Sarcolemmal and Mitochondrial Adenosine Triphosphate- dependent Potassium Channels: Mechanism of Desflurane-induced Cardioprotection

Background: Volatile anesthetic-induced preconditioning is mediated by adenosine triphosphate-dependent potassium (KATP) channels; however, the subcellular location of these channels is unknown. The authors tested the hypothesis that desflurane reduces experimental myocardial infarct size by activation of specific sarcolemmal and mitochondrial KATP channels.

Methods: Barbiturate-anesthetized dogs (n = 88) were acutely instrumented for measurement of aortic and left ventricular pressures. All dogs were subjected to a 60-min left anterior descending coronary artery occlusion followed by 3-h reperfusion. In four separate groups, dogs received vehicle (0.9% saline) or the nonselective KATP channel antagonist glyburide (0.1 mg/kg intravenously) in the presence or absence of 1 minimum alveolar concentration desflurane. In four additional groups, dogs received 45-min intracoronary infusions of the selective sarcolemmal (HMR 1098; 1 [mu]g [middle dot] kg-1 [middle dot] min-1) or mitochondrial (5-hydroxydecanoate [5-HD]; 150 [mu]g [middle dot] kg-1 [middle dot] min-1) KATP channel antagonists in the presence or absence of desflurane. Myocardial perfusion and infarct size were measured with radioactive microspheres and triphenyltetrazolium staining, respectively.

Results: Desflurane significantly (P < 0.05) decreased infarct size to 10 +/- 2% (mean +/- SEM) of the area at risk as compared with control experiments (25 +/- 3% of area at risk). This beneficial effect of desflurane was abolished by glyburide (25 +/- 2% of area at risk). Glyburide (24 +/- 2%), HMR 1098 (21 +/- 4%), and 5-HD (24 +/- 2% of area at risk) alone had no effects on myocardial infarct size. HMR 1098 and 5-HD abolished the protective effects of desflurane (19 +/- 3% and 22 +/- 2% of area at risk, respectively).     

Mechanisms of Desflurane-induced Preconditioning in Isolated Human Right Atria In Vitro

Background: The authors examined the role of adenosine triphosphate-sensitive potassium (KATP) channels, adenosine A1 receptor, and [alpha] and [beta] adrenoceptors in desflurane-induced preconditioning in human myocardium, in vitro.

Methods: The authors recorded isometric contraction of human right atrial trabeculae suspended in oxygenated Tyrode's solution (34[degrees]C; stimulation frequency, 1 Hz). Before a 30-min anoxic period, 3, 6, and 9% desflurane was administered during 15 min. Desflurane, 6%, was also administered in the presence of 10 [mu]m glibenclamide, a KATP channels antagonist; 10 [mu]m HMR 1098, a sarcolemmal KATP channel antagonist; 800 [mu]m 5-hydroxy-decanoate (5-HD), a mitochondrial KATP channel antagonist; 1 [mu]m phentolamine, an [alpha]-adrenoceptor antagonist; 1 [mu]m propranolol, a [beta]-adrenoceptor antagonist; and 100 nm 8-cyclopentyl-1,3-dipropylxanthine (DPX), the adenosine A1 receptor antagonist. Developed force at the end of a 60-min reoxygenation period was compared (mean +/- SD).

Results: Desflurane at 3% (95 +/- 13% of baseline), 6% (86 +/- 6% of baseline), and 9% (82 +/- 6% of baseline) enhanced the recovery of force after 60 min of reoxygenation as compared with the control group (50 +/- 11% of baseline). Glibenclamide (60 +/- 12% of baseline), 5-HD (57 +/- 21% of baseline), DPX (63 +/- 19% of baseline), phentolamine (56 +/- 20% of baseline), and propranolol (63 +/- 13% of baseline) abolished desflurane-induced preconditioning. In contrast, HMR 1098 (85 +/- 12% of baseline) did not modify desflurane-induced preconditioning.     

