Limitation of infarct size by erythropoietin is associated with translocation of Akt to the mitochondria after reperfusion

1. The aim of the present study was to determine the critical timing of Akt activation and its interaction with the mitochondrial permeability transition pore (mPTP) in the mechanism of infarct size limitation by erythropoietin (Epo). 2. In an isolated, buffer-perfused preparation, rabbit hearts were subjected to 30 min ischaemia/2 h reperfusion. Infusion of Epo (1 unit/mL) before ischaemia reduced infarct size from 36.6 +/- 2.6% of the risk area to 15.4 +/- 3.2%, whereas a 10-fold higher dose of Epo infused for 65 min commencing 5 min before reperfusion failed to afford significant cardioprotection. The protection afforded by Epo pretreatment was abolished by coinfusion of 5 micromol/L LY294002, a phosphatidylinositol 3-kinase (PI3-K) inhibitor. Infusion of Epo induced phosphorylation of Akt, extracellular signal-regulated kinase, glycogen synthase kinase 3beta and p70s6 kinase before ischaemia and tended to enhance reperfusion-induced phosphorylation of these protein kinases. Erythropoietin increased phospho-Akt in the mitochondria and induced complex formation of Akt with adenine nucleotide translocase (ANT), a major subunit of mPTP, upon reperfusion. 3. In another series of experiments, cardiomyocytes were isolated from rat hearts and loaded with Rhod-2 to determine mitochondrial Ca(2+) levels. Increases in mitochondrial Ca(2+) levels following exposure to 1 mmol/L ouabain for 30 min were similar in untreated and Epo-pretreated cells. However, ouabain-induced hypercontracture was significantly suppressed from 45.1 +/- 1.6 to 39.2 +/- 1.9% by Epo. 4. In conclusion, activation of PI3-K-Akt signalling before ischaemia is crucial for Epo-induced myocardial protection and this protection may be achieved by complex formation of activated Akt with mPTP components upon reperfusion, leading to elevation of the threshold for opening of mPTP.     

Direct evidence for inhibition of mitochondrial permeability transition pore opening by sevoflurane preconditioning in cardiomyocytes: comparison with cyclosporine A

To assess whether sevoflurane preconditioning is associated with inhibition of mitochondrial permeability transition pore (MPTP), the effects of sevoflurane were compared with those of cyclosporine A, a known inhibitor of MPTP opening. Isolated perfused guinea pig hearts underwent 30 min global ischemia and 120 min reperfusion (control). Sevoflurane preconditioning was elicited by administration of 2% sevoflurane for 10 min with 10 min washout before ischemia (sevoflurane). A preconditioning-like cardioprotection was also induced by administering cyclosporine A (0.2 μM) for 15 min, starting 5 min before ischemia and for 10 min after the onset of reperfusion (cyclosporine A). Left ventricular developed and end-diastolic pressures, coronary flow and infarct size were measured. Expressions of Akt and glycogen synthase kinase 3β (GSK3β), known mediators of inhibition of MPTP opening, were determined by Western blot analysis. GSK3β inhibition was achieved with LY294002. The effects of sevoflurane and cyclosporine A on calcium-induced MPTP opening in isolated calcein-loaded mitochondria were assessed. After ischemia-reperfusion, sevoflurane and cyclosporine A had higher left ventricular developed pressure. Infarct size was significantly reduced in sevoflurane and cyclosporine A vs. control. This was abolished by LY294002 in sevoflurane, but not in cyclosporine A. Akt and GSK3β phosphorylation after reperfusion were significantly increased in sevoflurane and cyclosporine A. Ca2?-induced reduction in calcein fluorescence was significantly attenuated in sevoflurane and cyclosporine A. Preconditioning agents, sevoflurane and cyclosporine A increase the threshold of calcium-induced MPTP opening to a similar extent. This effect by sevoflurane, but not cyclosporine A is at least partially mediated by GSK3β inactivation.     

