Modulation of electron transport protects cardiac mitochondria and decreases myocardial injury during ischemia and reperfusion

Mitochondria are increasingly recognized as lynchpins in the evolution of cardiac injury during ischemia and reperfusion. This review addresses the emerging concept that modulation of mitochondrial respiration during and immediately following an episode of ischemia can attenuate the extent of myocardial injury. The blockade of electron transport and the partial uncoupling of respiration are two mechanisms whereby manipulation of mitochondrial metabolism during ischemia decreases cardiac injury. Although protection by inhibition of electron transport or uncoupling of respiration initially appears to be counterintuitive, the continuation of mitochondrial oxidative phosphorylation in the pathological milieu of ischemia generates reactive oxygen species, mitochondrial calcium overload, and the release of cytochrome c. The initial target of these deleterious mitochondrial-driven processes is the mitochondria themselves. Consequences to the cardiomyocyte, in turn, include oxidative damage, the onset of mitochondrial permeability transition, and activation of apoptotic cascades, all favoring cardiomyocyte death. Ischemia-induced mitochondrial damage carried forward into reperfusion further amplifies these mechanisms of mitochondrial-driven myocyte injury. Interruption of mitochondrial respiration during early reperfusion by pharmacologic blockade of electron transport or even recurrent hypoxia or brief ischemia paradoxically decreases cardiac injury. It increasingly appears that the cardioprotective paradigms of ischemic preconditioning and postconditioning utilize modulation of mitochondrial oxidative metabolism as a key effector mechanism. The initially counterintuitive approach to inhibit mitochondrial respiration provides a new cardioprotective paradigm to decrease cellular injury during both ischemia and reperfusion. cardiolipin; cytochrome c; complex I; cytochrome oxidase     

Adenosine-enhanced ischemic preconditioning: adenosine receptor involvement during ischemia and reperfusion

Adenosine-enhanced ischemic preconditioning (APC) extends the cardioprotection of ischemic preconditioning (IPC) by both significantly decreasing myocardial infarct size and significantly enhancing postischemic functional recovery. In this study, the role of adenosine receptors during ischemia-reperfusion was determined. Rabbit hearts (n = 92) were used for Langendorff perfusion. Control hearts were perfused for 180 min, global ischemia hearts received 30-min ischemia and 120-min reperfusion, and IPC hearts received 5-min ischemia and 5-min reperfusion before ischemia. APC hearts received a bolus injection of adenosine coincident with IPC. Adenosine receptor (A(1), A(2), and A(3)) antagonists were used with APC before ischemia and/or during reperfusion. GR-69019X (A(1)/A(3)) and MRS-1191/MRS-1220 (A(3)) significantly increased infarct size in APC hearts when administered before ischemia and significantly decreased functional recovery when administered during both ischemia and reperfusion (P < 0.05 vs. APC). DPCPX (A(1)) administered either before ischemia and/or during reperfusion had no effect on APC cardioprotection. APC-enhanced infarct size reduction is modulated by adenosine receptors primarily during ischemia, whereas APC-enhanced postischemic functional recovery is modulated by adenosine receptors during both ischemia and reperfusion.     

Involvement of the mitochondrial calcium uniporter in cardioprotection by ischemic preconditioning

The objective of the present study was to determine whether the mitochondrial calcium uniporter plays a role in the cardioprotection induced by ischemic preconditioning (IPC). Isolated rat hearts were subjected to 30 min of regional ischemia by ligation of the left anterior descending artery followed by 120 min of reperfusion. IPC was achieved by two 5-min periods of global ischemia separated by 5 min of reperfusion. IPC reduced the infarct size and lactate dehydrogenase release in coronary effluent, which was associated with improved recovery of left ventricular contractility. Treatment with ruthenium red (RR, 5 μM), an inhibitor of the uniporter, or with Ru360 (10 μM), a highly specific uniporter inhibitor, provided cardioprotective effects like those of IPC. The cardioprotection induced by IPC was abolished by spermine (20 μM), an activator of the uniporter. Cyclosporin A (CsA, 0.2 μM), an inhibitor of the mitochondrial permeability transition pore, reversed the effects caused by spermine. In mitochondria isolated from untreated hearts, both Ru360 (10 μM) and RR (1 μM) decreased pore opening, while spermine (20 μM) increased pore opening which was blocked by CsA (0.2 μM). In mitochondria from preconditioned hearts, the opening of the pore was inhibited, but this inhibition did not occur in the mitochondria from hearts treated with IPC plus spermine. These results indicate that the mitochondrial calcium uniporter is involved in the cardioprotection conferred by ischemic preconditioning.     

