Effects of trimetazidine on the calcium transport and oxidative phosphorylation of isolated rat heart mitochondrial

Trimetazidine (TMZ) added in vitro to isolated cardiac mitochondria at concentrations 10–100 M in the presence of 25–100 nM extramitochondrial Ca²⁺ increased Ca²⁺ uptake and matrix Ca²⁺ concentration. This effect was less evident in the presence of physiologically Na⁺ and Mg²⁺ extramitochondrial concentrations since only 100 M TMZ was able to increase mitochondrial Ca²⁺ entry in the presence of 100 nM Ca²⁺. The drug stimulated a Ca²⁺-cooperative effect on mitochondrial Ca²⁺ transport but did not modify the rate of Ca²⁺ egress stimulated by 10 mM NaCl. An increase in mitochondrial Ca²⁺ level produced by TMZ enhanced oxoglutarate dehydrogenase activity and then ATP synthesis, particularly when 50 nM extramitochondrial Ca²⁺ was used. These data suggest that a possible cardiac mechanism of action of TMZ at mitochondrial level could support ATP synthesis by elevating the mitochondrial Ca²⁺ level.     

Effect of preconditioning temperature on cardioprotection during global ischemia-reperfusion in the rat heart

BACKGROUND: Myocardial ischemic preconditioning (PC) is a protective intervention that aims to reduce the deleterious effects of ischemia-reperfusion injury. OBJECTIVES: : To assess the comparative efficacy of ischemic PC induced at hypothermic, normothermic and hyperthermic temperatures on the postischemic recovery of left ventricular contractile and coronary vascular functions in the aortic perfused rat heart model. METHODS: An isolated aorta-perfused (Langendorff) rat heart model was used. Hearts were studied in eight different groups (n=5 each). Unprotected ischemia for 60 min served as control. For the remaining seven groups, ischemia was preceded by PC at 10 degrees C, 20 degrees C, 30 degrees C, 34 degrees C, 37 degrees C, 40 degrees C and 42 degrees C achieved by two episodes of 5 min ischemia at the designated PC temperature and 10 min of reperfusion, respectively. The postischemic recovery in contractile (maximum developed pressure and left ventricular end-diastolic pressure) and coronary vascular functions (coronary flow and coronary vascular resistance) was assessed at the end of 30 min reperfusion. RESULTS: Hyperthermic PC provided optimal preservation and resulted in a 25% increase in the myocardial and 15% increase in the coronary vascular tolerance to ischemia. Normothermic PC resulted in a 21% increase in myocardial and 14% increase in coronary vascular tolerance to ischemia. Hypothermic PC was comparatively less effective and resulted in 11% increase in myocardial and 15% increase in the coronary vascular tolerance to ischemia. The temperature-dependence of PC may be summarized as: PC-42 degrees C > PC-40 degrees C > PC-37 degrees C > PC-34 degrees C > PC-30 degrees C > PC-20 degrees C > PC-10 degrees C. CONCLUSIONS: The results of the present study indicate that the extent of reversibility of the ischemic damage depends on the PC temperature and that optimal preservation occurred at the ideal PC temperature between 40 degrees C and 42 degrees C.     

Effects of CCCP-induced mitochondrial uncoupling and cyclosporin A on cell volume,cell injury and preconditioning protection of isolated rabbit cardiomyocytes