ISCHAEMIC POST-CONDITIONING PROTECTS BOTH ADULT AND AGED SPRAGUE-DAWLEY RAT HEART FROM ISCHAEMIA–REPERFUSION INJURY THROUGH THE PHOSPHATIDYLINOSITOL 3-KINASE–AKT AND GLYCOGEN SYNTHASE KINASE-3β PATHWAYS

• 1 Numerous studies have demonstrated that ischaemic post‐conditioning (IPoC) protects adult rats from myocardial ischaemia‐reperfusion (I/R) injury. Recent evidence suggests compromised cardioprotection by IPoC in aged mice. The present study was designed to test the hypothesis that IPoC protects against I/R injury in aged hearts, potentially through a phosphatidylinositol 3‐kinase (PI3‐K)–Akt‐ and glycogen synthase kinase (GSK)‐3β‐dependent mechanism.
• 2 Hearts from adult (3–4 months) or aged (16–18 months) Sprague‐Dawley rats were subjected in vivo to 30 min ischaemia followed by 3 h reperfusion. Ischaemic post‐conditioning (four cycles of 10 s reperfusion–10 s ischaemia) was applied at the beginning of reperfusion, either alone or in combination with the PI3‐K inhibitor LY294002 (0.3 mg/kg). Infarct size and the phosphorylation of Akt and GSK‐3β were determined.
• 3 Ischaemic post‐conditioning reduced infarct size in both adult and aged rat hearts. This protection was accompanied by a significant increase in phosphorylation of Akt and GSK‐3β. LY294002 abolished the IPoC‐induced phosphorylation of Akt and GSK‐3β, as well as the infarct‐limiting effect of IPoC in adult and aged rats. In addition, IPoC significantly attenuated plasma concentrations of creatine kinase and lactate dehydrogenase after reperfusion in both adult and aged rats.
• 4 In conclusion, IPoC, at the onset of reperfusion, reduces myocardial infarct size in both adult and aged rat hearts, potentially through a PI3‐K‐, Akt‐ and GSK‐3β‐dependent mechanism.

     

Activation of PI3-K/Akt pathway for thermal preconditioning to protect cultured cerebellar granule neurons against low potassium-induced apoptosis

AIM: This study was designed to investigate whether the activation of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway is required for thermal preconditioning to protect rat cerebellar granule neurons (CGN) against apoptosis induced by low potassium, and to explore the possibility of a link between the upregulated heat shock protein (HSP)70 expression and Akt activation in the acquisition of neuroprotection induced by thermal preconditioning. METHODS: CGN cultured for 8 d in vitro were switched to 5K medium for 24 h after thermal preconditioning (TP; 43.5 degree for 90 min, then 37 degree for 1 h). To study the role of the PI3-K/Akt pathway, a PI3-K inhibitor, LY294002 (20 micromol/L) was added into the cultures 1 h before TP. 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) assay and fluorescein diacetate staining were used to determine cell viability. Hoechst 33258 staining and agar gel electrophoresis were used to test the morphological and biological characters of CGN. Western blot analysis was employed to detect the levels of phospho-Akt, phospho-glycogen synthase kinase 3beta (GSK3beta) Akt, GSK3beta, and HSP70. RESULTS: TP protected CGN against apoptosis induced by low potassium. LY294002 inhibited the neuroprotective effect on CGN induced by TP. TP induced a robust activation of Akt and the inactivation of GSK3beta via PI3-K. Furthermore, the activation of the PI3-K/Akt pathway by TP persisted for 24 h in the 5K cultures. LY294002 (20 micromol/L) failed to inhibit the upregulated HSP70 expression induced by TP. CONCLUSION: The activation of the PI3-K/Akt pathway is required for TP to protect CGN against apoptosis induced by low potassium, but the neuroprotective effect by Akt activation is not mediated through the downstream induction of HSP70 expression.     

Rosiglitazone‐induced myocardial protection against ischaemia–reperfusion injury is mediated via a phosphatidylinositol 3‐kinase/Akt‐dependent pathway

1. Rosiglitazone is widely used in the treatment of Type 2 diabetes. However, in recent years it has become evident that the therapeutic effects of peroxisome proliferator‐activated receptor γ ligands reach far beyond their use as insulin sensitizers. Recently, the ability of rosiglitazone pretreatment to induce cardioprotection following ischaemia–reperfusion (I/R) has been well documented; however, the protective mechanisms have not been elucidated. In the present study, examined the role of the phosphatidylinositol 3‐kinase (PI3‐K)/Akt signalling pathway in rosiglitazone cardioprotection following I/R injury. 2. Mice were pretreated with 3 mg/kg per day rosiglitazone for 14 days before hearts were subjected to ischaemia (30 min) and reperfusion (2 h). Wortmannin (1.4 mg/kg, i.p.), an inhibitor of PI3‐K, was administered 10 min prior to myocardial I/R. Then, activation of the PI3‐K/Akt/glycogen synthase kinase (GSK)‐3α signalling pathway was examined. The effects of PI3‐K inhibition on rosiglitazone‐induced cardioprotection were also evaluated. 3. Compared with control rats, the ratio of infarct size to ischaemic area (area at risk) and the occurrence of sustained ventricular fibrillation in rosiglitazone‐pretreated rats was significantly reduced (P < 0.05). Rosiglitazone pretreatment attenuated cardiac apoptosis, as assessed by ELISA to determine cardiomyocyte DNA fragmentation. Rosiglitazone pretreatment significantly increased levels of phosphorylated (p‐) Akt and p‐GSK‐3α in the rat myocardium. Pharmacological inhibition of PI3‐K by wortmannin markedly abolished the cardioprotection induced by rosiglitazone. 4. These results indicate that rosiglitazone‐induced cardioprotection in I/R injury is mediated via a PI3‐K/Akt/GSK‐3α‐dependent pathway. The data also suggest that modulation of PI3‐K/Akt/GSK‐3α‐dependent signalling pathways may be a viable strategy to reduce myocardial I/R injury.     

