Thioredoxin regulation of ischemic preconditioning

Thioredoxins are a class of small redox-regulating proteins that appear to play a crucial role in many oxidative stress-inducible degenerative diseases. A recent study demonstrated a reduction of thioredoxin-1 (Trx1) protein in the ischemic reperfused myocardium. When the same heart was adapted to ischemic stress by preconditioning with repeated cyclic episodes of small duration of ischemia and reperfusion, there was an increased induction of Trx1 expression. Inhibition of Trx1 expression resulted in reduced postischemic ventricular recovery and increased myocardial infarct size in the preconditioned heart. Corroborating these findings, transgenic mouse hearts overexpressing Trx1 were resistant to ischemic reperfusion injury as compared with the hearts from wild-type mice. Thus, it appears that thioredoxin plays a crucial role in cardioprotection induced by preconditioning.     

Attenuation of conduction delay by ischemic preconditioning reduces ischemia-induced ventricular arrhythmias

Ischemic preconditioning has been acknowledged as a powerful method of decreasing ischemic injury. However, the antiarrhythmic mechanism of ischemic preconditioning during ischemia is unclear. We studied the effects of ischemic preconditioning on arrhythmias and cardiac electrophysiology during ischemia in Langendorff rat hearts (n = 44). In the non-preconditioned group (PC(-); n = 24), the hearts underwent 5-min zero-flow global ischemia without any prior ischemic preconditioning. In the preconditioned group (PC(+); n = 20), the hearts were preconditioned by three cycles of 3-min zero-flow global ischemia and 5-min reperfusion before undergoing 5-min global ischemia. Ischemic preconditioning reduced the incidence of ischemia-induced arrhythmias (PC(-); 38.9%, PC(+): 8.3%, p < 0.05), shortened monophasic action potential duration (MAPD, P < 0.05), attenuated conduction delay (conduction time; PC(-): 234.2%, PC(+): 173.4%, P < 0.05) and increased the ventricular fibrillation threshold. Although the shortening of MAPD in PC(-) hearts was not influenced by the presence or absence of arrhythmias, conduction time prolongation at 3-min was more obvious in PC(-) hearts with arrhythmia than in PC(-) hearts without arrhythmia (PC(-) with arrhythmia: 220.2%, PC(-) without arrhythmia: 190.7%, P < 0.05). We concluded that ischemic preconditioning could protect the rat hearts from ischemia-induced arrhythmias and postulated that attenuation of conduction delay during ischemia might be an important factor in the antiarrhythmic action of ischemic preconditioning.     

Brief apnea induces myocardial ischemic tolerance by an opioid-insensitive mechanism.

BACKGROUND: Intermittent brief "preconditioning" (PC) ischemia has been shown to render the heart resistant to a subsequent sustained ischemic insult, in part through an opioid-dependent mechanism. Using the rabbit model, we tested the hypothesis that intermittent in vivo apnea elicits a cardioprotective response similar to that achieved with conventional PC ischemia. In addition, we sought to determine if infarct size reduction seen in this model was stimulated via opioid receptor activation. METHODS: Anesthetized, intubated rabbits (n=35) were randomized to receive three 4.5-min bouts of apnea interspersed with 5 min normal ventilation or time-matched standard ventilation (controls). Upon completion of the in vivo PC/control period, the hearts were excised and assessed for ischemic tolerance on a modified Langendorff apparatus (40 min global ischemia+2h reperfusion). To assess the contribution of opioid receptor stimulation, two additional control and PC groups received the nonspecific opioid antagonist naloxone (10 mg/kg) prior to the in vivo intervention phase. Infarct size (delineated by tetrazoliam staining and expressed as a percentage of the left ventricle [LV]) was compared among the four groups by ANOVA. RESULTS: Infarct size was significantly reduced in hearts that received antecedent apneic PC when compared with controls (63+/-5% vs. 34+/-8%) of the LV, respectively; P<.05). Pretreatment with naloxone had no significant effect on infarct size in nonpreconditioned hearts (80+/-6%) and did not inhibit the protective effects of apnea-induced PC (52+/-10% in naloxone+PC group). CONCLUSIONS: Intermittent apnea evokes significant myocardial ischemic tolerance through an opioid-insensitive mechanism.     