Cell swelling may contribute to acute cell injury subsequent to ischemia/reperfusion. The potential role of mitochondrial uncoupling and the resultant mitochondrial swelling, due to opening of the mitochondrial permeability transition pore (MPTP), were examined in an in vitro ischemically pelleted isolated rabbit cardiomyocyte model using the protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP) to uncouple mitochondria. Cyclosporin A (CsA) was employed to inhibit MPTP opening. Cell volume was determined by a cell-flotation, density-gradient assay, using bromododecane. Cell viability, subsequent to an osmotic stress, was determined by trypan blue permeability. Ischemic preconditioning (IPC) facilitated volume regulation following an osmotic stress. Ischemic-cell swelling was reduced by IPC. IPC protected ischemically pelleted cells, but CsA had no significant effects on injury or IPC protection. CCCP ischemia accelerated rates of ischemic contracture and injury, and abolished IPC protection. IPC protection was restored by CsA. In CCCP-ischemic-uncoupled cells, subjected to a reduced (170 mOsm) osmotic stress, CsA and IPC afforded independent and additive protection. Chelerythrine and 5-hydroxydecanoate (5-HD) blocked IPC, but did not reduce CsA protection. Electron microscopy confirmed that CCCP ischemia induced mitochondrial matrix swelling that was reduced by CsA. Cardioprotection by IPC and CsA was accompanied by proportional reductions in cell swelling. Morphometric analysis of the electron photomicrographs demonstrated that the mitochondrial volume fractions were significantly reduced in the CsA/CCCP (29.8 +/- 2.3%, P < 0.004) and IPC/CsA/CCCP (31.5 +/- 1.7%, P < 0.0008) groups as compared to the CCCP-ischemic group (40.5 +/- 1.7%) The IPC/CCCP group (39.5 +/- 4.2%) was not significantly different from the CCCP-ischemic group. NIM 811, a CsA analogue MPTP blocker with no calcineurin inhibitory activity, afforded protection similar to CsA. The results suggest that CsA protection may, in part, be mediated by reduction of mitochondrial swelling.     

Identification of a novel role for sphingolipid signaling in TNF alpha and ischemic preconditioning mediated cardioprotection

TNF alpha administration mimics ischemic preconditioning and neutralizing antibodies to TNF alpha and IL-1 beta abolish exercise-induced preconditioning. However, the pharmacology of TNF alpha's cardioprotective effects and associated downstream signaling events has not been delineated. We evaluated the temporal and dose specific requirements of TNF alpha to function as a preconditioning mimetic. Furthermore we postulated that the preconditioning effect of TNF alpha might be orchestrated via sphingolipid signaling. The cardioprotective effect of TNF alpha and the role of sphingolipid signaling were assessed using a classical preconditioning protocol in the isolated perfused rat heart with the measurement of infarct size and contractile function modulation in response to index ischemia and reperfusion. Recombinant TNF alpha at an optimal dose of 0.5 ng/ml mimicked ischemic preconditioning by reducing infarct size by 60%v non-preconditioned ischemia-reperfusion controls (P<0.01). The infarct sparing effect of TNF alpha required a wash-out period prior to the index ischemic-reperfusion. Moreover, the classic ischemic preconditioning antagonist such as 5-hydroxydecanoate abolished TNF alpha preconditioning. An inhibitor of the sphingolipid signaling pathway, N-oleoylethanolamine (NOE, 1 microm) attenuated ischemic and TNF alpha preconditioning. Likewise, cell-permeable C(2)-ceramide and sphingosine 1-phosphate (sphingolipid signaling intermediates) both reproduced the preconditioning cardioprotective phenotype. Finally, TNF alpha and ceramide conferred preconditioning-like cardioprotection against post-ischemic contractile dysfunction and this cardioprotective effect was attenuated by NOE. In contrast, NOE did not reverse ischemic preconditioning enhanced post-ischemic contractile function. In conclusion, TNF alpha activates preconditioning-like tolerance against infarction and contractile dysfunction. This cardioprotection is mediated, in part, via activation of novel sphingolipid signaling intermediates.     