Sevoflurane post-conditioning protects isolated rat hearts against ischemia-reperfusion injury via activation of the ERK1/2 pathway

Aim:

To investigate the role of extracellular signal-regulated kinases (ERKs) in sevoflurane post-conditioning induced cardioprotection in vitro.

Methods:

Isolated rat hearts were subjected to 30 min ischemia followed by 120 min reperfusion (I/R). Sevoflurane post-conditioning was carried out by administration of O₂-enriched gas mixture with 3% sevoflurane (SEVO) for 15 min from the onset of reperfusion. Cardiac functions, myocardial infarct size, myocardial ATP and NAD⁺ contents, mitochondrial ultrastructure, and anti-apototic and anti-oncosis protein levels were measured.

Results:

Sevoflurane post-conditioning significantly improved the heart function, decreased infarct size and mitochondria damage, and increased myocardial ATP and NAD⁺ content in the I/R hearts. Furthermore, sevoflurane post-conditioning significantly increased the levels of p-ERK and p-p70S6K, decreased the levels of porimin, caspase-8, cleaved caspase-3, and cytosolic cytochrome c in the I/R hearts. Co-administration of the ERK1/2 inhibitor PD98059 (20 μmol/L) abolished the sevoflurane-induced protective effects against myocardial I/R.

Conclusion:

Sevoflurane post-conditioning protects isolated rat hearts against myocardial I/R injury and inhibits cell oncosis and apoptosis via activation of the ERK1/2 pathway.     

Glimepiride Treatment Upon Reperfusion Limits Infarct Size via the phosphatidylinositol 3-Kinase/Akt Pathway in Rabbit Hearts

The phenomenon termed postconditioning, that is, brief episodes of ischemia/reperfusion at the onset of reperfusion reduce infarct size, is thought to involve the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. Treatment with a drug activating PI3K at the onset of reperfusion may confer a similar cardioprotection. The sulfonylurea glimepiride has been shown to activate PI3K in human endothelial cells. We therefore tested in rabbit hearts whether glimepiride can produce postconditioning-mimetic actions. Langendorff-perfused rabbit hearts were subjected to 30 min of global ischemia and 120 min of reperfusion, and infarct size was determined by triphenyltetrazolium staining. Phosphorylation of Akt was analyzed by Western blotting. Glimepiride (10 μM) treatment for the first 10 min of reperfusion significantly reduced infarct size from 67.2 ± 1.3% in controls to 35.8 ± 4.5% (P<0.01). This infarct size–limiting effect of glimepiride was abolished by a selective inhibitor of PI3K (5 μM LY294002, 65.4 ± 3.4%). Phosphorylation of the PI3K substrate Akt was significantly increased in glimepiride-treated hearts when compared to controls (P<0.05). Glimepiride-induced Akt phosphorylation was inhibited by LY294002. In conclusion, our study demonstrates that glimepiride treatment upon reperfusion reduces infarct size in rabbit hearts via a PI3K/Akt-mediated pathway. The postconditioning-mimetic action of glimepiride may be beneficial for the treatment of diabetic patients with ischemic heart disease.     