Limb remote-preconditioning protects against focal ischemia in rats and contradicts the dogma of therapeutic time windows for preconditioning

Remote ischemic preconditioning is an emerging concept for stroke treatment, but its protection against focal stroke has not been established. We tested whether remote preconditioning, performed in the ipsilateral hind limb, protects against focal stroke and explored its protective parameters. Stroke was generated by a permanent occlusion of the left distal middle cerebral artery (MCA) combined with a 30 min occlusion of the bilateral common carotid arteries (CCA) in male rats. Limb preconditioning was generated by 5 or 15 min occlusion followed with the same period of reperfusion of the left hind femoral artery, and repeated for two or three cycles. Infarct was measured 2 days later. The results showed that rapid preconditioning with three cycles of 15 min performed immediately before stroke reduced infarct size from 47.7+/-7.6% of control ischemia to 9.8+/-8.6%; at two cycles of 15 min, infarct was reduced to 24.7+/-7.3%; at two cycles of 5 min, infarct was not reduced. Delayed preconditioning with three cycles of 15 min conducted 2 days before stroke also reduced infarct to 23.0+/-10.9%, but with two cycles of 15 min it offered no protection. The protective effects at these two therapeutic time windows of remote preconditioning are consistent with those of conventional preconditioning, in which the preconditioning ischemia is induced in the brain itself. Unexpectedly, intermediate preconditioning with three cycles of 15 min performed 12 h before stroke also reduced infarct to 24.7+/-4.7%, which contradicts the current dogma for therapeutic time windows for the conventional preconditioning that has no protection at this time point. In conclusion, remote preconditioning performed in one limb protected against ischemic damage after focal cerebral ischemia.     

NO对心脏缺血再灌注损伤的影响及其在缺血预处理中的作用

目的:明确NO对心脏缺血再灌注(IR)损伤的影响及其在缺血预处理(IP)保护机制中的作用,同时观察NO对缺血再灌注凋亡的影响。方法:使用在体大鼠心脏缺血再灌注模型,实验共分为6组:IR组,IR+L-arg组,IR+L-NAME组,IP组,IP+L-arg组,IP+L-NAME组,观察分析心功能、梗塞面积、中性粒细胞(PMN)计数、心肌髓过氧化物酶(MPO)活性、TUNEL阳性细胞计数等指标。结果:L-arg,L-NAME均明显减轻了IR引起的PMN浸润和心肌细胞凋亡。缺血预处理前给予NO前体L-arg增加NO生成或使用L-NAME阻断NO生成对缺血预处理保护作用无明显影响。结论:缺血前组予L-arg增加内源性NO生成可对心肌缺血再灌注发挥保护作用;组予L-NAME可能通过减少再灌注其ONOO^-的生成而减轻心肌损伤和凋亡。     

Infarct size-limiting effect of calcium preconditioning in rabbit hearts

Recent studies demonstrated that brief period of Ca2+ depletion and repletion (Ca2+ preconditioning, CPC) has strong protective effects against ischemia in a rat heart. CPC and classic preconditioning (IPC) were compared in relation with infarct size and protein kinase C (PKC) isozymes. Isolated Langendorff-perfused rabbit hearts were subjected to 45-min ischemia (Isc) followed by 120-min reperfusion (R) with or without IPC, induced by 5-min Isc and 10-min R. In the CPC hearts, 5-min Ca2+ depletion and 10-min repletion (CPC) were given before 45-min Isc, with or without concurrent PKC inhibition (calphostin C, 200 nmol/L). IPC enhanced recovery of LV function, while CPC did not. Infarct size was significantly reduced by both CPC and IPC (p < 0.05 vs. ischemic control). Membrane PKC was significantly increased from 2.53 +/- 0.07 (baseline, nmol/g tissue) to 3.11+/-0.07, 3.34 +/- 0.11, 3.15 +/- 0.09, and 3.06 +/- 0.08 by IPC, IPC and 45-min Isc, CPC and 45-min Isc, respectively (p < 0.01). Immunoblots of membrane PKC were increased by IPC, IPC and 45-min Isc, and CPC. These effects were abolished by PKC inhibition. Thus, activation of PKC may have trigger role in the mechanism of cardioprotective effect by CPC.     