Ischemic defects in the electron transport chain increase the production of reactive oxygen species from isolated rat heart mitochondria

Cardiac ischemia decreases complex III activity, cytochrome c content, and respiration through cytochrome oxidase in subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM). The reversible blockade of electron transport with amobarbital during ischemia protects mitochondrial respiration and decreases myocardial injury during reperfusion. These findings support that mitochondrial damage occurs during ischemia and contributes to myocardial injury during reperfusion. The current study addressed whether ischemic damage to the electron transport chain (ETC) increased the net production of reactive oxygen species (ROS) from mitochondria. SSM and IFM were isolated from 6-mo-old Fisher 344 rat hearts following 25 min global ischemia or following 40 min of perfusion alone as controls. H(2)O(2) release from SSM and IFM was measured using the amplex red assay. With glutamate as a complex I substrate, the net production of H(2)O(2) was increased by 178 +/- 14% and 179 +/- 17% in SSM and IFM (n = 9), respectively, following ischemia compared with controls (n = 8). With succinate as substrate in the presence of rotenone, H(2)O(2) increased by 272 +/- 22% and 171 +/- 21% in SSM and IFM, respectively, after ischemia. Inhibitors of electron transport were used to assess maximal ROS production. Inhibition of complex I with rotenone increased H(2)O(2) production by 179 +/- 24% and 155 +/- 14% in SSM and IFM, respectively, following ischemia. Ischemia also increased the antimycin A-stimulated production of H(2)O(2) from complex III. Thus ischemic damage to the ETC increased both the capacity and the net production of H(2)O(2) from complex I and complex III and sets the stage for an increase in ROS production during reperfusion as a mechanism of cardiac injury.     

Myocardial preconditioning against ischemia-reperfusion injury is abolished in Zucker obese rats with insulin resistance

Insulin resistance (IR) precedes the onset of Type 2 diabetes, but its impact on preconditioning against myocardial ischemia-reperfusion injury is unexplored. We examined the effects of diazoxide and ischemic preconditioning (IPC; 5-min ischemia and 5-min reperfusion) on ischemia (30 min)-reperfusion (240 min) injury in young IR Zucker obese (ZO) and lean (ZL) rats. ZO hearts developed larger infarcts than ZL hearts (infarct size: 57.3 +/- 3% in ZO vs. 39.2 +/- 3.2% in ZL; P < 0.05) and also failed to respond to cardioprotection by IPC or diazoxide (47.2 +/- 4.3% and 52.5 +/- 5.8%, respectively; P = not significant). In contrast, IPC and diazoxide treatment reduced the infarct size in ZL hearts (12.7 +/- 2% and 16.3 +/- 6.7%, respectively; P < 0.05). The mitochondrial ATP-activated potassium channel (K(ATP)) antagonist 5-hydroxydecanoic acid inhibited IPC and diazoxide-induced preconditioning in ZL hearts, whereas it had no effect on ZO hearts. Diazoxide elicited reduced depolarization of isolated mitochondria from ZO hearts compared with ZL (73 +/- 9% in ZL vs. 39 +/- 9% in ZO; P < 0.05). Diazoxide also failed to enhance superoxide generation in isolated mitochondria from ZO compared with ZL hearts. Electron micrographs of ZO hearts revealed a decreased number of mitochondria accompanied by swelling, disorganized cristae, and vacuolation. Immunoblots of mitochondrial protein showed a modest increase in manganese superoxide dismutase in ZO hearts. Thus obesity accompanied by IR is associated with the inability to precondition against ischemic cardiac injury, which is mediated by enhanced mitochondrial oxidative stress and impaired activation of mitochondrial K(ATP).     