Evidence for mitochondrial K+ channels and their role in cardioprotection

Twenty years after the discovery of sarcolemmal ATP-sensitive K+ channels and 12 years after the discovery of mitochondrial K(ATP) (mitoK(ATP)) channels, progress has been remarkable, but many questions remain. In the case of the former, detailed structural information is available, and it is well accepted that the channel couples bioenergetics to cellular electrical excitability; however, in the heart, a clear physiological or pathophysiological role has yet to be defined. For mitoK(ATP), structural information is lacking, but there is abundant evidence linking the opening of the channel to protection against ischemia-reperfusion injury or apoptosis. This review updates recent progress in understanding the physiological role of mitoK(ATP) and highlights outstanding questions and controversies, with the intent of stimulating additional investigation on this topic.     

AlphaB crystallin translocation and phosphorylation: signal transduction pathways and preconditioning in the isolated rat heart

In this program of studies we have characterized in detail the translocation (assessed by Triton-insolubility) and phosphorylation (using serine-45 or -59 phosphospecific antibodies) of alphaB crystallin during myocardial ischemia [both with or without ischemic preconditioning (IPC)]. Pharmacological activators and inhibitors allowed us to characterize the signaling pathways involved in alphaB crystallin phosphorylation during ischemia. Ischemic preconditioning alone caused 30% of the heart's alphaB crystallin pool to translocate, providing a significant translocation 'head-start' in protected tissue. This enhanced translocation is coupled with increased (3-fold) alphaB crystallin phosphorylation at both serine residues. The possible role of alphaB crystallin in the protection afforded by ischemic preconditioning is supported by the signal transduction data; which showed preconditioning-induced alphaB crystallin phosphorylation can be blocked by tyrosine kinase inhibition (using genistein) and by p38 MAP kinase or PKC inhibition (using SB203580 or bisindolylmaleimide, respectively). The activation of both p38 MAP kinase and PKC are recognized requirements for the induction of preconditioning and their inhibition is known to block protection. Western immunoblotting analysis after isoelectric focusing electrophoresis, confirmed the observations made with the phosphospecific antibodies; but also showed that 27+/-4% of total cardiac crystallin was phosphorylated after 30 min of ischemia. AlphaB crystallin exists as large polymeric aggregates in cardiac tissue under basal conditions (approximately 1 MDa as determined by gel filtration chromatography). We induced phosphorylation of alphaB crystallin during aerobic perfusion by the administration of phenylephrine. However this treatment did not alter the molecular aggregate size of alphaB crystallin. It appears that alphaB crystallin molecular aggregate size is not simply regulated by phosphorylation. AlphaB crystallin may have a role to play in the myocardial protection induced by ischemic preconditioning, as both translocation and phosphorylation are both accelerated and enhanced by ischemic preconditioning.     

The mitochondrial permeability transition pore: Molecular nature and role as a target in cardioprotection

The mitochondrial permeability transition (PT) – an abrupt increase permeability of the inner membrane to solutes – is a causative event in ischemia–reperfusion injury of the heart, and the focus of intense research in cardioprotection. The PT is due to opening of the PT pore (PTP), a high conductance channel that is critically regulated by a variety of pathophysiological effectors. Very recent work indicates that the PTP forms from the F-ATP synthase, which would switch from an energy-conserving to an energy-dissipating device. This review provides an update on the current debate on how this transition is achieved, and on the PTP as a target for therapeutic intervention. This article is part of a Special Issue entitled "Mitochondria: from basic mitochondrial biology to cardiovascular disease".     

缺血预处理减轻肥厚心肌缺血再灌注损伤及其信号途径

目的探讨缺血预处理(IPC)对肥厚心肌体外缺血再灌注(IR)损伤的影响及其信号机制。方法48只心肌肥厚大鼠随机分为4组:IR对照组I、PC组I、PC加磷脂酰肌醇-3激酶(PI3K)抑制剂Wortmannin处理组、Wortmannin处理对照组,观察IPC对心肌肥厚大鼠体外IR心脏左心室收缩压、冠状动脉流量、肌酸磷酸激酶(CPK)和乳酸脱氢酶(LDH)释放、心肌梗死范围以及心肌蛋白激酶B(Akt)、糖原合成酶激酶-3β(GSK-3β)磷酸化的影响。结果与IR对照组比较,IPC组心脏左心室收缩压、冠状动脉流量显著提高,CPK、LDH释放减少,心肌梗死范围减小,心肌Akt、GSK-3β磷酸化水平增高,Wortmannin能够抑制IPC所致的Akt、GSK-3β磷酸化,但只能部分消除IPC的心脏保护效应。结论IPC能够减轻心肌肥厚大鼠体外心脏IR损伤,PI3K、Akt、GSK-3β信号途径参与介导IPC对体外IR肥厚心肌的保护作用。     