Relation between ischemic preconditioning and the duration of sustained ischemia.

It has been reported that repetitive brief periods of ischemia and reperfusion (ischemic preconditioning, IP) cause a significant reduction in the extent of myocardial necrosis or in the incidence of reperfusion arrhythmias in rat heart. However, recent reports have stated that IP effect is diminished or lost in the canine or bovine heart if ischemia (mostly regional) is sustained for 40 min or longer. The main objective of this study is to assess whether IP provides myocardial protection in prolonged sustained ischemia under the condition of global ischemia in isolated rabbit heart. The hearts were subjected to 10-60 min sustained ischemia (SI) followed by 60 min reperfusion with (IP heart) or without IP (ISCH heart). IP was induced by 4 cycles of 5 min global ischemia and 5 min reperfusion. Left ventricular function (LVF), extent of infarction (EI) and ultrastructural changes were examined. As a whole, the LVF began to recover on reperfusion but there was no significant difference in the functional parameters. However, extracellular Ca2+ concentration was lower in the ISCH hearts (p < 0.05) and the EI was significantly different between the hearts which had received 60 min SI (67% in the ISCH versus 32% in the IP heart, p < 0.01). Ultrastructural changes were homogeneous in the ISCH hearts and became irreversible in accordance with increase of the duration of ischemia, while these changes were heterogeneous and restricted in the IP heart. These results suggest that IP does not attenuate the postischemic dysfunction in prolonged ischemia but it can provide an infarct size-limiting effect and delay ultrastructural changes. This cardioprotective effect may be related to calcium homeostasis.     

Effect of an Na+/H+ exchange inhibitor,SM-20550, on ischemic preconditioning in rabbits

The effects of SM-20550 [N-(aminoiminomethyl)-1,4-dimethyl-1H-indole-2-carboxamide methanesulfonic acid], an Na+/H+ exchange inhibitor, on ischemic preconditioning (IPC) were studied in a rabbit model of myocardial ischemia and reperfusion injury. Anesthetized rabbits underwent occlusion of the coronary artery (30 min) followed by reperfusion (5 h). In SM-20550-treated animals, SM-20550 was intravenously administered at 0.03 mg/kg or 0.1 mg/kg before ischemia (30 min). Treatment with SM-20550 at 0.03 mg/kg had a nonsignificant tendency to reduce infarct size (18%). In contrast, 0.1 mg/kg of SM-20550 significantly reduced infarct size by 62%. In animals with IPC, the condition was induced by 2 or 5 min of ischemia and 10 min of reperfusion prior to sustained ischemia (30 min). Although 5 min of IPC significantly reduced infarct size by 72%, 2 min of IPC reduced infarct size by only 27%, which was not significant. The combination of 5 min of IPC and 0.1 mg/kg of SM-20550 significantly reduced infarct size by 78%. This reduction in infarct size was similar to that produced by 0.1 mg/kg SM-20550 or 5 min of IPC alone. Moreover, the combination of 2 min of IPC and 0.03 mg/kg of SM-20550 significantly reduced infarct size by 64%, although neither 0.03 mg/kg SM-20550 nor 2 min of IPC alone reduced infarct size significantly. These results indicate that an Na+/H+ exchange inhibitor SM-20550, does not antagonize the cardioprotective effect of IPC. SM-20550 and IPC appeared to act synergistically to exert a combined cardioprotective effect.     