Inducing late phase of infarct protection in skeletal muscle by remote preconditioning: efficacy and mechanism

We have previously demonstrated that remote ischemic preconditioning (IPC) by instigation of three cycles of 10-min occlusion/reperfusion in a hindlimb of the pig elicits an early phase of infarct protection in local and distant skeletal muscles subjected to 4 h of ischemia immediately after remote IPC. The aim of this project was to test our hypothesis that hindlimb remote IPC also induces a late phase of infarct protection in skeletal muscle and that K(ATP) channels play a pivotal role in the trigger and mediator mechanisms. We observed that pig bilateral latissimus dorsi (LD) muscle flaps sustained 46 +/- 2% infarction when subjected to 4 h of ischemia/48 h of reperfusion. The late phase of infarct protection appeared at 24 h and lasted up to 72 h after hindlimb remote IPC. The LD muscle infarction was reduced to 28 +/- 3, 26 +/- 1, 23 +/- 2, 24 +/- 2 and 24 +/- 4% at 24, 28, 36, 48 and 72 h after remote IPC, respectively (P < 0.05; n = 8). In subsequent studies, hindlimb remote IPC or intravenous injection of the sarcolemmal K(ATP) (sK(ATP)) channel opener P-1075 (2 microg/kg) at 24 h before 4 h of sustained ischemia (i.e., late preconditioning) reduced muscle infarction from 43 +/- 4% (ischemic control) to 24 +/- 2 and 19 +/- 3%, respectively (P < 0.05, n = 8). Intravenous injection of the sK(ATP) channel inhibitor HMR 1098 (6 mg/kg) or the nonspecific K(ATP) channel inhibitor glibenclamide (Glib; 1 mg/kg) at 10 min before remote IPC completely blocked the infarct- protective effect of remote IPC in LD muscle flaps subjected to 4 h of sustained ischemia at 24 h after remote IPC. Intravenous bolus injection of the mitochondrial K(ATP) (mK(ATP)) channel inhibitor 5-hydroxydecanoate (5-HD; 5 mg/kg) immediately before remote IPC and 30-min intravenous infusion of 5-HD (5 mg/kg) during remote IPC did not affect the infarct-protective effect of remote IPC in LD muscle flaps. However, intravenous Glib or 5-HD, but not HMR 1098, given 24 h after remote IPC completely blocked the late infarct-protective effect of remote IPC in LD muscle flaps. None of these drug treatments affected the infarct size of control LD muscle flaps. The late phase of infarct protection was associated with a higher (P < 0.05) muscle content of ATP at the end of 4 h of ischemia and 1.5 h of reperfusion and a lower (P < 0.05) neutrophilic activity at the end of 1.5 h of reperfusion compared with the time-matched control. In conclusion, these findings support our hypothesis that hindlimb remote IPC induces an uninterrupted long (48 h) late phase of infarct protection, and sK(ATP) and mK(ATP) channels play a central role in the trigger and mediator mechanism, respectively.     

Effect of the first window of ischemic preconditioning on mitochondrial dysfunction following global cerebral ischemia

Rats may develop sustained tolerance against lethal cerebral ischemia after exposure to a sublethal ischemic insult (ischemic preconditioning (IPC)). Two windows for the induction of tolerance by IPC have been proposed, one that occurs within 1h following IPC, and the other one that occurs 1-3 days after IPC. An important difference between these two windows is that in contrast to the second window, neuroprotection against lethal ischemia is transient in the first window. We tested the hypothesis that rapid IPC would reduce or prevent ischemia-induced changes in mitochondrial function. IPC and ischemia were produced by bilateral carotid occlusions and systemic hypotension (50 mmHg) for 2 and 10 min, respectively. The non-synaptosomal mitochondria were harvested 30 min following the 10 min 'test' ischemia. Mitochondrial rate of respiration decreased by 10% when the substrates were pyruvate and malate, and 29% when the substrates were ascorbic acid and N,N,N',N'-tetramethyl-p-phenylenediamine ( P< 0.01). The activities of complex I-III decreased in ischemic group by 16, 23 (P < 0.05) and 24%, respectively. IPC was unable to prevent decreases in the rate of respiration and activities of different complexes. These data suggest that rapidly induced IPC is unable to protect the integrity of mitochondrial oxidative phosphorylation following cerebral ischemia, perhaps explaining why IPC only provides transitory protection in the 'first window'.     