Mechanisms of desflurane-induced preconditioning in isolated human right atria in vitro

BACKGROUND: The authors examined the role of adenosine triphosphate-sensitive potassium (K(ATP)) channels, adenosine A1 receptor, and alpha and beta adrenoceptors in desflurane-induced preconditioning in human myocardium, in vitro. METHODS: The authors recorded isometric contraction of human right atrial trabeculae suspended in oxygenated Tyrode's solution (34 degrees C; stimulation frequency, 1 Hz). Before a 30-min anoxic period, 3, 6, and 9% desflurane was administered during 15 min. Desflurane, 6%, was also administered in the presence of 10 microm glibenclamide, a K(ATP) channels antagonist; 10 microm HMR 1098, a sarcolemmal K(ATP) channel antagonist; 800 microm 5-hydroxy-decanoate (5-HD), a mitochondrial K(ATP) channel antagonist; 1 microm phentolamine, an alpha-adrenoceptor antagonist; 1 microm propranolol, a beta-adrenoceptor antagonist; and 100 nm 8-cyclopentyl-1,3-dipropylxanthine (DPX), the adenosine A1 receptor antagonist. Developed force at the end of a 60-min reoxygenation period was compared (mean +/- SD). RESULTS: Desflurane at 3% (95 +/- 13% of baseline), 6% (86 +/- 6% of baseline), and 9% (82 +/- 6% of baseline) enhanced the recovery of force after 60 min of reoxygenation as compared with the control group (50 +/- 11% of baseline). Glibenclamide (60 +/- 12% of baseline), 5-HD (57 +/- 21% of baseline), DPX (63 +/- 19% of baseline), phentolamine (56 +/- 20% of baseline), and propranolol (63 +/- 13% of baseline) abolished desflurane-induced preconditioning. In contrast, HMR 1098 (85 +/- 12% of baseline) did not modify desflurane-induced preconditioning. CONCLUSIONS: In vitro, desflurane preconditions human myocardium against simulated ischemia through activation of mitochondrial K(ATP) channels, adenosine A1 receptor, and alpha and beta adrenoceptors.     

Sevoflurane Reduces Myocardial Infarct Size and Decreases the Time Threshold for Ischemic Preconditioning in Dogs

Background: Recent evidence indicates that volatile anesthetics exert protective effects during myocardial ischemia and reperfusion. The authors tested the hypothesis that sevoflurane decreases myocardial infarct size by activating adenosine triphosphate-sensitive potassium (KATP) channels and reduces the time threshold of ischemic preconditioning necessary to protect against infarction.

Methods: Barbiturate-anesthetized dogs (n = 75) were instrumented for measurement of aortic and left ventricular pressures and maximum rate of increase of left ventricular pressure and were subjected to a 60-min left anterior descending (LAD) coronary artery occlusion followed by 3-h reperfusion. In four separate groups, dogs received vehicle or the KATP channel antagonist glyburide (0.1 mg/kg intravenously), and 1 minimum alveolar concentration sevoflurane (administered until immediately before coronary artery occlusion) in the presence or absence of glyburide. In three additional experimental groups, sevoflurane was discontinued 30 min (memory) before the 60-min LAD occlusion or a 2-min LAD occlusion as an ischemic preconditioning stimulus was used with or without subsequent sevoflurane (with memory) pretreatment. Regional myocardial perfusion and infarct size were measured with radioactive microspheres and triphenyltetrazolium staining, respectively.

Results: Vehicle (23 +/- 1% of the area at risk; mean +/- SEM) and glyburide (23 +/- 2%) alone produced equivalent effects on myocardial infarct size. Sevoflurane significantly (P < 0.05) decreased infarct size (13 +/- 2%). This beneficial effect was abolished by glyburide (21 +/- 3%). Neither the 2-min LAD occlusion nor sevoflurane followed by 30 min of memory were protective alone, but together, sevoflurane enhanced the effects of the brief ischemic stimulus and profoundly reduced infarct size (9 +/- 2%).     

Mitochondrial Adenosine Triphosphate-regulated Potassium Channel Opening Acts as a Trigger for Isoflurane-induced Preconditioning by Generating Reactive Oxygen Species

Background: Whether the opening of mitochondrial adenosine triphosphate-regulated potassium (KATP) channels is a trigger or an end effector of anesthetic-induced preconditioning is unknown. We tested the hypothesis that the opening of mitochondrial KATP channels triggers isoflurane-induced preconditioning by generating reactive oxygen species (ROS) in vivo.