The gap junction uncoupler heptanol abrogates infarct size reduction with preconditioning in mouse hearts.

BACKGROUND: Emerging evidence suggests that gap junction-mediated intercellular transmission of ions, metabolites and/or second messengers may serve as important determinants of myocyte viability. Our aim was to determine, using isolated buffer-perfused mouse hearts, whether the cardioprotection achieved with ischemic preconditioning (PC) is due in part to: (i) disruption of cell-cell coupling (manifest as a loss in the primary gap junction protein, connexin 43 [Cx43]) and resultant impaired transmission of a 'death' messenger, or conversely, (ii) transfer of a humoral 'survival' factor via existing gap junctions. METHODS: To explore the first possibility, we employed immunostaining to visualize and quantify Cx43 in hearts subjected to 212 min of PC ischemia or a matched control period. To test the converse corollary, we assessed the effect of heptanol-an agent well recognized to rapidly and reversibly uncouple gap junctions--on the reduction of infarct size (delineated by tetrazolium staining) achieved with PC. RESULTS: We found no evidence of a deficit in Cx43 immunoreactive signal in response to the PC stimulus. Area of necrosis (AN) was, as expected, reduced in hearts that received PC ischemia vs. controls (31+/-3% vs. 40+/-3% of the left ventricle [LV]; P<.01). However, treatment with heptanol rendered PC ineffective in eliciting protection (AN/LV: 42+/-1%). CONCLUSIONS: Our results suggest that gap junction-mediated transfer of an as-yet unknown 'survival' factor-rather than disrupted transfer of a 'death messenger'-may play a role in the increased resistance to infarction conferred by antecedent PC ischemia in mouse heart.     

Changes in catecholamine, angiotensin converting enzyme and adenosine triphosphatase in ischemic preconditioning rat hearts

Changes in catecholamine ,angiotensin converting enzy me and adenosine triphosphatase in ischemic preconditioning rat hearts     

非创伤性预处理在离体心脏抗再灌注损伤中作用机制的探讨

目的:观察非创伤性肢体缺血预处理对大鼠离体再灌注心肌是否有保护作用。方法:实验采用体重(250±30)gSD雄性大鼠25只随机分成3组,在Langendorff装置上对大鼠离体心脏进行灌流。对照组(C,n=8):在灌注全程均用富氧K-H液(充以95%O₂+5%CO₂),在恒压(8.33kPa)、恒温(37℃)条件下灌注;缺氧/复氧组(A,n=8):预灌15min后,灌注心脏先全心缺血缺氧15min,随后15min复氧再灌注(37℃);非创伤性肢体缺血预处理组(N-WIP,n=9):先将大鼠双后肢捆绑5min,松开5min,反复4次后,随后的方法同R组。在相应时点分别测定冠脉流出液和心肌匀浆中超氧化物歧化酶(SOD)活性,Ca²⁺-Mg²⁺-ATP酶活性和丙二醛(MDA)含量,同时记录心肌细胞的单相动作电位(MAP)和心肌收缩张力曲线。结果:非创伤性肢体缺血预处理能使再灌注心律失常发生率显著低于A组;心肌组织中MDA含量显著低于A组,心肌组织中SOD活性显著高于A组,心肌细胞的膜电位、Ca²⁺-Mg²⁺-ATP酶活性及肌张力较稳定。结论:非创伤性肢体缺血预处理对大鼠离体再灌注心肌有明显的保护作用,可能是通过增强心肌的抗氧化能力、稳定心肌Ca²⁺-Mg²⁺-ATP酶活性和膜相结构等途径,提高心肌细胞对再灌注损伤的抵抗力。     

Isoflurane preconditioning neuroprotection in experimental focal stroke is androgen-dependent in male mice