Preconditioning and postconditioning: innate cardioprotection from ischemia-reperfusion injury.

Reperfusion is the definitive treatment to salvage ischemic myocardium from infarction. A primary determinant of infarct size is the duration of ischemia. In myocardium that has not been irreversibly injured by ischemia, reperfusion induces additional injury in the area at risk. The heart has potent innate cardioprotective mechanisms against ischemia-reperfusion that reduce infarct size and other presentations of postischemic injury. Ischemic preconditioning (IPC) applied before the prolonged ischemia exerts the most potent protection observed among known strategies. It has been assumed that IPC exerts protection during ischemia. However, recent data suggest that cardioprotection is also exerted during reperfusion. Postconditioning (PoC), defined as brief intermittent cycles of ischemia alternating with reperfusion applied after the ischemic event, has been shown to reduce infarct size, in some cases equivalent to that observed with IPC. Although there are similarities in mechanisms of cardioprotection by these two interventions, there are key differences that go beyond simply exerting these mechanisms before or after ischemia. A significant limitation of IPC has been the inability to apply this maneuver clinically except in situations where the ischemic event can be predicted. On the other hand, PoC is applied at the point of service in the hospital (cath-lab for percutaneous coronary intervention, coronary artery bypass grafting, and other cardiac surgery) where and when reperfusion is initiated. Initial clinical studies are in agreement with the success and extent to which PoC reduces infarct size and myocardial injury, even in the presence of multiple comorbidities.     

Mitochondrial Src tyrosine kinase plays a role in the cardioprotective effect of ischemic preconditioning by modulating complex I activity and mitochondrial ROS generation

Abstract

While ischemic preconditioning (IPC) and other cardioprotective interventions have been proposed to protect the heart from ischemia/reperfusion (I/R) injury by inhibiting mitochondrial complex I activity upon reperfusion, the exact mechanism underlying the modulation of complex I activity remains elusive. This study was aimed to test the hypothesis that IPC modulates complex I activity at reperfusion by activating mitochondrial Src tyrosine kinase, and induces cardioprotection against I/R injury. Isolated rat hearts were preconditioned by three cycles of 5-min ischemia and 5-min reperfusion prior to 30-min index ischemia followed by 2 h of reperfusion. Mitochondrial Src phosphorylation (Tyr⁴¹⁶) was dramatically decreased during I/R, implying inactivation of Src tyrosine kinase by I/R. IPC increased mitochondrial Src phosphorylation upon reperfusion and this was inhibited by the selective Src tyrosine kinase inhibitor PP2. IPC's anti-infarct effect was inhibited by the selective Src tyrosine kinase inhibitor PP2. Complex I activity was significantly increased upon reperfusion, an effect that was prevented by IPC in a Src tyrosine kinase-dependent manner. In support, Src and phospho-Src were found in complex I. Furthermore, IPC prevented hypoxia/reoxygenation-induced mitochondrial reactive oxygen species (ROS) generation and cellular injury in rat cardiomyocytes, which was revoked by PP2. Finally, IPC reduced LDH release induced by both hypoxia/reoxygenation and simulated ischemia/reperfusion, an effect that was reversed by PP2 and Src siRNA. These data suggest that mitochondrial Src tyrosine kinase accounts for the inhibitory action of IPC on complex I and mitochondrial ROS generation, and thereby plays a role in the cardioprotective effect of IPC.     