Methods: Pentobarbital-anesthetized rabbits were subjected to a 30-min coronary artery occlusion followed by 3 h reperfusion. Rabbits were randomly assigned to receive a vehicle (0.9% saline) or the selective mitochondrial KATP channel blocker 5-hydroxydecanoate (5-HD) alone 10 min before or immediately after a 30-min exposure to 1.0 minimum alveolar concentration (MAC) isoflurane. In another series of experiments, the fluorescent probe dihydroethidium was used to assess superoxide anion production during administration of 5-HD or the ROS scavengers N-acetylcysteine or N-2-mercaptopropionyl glycine (2-MPG) in the presence or absence of 1.0 MAC isoflurane. Myocardial infarct size and superoxide anion production were measured using triphenyltetrazolium staining and confocal fluorescence microscopy, respectively.

Results: Isoflurane (P < 0.05) decreased infarct size to 19 +/- 3% (mean +/- SEM) of the left ventricular area at risk as compared to the control (38 +/- 4%). 5-HD administered before but not after isoflurane abolished this beneficial effect (37 +/- 4% as compared to 24 +/- 3%). 5-HD alone had no effect on infarct size (42 +/- 3%). Isoflurane increased fluorescence intensity. Pretreatment with N-acetylcysteine, 2-MPG, or 5-HD before isoflurane abolished increases in fluorescence, but administration of 5-HD after isoflurane only partially attenuated increases in fluorescence produced by the volatile anesthetic agent.     

The role of mitochondrial and sarcolemmal K(ATP) channels in canine ethanol-induced preconditioning in vivo

Chronic consumption of small doses of ethanol protects myocardium from ischemic injury. We tested the hypothesis that mitochondrial and sarcolemmal adenosine triphosphate-dependent potassium (K(ATP)) channels mediate these beneficial effects. Dogs (n = 76) were fed with ethanol (1.5 g/kg) or water mixed with dry food bid for 6 or 12 wk, fasted overnight before experimentation, and instrumented for measurement of hemodynamics. Dogs received intracoronary saline (vehicle), 5-hydroxydecanoate (a mitochondrial K(ATP) channel antagonist; 6.75 mg/kg over 45 min), or HMR-1098 (a sarcolemmal K(ATP) channel antagonist; 45 microg/kg over 45 min) and were subjected to a 60 min coronary artery occlusion followed by 3 h of reperfusion. A final group of dogs was pretreated with ethanol and chow for 6 wk before occlusion and reperfusion. Myocardial infarct size and transmural coronary collateral blood flow were measured with triphenyltetrazolium chloride staining and radioactive microspheres, respectively. The area at risk of infarction was similar between groups. A 12-wk pretreatment with ethanol significantly reduced infarct size to 13% +/- 2% (mean +/- SEM; n = 8) of the area at risk compared with control experiments (25% +/- 2%; n = 8), but a 6-wk pretreatment did not (21% +/- 2%; n = 8). 5-hydroxydecanoate and HMR-1098 abolished the protective effects of 12-wk ethanol pretreatment (24% +/- 2% and 29% +/- 3%, respectively; n = 8 for each group) but had no effect in dogs that did not receive ethanol (22% +/- 2% and 23% +/- 4%, respectively; n = 8 for each group). No differences in hemodynamics or transmural coronary collateral blood flow were observed between the groups. The results indicate that mitochondrial and sarcolemmal K(ATP) channels mediate ethanol-induced preconditioning in dogs independent of alterations in systemic hemodynamics or coronary collateral blood flow. IMPLICATIONS: Mitochondrial and sarcolemmal K(ATP) channels mediate ethanol-induced preconditioning independent of alterations in systemic hemodynamics or coronary collateral perfusion in vivo.     

Isoflurane preconditions myocardium against infarction via activation of inhibitory guanine nucleotide binding proteins

