乎是同步的。在发育晚期(E16．5),房室传导延迟为(82．21±10．50)ms。进一步研究基本的神经体液因素对心脏兴奋的调控,表明: 在E9．5,异丙肾上腺素(isoproterenol,Iso)使胚胎兴奋频率加快(34．04±7．31)％,房室传导延迟缩短(20．00±6．44)％,同时场电位时程增宽;相反,卡巴唑(carbachol,CCh)则使兴奋频率降低(42．32±5．36)％,房室传导缩短(26．00±4．81)％, 场电位时程减小。而在E16．5,Iso的作用显著增强,兴奋频率加快(101．54±10．23)％,房室传导延迟缩短(56．62±6．43)％, 而CCh则几乎使所有晚期心脏兴奋完全消失。所以,心脏的传导系统在胚胎发育早期4个腔室还未形成时已经建立,神经体液因子对心脏基本电生理活动的调控是在发育过程中逐渐成熟的。     

兔肺静脉肌袖心肌细胞动作电位的特性和一些离子流机制

研究兔肺静脉肌袖心肌细胞（cardiomyocytes from rabbit pulmonary vein sleeves, PVC）动作电位的特性和一些离子流机制——内向整流钾电流（IKl）、瞬时外向钾电流（ITo）和非选择性阳离子流（I NSCC）,并与左心房心肌细胞（left atrial cardiomyocytes,LAC）进行比较。采用全细胞膜片钳技术,记录动作电位和上述各离子流。发现PVC动作电位时程（action potential duration,APD）较LAC的明显延长,并可以诱发出第二平台反应。PVC上存在I NSCC. PVC的IKl、I To和I NSCC电流密度均较LAC的明显减小。PVC和LAC存在复极离子流的差异,这种差异构成了两者动作电位差异的基础,进而可能成为肺静脉肌袖致心律失常特性的重要离子流机制。     

Stochastic Cardiac Pacing Increases Ventricular Electrical Stability—A Computational Study

The ventricular tissue is activated in a stochastic rather than in a deterministic rhythm due to the inherent heart rate variability (HRV). Low HRV is a known predictor for arrhythmia events and traditionally is attributed to autonomic nervous system tone damage. Yet, there is no model that directly assesses the antiarrhythmic effect of pacing stochasticity per se. One-dimensional (1D) and two-dimensional (2D) human ventricular tissues were modeled, and both deterministic and stochastic pacing protocols were applied. Action potential duration restitution (APDR) and conduction velocity restitution (CVR) curves were generated and analyzed, and the propensity and characteristics of action potential duration (APD) alternans were investigated. In the 1D model, pacing stochasticity was found to sustain a moderating effect on the APDR curve by reducing its slope, rendering the tissue less arrhythmogenic. Moreover, stochasticity was found to be a significant antagonist to the development of concordant APD alternans. These effects were generally amplified with increased variability in the pacing cycle intervals. In addition, in the 2D tissue configuration, stochastic pacing exerted a protective antiarrhythmic effect by reducing the spatial APD heterogeneity and converting discordant APD alternans to concordant ones. These results suggest that high cardiac pacing stochasticity is likely to reduce the risk of cardiac arrhythmias in patients.     

Effect of Global Cardiac Ischemia on Human Ventricular Fibrillation: Insights from a Multi-scale Mechanistic Model of the Human Heart