Altered NADH and improved function by anesthetic and ischemic preconditioning in guinea pig intact hearts

NADH increases during ischemia because O(2) shortage limits NADH oxidation at the electron transport chain. Ischemic (IPC) and anesthetic preconditioning (APC) attenuate cardiac reperfusion injury. We examined whether IPC and APC similarly alter NADH, i.e., mitochondrial metabolism. NADH fluorescence was measured at the left ventricular wall of 40 Langendorff-prepared guinea pig hearts. IPC was achieved by two 5-min periods of ischemia and APC by exposure to 0.5 or 1.3 mM sevoflurane for 15 min, each ending 30 min before 30 min of global ischemia. During ischemia, NADH initially increased in nonpreconditioned control hearts and then gradually declined below baseline levels. This increase in NADH was lower after APC but not after IPC. The subsequent decline was slower after IPC and APC. On reperfusion, NADH was less decreased after IPC or APC, mechanical and metabolic functions were improved, and infarct size was lower compared with controls. Our results indicate that IPC and APC cause distinctive changes in mitochondrial metabolism during ischemia and thus lead to improved function and tissue viability on reperfusion.     

Warm ischemic preconditioning improves mitochondrial redox balance during and after mild hypothermic ischemia in guinea pig isolated hearts

Ischemic preconditioning (IPC) induces distinctive changes in mitochondrial bioenergetics during warm (37 degrees C) ischemia and improves function and tissue viability on reperfusion. We examined whether IPC before 2 h of hypothermic (27 degrees C) ischemia affords additive cardioprotection and improves mitochondrial redox balance assessed by mitochondrial NADH and flavin adenine dinucleotide (FAD) autofluorescence in intact hearts. A mediating role of ATP-sensitive K(+) (K(ATP)) channel opening was investigated. NADH and FAD fluorescence was measured in the left ventricular wall of guinea pig isolated hearts assigned to five groups of eight animals each: hypothermia alone, hypothermia with ischemia, IPC with cold ischemia, 5-hydroxydecanoic acid (5-HD) alone, and 5-HD with IPC and cold ischemia. IPC consisted of two 5-min periods of warm global ischemia spaced 5 min apart and 15 min of reperfusion before 2 h of ischemia at 27 degrees C and 2 h of warm reperfusion. The K(ATP) channel inhibitor 5-HD was perfused from 5 min before until 5 min after IPC. IPC before 2 h of ischemia at 27 degrees C led to better recovery of function and less tissue damage on reperfusion than did 27 degrees C ischemia alone. These improvements were preceded by attenuated increases in NADH and decreases in FAD during cold ischemia and the reverse changes during warm reperfusion. 5-HD blocked each of these changes induced by IPC. This study indicates that IPC induces additive cardioprotection with mild hypothermic ischemia by improving mitochondrial bioenergetics during and after ischemia. Because effects of IPC on subsequent changes in NADH and FAD were inhibited by 5-HD, this suggests that mitochondrial K(ATP) channel opening plays a substantial role in improving mitochondrial bioenergetics throughout mild hypothermic ischemia and reperfusion.     

Sarcolemmal KATP channel triggers delayed ischemic preconditioning in rats

Previous work from our laboratory has shown that the sarcolemmal K(ATP) channel (sK(ATP)) is required as a trigger for delayed cardioprotection upon exogenous opioid administration. We also established that the mitochondrial K(ATP) (mK(ATP)) channel is not required for triggering delayed delta-opioid-induced infarct size reduction. Because mechanistic differences have been found among delta-opioids and that due to ischemic preconditioning (IPC), we determined whether the triggering mechanism of delayed IPC-induced infarct size reduction involves either the sK(ATP) or mK(ATP). Male Sprague-Dawley rats received either sham surgery or IPC (3- to 5-min cycles of ischemia and reperfusion) 24 h before being subjected to 30 min of ischemia and 2 h of reperfusion. Infarct size was determined and expressed as a percentage of the area at risk, with significance compared with sham reported at P 相似文献   