Isoflurane preconditioning neuroprotection in experimental stroke is male-specific. The role of androgens in the ischemic sensitivity of isoflurane preconditioned male brain and whether androgen effects are androgen receptor dependent were assessed. Male C57BL/6 mice were implanted with flutamide (androgen receptor antagonist), or castrated and implanted with testosterone, dihydrotestosterone, flutamide, letrozole (aromatase inhibitor), or vehicle 7–13 days before preconditioning. P450 estrogen aromatase wild-type and knockout mice were also evaluated. All mice were preconditioned for 4 h with 0% (sham preconditioning) or 1% isoflurane (isoflurane preconditioning) and recovered for 24 h. Mice then underwent 2 h of middle cerebral artery occlusion and were evaluated 22 h later for infarct volume. For neurobehavioral outcomes, sham and isoflurane preconditioned castrated male±dihydrotestosterone groups underwent 1 h of middle cerebral artery occlusion followed by 9 days of reperfusion. Isoflurane preconditioning neuroprotection relative to infarct volume outcomes were testosterone and dihydrotestosterone dose-specific and androgen receptor-dependent. Relative to long-term neurobehavioral outcomes, front paw sensorimotor function improved in isoflurane preconditioned mice regardless of androgen status while androgen replacement independently improved sensorimotor function. In contrast, isoflurane preconditioning improved cognitive function in castrates lacking endogenous androgens, but this improvement was absent in androgen replaced mice. Our findings suggest that androgen availability during isoflurane preconditioning may influence infarct volume and neurobehavioral outcomes in male mice following experimental stroke.     

Mechanical unloading and infarct size: studies with the heterotopically transplanted rabbit heart.

The possibility that unloading the heart during regional ischemia and/or reperfusion may limit infarct size was investigated by inducing regional ischemia in both a heterotopically transplanted heart (unloaded) and the recipient's heart (loaded control). In this way, the extent of myocardial infarction was compared in paired hearts in the same animal under similar experimental conditions. Hearts excised from donor rabbits, were arrested with St. Thomas' Hospital cardioplegic solution and maintained at 15 degrees C for 1 hour during which time they were transplanted into the necks of recipient rabbits. 24 hours later, rabbits were reanesthetized and the left circumflex coronary artery ligated in both the transplanted and the recipient's hearts. After 1 hour of regional ischemia hearts were reperfused for 3 hours. The transplanted heart was paced at 205 beats per minute (bpm) throughout the experiment. Similar values for infarct size were obtained in both the loaded and unloaded hearts (73 +/- 4% vs 75 +/- 6%, respectively). No significant differences were seen in any other parameters. In conclusion, our results suggest that during regional ischemia the amount of work performed by the heart does not appear to be a major factor in determining the ultimate size of an infarct.     

Preconditioning in intact and previously diseased myocardium: laboratory or clinical dilemma?

We studied the effects of various cycles of preconditioning (PC) (one cycle, 1 x PC; two cycles, 2 x PC; three cycles, 3 x PC; and four cycles, 4 x PC) on cardiac function, infarct size, and the incidence of reperfusion-induced arrhythmias in isolated hearts obtained from rabbits with hypercholesterolemia. After 8 weeks of hypercholesterolemia, hearts were subjected to 30 min of ischemia followed by 120 min of reperfusion. Various cycles of PC resulted in a "cycle-dependent" reduction in infarct size in the age-matched nonhypercholesterolemic group. In the 8-week hypercholesterolemic group, increasing cycles of PC resulted in a significant increase in infarct size from their nonpreconditioned ischemic/reperfused control value of 44 +/- 5% to 45 +/- 6%, 49 +/- 5%, 59 +/- 6% (p < 0.05), and 58 +/- 5% (p < 0.05), respectively. PC increased the vulnerability of the myocardium to reperfusion-induced arrhythmias in hypercholesterolemics indicating that PC may be an "intact heart" phenomenon. The effects of PC appear currently to be a dilemma in laboratories and clinics. The solution to the problem of PC in intact and diseased myocardium requires further data from two different sources: (a) previously "diseased" animals, and (b) diseased human myocardium from clinics. Once these data are available, then the effects under which PC will be beneficial rather than harmful could be established and the dilemma solved.     

