线粒体通透件转换孔在缺血/再灌注损伤中的作用

背景 线粒体作为“能量工厂”提供细胞生长及代谢所需的三磷酸腺苷（adenosine triphosphate,ATP）,同时也是细胞存活与否的重要信号管理者.线粒体通透性转换孔（mitochondrial permeability transition pore,mPTP）是横跨线粒体内外膜之间的允许相对分子质量1.5 kD以下的分子自由通过的孔道.在脑缺血/再灌注（ischemia/reperfusion,I/R）损伤中,线粒体是研究的焦点,而mPTP作为线粒体的门户更是影响着线粒体膜电位（mitochondrial membrane potential,△ψm）、线粒体Ca2＋超载及促细胞死亡物质释放等一系列过程. 目的 对mPTP在I/R损伤中可能的作用机制及治疗方法进行综述. 内容 整理和阐述了mPTP的结构、mPTP与I/R损伤的机制和预防与治疗I/R损伤的可能方法. 趋向 随着mPTP在I/R损伤中的作用机制不断被揭示,其将成为治疗I/R损伤的重要靶点.     

心肌缺血再灌注损伤的线粒体通透性转换机制

线粒体功能障碍存心肌缺血再灌注（ischema／reperfusion I／R）损伤中占有重要地位．近年研究发现线粒体的功能障碍和线粒体通透性转换孔道（mitochondfial permeability transition pore，mPTP）密切相关，     

The effect of anaesthetics on the myocardium--new insights into myocardial protection

A variety of laboratory and clinical studies clearly indicate that exposure to anaesthetic agents can lead to a pronounced protection of the myocardium against ischaemia-reperfusion injury. Several changes in the protein structure of the myocardium that may mediate this cardioprotection have been identified. Ischaemia-reperfusion of the heart occurs in a variety of clinical situations including transplantations, coronary artery bypass grafting or vascular surgery. Ischaemia may also occur during a stressful anaesthetic induction. Early restoration of arterial blood flow and measures to improve the ischaemic tolerance of the tissue are the main therapeutic options (i.e. cardioplegia and betablockers). There exists increasing evidence that anaesthetic agents interact with the mechanisms of ischaemia-reperfusion injury and protect the myocardium by a 'preconditioning' and a 'postconditioning' mechanism. Hence, the anaesthesiologist may substantially influence the critical situation of ischaemia-reperfusion during surgery by choosing the appropriate anaesthetic agent. This review summarizes the current understanding of the mechanisms of anaesthetic-induced myocardial protection. In this context, three time windows of anaesthetic-induced cardioprotection are discussed: administration (1) during ischaemia, (2) after ischaemia-during reperfusion (postconditioning) and (3) before ischaemia (preconditioning). Possible clinical implications of these interventions will be reviewed.     

The concept of anaesthetic-induced cardioprotection: mechanisms of action

The mechanisms by which ischaemia reperfusion injury can be influenced have been the subject of extensive research in the last decades. Early restoration of arterial blood flow and surgical measures to improve the ischaemic tolerance of the tissue are the main therapeutic options currently in clinical use. In experimental settings ischaemic preconditioning has been described as protecting the heart, but the practical relevance of interventions by ischaemic preconditioning is strongly limited to these experimental situations. However, ischaemia reperfusion of the heart routinely occurs in a variety of clinical situations, such as during transplantations, coronary artery bypass grafting or vascular surgery. Moreover, ischaemia reperfusion injury occurs without any surgical intervention as a transient myocardial ischaemia during a stressful anaesthetic induction. Besides ischaemic preconditioning, another form of preconditioning was discovered over 10 years ago: the anaesthetic-induced preconditioning. There is increasing evidence that anaesthetic agents can interact with the underlying pathomechanisms of ischaemia reperfusion injury and protect the myocardium by a preconditioning mechanism. Hence, the anaesthetist himself can substantially influence the critical situation of ischaemia reperfusion during the operation by choosing the right anaesthetic. A better understanding of the underlying mechanisms of anaesthetic-induced cardioprotection not only reflects an important increase in scientific knowledge but may also offer the new perspective of using different anaesthetics for targeted intraoperative myocardial protection. There are three time windows when a substance may interact with the ischaemia reperfusion injury process: (1) during ischaemia, (2) after ischaemia (i.e. during reperfusion), and (3) before ischaemia (preconditioning).     