Blockade of electron transport during ischemia protects cardiac mitochondria

Subsarcolemmal mitochondria sustain progressive damage during myocardial ischemia. Ischemia decreases the content of the mitochondrial phospholipid cardiolipin accompanied by a decrease in cytochrome c content and a diminished rate of oxidation through cytochrome oxidase. We propose that during ischemia mitochondria produce reactive oxygen species at sites in the electron transport chain proximal to cytochrome oxidase that contribute to the ischemic damage. Isolated, perfused rabbit hearts were treated with rotenone, an irreversible inhibitor of complex I in the proximal electron transport chain, immediately before ischemia. Rotenone pretreatment preserved the contents of cardiolipin and cytochrome c measured after 45 min of ischemia. The rate of oxidation through cytochrome oxidase also was improved in rotenone-treated hearts. Inhibition of the electron transport chain during ischemia lessens damage to mitochondria. Rotenone treatment of isolated subsarcolemmal mitochondria decreased the production of reactive oxygen species during the oxidation of complex I substrates. Thus, the limitation of electron flow during ischemia preserves cardiolipin content, cytochrome c content, and the rate of oxidation through cytochrome oxidase. The mitochondrial electron transport chain contributes to ischemic mitochondrial damage that in turn augments myocyte injury during subsequent reperfusion.     

Cardioprotection by multiple preconditioning cycles does not require mitochondrial K(ATP) channels in pigs

To test whether cardioprotection induced by ischemic preconditioning depends on the opening of mitochondrial ATP-sensitive K(+) (K(ATP)) channels, the effect of channel blockade was studied in barbital-anesthetized open-chest pigs subjected to 30 min of complete occlusion of the left anterior descending coronary artery and 3 h of reflow. Preconditioning was elicited by two cycles of 5-min occlusion plus 10-min reperfusion before the 30-min occlusion period. 5-Hydroxydecanoate (5 mg/kg iv) was injected 15 min before preconditioning or pharmacological preconditioning induced by diazoxide (3.5 mg/kg, 1 ml/min iv). Infarct size (percentage of the area at risk) after 30 min of ischemia was 35.1 +/- 9.9% (n = 7). Preconditioning markedly limited myocardial infarct size (2.7 +/- 1.6%, n = 7), and 5-hydroxydecanoate did not abolish protection (2.4 +/- 0.9%, n = 8). Diazoxide infusion also significantly limited infarct size (14.6 +/- 7.4%, n = 7), and 5-hydroxydecanoate blocked this effect (30.8 +/- 8.0%, n = 7). Thus the opening of mitochondrial K(ATP) channels is cardioprotective in pigs, but these data do not support the hypothesis that opening of mitochondrial K(ATP) channels is required for the endogenous protection afforded by preconditioning.     

Akt and Erk1/2 activate the ornithine decarboxylase/polyamine system in cardioprotective ischemic preconditioning in rats: the role of mitochondrial permeability transition pores

Ornithine decarboxylase (ODC) is the first rate-limiting enzyme in polyamine biosynthesis, which is essential for cell survival. We hypothesized that the ODC/polyamine system is involved in ischemic preconditioning (IPC)-mediated cardioprotection through the activation of Erk1/2 and Akt and through the inhibition of the mitochondrial permeability transition (mPT). Isolated rat hearts were subjected to 40 min of ischemia either with or without IPC (3 cycles of 5-min global ischemia), and ODC protein expression, polyamine content, and Akt and Erk1/2 phosphorylation were evaluated after 30 min of reperfusion. IPC significantly upregulated the ODC/polyamine pathway, promoted Erk1/2 and Akt phosphorylation, and reduced the infarct size and heart dysfunction after reperfusion. An inhibitor of ODC, α-difluoromethylornithine (DFMO), abolished the IPC-induced cardioprotection. Moreover, the inhibition of the IPC-induced activation of Erk1/2 and Akt using PD98059 or wortmannin downregulated the ODC/polyamine system. In separate studies, the Ca²⁺ load required to open the mPT pore was significantly lower in DFMO-treated cardiac mitochondria than in mitochondria from IPC hearts. Furthermore, spermine or spermidine significantly inhibited the mPT induced by CaCl₂. These results suggest that IPC upregulates the ODC/polyamine system and mediates preconditioning cardioprotection, which may depend on the phosphorylation/activation of Erk1/2 and Akt and on the inhibition of the mPT during reperfusion.     