Acute regional ischemia in the heart can lead to cardiac arrhythmias such as ventricular fibrillation (VF), which in turn compromise cardiac output and result in secondary global cardiac ischemia. The secondary ischemia may influence the underlying arrhythmia mechanism. A recent clinical study documents the effect of global cardiac ischaemia on the mechanisms of VF. During 150 seconds of global ischemia the dominant frequency of activation decreased, while after reperfusion it increased rapidly. At the same time the complexity of epicardial excitation, measured as the number of epicardical phase singularity points, remained approximately constant during ischemia. Here we perform numerical studies based on these clinical data and propose explanations for the observed dynamics of the period and complexity of activation patterns. In particular, we study the effects on ischemia in pseudo-1D and 2D cardiac tissue models as well as in an anatomically accurate model of human heart ventricles. We demonstrate that the fall of dominant frequency in VF during secondary ischemia can be explained by an increase in extracellular potassium, while the increase during reperfusion is consistent with washout of potassium and continued activation of the ATP-dependent potassium channels. We also suggest that memory effects are responsible for the observed complexity dynamics. In addition, we present unpublished clinical results of individual patient recordings and propose a way of estimating extracellular potassium and activation of ATP-dependent potassium channels from these measurements.     

兔LQT2模型心室肌复极化的性别差异

本研究旨在探讨长QT综合征（long QT syndromes,LQTS）室性心律失常发生的性别差异及其电生理机制,初步观察了不同性别兔LQT2模型左心事原已存在的电生理异质性和心事复极动力学的特征。实验分为3组,上下常组以标准台氏液灌流;LQT2模型组给予含100gmol／L dl-sotalol的台式液灌流;LQT2模型＋低钾组给了含3．0mmol／LKCl、100μmol／L dl-sotalol的台式液灌流。采用冠状动脉旋支灌注兔左室心肌楔形组织块标本,应用浮置玻璃微电极记录技术进行记录。给予基础刺激周长（basic cycle length,BCL）为500、l000和2000ms的S1刺激,同步记录心事肌内膜侧、外膜侧细胞动作电位,并记录跨壁心电图：在BCL为500和1000ms时加用S2程序刺激以记录动作电位时程（action potential duration,APD）恢复曲线。研究发现：在不同刺激频率时,3组实验雌兔心肌细胞的跨壁复极化离散（transmural dispersion of repolarization,TDR）、APD恢复曲线斜率均大于雄兔,有显著性差异（P〈0．05）,并呈频率依赖性;LQT2模型组及LQT2模型＋低钾组雌雄兔TDR、APD恢复曲线斜率较正常组明显增人（P〈0．01）。BCL为1000ms时,LQT2模型组雌兔7例中1例发生尖端扭转性窀性心动过速（torsade de pointes,TdP）;LQT2模型＋低钾组雌兔7例中5例诱发TdP,雄兔7例中2例诱发TdP,有显著性差异（P〈0．05）。结果提示：LQT2模型心肌原已存在的电生理异质性和动态异质性均有明显的性别差异,并≯频率依赖性。存LQT2模型中,TDR以及APD恢复曲线斜率的增大可能是雌性动物较雄性更易发生尖端扭转性心律失常的原因。     

Effects of simulated ischemia on spiral wave stability

Regional hyperkalemia during acute myocardial ischemia is a major factor promoting electrophysiological abnormalities leading to ventricular fibrillation (VF). However, steep action potential duration restitution, recently proposed to be a major determinant of VF, is typically decreased rather than increased by hyperkalemia and acute ischemia. To investigate this apparent contradiction, we simulated the effects of regional hyperkalemia and other ischemic components (anoxia and acidosis) on the stability of spiral wave reentry in simulated two-dimensional cardiac tissue by use of the Luo-Rudy ventricular action potential model. We found that the hyperkalemic "ischemic" area promotes wavebreak in the surrounding normal tissue by accelerating the rate of spiral wave reentry, even after the depolarized ischemic area itself has become unexcitable. Furthermore, wavebreak and fibrillation can be prevented if the dynamical instability of the normal tissue is reduced significantly by targeting electrical restitution properties, suggesting a novel therapeutic approach.     