Evidence of protein kinase C translocation by ischemic preconditioning in global ischemia model.

We tested recent evidence that ischemic preconditioning (PC) involves in translocation of protein kinase C (PKC) from the cytosol to myocyte membrane. Isolated Langendorff-perfused rabbit hearts (n=96) were subjected to 60 or 45 min of ischemia (I) and 120 min of reperfusion (R) with or without PC (4 cycles of 5 min I and 5 min R; or single dose of 5 min I and 10 min R), respectively. Left ventricular function and infarct size (IS) were measured; myocardial cytosolic and membrane PKC activity were determined by 32P-gamma-ATP incorporation into PKC-specific peptide. PC enhanced improvement of functional recovery and reduced IS (26.9+/-1.4% versus 15.3+/-1.9%, p<0.01, in 60 min of I; 18.3+/-2.6% versus 8.6+/-2.5%, p<0.05, in 45 min of I); cytosolic PKC activity decreased 74% of total activity (p<0.05) both in 60 and 45 min of I; membrane PKC activity increased (1.7-fold of baseline, p<0.01, in 60 min of I; 1.8-fold, p<0.01, in 45 min of I; 1.5-fold, p<0.05, in 60 of min I and 120 min of R). From these results, it is concluded that translocation of PKC from the cytosol to myocyte membranes is an important mechanism responsible for PC effect.     

Ischemic preconditioning modulates mitochondrial respiration, irrespective of the employed signal transduction pathway

We tested in the in vivo rat heart the hypothesis that although ischemic preconditioning can employ different signal transduction pathways, these pathways converge ultimately at the level of the mitochondrial respiratory chain. Infarct size produced by a 60-min coronary artery occlusion (69%+/-2% of the area at risk) was limited by a preceding 15-min coronary occlusion (48%+/-4%). Cardioprotection by this stimulus was triggered by adenosine receptor stimulation, which was followed by protein kinase C and tyrosine kinase activation and then mitochondrial K(+)(ATP)-channel opening. In contrast, cardioprotection by 3 cycles of 3-min coronary occlusions (infarct size 27%+/-5% of the area at risk) involved the release of reactive oxygen species, which was followed by protein kinase C and tyrosine kinase activation, but was independent of adenosine receptor stimulation and K(+)(ATP)-channel activation. However, both pathways decreased respiratory control index (RCI; state-3/state-2, using succinate as complex-II substrate) from 3.1+/-0.2 in mitochondria from sham-treated hearts to 2.4+/-0.2 and 2.5+/-0.1 in hearts subjected to a single 15-min and triple 3-min coronary occlusions, respectively (both P<0.05). The decreases in RCI were due to an increase in state-2 respiration, whereas state-3 respiration was unchanged. Abolition of cardioprotection by blockade of either signal transduction pathway was paralleled by a concomitant abolition of mitochondrial uncoupling. These observations are consistent with the concept that mild mitochondrial uncoupling contributes to infarct size limitation by various ischemic preconditioning stimuli, despite using different signal transduction pathways. In conclusion, in the in vivo rat heart, different ischemic preconditioning (IPC) stimuli can activate highly different signal transduction pathways, which seem to converge at the level of the mitochondria where they increase state-2 respiration.     

Cardiac preconditioning by volatile anesthetic agents: a defining role for altered mitochondrial bioenergetics