PI3K/Akt调节线粒体Cx43蛋白表达在H_2S后处理离体大鼠心肌中的保护作用

目的探讨PI3K/Akt信号通路是否通过调节线粒体缝隙连接蛋白Cx43而在硫化氢(H2S)后处理中减轻离体大鼠心脏缺血/再灌注(I/R)损伤。方法 56只♂SpragueDawley(SD)大鼠随机分为4组(n=14):缺血/再灌注组(I/R组),PI3K/Akt信号通路抑制剂LY294002组(LY组),硫化氢后处理组(NP组),硫化氢后处理+PI3K/Akt信号通路抑制剂LY294002组(N+L组)。采用离体心脏Langen-dorff灌注模型,平衡灌注20 min后停灌30 min复灌60 min。记录平衡末及灌注结束时的心率(HR)、左室舒张末期压(LVEDP)、左室发展压(LVDP)、左室内压上升最大速率(+dp/dtmax)、左室内压下降最大速率(-dp/dtmax);灌注结束时,TTC法染色心肌切片并计算心肌梗死面积百分比;TUNEL法检测心肌细胞凋亡,计算凋亡指数(AI);Westernblot半定量线粒体总的Cx43(total connexin 43,tCx43)和磷酸化Cx43(phosphorylated connexin 43,pCx43)表达水平。结果平衡灌注末各组间心功能指标差异无统计学意义。再灌注后,与I/R组比较,NP组心功能的各项指标明显改善(P<0.05);心肌梗死面积减少(26.5±4.2)%vs(44.5±5.3)%(P<0.05);凋亡指数降低(25.9±3.0)%vs(43.1±1.9)%(P<0.05);线粒体tCx43和pCx43蛋白表达水平明显升高。LY294002逆转了H2S后处理产生的心肌保护效应,使N+L组心功能指标及线粒体中tCx43和pCx43的表达水平降低(P<0.05),心肌梗死面积及凋亡指数均增加(P<0.05)。结论 PI3K/Akt信号通路通过上调线粒体缝隙连接蛋白Cx43蛋白的表达而在硫化氢(H2S)后处理中减轻离体大鼠I/R损伤。     

Mechanisms mediating the cardioprotective effects of rapamycin in ischaemia-reperfusion injury

1. In the present study, the temporal and concentration-dependent cardioprotective effects of rapamycin against ischaemia-reperfusion (I/R) injury, as well as the underlying mechanisms, were investigated. 2. Rat Langendorff-perfused isolated hearts were exposed to 40 min global ischaemia followed by 120 min reperfusion. Hearts were perfused with different concentrations of rapamycin before and after ischaemia. Myocardial injury was assessed in terms of infarct size and the release of lactate dehydrogenase (LDH) and creatine kinase (CK). The phosphorylation of Akt, extracellular signal-regulated kinase (ERK) 1/2 and endothelial nitric oxide synthase (eNOS) was determined at the end of reperfusion. 3. When administered prior to ischaemia, 25, 50 and 100 nmol/L rapamycin significantly reduced infarct size compared with control (40.1 ± 1.5, 26.3 ± 4.1 and 21.2 ± 3.4 vs 52.5 ± 4.5%, respectively) without affecting the recovery of ventricular function. No reduction in infarct size was observed when 50 nmol/L rapamycin was administered 10 or 120 min into the reperfusion period. 4. Rapamycin (50 nmol/L) enhanced the phosphorylation of Akt kinase but did not affect the phosphorylation of ERK1/2 or eNOS at the end of reperfusion. The cardioprotective effect of rapamycin was blocked by the phosphatidylinositol 3-kinase (Akt) inhibitor LY294002 (15 nmol/L). 5. In conclusion, rapamycin mediates cardioprotection prior to ischaemia and after reperfusion. This protection may involve activation of the phosphatidylinositol 3-kinase pathway.     

七氟烷激活PI_3-K/Akt/P~(70S6K)信号转导通路抑制缺血/再灌注损伤神经元的凋亡

目的研究七氟烷对神经元缺血/再灌注损伤后PI3-K/Akt/P70S6K信号转导通路的影响,探讨七氟烷脑保护机制。方法将96孔和6孔培养板上培养7d的海马神经元随机分为6组:正常培养组(C组)、缺血/再灌注组(I/R组)、缺血/再灌注+2%Sevoflurane组(Sevo组)、缺血/再灌注+2%Sevoflurane+10μmol.L-1LY294002(PI3-K拮抗剂)组(LY组)、缺血/再灌注+2%Sevoflurane+10μmol.L-1Tric irib in(Akt拮抗剂)组(Tri组)、缺血/再灌注+2%Sevoflurane+10 nmol.L-1Rapamyc in(P70S6K拮抗剂)组(Rap组)。C组神经元按正常培养方法培养。Sevo组在神经元缺糖缺氧的同时接受2%Sevoflurane麻醉。LY组、Tri组和Rap组在神经元进行缺糖同时分别加入LY294002、Tric irib in或Rapamyc in使其终浓度分别为10μmol.L-1、10μmol.L-1或10 nmol.L-1后同Sevo组处理。96孔培养板的神经元进行细胞存活力的检测。6孔培养板的神经元进行神经元纯度鉴定、神经元凋亡和PI3-K、Akt和P70S6K蛋白表达的检测。结果Sevo组PI3K、Akt、P70S6K蛋白表达增加,神经元存活率增加、神经元凋亡率降低(vsI/R组,P<0.01)。LY组PI3K、Akt和P70S6K表达降低,神经元存活率降低、神经元凋亡率增加(vsSevo组,P<0.05或P<0.01);Tri组Akt和P70S6K表达降低,神经元存活率降低、神经元凋亡率增加(vsSevo组,P<0.05或P<0.01);Rap组P70S6K表达降低,神经元存活率降低、神经元凋亡率增加(vsSevo组,P<0.01)。结论Sevoflurane激活了PI3-K/Akt/P70S6K信号通路,在海马神经元缺血/再灌注损伤过程中抑制了神经元凋亡,保护了神经元。     