缺血预处理和后处理减轻缺血/再灌注损伤的分子机制

背景 组织长时间缺血后再灌注能导致缺血/再灌注(ischaemia/reperfusion,I/R)损伤.研究证实缺血预处理和缺血后处理可减轻I/R损伤大约75％. 目的 综述缺血预处理和缺血后处理减轻I/R损伤的分子机制. 内容 缺血预处理和缺血后处理的分子机制涉及腺苷、缓激肽、阿片和大麻素激活的细胞表面G耦联蛋白受体.这些物质依次兴奋生长受体,继而激活细胞保护性通路,其中包括通过有丝分裂原激活蛋白激酶(mitogen-activated protein kinase,MEK)/细胞外信号调节激酶1/2(extracellular signal-regular kinase 1/2,ERK1/2)途径减少细胞凋亡以及通过磷脂酰肌醇-3激酶途径减少线粒体通透性转换孔(mitochondrial permeability transition pore,mPTP)开放.mPTp开放能够导致细胞死亡.最近研究提示,细胞表面激活的肿瘤坏死因子-α受体通过激活Janus激酶以及信号转导子和转录激活因子3途径而发挥细胞保护作用. 趋向 缺血预处理和缺血后处理减轻I/R损伤的分子机制目前仍在研究中,有望在对此更深入理解的基础上获得可转化为有意义的临床治疗措施.     

Isoflurane postconditioning prevents opening of the mitochondrial permeability transition pore through inhibition of glycogen synthase kinase 3beta

BACKGROUND: Postischemic administration of volatile anesthetics activates reperfusion injury salvage kinases and decreases myocardial damage. However, the mechanisms underlying anesthetic postconditioning are unclear. METHODS: Isolated perfused rat hearts were exposed to 40 min of ischemia followed by 1 h of reperfusion. Anesthetic postconditioning was induced by 15 min of 2.1 vol% isoflurane (1.5 minimum alveolar concentration) administered at the onset of reperfusion. In some experiments, atractyloside (10 microm), a mitochondrial permeability transition pore (mPTP) opener, and LY294002 (15 microm), a phosphatidylinositol 3-kinase inhibitor, were coadministered with isoflurane. Western blot analysis was used to determine phosphorylation of protein kinase B/Akt and its downstream target glycogen synthase kinase 3beta after 15 min of reperfusion. Myocardial tissue content of nicotinamide adenine dinucleotide served as a marker for mPTP opening. Accumulation of MitoTracker Red 580 (Molecular Probes, Invitrogen, Basel, Switzerland) was used to visualize mitochondrial function. RESULTS: Anesthetic postconditioning significantly improved functional recovery and decreased infarct size (36 +/- 1% in unprotected hearts vs. 3 +/- 2% in anesthetic postconditioning; P < 0.05). Isoflurane-mediated protection was abolished by atractyloside and LY294002. LY294002 inhibited isoflurane-induced phosphorylation of protein kinase B/Akt and glycogen synthase kinase 3beta and opened mPTP as determined by nicotinamide adenine dinucleotide measurements. Atractyloside, a direct opener of the mPTP, did not inhibit phosphorylation of protein kinase B/Akt and glycogen synthase kinase 3beta by isoflurane but reversed isoflurane-mediated cytoprotection. Microscopy showed accumulation of the mitochondrial tracker in isoflurane-protected functional mitochondria but no staining in mitochondria of unprotected hearts. CONCLUSIONS: Anesthetic postconditioning by isoflurane effectively protects against reperfusion damage by preventing opening of the mPTP through inhibition of glycogen synthase kinase 3beta.     