Volatile anesthetic agents, such as halothane, isoflurane, and sevoflurane, are the drugs most commonly used to maintain the state of general anesthesia. They have long been known to provide some protection against the effects of cardiac ischemia and reperfusion. Several mechanisms likely contribute to this cardioprotection, including coronary vasodilation, reduced contractility with corresponding decreased metabolic demand, and a direct effect to decrease myocardial Ca(2+) entry through L-type Ca(2+) channels. Recently, a memory phase to cardioprotection has been observed by these agents, which is inhibited by ATP-sensitive potassium channel inhibition. These features suggest a pathway that shares components with those required for ischemic preconditioning, despite the remarkable differences between these two stimuli, and the term anesthetic preconditioning (APC) has been adopted. Scavengers of reactive oxygen species (ROS) abrogate APC, suggesting an effect of anesthetic agents to cause ROS formation. Such an effect has recently been directly demonstrated. The mechanism by which these drugs induce ROS formation is unclear. However, direct inhibition of mitochondrial electron transport system enzymes, and altered mitochondrial bioeneregtics in hearts preconditioned by volatile anesthetics, strongly implicate the mitochondria as the target for these effects. Furthermore, decreased mitochondrial ROS formation during ischemia and reperfusion in hearts preconditioned by volatile anesthetics might underlie the improved postischemic structure and function. APC presents a safe mode to apply preconditioning to human hearts. This review summarizes the major developments in a field that is exciting to clinicians and basic scientists alike.     

Cardiac sodium/calcium exchanger preconditioning promotes anti-arrhythmic and cardioprotective effects through mitochondrial calcium-activated potassium channel

Background: Reverse-mode of the Na⁺/Ca²⁺ exchanger (NCX) stimulation provides cardioprotective effects for the ischemic/reperfused heart during ischemic preconditioning (IP). This study was designed to test the hypothesis that pretreatment with an inhibitor of cardiac delayed-rectifying K⁺ channel (I_Kr), E4031, increases reverse-mode of NCX activity, and triggers preconditioning against infarct size (IS) and arrhythmias caused by ischemia/reperfusion injury through mitoK_Ca channels. Materials and methods: In the isolated perfused rat heart, myocardial ischemia/reperfusion injury was created by occlusion of the left anterior descending coronary artery for 30 min followed by 120 min reperfusion. Two cycles of coronary occlusion for 5 min and reperfusion were performed, or pretreatment with E4031 or sevoflurane (Sevo) before the 30 min occlusion with the reversed-mode of NCX inhibitor (KB-R7943) or not. Results: E4031 or Sevo preconditioning not only markedly decreased IS but also reduced arrhythmias, which was significantly blunted by KB-R7943. Furthermore, these effects of E4031 preconditioning on IS and arrhythmias were abolished by inhibition of the mitoK_Ca channels. Similarly, pretreatment with NS1619, an opener of the mitoK_Ca channels, for 10 min before occlusion reduced both the infarct size and arrhythmias caused by ischemia/reperfusion. However, these effects weren’t affected by blockade of the NCX with KB-R7943. Conclusion: Taken together, these preliminary results conclude that pretreatment with E4031 reduces infarct size and produces anti-arrhythmic effect via stimulating the reverse-mode NCX, and that the mitoK_Ca channels mediate the protective effects.     

Pretreatment with the gap junction uncoupler heptanol does not limit infarct size in rabbit heart.

Previous findings indicate that heptanol, an agent well-recognized to disrupt chemical signaling between myocytes by uncoupling of gap junctions, significantly limited infarct size when administered at the time of reperfusion. Our aim was to assess on the potential role of cell--cell communication via gap junctions during ischemia by investigating whether "loading" the soon-to-be ischemic territory with heptanol would limit myocardial necrosis. Five isolated buffer-perfused rabbit hearts were pretreated with heptanol (0.5 mM) for 10 min, while 12 served as controls. In the final 30 s of treatment, a large marginal branch of the left circumflex coronary artery was occluded for 30 min followed by 2 h of reperfusion, and infarct size was delineated by tetrazolium staining. Heptanol had no significant effect on the extent of infarct: area of necrosis (AN, expressed as a percentage of the myocardium at risk) was 75+/-3% and 72+/-8% in vehicle- and heptanol-treated groups (P=.76). Thus, our results suggest that cell-to-cell communication via gap junctions during coronary artery occlusion does not contribute importantly to the development of necrosis in rabbit heart.