ERK1/2和Akt通路对控制性低压后处理兔缺血/再灌注损伤脊髓线粒体功能的影响

目的研究PI3K/Akt和ERK1/2通路对控制性低压后处理兔缺血/再灌注损伤脊髓线粒体功能的影响。方法30只日本大耳白兔随机分为5组(n=6):假手术组(Sham)、缺血/再灌注组(I/R),控制性低压后处理组(Post),控制性低压后处理+PD98059组(Post+PD)、控制性低压后处理+LY294002组(Post+LY)组。除Sham组外,其余各组分别于肾动脉下水平阻断腹主动脉25 min。Post组:再灌注开始10 min采用控制性低灌注压后处理法球囊部分排空,将腹主动脉远端血压控制在5.99～7.32 kPa,10min后球囊完全开放。Post+PD组、Post+LY组:同Post组,并分别于腹主动脉开放前1 min鞘内注射ERK抑制剂PD98059(3μg,20μl)、PI3K/AKT抑制剂LY294002(10μg,20μl)。再灌注24 h后将实验动物处死,取脊髓组织用Western blot技术测定Caspase-3、胞质Cytochrome C蛋白表达;电镜观察线粒体结构。结果与I/R组比较,Post组Caspase-3和胞质Cytochrome C蛋白表达明显减少,线粒体结构破坏减轻。ERK抑制剂PD98059和PI3K/Akt抑制剂LY294002减弱了Post的作用。结论控制性低压后处理对缺血/再灌注损伤脊髓线粒体功能有保护作用,其机制可能与激活PI3K/Akt和ERK1/2通路有关。     

PI3K/Akt信号通路在外源性硫化氢后处理大鼠离体心肌中的作用

目的探讨PI3K/Akt信号通路是否参与硫化氢后处理减轻离体大鼠心肌缺血/再灌注损伤。方法 70只♂Sprague Dawley(SD)大鼠随机分为5组(n=14):缺血/再灌注组(I/R组),硫化氢后处理组(N组),溶媒组(D组),LY294002组(L组),硫化氢后处理+LY294002组(N+L组)。采用离体心脏Langendorff灌注模型,平衡灌注20min后停灌40min复灌60min。记录平衡末及灌注结束时的左室舒张末期压(LVEDP)、左室发展压(LVDP)、左室内压上升最大速率(+dp/dt)、左室内压下降最大速率(-dp/dt)、心率(HR)、冠脉血流量(CF);灌注结束时,TTC法染色心肌切片并计算心肌梗死面积百分比,TUNEL法检测心肌细胞凋亡计算凋亡指数(AI),Western blot半定量p-Akt和总的Akt表达水平。结果平衡灌注末各组间心功能指标(基础值)差异未见统计学意义(P>0.05)。灌注结束时,与I/R组比较,N组可改善再灌注损伤心功能的各项指标(P<0.05),使心肌梗死面积缩小和凋亡指数降低(P<0.05),p-Akt表达水平升高(P<0.05)。LY294002逆转了硫化氢后处理的心功能指标、心肌梗死面积、凋亡指数及p-Akt表达水平(P<0.05),使L组和N+L组p-Akt蛋白表达明显低于N组(P<0.05)。结论外源性硫化氢后处理通过PI3K/Akt信号通路减轻离体大鼠心肌缺血/再灌注损伤。     

Combined pharmacological preconditioning with a G-protein-coupled receptor agonist,a mitochondrial KATP channel opener and a nitric oxide donor mimics ischaemic preconditioning