海马神经细胞线粒体通透性转换孔在富氢液减轻大鼠全脑缺血再灌注损伤中的作用

目的 评价海马神经细胞线粒体通透性转换孔(mPTP)在富氢液减轻大鼠全脑缺血再灌注损伤中的作用.方法 雄性SD大鼠72只,体重250 ～ 300 g,采用随机数字表法,将其随机分为6组(n=12):假手术组(S组)、缺血再灌注组(IR组)、生理盐水组(NS组)、富氢液组(H组)、苍术苷组(A组)和富氢液+苍术苷组(HA组).采用四血管阻塞法建立大鼠全脑缺血再灌注模型,缺血15 min后恢复灌注.H组和HA组于再灌注即刻腹腔注射富氢液5 ml/kg,其余组腹腔注射等容量生理盐水;A组和HA组于再灌注前10 min行侧脑室注射苍术苷15 μl,NS组和H组侧脑室注射等容量生理盐水.再灌注24h时行神经行为学损伤评分后各组随机处死8只大鼠,迅速断头,分离海马神经细胞线粒体,采用分光光度计法测定mPTP的开放程度,Rhodamine123法测定线粒体膜电位.再灌注72 h时各组处死4只大鼠,取海马组织,光镜下观察CA1区病理学结果,计数该区神经细胞存活数.结果 与S组比较,其余组再灌注24h时行为学损伤加重,mPTP活性升高,线粒体膜电位降低(P＜0.05);与IR组比较,H组和HA组再灌注24h时行为学损伤减轻,mPTP活性降低,线粒体膜电位升高(P＜0.05);与H组比较,HA组行为学损伤加重,mPTP活性升高,线粒体膜电位降低(P＜0.05).再灌注72 h时HA组较IR组神经细胞存活数增加(P＜0.05),H组海马CA1区神经元损伤较IR组、NS组、A组和HA组减轻.结论 富氢液可减轻大鼠全脑缺血再灌注损伤,其机制与抑制海马神经细胞mPTP开放,减少线粒体膜电位降低,从而维持线粒体功能有关.     

Taurine protects against early and late skeletal muscle dysfunction secondary to ischaemia reperfusion injury.

OBJECTIVE: To assess the efficacy of the cytoprotective B-amino acid taurine in prevention of skeletal muscle dysfunction secondary to ischaemia-reperfusion (IR) injury. DESIGN: Randomised controlled animal study. SETTING: Biomedical research laboratory, teaching hospital, Republic of Ireland. ANIMALS: 96 Sprague Dawley rats. INTERVENTIONS: Rats were randomised into three groups (n = 24/group): control (sham); ischaemia-reperfusion (untreated); and ischaemia-reperfusion + taurine. A further 24 rats were given taurine alone. The rat cremaster skeletal muscle model of four hours of ischaemia followed by reperfusion was used. Taurine 4%wt/vol was given in the animals' water throughout the experiment, beginning 48 hours before the ischaemia was initiated. OUTCOME MEASURES: 8 rats were killed from each group and muscle contractile function was assessed using electrical field stimulation in a tissue bath at 24 hrs, 48 hrs and 7 days. RESULTS: Ischaemia followed by 24 hours, 48 hours or 7 days of reperfusion resulted in significant reduction in both muscle twitch and tetanic contractile function (p < 0.05). This was reversed by taurine, which resulted in significant preservation of twitch and tetanic contractility at all time points including one week of reperfusion (p < 0.05). There was no difference in muscle function between muscle treated with taurine after ischaemia-reperfusion and control muscle, with the same operation but without ischaemia, from 48 hours onwards. CONCLUSIONS: These data show that pharmaceutical use of the endogenous amino acid taurine, unlike many-other agents, protects electrophysiological function in skeletal muscle against both early and late ischaemia-reperfusion injury.     

Age-associated differences in the inhibition of mitochondrial permeability transition pore opening by cyclosporine A

Background: Inhibiting mitochondrial permeability transition pore (mPTP) opening is a key protection of the myocardium from ischemia/reperfusion (I/R) injury. Here, we investigated age‐associated differences in the ability of cyclosporine A (CsA) to protect the heart and to modulate mPTP opening during I/R injury in vivo and its opening induced by reactive oxygen species (ROS) in vitro. Methods: Fischer 344 male rats were assigned from their respective age groups, young or old groups, to (1) I/R or (2) I/R+CsA. All animals were subjected to 30 min of ischemia following 120 min of reperfusion to determine myocardial infarct size in vivo. To measure mPTP opening in vivo, left ventricular tissues were collected 10 min after reperfusion and nicotinamide adenine dinucleotide (NAD⁺) levels were measured. In parallel experiments, rat ventricular myocytes were prepared from young and old hearts, loaded with tetramethylrhodamine ethylester and then subjected to oxidative stress in the presence or absence of CsA, and the mPTP opening time was measured using laser scanning confocal microscopy. Results: CsA reduced myocardial infarct size in young I/R rats. Whereas CsA failed to significantly affect myocardial infarct size in old I/R rats, NAD⁺ levels were better preserved in young CsA‐treated rats, but this relative improvement was not observed in old rats. CsA also significantly prolonged the time necessary to induce mPTP opening in young cardiomyocytes, but not in cardiomyocytes isolated from the old rats. Conclusions: mPTP regulation is dysfunctional in the aged myocardium and this could account for loss of cardioprotection with aging.     