Delayed cardioprotection in a human cardiomyocyte-derived cell line: the role of adenosine, p38MAP kinase and mitochondrial KATP

Evidence of delayed preconditioning (PC) in man is limited. Adenosine is proposed as a trigger via action on the A₁ receptor in many species and the mitochondrial K_ATP channel is a likely end effector. We examined the ability of a brief, simulated ischemic episode on day one to provide delayed cardioprotection against lethal, simulated ischemia on day two in a human cardiac cell line with reference to the role of adenosine, the p38MAP kinase signalling pathway and mitochondrial K_ATP channel. Results: PC and adenosine administered on day 1 protected against cell death on day 2 as measured by LDH release and propidium iodide (PI) exclusion: (%LDH release: PC: 12.1 ± 1.1%, ADO: 11.9 ± 2.0% vs control: 36.4 ± 1.1%, %PI positive: PC: 14.6% ± 1.4%, ADO: 17.9 ± 2.0% vs control: 34.4 ± 2.0% respectively). This protection is abolished by treatment with SB203580 prior to the protective stimulus on day 1: [PC + SB (%LDH release 28.6 ± 2.8%, %PI positive 34.7 ± 2.2%) and ADO + SB (%LDH release 25.3 ± 2.9%; %PI positive 33.7 ± 7.3%)]. Similarly 5-hydroxydecanoate abolished protection, when given immediately prior to lethal simulated ischemia on day 2: [PC + 5-HD; (%LDH release 31.9 ± 4.8%; %PI positive 29.5 ± 2.0%) and ADO + 5-HD (%LDH release 36.9 ± 4.0%; %PI positive 34.8 ± 2%)]. Conclusion: In this model delayed PC can be mimicked by adenosine and involves the p38MAP kinase pathway and the mitochondrial K_ATP channel. Received: 2 November 1999, Returned for revision: 24 November 1999, Revision received: 23 December 1999, Accepted: 20 January 2000     

Opposing effects on infarction of delta and kappa opioid receptor activation in the isolated rat heart: implications for ischemic preconditioning

δ-Opioid receptors are known to participate in the protection found following ischemic preconditioning (IPC), but the role of κ-receptors in IPC is currently controversial. Langendorff-perfused rat hearts received 35 min regional ischemia and 2 h reperfusion. PC (2 cycles 5 min global ischemia) substantially reduced infarct size. Pharmacological PC with the δ-agonist DADLE (10 nmol/L) had similar protective effects. However, higher dose DADLE (1 μmol/L) had a less beneficial effect, and in conjunction with the δ-antagonist naltrindole unexpectedly increased infarct size (61.5 ± 2.0%, p < 0.05 v 45.9 ± 2.3% in controls) sugggesting a non-δ effect. The universal κ-opioid agonist bremazocine (30 nmol/L) increased infarct size (61.3 ± 1.6%, p < 0.05 v controls), an effect abrogated by the selective κ₁-antagonist nor-binaltorphimine (BNI). Since opiates are known to have anti-adrenergic effects, which hypothetically may help to mediate IPC, cyclic AMP levels were measured in DADLE and in bremazocine-treated hearts. Decreased levels of cyclic AMP at the start of the regional ischemic period were found in low dose DADLE hearts (0.485 ± 0/020, n = 8, vs controls, 0.654 ± 0.025 nmol/g wet weight, p < 0.001), but not in high dose DADLE nor in bremazocine treated hearts. Thus, in the isolated rat heart κ₁-opioid receptor activation exacerbates infarct size through an as yet unknown mechanism, suggesting that there could be an “anti-preconditioned state”. In contrast, δ-activity mediates protection which may be associated with a reduction of tissue cyclic AMP levels. Received: 16 November 1999, Accepted: 7 December 1999     