1. Although pharmacological preconditioning (PPC) has emerged as an alternative to ischaemic preconditioning (IPC) in cardioprotection, the efficacy of PPC compared with IPC has not been investigated. Because IPC is mediated by complex signalling cascades arising from multiple triggers, we have hypothesized that combined PPC is necessary to mimic IPC. 2. Isolated and perfused rat hearts underwent IPC by three cycles of 5 min ischaemia and 5 min reperfusion before 30 min global ischaemia followed by 120 min reperfusion. Adenosine (30 micromol/L), diazoxide (50 micromol/L) and s-nitroso-N-acetylpenicillamine (SNAP; 50 micromol/L) were added for 25 min just before (pretreatment modality) or 45 min before (PPC modality) the index ischaemia. 3. Ischaemic preconditioning significantly improved isovolumic left ventricular (LV) function and reduced infarct size. Although pretreatment with adenosine, diazoxide or SNAP alone was capable of reducing infarct size, PPC with each drug alone or in a combination of two drugs except for diazoxide plus SNAP failed to reduce infarct size. In contrast, PPC in combination with adenosine, diazoxide and SNAP (triple combination PPC) conferred significant improvement of LV function and reduction of infarct size that was as effective as IPC. 4. Cardioprotection afforded by triple combination PPC was abolished by the Gi/o-protein inhibitor pertussis toxin, the mitochondiral KATP channel inhibitor 5-hydroxydecanoate or the nitric oxide (NO) scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl 3-oxide (carboxy-PTIO). 5. Protein kinase C (PKC)-epsilon in the particulate fraction was activated throughout preconditioning ischaemia and reperfusion. Although PKC-epsilon was activated during treatment with adenosine, diazoxide or SNAP alone, it was inactivated after washout. In contrast, PKC-epsilon remained activated after triple combination PPC. The PKC inhibitor chelerythrine abolished activation of PKC-epsilon and cardioprotection afforded by IPC and triple combination PPC. 6. These results demonstrate that combined PPC with a G-protein-coupled receptor agonist, a mitochondrial KATP channel opener and an NO donor is necessary to mimic IPC and such synergistic cardioprotection is associated with enhanced and sustained activation of PKC-epsilon.     

Myocardial adenosine does not correlate with the protection mediated by ischaemic or pharmacological preconditioning in rat heart

1. We tested the hypothesis that ischaemic preconditioning of the rat heart activates cardiovascular adenosine formation to provide enhanced cardioprotection. 2. Rat isolated perfused hearts were either non-preconditioned, preconditioned with 5 min ischaemia or treated for 5 min with the alpha1-adrenoceptor agonist phenylephrine (50 micro mol/L) before being subjected to 30 min sustained ischaemia followed by 30 min reperfusion. Isolated cardiomyocytes were either non-preconditioned, subjected to 10 min simulated ischaemia or treated for 10 min with phenylephrine (50 micro mol/L) before being subjected to 30 min simulated ischaemia. Functional recovery of hearts and cell viability were used as indices of the effects of ischaemia. 3. Myocardial adenosine, as well as intracellular pH, was determined at the end of the preconditioning period and at 10, 20 and 30 min of sustained ischaemia. Intracellular pH was also determined during the reperfusion. 4. Ischaemic or pharmacological preconditioning with phenylephrine correlated with an improved functional recovery of perfused hearts during reperfusion and increased cell viability during ischaemia. 5. In perfused hearts, ischaemic preconditioning resulted in increased adenosine production in the myocardium during the following sustained ischaemia. However, in isolated cardiomyocytes, adenosine levels during sustained ischaemia were lower in ischaemically preconditioned cells compared with the respective non-preconditioned cardiomyocytes. 6. The increase in adenosine production was not observed in hearts preconditioned with phenylephrine instead of transient ischaemia. Similarly, pharmacological preconditioning resulted in decreased adenosine levels during sustained ischaemia in isolated cardiomyocytes. 7. Intracellular pH was preserved during ischaemia to the same extent in both ischaemically or pharmacologically preconditioned hearts and cardiomyocytes, indicating that less acidosis during ischaemia is related to protection. 8. Taken together, the results suggest that cardioprotection does not necessarily correlate with increased adenosine production. Thus, adenosine concentration is not crucial to the beneficial effects of preconditioning in rat heart.     