BACKGROUND: Isoflurane-induced myocardial protection during ischemia is mediated by adenosine triphosphate-regulated potassium (KATP) channels; however, the intracellular signal transduction cascade responsible for this process has been incompletely evaluated. The authors tested the hypothesis that isoflurane reduces myocardial infarct size through a Gi protein-mediated process. METHODS: Forty-eight hours after pretreatment with vehicle (0.9% saline) or the Gi protein inhibitor pertussis toxin (10 microg/kg intravenously), barbiturate-anesthetized dogs (n = 43) were instrumented for measurement of aortic and left ventricular pressures and maximum rate of increase of left ventricular pressure. All dogs were subjected to a 60-min left anterior descending coronary artery occlusion followed by 3-h reperfusion. In four separate groups, vehicle- or pertussis toxin-pretreated dogs were studied with or without administration of 1 minimum alveolar concentration isoflurane. In two additional groups, dogs received the direct KATP channel agonist nicorandil (100 microg/kg bolus and 10 microg x kg-1 x min-1 intravenous infusion) in the presence or absence of pertussis toxin pretreatment. Myocardial perfusion and infarct size were measured with radioactive microspheres and triphenyltetrazolium staining, respectively. RESULTS: Isoflurane significantly (P < 0.05) decreased infarct size to 7 +/- 2% of the area at risk compared with control experiments (26 +/- 2%). Pertussis toxin pretreatment alone had no effects on myocardial infarct size (31 +/- 4%) but blocked the beneficial effects of isoflurane (21 +/- 3%). Nicorandil decreased infarct size (11 +/- 2%), but, in contrast to isoflurane, this effect was independent of pertussis toxin pretreatment (11 +/- 1%). CONCLUSION: Isoflurane reduces myocardial infarct size by a Gi protein-mediated mechanism in vivo.     

含钾通道开放剂的HTK液对大鼠心功能以及线粒体结构和功能的影响

目的 观察含钾通道开放剂的供心保存液对心功能以及能量代谢、线粒体呼吸酶活性及超微结构的影响.方法 将SD大鼠分为HTK组、Pi组、5HD组、1098组和5HD+1098组.切取SD大鼠心脏,建立Langendorff灌注模型,平衡10 min,然后按分组进行如下处理:HTK组心脏以Histidine-Tryptophan-Ketoglutarate液(HTK液)停搏;Pi组心脏以含0.5 mmol/L吡那地尔(Pi)的HTK液停搏;1098组心脏以含0.5 mmol/L Pi和100 μmol/L HMR1098的HTK液停搏;5HD组心脏以含0.5 mmol/L Pi和100 μmol/L五羟葵酸(5HD)的HTK液停搏;5HD+1098组心脏以含0.5 μmol/L Pi、100 μmol/L 5HD和100μmol/L HMR1098的HTK液停搏.停搏后,将心脏置于各组相应的液体(4℃)中保存8 h,然后用含氧的37℃克-亨液(K-H液)再灌注60 min.观察各组平衡末、保存末、再灌注末时的心功能、线粒体呼吸酶活性、心肌ATP含量及心肌细胞线粒体超微结构的改变.结果 Pi组保存末、再灌注末的心功能(心率、左心室舒张末压、左心室发展压和冠状动脉流量)、心肌线粒体呼吸酶(NADH氧化酶、琥珀酸氧化酶、细胞色素C氧化酶)活性及ATP含量均优于其他各组(P<0.01或P<0.05),同时线粒体的结构改变也最轻.结论 含Pi的HTK液能改善大鼠心脏保存效果;Pi对能量状态的维持以及对线粒体结构与功能的保护可能是其心肌保护的重要机制.     

Glyburide decreases myocardial oxygen pressure in dogs

BACKGROUND: Reports show that glyburide, an adenosine triphosphate sensitive potassium (K+ATP) channel blocker, will reverse the myocardial protective effect of inhalational anesthesia. We evaluated the effect of glyburide on myocardial tissue oxygen pressure (PmO2) in dogs anesthetized with desflurane. METHODS: Twelve dogs were anesthetized with 8% end-tidal desflurane for baseline anesthesia. A flow probe was placed on the left anterior descending (LAD) artery. A probe that measured PmO2 was inserted into the middle myocardium in the LAD region. After baseline measures, six dogs received i.v. 1 mg kg(-1) of glyburide and six dogs received sham vehicle treatment. After the glyburide or sham treatment, each dog received an i.v. infusion of adenosine 0.1 microg kg(-1) x min(-1), sodium nitroprusside (SNP) 2-4 microg kg(-1) x min(-1) and 14% end-tidal desflurane in random order. RESULTS: Glyburide decreased LAD artery flow from 59 +/- 9 ml min(-1) to 30 +/- 6 ml min(-1) (P < 0.05) and PmO2 from 44 +/- 16 mmHg to 30 +/- 9 mmHg (P < 0.05). Adenosine infusion increased LAD artery blood flow 180% in the sham-treated dogs but produced no change in the glyburide-treated dogs. Sodium nitroprusside infusion increased LAD artery flow and decreased PmO2 in both the glyburide- and sham-treated dogs. Desflurane (14%) did not reverse the glyburide-induced vasoconstriction but increased PmO2 to 38 +/- 20 mmHg (P < 0.05). CONCLUSION: Glyburide produced myocardial tissue hypoxia, which was not changed by adenosine, worsened by SNP and improved by 14% desflurane. The improvement in PmO2 with desflurane occurred without a change in myocardial blood flow.     