On the mode of cardioprotection produced by a new bradycardic agent, FR 76830, during ischaemia and after reperfusion in the isolated perfused rat heart: a 31P-NMR study

STUDY OBJECTIVE--The aim was to investigate the effects of a newly synthesised bradycardiac agent, FR 76830, on cardiac mechanical function and metabolism during ischaemia and reperfusion. DESIGN--FR 76830 and diltiazem were infused during 15 min before ischaemia. Hearts were then subjected to ischaemia (40 min) followed by reperfusion (40 min). High energy phosphate compounds and myocardial pH were assessed by 31P-NMR. The effects of bradycardia induced by FR 76830 before induction of ischaemia on the metabolic derangement resulting from ischaemia and on functional and metabolic recovery after reperfusion were examined in comparison with diltiazem. EXPERIMENTAL MATERIAL--Male Wistar rats (about 250 g) were used. MEASUREMENTS AND MAIN RESULTS--FR 76830 and diltiazem produced a dose dependent decrease in heart rate before ischaemia. However, the decrease in the double product (heart rate x left ventricular pressure) was observed only with diltiazem. Both FR 76830 and diltiazem attenuated the fall in myocardial pH during early ischaemia and improved the level of ATP during late ischaemia. Diltiazem also produced an improvement in myocardial acidosis during late ischaemia and in the level of ATP during early ischaemia. CONCLUSIONS--The importance of bradycardia in protection of the myocardial cells during early ischaemia and in preservation of ATP content during late ischaemia and after reperfusion was shown. However, to produce an improvement in myocardial pH during late ischaemia a decrease in the double product is needed.     

Effects of propionyl-L-carnitine on isolated mitochondrial function in the reperfused diabetic rat heart

The effects of propionyl-L-carnitine (PLC) on isolated mitochondrial respiration in the ischemic reperfused diabetic heart were studied. Oral PLC treatment of STZ-diabetic rats was initiated for a period of 6 weeks. After treatment, isolated working hearts from diabetic rats were perfused under aerobic conditions then subjected to 25 min of no-flow ischemia followed by 15 min of aerobic reperfusion. At the end of reperfusion, heart mitochondria was isolated using differential centrifugation and respiration measured in the presence of pyruvate, glutamate, and palmitoylcarnitine. Our results indicate that diabetes was characterized by a pronounced decrease in heart function under aerobic conditions as well as during reperfusion following ischemia. Treatment with PLC resulted in a significant improvement in heart function under these conditions. The depressions in state 3 mitochondrial respiration with both pyruvate and glutamate seen in reperfused hearts from diabetic rats were prevented by PLC. State 3 respiration in the presence of palmitoylcarnitine was also improved in the ischemic reperfused diabetic rat heart. Our results show that PLC improves recovery of mechanical function following ischemia in the diabetic rat heart. The beneficial effects of PLC are associated with enhanced mitochondrial oxidation of fuels.     

Intermittent ischemia produces a cumulative depletion of mitochondrial adenine nucleotides in the isolated perfused rat heart