Protective effect of propranolol on mitochondrial function in the ischaemic heart

1. The present study was aimed to determine whether propranolol improves contractile function of the ischaemic/reperfused heart through protection of the mitochondrial function during ischaemia. 2. Isolated perfused rat hearts were subjected to 35-min ischaemia followed by 60-min reperfusion. Pre-treatment with propranolol at the concentrations of 10 to 100 microM for the final 3 min of pre-ischaemia resulted in the improvement of ischaemia/reperfusion-induced contractile dysfunction, release of creatine kinase (CK) into perfusate, and decrease in myocardial high-energy phosphates. Propranolol also attenuated ischaemia-induced accumulation in Na+, suggesting that cytosolic sodium overload during ischaemia was prevented by propranolol. 3. The mitochondrial oxygen consumption rate of skinned bundles from the perfused heart decreased at the end of ischaemia and it further decreased at the end of reperfusion. These decreases were cancelled by treatment with propranolol. A release of cytochrome c from the perfused heart was observed during ischaemia, and this release was suppressed by treatment with propranolol. 4. To elucidate the direct effect of propranolol on mitochondria, the mitochondria were isolated from normal hearts and their activities were determined in the presence of various concentrations of Na+ and propranolol. The addition of sodium lactate, which mimicked sodium overload in the ischaemic heart, reduced the state 3 respiration, whereas this reduction was not attenuated by the presence of propranolol. 5. These results suggest that cardioprotection of propranolol may be exerted via attenuating Na+ influx into cardiac cells followed by prevention of the mitochondrial dysfunction in the ischaemic heart, leading to improvement of energy production of the heart during reperfusion.     

Mu-opioid receptor activation prevents apoptosis following serum withdrawal in differentiated SH-SY5Y cells and cortical neurons via phosphatidylinositol 3-kinase

Opioid peptides and alkaloids exert their effects via G protein-coupled receptors (GPCRs). It has been shown that, in addition to trophic factors, some GPCRs are able to activate the phosphatidylinositol 3-kinase/Akt (PI 3-K/Akt) signal transduction pathway, thus leading to cell survival. The aim of this study was to test whether activation of mu-opioid receptors has protective effects on serum withdrawal-induced cell death and to study the possible implication of PI 3-K in this process. In SH-SY5Y neuroblastoma cells fully differentiated by exposure to retinoic acid for five days, the enkephalin derivative selective mu-agonist DAMGO (0.1-2 microM) and the alkaloid morphine (0.1-10 microM) promoted cell survival after serum deprivation (MTT and trypan blue exclusion assays), without inducing cell proliferation. These effects were fully reversed by naloxone, by the selective mu-antagonist beta-funaltrexamine (beta-FNA) and also by the specific PI 3-K inhibitor LY294002. The two agonists stimulated Akt phosphorylation and the effect was also abolished by beta-FNA and by LY294002. In mouse primary cortical neurons, DAMGO reduced the percentage of apoptosis after 6, 12, 24 and 48 h of serum withdrawal; as determined by Hoechst staining. This effect was blocked by beta-FNA, by pre-treatment with pertussis toxin and by LY294002. DAMGO also stimulated Akt phosphorylation via PI 3-K in this primary neuronal culture. Together, these results indicate that stimulation of the mu-opioid receptor promotes neuronal survival in a G(i/o)-linked, PI 3-K-dependent signaling cascade and suggest that Akt may be a key downstream kinase involved in this anti-apoptotic effect.     

Effects of the Na+/H+ exchange inhibitor cariporide (HOE 642) on cardiac function and cardiomyocyte cell death in rat ischaemic-reperfused heart

1. Na+/H+ exchange has been implicated in the mechanism of reperfusion injury. We examined the effects of the cardiac-specific Na+/H+ exchange inhibitor cariporide (HOE 642) on postischaemic recovery of cardiac function and cardiomyocyte cell death (i.e. necrosis and apoptosis). 2. Rat isolated and buffer-perfused hearts were subjected to 25 min normothermic global ischaemia followed by 120 min reperfusion. Cariporide (10 micromol/L) or its vehicle (0.01% dimethylsulphoxide) was administered for 15 min before ischaemia and for the first 30 min after reperfusion. 3. Cariporide significantly improved the recovery of isovolumic left ventricular function (heart rate, left ventricular developed pressure and left ventricular end-diastolic pressure) and coronary flow throughout reperfusion. Creatine kinase release during reperfusion was significantly less in the cariporide-treated heart. In situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL)-positive cardiomyocytes were also significantly less in the cariporide-treated heart after 120 min reperfusion. Electron microscopy showed necrotic changes without typical apoptotic features in cardiomyocytes after reperfusion. Such necrotic changes were mitigated by cariporide. Simultaneous detection of necrotic and apoptotic cardiomyocytes using propidium iodide (PI) and Annexin V revealed that cardiomyocytes in the infarct area were stained with only PI or both PI and Annexin V. Cariporide did not alter the pattern of cardiomyocyte staining with PI and Annexin V, although the number of cardiomyocytes stained with PI or PI plus Annexin V was less than that in vehicle-treated hearts. 4. These results suggest that apoptosis is not a major manifestation of cardiomyocyte cell death in the ischaemic-reperfused myocardium and a cariporide-sensitive mechanism of reperfusion injury promotes both necrotic and apoptotic processes of cell death.     