Real-time monitoring of nitric oxide in ischemic myocardium using an NO-selective electrode calibrated by electron spin resonance

Using a Langendorff-perfused rat heart preparation and selective electrodes, we determined nitric oxide (NO) and oxygen levels in cardiac tissue. An NO-selective electrode that was calibrated by electron spin resonance (ESR) spectroscopy was inserted into the middle of the myocardium in the left ventricle. Simultaneously, we used an O2-selective electrode to measure the partial pressure of oxygen (pO2) in the perfusate, Krebs-Henseleit (K-H) solution, that was ejected from the heart. After 30 min of aerobic control perfusion, hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. Under ischemic conditions, with a gradually decreasing pO2, NO detected by an NO-sensitive electrode within the myocardium was gradually increased. The maximum concentration increases in NO and decreases in pO2 during global ischemia were +10.200 +/- 1.223 microM and -58.608 +/- 4.123 mmHg, respectively. NO and pO2 levels both recovered to pre-ischemia baseline values when perfusion was restarted after global ischemia (reperfusion). The presence of Nomega-nitro-L-arginine methyl ester (L-NAME, 10 mM), a NOS inhibitor, prevented ischemia/reperfusion-induced changes in NO. This study shows that an NO-selective electrode that is calibrated by ESR can provide accurate, real-time monitoring of cardiac NO in normal and ischemic myocardium.     

Anti-Arrhythmic Effect of Verapamil Is Accompanied by Preservation of Cx43 Protein in Rat Heart

The present study was to test the hypothesis that anti-arrhythmic properties of verapamil may be accompanied by preserving connexin43 (Cx43) protein via calcium influx inhibition. In an in vivo study, myocardial ischemic arrhythmia was induced by occlusion of the left anterior descending (LAD) coronary artery for 45 min in Sprague-Dawley rats. Verapamil, a calcium channel antagonist, was injected i.v. into a femoral vein prior to ischemia. Effects of verapamil on arrhythmias induced by Bay K8644 (a calcium channel agonist) were also determined. In an ex vivo study, the isolated heart underwent an initial 10 min of baseline normal perfusion and was subjected to high calcium perfusion in the absence or presence of verapamil. Cardiac arrhythmia was measured by electrocardiogram (ECG) and Cx43 protein was determined by immunohistochemistry and western blotting. Administration of verapamil prior to myocardial ischemia significantly reduced the incidence of ventricular arrhythmias and total arrhythmia scores, with the reductions in heat rate, mean arterial pressure and left ventricular systolic pressure. Verapamil also inhibited arrhythmias induced by Bay K8644 and high calcium perfusion. Effect of verapamil on ischemic arrhythmia scores was abolished by heptanol, a Cx43 protein uncoupler and Gap 26, a Cx43 channels inhibitor. Immunohistochemistry data showed that ischemia-induced redistribution and reduced immunostaining of Cx43 were prevented by verapamil. In addition, diminished expression of Cx43 protein determined by western blotting was observed following myocardial ischemia in vivo or following high calcium perfusion ex vivo and was preserved after verapamil administration. Our data suggest that verapamil may confer an anti-arrhythmic effect via calcium influx inhibition, inhibition of oxygen consumption and accompanied by preservation of Cx43 protein.     

Myocardial ischemic postconditioning: a brief ischemia causes conversion of resistent reperfusion-induced ventricular fibrillation into the normal rhythm

Brief episodes of myocardial ischemia-reperfusion were shown to be protective against reperfusion injury when used during early reperfusion after a prolonged ischemic episode. This phenomenon has been termed myocardial ischemic postconditioning. In this study, an effect of ischemic postconditioning on persistent reperfusion-induced ventricular fibrillation was studied in the rat isolated heart. 2 minutes of global ischemia on the 15th minute of reperfusion after 30 minutes of regional ischemia effectively abolished the persistent ventricular fibrillation. In non-postconditioned hearts, the ventricular fibrillation continued to the end of reperfusion. The ischemic postconditioning seems to exert a strong antiarrhythmic effect protecting the heart against persistent reperfusion-induced ventricular tachyarrhythmias.     