Opening of mitochondrial K(ATP) channel occurs downstream of PKC-epsilon activation in the mechanism of preconditioning

We examined whether the mitochondrial ATP-sensitive K channel (K(ATP)) is an effector downstream of protein kinase C-epsilon (PKC-epsilon) in the mechanism of preconditioning (PC) in isolated rabbit hearts. PC with two cycles of 5-min ischemia/5-min reperfusion before 30-min global ischemia reduced infarction from 50.3 +/- 6.8% of the left ventricle to 20.3 +/- 3.7%. PC significantly increased PKC-epsilon protein in the particulate fraction from 51 +/- 4% of the total to 60 +/- 4%, whereas no translocation was observed for PKC-delta and PKC-alpha. In mitochondria separated from the other particulate fractions, PC increased the PKC-epsilon level by 50%. Infusion of 5-hydroxydecanoate (5-HD), a mitochondrial K(ATP) blocker, after PC abolished the cardioprotection of PC, whereas PKC-epsilon translocation by PC was not interfered with 5-HD. Diazoxide, a mitochondrial K(ATP) opener, infused 10 min before ischemia limited infarct size to 5.2 +/- 1.4%, but this agent neither translocated PKC-epsilon by itself nor accelerated PKC-epsilon translocation after ischemia. Together with the results of earlier studies showing mitochondrial K(ATP) opening by PKC, the present results suggest that mitochondrial K(ATP)-mediated cardioprotection occurs subsequent to PKC-epsilon activation by PC.     

Isolating the segment of the mitochondrial electron transport chain responsible for mitochondrial damage during cardiac ischemia

Ischemia damages the mitochondrial electron transport chain (ETC), mediated in part by damage generated by the mitochondria themselves. Mitochondrial damage resulting from ischemia, in turn, leads to cardiac injury during reperfusion. The goal of the present study was to localize the segment of the ETC that produces the ischemic mitochondrial damage. We tested if blockade of the proximal ETC at complex I differed from blockade distal in the chain at cytochrome oxidase. Isolated rabbit hearts were perfused for 15 min followed by 30 min stop-flow ischemia at 37 °C. Amobarbital (2.5 mM) or azide (5 mM) was used to block proximal (complex I) or distal (cytochrome oxidase) sites in the ETC. Time control hearts were buffer-perfused for 45 min. Subsarcolemmal mitochondria (SSM) and interfibrillar mitochondria (IFM) were isolated. Ischemia decreased cytochrome c content in SSM but not in IFM compared to time control. Blockade of electron transport at complex I preserved the cytochrome c content in SSM. In contrast, blockade of electron transport at cytochrome oxidase with azide did not retain cytochrome c in SSM during ischemia. Since blockade of electron transport at complex III also prevented cytochrome c loss during ischemia, the specific site that elicits mitochondrial damage during ischemia is likely located in the segment between complex III and cytochrome oxidase.     

雷米普利对糖尿病大鼠心肌缺血／再灌注损伤保护作用的超微结构研究

目的：研究雷米普利对糖尿病大鼠心肌缺血／再灌注损伤的保护作用,并从超微结构的角度初步探讨其作用机制。方法：链脲佐菌素致糖尿病大鼠被随机分为3组（n=16）：缺血／再灌注（I／R）、缺血预适应（IPC）和雷米普利（RAM）组。RAM组每天用雷米普利（1mg／kg）灌胃,I／R和IPC组用等体积生理盐水灌胃。4周后各组动物均经历心肌缺血／再灌注损伤,IPC组于缺血前行心肌缺血预适应。连续监测心电图变化,测定心肌梗死面积,光、电镜下观察心肌形态学改变。结果：与I／R组比较,RAM及IPC组缺血期心脏ST-段抬高幅度降低,室早出现时间推迟,持续时间缩短,室速、室颤发生率降低,心肌梗死面积缩小,形态学观察心肌损伤减轻,心肌纤维及线粒体特征性结构保持清晰,血管通畅,内皮损伤减轻。结论：连续4周使用RAM对实验性糖尿病大鼠具有与IPC相似的心脏保护效应,机制可能与保护心肌细胞及线粒体、改善内皮功能等有关。