Role of calcitonin gene-related peptide in ischaemic preconditioning in diabetic rat hearts

1. It has been suggested that calcitonin gene-related peptide (CGRP) is involved in the protection provided by ischaemic preconditioning in rat hearts and that ischaemic preconditioning is absent in diabetic rat hearts. 2. In the present study, we tested the relationship between sensory nerve function and ischaemic preconditioning in diabetic rats. 3. In 4- and 8-week diabetic rats and age-matched non- diabetic controls, 30 min global ischaemia and 40 min reperfusion caused a significant decrease in cardiac function and a marked increase in creatine kinase (CK) release. Ischaemic preconditioning, by three cycles of 5 min ischaemia and 5 min reperfusion, improved the recovery of cardiac function and decreased CK release during reperfusion in 4-week diabetic rat hearts. However, the cardioprotection afforded by ischaemic preconditioning was lost in 8-week diabetic rat hearts. Pretreatment with CGRP for 5 min also significantly improved the recovery of cardiac function and decreased CK release in rats subjected to 4 or 8 weeks of diabetes. 4. The content of CGRP in the coronary effluent during ischaemic preconditioning was significantly increased in 4-week diabetic rat hearts (P < 0.05). However, only a slight increase in the release of CGRP was shown in 8-week diabetic rat hearts (P > 0.05). 5. In summary, the present results suggest that the protection afforded by ischaemic preconditioning is attenuated in diabetic rats and that the change may be related to the reduction in CGRP release in diabetic rat hearts.     

Sevoflurane postconditioning affects post‐ischaemic myocardial mitochondrial ATP‐sensitive potassium channel function and apoptosis in ageing rats

This study investigated the effect of sevoflurane postconditioning on post‐ischaemic cardiac function, infarct size, myocardial mitochondrial ATP‐sensitive potassium channel (mitoKATP) function and apoptosis in ageing rats to determine the possible mechanism underlying the cardioprotective property of sevoflurane. Ageing rat hearts were isolated and attached to a Langendorff apparatus. The hearts were then exposed or not to sevoflurane postconditioning in the presence or absence of 100 μmol/L 5‐hydroxydecanoate (5‐HD), a selective mitoKATP inhibitor. The infarct size was measured by triphenyltetrazolium chloride (TTC) staining. Mitochondrial morphology was observed by electron microscopy and scored using FlaMeng semiquantitative analysis. In addition, the expression levels of Bax, Bcl‐2, and cytochrome‐C (Cyt‐C) were determined by Western blot analysis at the end of reperfusion. Sevoflurane postconditioning increased coronary flow, improved functional recovery, reduced Bax/Bcl‐2 and Cyt‐C phosphorylation levels, and decreased mitochondrial lesion severity and the extent of apoptosis. The protective effects of sevoflurane postconditioning were prevented by the mitoKATP inhibitor 5‐HD. Sevoflurane postconditioning significantly protected the function of ageing hearts that were subjected to ischaemia and reperfusion, and these protective effects were mediated by mitoKATP opening.     

The influence of nifedipine and mioflazine on mitochondrial calcium overload in normoxic and ischaemic guinea-pig hearts

The influence of nifedipine (20 nM) and mioflazine (300 nM), i.e. concentrations inducing a 60-70% recovery of cardiac function during reperfusion of globally ischaemic guinea-pig working hearts, on the mitochondrial calcium content was investigated in normoxic, globally ischaemic and reperfused globally ischaemic guinea-pig working hearts. Mitochondrial calcium was determined electronmicroscopically with oxalate-pyroantimonate method. In normoxic hearts both nifedipine and mioflazine reduced the mitochondrial calcium content. Global ischaemia for 45 min and subsequent reperfusion for 25 min resulted in a pronounced mitochondrial calcium overload and damage to the cellular structure. In ischaemic and in reperfusion hearts the drugs maintained mitochondrial calcium at pre-ischaemic levels and decreased the damage to the cellular structure.