The purpose of the present study was to determine if repetitive myocardial ischemia would result in the cumulative loss of mitochondrial adenine nucleotides. Isolated perfused rat hearts were subjected to continuous or intermittent ischemia. A single 5-minute period of continuous ischemia did not result in a significant decrease in the mitochondrial adenine nucleotide pool; a single 10-minute period of ischemia resulted in a decrease of approximately 17%. Next, the adenine nucleotide content of mitochondria from preischemic and 30-minute continuous ischemic hearts was compared with two groups of hearts undergoing intermittent ischemia (both groups receiving a total of 30 minutes of ischemia). One group received three 10-minute episodes of ischemia interrupted by 5-minute periods of reperfusion (3 x 10-minute intermittent ischemia); the other intermittent ischemic group received six 5-minute episodes of ischemia interrupted by 5-minute periods of perfusion (6 x 5-minute intermittent ischemia). The mitochondrial adenine nucleotide content (expressed as nanomoles per nanomole cytochrome a) for the preischemic and 30-minute continuous ischemic hearts was 14.7 +/- 0.6 and 8.0 +/- 0.4, respectively. The mitochondrial adenine nucleotide content of the 3 x 10-minute intermittent ischemia group (8.5 +/- 0.5) was not significantly different from the 30-minute continuous ischemic group. The mitochondrial adenine nucleotide content of the 6 x 5-minute intermittent ischemia group (11.0 +/- 0.6) was significantly larger than that of the 30-minute continuous and the 3 x 10-minute intermittent ischemia groups (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

丙泊酚预处理与缺血预处理保护大鼠体外心脏缺血再灌注损伤作用的比较

目的:以缺血预处理(IPC)为标准观察丙泊酚预处理对大鼠体外心脏再灌注损伤的保护作用并探索其可能机制。方法:建立大鼠体外心脏Langendorff灌流模型并随机分为对照组(A组, n=8)、丙泊酚预处理组(B组,n=6)、IPC组(C组,n=6)及5 羟癸酸(5 HD)对照组(D组,n=8)、5 HD加丙泊酚预处理组(E组,n=6)、5 HD加 IPC组(F组,n=7)共6组。连续记录各组心脏血流动力学指标及冠状动脉流量变化,进行再灌注性心律失常评分,并计算心脏梗死面积。结果:B、C、E组血流动力学指标、冠状动脉流量、心律失常评分、梗死面积显著优于A组,以C组最显著(P<0.01或0.05),而D、F组与A组比较差异无统计学意义。结论:丙泊酚预处理与 IPC均可改善体外大鼠心脏再灌注所致的血流动力学紊乱、冠状动脉循环受损及再灌注性心律失常的发生,并缩小心脏梗死面积,但丙泊酚上述保护效应较 IPC弱。阻滞线粒体 KATP通道开放对丙泊酚预处理作用无影响,推测该通道与其保护效应无关。     

Inhibition of taurocholate and ouabain transport in isolated rat hepatocytes by cyclosporin A

The use of cyclosporin A in transplantation procedures has been reported to cause hepatotoxicity as evidenced by elevated serum bilirubin and bile salt levels. However, these biochemical abnormalities could also result from interference with hepatic transport processes. This possibility was investigated in the present study in which the effect of cyclosporin A on transport processes was examined in isolated rat liver cells. Taurocholate, ouabain, and alpha-aminoisobutyric acid were selected as compounds known to enter liver cells by distinct active transport systems and cadmium was selected as a substance taken up by a combination of simple and facilitated diffusion. Cyclosporin A was found to cause a dose-related inhibition of both taurocholate and ouabain uptake. On the other hand, the uptake of alpha-aminoisobutyric acid and of cadmium were unaffected by cyclosporin A. These findings indicate a substrate-specific effect of cyclosporin A rather than a general effect on cellular transport. Efflux of taurocholate from preloaded hepatocytes was also inhibited by cyclosporin A. Cyclosporin A caused a decrease in maximum velocity for ouabain uptake with no change in Km. Kinetic analysis for both uptake and efflux of taurocholate showed an unchanged maximum velocity and an increased Km. The data indicate that the ability of liver cells to take up and release bile acids is impaired in the presence of cyclosporin A. These findings provide a possible explanation for the finding of increased serum bile acids during cyclosporin A therapy and suggest that hepatic clearance of other compounds could also be impaired.