Allopurinol plus pentoxifilline in hepatic ischaemia/reperfusion injury

OBJECTIVES: Ischaemia/reperfusion injury of the liver is the major cause of liver dysfunction and cellular death in transplantation and in liver resection with hepatic pedicle clamping. Many agents are used to prevent this phenomenon, which occurs following interaction of different mediators during both ischaemia and reperfusion. In this study, we aimed to assess the effects of allopurinol, a xanthine oxidase inhibitor, and pentoxifilline, on liver ischaemia/reperfusion injury when used together and to compare these with the effects of using these agents singly. METHODS: Thirty-two rats were divided into four groups consisting of eight rats: Group C, control; Group P, pentoxifilline; Group A, allopurinol; and Group PA, pentoxifilline + allopurinol. Alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH) levels were measured before hepatic pedicle clamping, on the 45th minute of ischaemia and 15 and 45 minutes after reperfusion. Group P rats were injected with 50 mg/kg pentoxifilline, Group A rats 50 mg/kg allopurinol and Group PA rats were injected with both agents 15 minutes before hepatic pedicle clamping. RESULTS: Ischaemia/reperfusion injury was produced by hepatic pedicle clamping, as demonstrated by AST, ALT and LDH increase. Injury prevention occurred in Groups P, A and PA. No significantly different (better) prevention was provided by giving allopurinol plus pentoxifilline to the rats. Furthermore, no difference was observed between the allopurinol and pentoxifilline injected groups in terms of preventing ischaemia/reperfusion injury. CONCLUSIONS: Pretreatment with allopurinol or pentoxifilline resulted in significantly lower hepatic enzyme elevation than that in controls in the rat liver ischaemia/reperfusion model. Using both agents does not provide better protection than using either agent alone.     

Effects of systemic and regional taurine on skeletal muscle function following ischaemia-reperfusion injury.

INTRODUCTION: Tissues subjected to prolonged ischaemia are paradoxically further damaged when their perfusion is restored. The mechanisms underlying this ischaemia-reperfusion injury are complex, but oxidative attack is a central feature. Among the therapeutic agents used to attenuate ischaemia-reperfusion injury, endogenous agents such as taurine which form part of the native defence mechanism against oxidative damage are of particular interest. METHODS: Using a model of hindlimb ischaemia-reperfusion injury in the rat, taurine solution was administered either into the operated hindlimb, into the systemic circulation, or both. Contraction strengths of gastrocnemius biopsies from the operated and contralateral (control) hindlimbs of each animal were measured. RESULTS: Fast twitch strength was impaired significantly by ischaemia-reperfusion injury, and taurine injected into the operated limb conferred partial protection. A similar trend was observed for tetany, but protection by taurine was not statistically significant for tetanic contraction strength. CONCLUSION: Preservation of fast twitch strength following ischaemia-reperfusion injury by administration of taurine before ischaemia has clinical potential. However, delivery to the affected tissues during ischaemia presents technical difficulties.     

Kidney ischaemia-reperfusion injury and polyribosome structure

BACKGROUND: Inhibition of protein synthesis and polyribosome disaggregation are the early events in cell injury provoked by various pathogenic mechanisms, including energy depletion. Polyribosome disaggregation might be expected to occur during ischaemia-reperfusion injury due to ischaemic energy depletion, but also due to detrimental effects of reactive oxygen species on various macromolecules and cellular structures. METHODS: Mouse kidney ischaemia-reperfusion injury was provoked by temporary clamping of the renal artery. The polyribosome sedimentation pattern was analyzed by sucrose density centrifugation of kidney postmitochondrial supernatant. RESULTS AND CONCLUSIONS: Ischaemia for 5 min in the mouse kidney provoked polyribosome disaggregation and an increase of monomer ribosome fraction which was augmented during 10-360 min of reperfusion. Recovery of polyribosome aggregates appeared between 6 and 24 h of reperfusion. Cycloheximide pretreatment prevented only polyribosome disaggregation caused by ischaemia and not that caused by reperfusion. This indicates different mechanisms of polyribosome disaggregation during ischaemia and reperfusion. It probably occurs in the former due to inhibition of initiation of translation, resulting in accumulation of unprogrammed monomer ribosomes, and in the latter due to the splitting of mRNA and breakdown of polyribosomes. Reperfusion did not increase ribonuclease activity in kidney cytosol, but increased the tissue concentration of malonaldehyde, indicating an augmentation in oxygen free radical generation. Possibly these may have caused a non-enzymatic breakdown of polyribosomes. However, pretreatment with allopurinol did not prevent polyribosome breakdown during ischaemia-reperfusion injury.     