Sevoflurane postconditioning attenuates reperfusion-induced ventricular arrhythmias in isolated rat hearts exposed to ischemia/reperfusion injury

Sevoflurane postconditioning has been proven to protect the hearts against ischemia/reperfusion injury, manifested mainly by improved cardiac function, reduced myocardial specific biomarker release, and decreased infarct size. This study is to observe the effects of sevoflurane postconditioning on reperfusion-induced ventricular arrhythmias and reactive oxygen species generation in Langendorff perfused rat hearts. Compared with the unprotected hearts subjected to 25 min of global ischemia followed by 30 min of reperfusion, exposure of 3% sevoflurane during the first 15 min of reperfusion significantly improved cardiac function, reduced cardiac troponin I release, decreased infarct size and attenuated reperfusion-induced ventricular arrhythmia. Further analysis on arrhythmia during the 30 min of reperfusion showed that, sevoflurane postconditioning decreased both the duration and incidence of ventricular tachycardia and ventricular fibrillation. In the meantime, intracellular malondialdehyde and reactive oxygen species levels were also reduced. These above results demonstrate that sevoflurane postconditioning protects the hearts against ischemia/reperfusion injury and attenuates reperfusion-induced arrhythmia, which may be associated with the regulation of lipid peroxidation and reactive oxygen species generation.     

Stretch-induced ventricular arrhythmias during acute ischemia and reperfusion.

Mechanical stretch has been demonstrated to have electrophysiological effects on cardiac muscle, including alteration of the probability of excitation, alteration of the action potential waveform, and stretch-induced arrhythmia (SIA). We demonstrate that regional ventricular ischemia due to coronary artery occlusion increases arrhythmogenic effects of transient diastolic stretch, whereas globally ischemic hearts showed no such increase. We tested our hypothesis that, during phase Ia ischemia, regionally ischemic hearts may be more susceptible to triggered arrhythmogenesis due to transient diastolic stretch. During the first 20 min of regional ischemia, the probability of eliciting a ventricular SIA (P(SIA)) by transient diastolic stretch increased significantly. However, after 30 min, P(SIA) decreased to a value comparable with baseline measurements, as expected during phase Ib, where most ventricular arrhythmias are of reentrant mechanisms. We also suggest that mechanoelectrical coupling may contribute to the nonreentrant mechanisms underlying reperfusion-induced arrhythmia. When coronary artery occlusion was relieved after 30 min of ischemia, we observed an increase in P(SIA) and the maintenance of this elevated level throughout 20 min of reperfusion. We conclude that mechanoelectrical coupling may underlie triggered arrhythmogenesis during phase 1a ischemia and reperfusion.     

The effects of focal ischemia and reperfusion on the glutathione content of mitochondria from rat brain subregions

Glutathione is a key cellular antioxidant that is contained in both cytoplasmic and mitochondrial compartments. Previous investigations indicate that depletion of the mitochondrial pool of glutathione can greatly reduce cell viability. In the present investigation, the effect of focal cerebral ischemia on total (reduced plus oxidized) glutathione in mitochondria was assessed using a rat model of middle cerebral artery occlusion. Total glutathione was substantially decreased in mitochondria prepared from severely ischemic focal tissue in both the cerebral cortex and striatum at 2 h of vessel occlusion and persisted for at least the first 3 h of reperfusion. The loss of mitochondrial glutathione was not associated with decreases of the total tissue glutathione content and was not due to the formation of mixed disulfides with mitochondrial proteins. Thus, an imbalance between uptake and release from the mitochondria in the ischemic tissue provides the most likely explanation for the loss. Decreases in glutathione also developed in mitochondria from the moderately ischemic perifocal tissue when the period of arterial occlusion was extended to 3 h. The presence of mitochondrial glutathione depletion during ischemia showed an apparent close association with the subsequent development of tissue infarction. These findings are consistent with a role for the glutathione depletion in determining the susceptibility of brain tissue to focal ischemia.