Inhibition of mitochondrial permeability transition enhances isoflurane-induced cardioprotection during early reperfusion: the role of mitochondrial KATP channels

Inhibition of the mitochondrial permeability transition pore (mPTP) mediates the protective effects of brief, repetitive ischemic episodes during early reperfusion after prolonged coronary artery occlusion. Brief exposure to isoflurane immediately before and during early reperfusion also produces cardioprotection, but whether mPTP is involved in this beneficial effect is unknown. We tested the hypothesis that mPTP mediates isoflurane-induced postconditioning and also examined the role of mitochondrial KATP (mKATP) channels in this process. Rabbits (n = 102) subjected to a 30-min coronary occlusion followed by 3 h reperfusion received 0.9% saline (control), isoflurane (0.5 or 1.0 MAC) administered for 3 min before and 2 min after reperfusion, or the mPTP inhibitor cyclosporin A (CsA, 5 or 10 mg/kg) in the presence or absence of the mPTP opener atractyloside (5 mg/kg) or the selective mK(ATP) channel antagonist 5-hydroxydecanoate (5-HD; 10 mg/kg). Other rabbits received 0.5 MAC isoflurane plus 5 mg/kg CsA in the presence and absence of atractyloside or 5-HD. Isoflurane (1.0 but not 0.5 MAC) and CsA (10 but not 5 mg/kg) reduced (P < 0.05) infarct size (21% +/- 4%, 44% +/- 6%, 24% +/- 3%, and 43% +/- 6%, respectively, mean +/- sd of left ventricular area at risk; triphenyltetrazolium staining) as compared with control (42% +/- 7%). Isoflurane (0.5 MAC) plus CsA (5 mg/kg) was also protective (27% +/- 4%). Neither atractyloside nor 5-HD alone affected infarct size, but these drugs abolished protection by 1.0 MAC isoflurane, 10 mg/kg CsA, and 0.5 MAC isoflurane plus 5 mg/kg CsA. The results indicate that mPTP inhibition enhances, whereas opening abolishes, isoflurane-induced postconditioning. This isoflurane-induced inhibition of mitochondrial permeability transition is dependent on activation of mitochondrial KATP channels in vivo.     

Effect of low-dose N-acetyl-cysteine infusion on tourniquet-induced ischaemia-reperfusion injury in arthroscopic knee surgery

BACKGROUND: Temporary occlusion of blood flow is used during arthroscopic knee surgery in order to provide a bloodless surgical field. The resulting ischaemia-reperfusion causes lipid peroxidation, which contributes to tissue injury. The aim of the study was to investigate the effect of low-dose n-acetyl cysteine (NAC) infusion on oxidative stress by determining malondialdehyde (MDA) levels during arthroscopic knee surgery. METHODS: Thirty patients, ASA I - II, undergoing arthroscopic knee debridement under a tourniquet were divided into NAC and control groups. Anaesthesia was induced with propofol, fentanyl and vecuronium bromide and maintained with desflurane in an equal parts O(2)-N(2)O mixture. In the NAC group, an infusion of NAC, 5 mg kg(-1).h(-1), was started after intubation, and continued until extubation. An equal volume of saline was infused to the control group. Duration of ischaemia, anaesthesia time, total dose of NAC infused were also recorded. Venous blood and synovial membrane tissue samples were obtained 10 min after the onset of NAC infusion but before tourniquet inflation (t1), after 30 min of ischaemia (t2), and after 5 min of reperfusion following tourniquet release (t3). RESULTS: Plasma MDA levels were significantly lower in the NAC group on reperfusion. There were no differences between the groups in tissue MDA levels at ischaemia and reperfusion times. CONCLUSION: Low-dose n-acetyl cysteine infusion attenuates lipid peroxidation and ischaemia-reperfusion injury in arthroscopic knee surgery requiring tourniquet application.     

Anaesthetic-induced myocardial preconditioning: fundamental basis and clinical implications

OBJECTIVE: Volatile halogenated anaesthetics offer a myocardial protection when they are administrated before a myocardial ischaemia. Cellular mechanisms involved in anaesthetic preconditioning are now better understood. The objectives of this review are to understand the anaesthetic-induced preconditioning underlying mechanisms and to know the clinical implications. DATA SOURCES: References were obtained from PubMed data bank (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi) using the following keywords: volatile anaesthetic, isoflurane, halothane, sevoflurane, desflurane, preconditioning, protection, myocardium. DATA SYNTHESIS: Ischaemic preconditioning (PC) is a myocardial endogenous protection against ischaemia. It has been described as one or several short ischaemia before a sustained ischemia. These short ischaemia trigger a protective signal against this longer ischaemia. An ischemic organ is able to precondition a remote organ. It is possible to replace the short ischaemia by a preadministration of halogenated volatile anaesthetic with the same protective effect, this is called anaesthetic PC (APC). APC and ischaemic PC share similar underlying biochemical mechanisms including protein kinase C, tyrosine kinase activation and mitochondrial and sarcolemnal K(ATP) channels opening. All halogenated anaesthetics can produce an anaesthetic PC effect. Myocardial protection during reperfusion, after the long ischaemia, has been shown by successive short ischaemia or volatile anaesthetic administration, this is called postconditioning. Ischaemic PC has been described in humans in 1993. Clinical studies in human cardiac surgery have shown the possibility of anaesthetic PC with volatile anaesthetics. These studies have shown a decrease of postoperative troponin in patient receiving halogenated anaesthetics.     

Roles of mitochondria in health and disease

Mitochondria play a central role in cell life and cell death. An increasing number of studies place mitochondrial dysfunction at the heart of disease, most notably in the heart and the central nervous system. In this article, I review some of the key features of mitochondrial biology and focus on the pathways of mitochondrial calcium accumulation. Substantial evidence now suggests that the accumulation of calcium into mitochondria may play a key role as a trigger to mitochondrial pathology, especially when that calcium uptake is accompanied by another stressor, in particular nitrosative or oxidative stress. The major process involved is the opening of the mitochondrial permeability transition pore, a large conductance pore that causes a collapse of the mitochondrial membrane potential, leading to ATP depletion and necrotic cell death or to cytochrome c release and apoptosis, depending on the rate of ATP consumption. I discuss two models in particular in which these processes have been characterized. The first is a model of oxidative stress in cardiomyocytes, in which reperfusion after ischemia causes mitochondrial calcium overload, and oxidative stress. Recent experiments suggest that cardioprotection by hypoxic preconditioning or exposure to the ATP-dependent K(+) channel opener diazoxide increases mitochondrial resistance to oxidative injury. In a second model, of calcium overload in neurons, the neurotoxicity of glutamate depends on mitochondrial calcium uptake, but the toxicity to mitochondria also requires the generation of nitric oxide. Glutamate toxicity after activation of N-methyl-D-aspartate (NMDA) receptors results from the colocalization of NMDA receptors with neuronal nitric oxide synthase (nNOS). The calcium increase mediated by NMDA receptor activation is thus associated with nitric oxide generation, and the combination leads to the collapse of mitochondrial membrane potential followed by cell death.     

Effects of nicorandil preconditioning on membrane dystrophin.

OBJECTIVE: Dystrophin is an integral membrane protein that stabilizes the sarcolemmal membrane integrity, and its loss may be involved in the mechanism of ischemia and reperfusion injury. It has been reported that ischemic preconditioning is related to the preservation of membrane dystrophin during ischemia and reperfusion. Preconditioning with nicorandil, a mitochondrial K(ATP) channel opener, may attenuate the injury by preventing a disturbance in the level of this membrane-associated protein. METHODS: The isolated rat hearts were subjected to 60 min of cardioplegic arrest, followed by 60 min of reperfusion. The hearts were divided into the following three groups according to the drugs given before cardioplegic arrest. The control group received saline intravenously 30 min before heart isolation. The nicorandil group received nicorandil (0.3 mg/kg) intravenously 30 min before isolation. The 5-HD group received 5-hydroxydecanoate (1 mg/kg) intravenously, a mitochondrial K(ATP) channel blocker, 5 min before nicorandil administration. Cardiac function, myocardial metabolism, dystrophin distribution and protein levels of dystrophin were assessed before and after cardioplegic arrest. RESULTS: The nicorandil group showed significantly better cardiac function and a significant reduction in creatine kinase release during reperfusion. After 60 min of cardioplegic arrest, dystrophin, which was distributed predominantly in the sarcolemmal membrane before ischemia, was translocated to the costameric cytoskeleton in all groups. During reperfusion, the level of membrane dystrophin remained decreased in the majority of cardiomyocytes in the control and 5-HD groups, whereas it was restored to nearly the baseline level in the nicorandil group. The immunoblot analysis supported this result. CONCLUSIONS: Depletion of sarcolemmal membrane dystrophin occurred during cardioplegic arrest and reperfusion. Nicorandil preconditioning may attenuate ischemia and reperfusion injury by maintaining the membrane structural integrity.     

ATP-dependent K+ channels in renal ischemia reperfusion injury

ATP-dependent K+ channels (KATP) account for most of the recycling of K+ which enters the proximal tubules cell via Na, K-ATPase. In the mitochondrial membrane, opening of these channels preserves mitochondrial viability and matrix volume during ischemia. We examined KATP channel modulation in renal ischemia-reperfusion injury (IRI), using an isolated perfused rat kidney (IPRK) model, in control, IRI, IRI+200 microM diazoxide (a KATP opener), IRI + 10 microM glibenclamide (a KATP blocker) and IRI + 200 microM diazoxide + 10 microM glibenclamide groups. IRI was induced by 2 periods of warm ischemia, followed by 45 min of reperfusion. IRI significantly decreased glomerular filtration rate (GFR) and increased fractional excretion of sodium (FENa) (p < 0.01). Neither diazoxide nor glibenclamide had an effect on control kidney function other than an increase in renal vascular resistance produced by glibenclamide. Pretreatment with 200 microM diazoxide reduced the postischemic increase in FENa (p < 0.05). Adding 10 microM glibenclamide inhibited the diazoxide effect on postischemic FENa (p < 0.01). Histology showed that kidneys pretreated with glibenclamide demonstrated an increase in injury in the thick ascending limb of outer medulla (p < 0.05). Glibenclamide significantly decreased post ischemic renal vascular resistance (p < 0.05), but had no significant effect on other renal function parameters. Our results suggest that sodium reabsorption is improved by KATP activation and blockade of KATP channels during IRI has an injury enhancing effect on renal epithelial function and histology. This may be mediated through KATP modulation in cell and/or mitochondrial inner membrane.     

吸入麻醉药后处理心肌保护作用机制的研究进展

背景 吸入麻醉药后处理(inhalational anesthetics postconditioning,APO)是指在缺血后冉灌注早期给予一定浓度吸入麻醉药处理.APO具有心肌保护作用,其作用机制目前尚未完全阐明.目的 对APO心肌保护作用机制的研究进展进行回顾和总结.内容 APO的心肌保护的信号转导机制与缺血后处...     

Selective mitochondrial KATP channel opening controls human myocardial preconditioning: too much of a good thing?

BACKGROUND: Paradoxically, patients with noninsulin-dependent diabetes mellitus experience a higher cardiovascular mortality rate than patients with insulin-dependent diabetes mellitus. We have shown that K(ATP) channel inhibition, with oral sulfonylureas, prevents myocardial preconditioning and may explain the paradox of cardiovascular death in patients with noninsulin-dependent diabetes mellitus. Cardiac preconditioning is an attractive protective strategy against any elective ischemia/reperfusion (I/R) injury. The relationship between the K(ATP) channels and human myocardial preconditioning has not previously been elucidated. METHODS: Human atrial trabeculae were harvested, placed in organ baths, and paced (1 Hz). Developed force was recorded during simulated 37 degrees C I/R (30/45 or 45/60 minutes). Before I/R, trabeculae were treated transiently with a selective mitochondrial K(ATP) channel opener for 5 minutes, followed by a 10-minute washout, or were exposed to the channel opener throughout ischemia. Recovery of function is expressed as percentage of baseline developed force. Conserved creatine kinase activity (units per gram of wet tissue) was measured at the end of reperfusion as an indicator of cellular protection. RESULTS: Transient mitochondrial K(ATP) channel opening provided protection from both I/R insults. Surprisingly, there was no protection afforded by continuous mitochondrial K(ATP) channel opening. CONCLUSIONS: Transient selective mitochondrial K(ATP) channel opening protects both viability and function of human myocardium against I/R injury, although prolonged opening of the mitochondrial K(ATP) channel does not. These results reinforce the concept of preconditioning as a transient event that must be completed before the onset of ischemia.