Sevoflurane reduces myocardial infarct size and decreases the time threshold for ischemic preconditioning in dogs

BACKGROUND: Recent evidence indicates that volatile anesthetics exert protective effects during myocardial ischemia and reperfusion. The authors tested the hypothesis that sevoflurane decreases myocardial infarct size by activating adenosine triphosphate-sensitive potassium (K(ATP)) channels and reduces the time threshold of ischemic preconditioning necessary to protect against infarction. METHODS: Barbiturate-anesthetized dogs (n = 75) were instrumented for measurement of aortic and left ventricular pressures and maximum rate of increase of left ventricular pressure and were subjected to a 60-min left anterior descending (LAD) coronary artery occlusion followed by 3-h reperfusion. In four separate groups, dogs received vehicle or the K(ATP) channel antagonist glyburide (0.1 mg/kg intravenously), and 1 minimum alveolar concentration sevoflurane (administered until immediately before coronary artery occlusion) in the presence or absence of glyburide. In three additional experimental groups, sevoflurane was discontinued 30 min (memory) before the 60-min LAD occlusion or a 2-min LAD occlusion as an ischemic preconditioning stimulus was used with or without subsequent sevoflurane (with memory) pretreatment. Regional myocardial perfusion and infarct size were measured with radioactive microspheres and triphenyltetrazolium staining, respectively. RESULTS: Vehicle (23 +/- 1% of the area at risk; mean +/- SEM) and glyburide (23 +/- 2%) alone produced equivalent effects on myocardial infarct size. Sevoflurane significantly (P < 0.05) decreased infarct size (13 +/- 2%). This beneficial effect was abolished by glyburide (21 +/- 3%). Neither the 2-min LAD occlusion nor sevoflurane followed by 30 min of memory were protective alone, but together, sevoflurane enhanced the effects of the brief ischemic stimulus and profoundly reduced infarct size (9 +/- 2%). CONCLUSION: Sevoflurane reduces myocardial infarct size by activating K(ATP) channels and reduces the time threshold for ischemic preconditioning independent of hemodynamic effects in vivo.     

Levosimendan, a new positive inotropic drug, decreases myocardial infarct size via activation of K(ATP) channels

We tested the hypothesis that levosimendan, a new positive inotropic drug that activates adenosine triphosphate-regulated potassium (K(ATP)) channels in vitro, decreases myocardial infarct size in vivo. Myocardial infarct size was measured after a 60-min left anterior descending coronary artery occlusion and 3 h of reperfusion in dogs receiving either IV vehicle (0.9% saline) or levosimendan (24 microg/kg bolus followed by an infusion of 0.4 microg x kg(-1) x min(-1)) in the presence or absence of glyburide (a K(ATP) channel antagonist) pretreatment (100 microg/kg). Levosimendan increased (P < 0.05) the maximal rate of increase of left ventricular pressure and decreased myocardial infarct size from 24%+/-2% (control experiments) to 11%+/-2% of the left ventricular area at risk for infarction. Glyburide did not alter the hemodynamic effects of levosimendan but blocked levosimendan-induced reductions of infarct size. Subendocardial collateral blood flow was similar among groups. However, levosimendan increased subepicardial and midmyocardial collateral perfusion in the absence, but not in the presence, of glyburide. Levosimendan exerts cardioprotective effects via activation of K(ATP) channels at a dose that simultaneously enhances myocardial contractility. IMPLICATIONS: Levosimendan may be advantageous in patients requiring inotropic support who are also at risk of myocardial ischemia. Activation of adenosine triphosphate-regulated potassium channels during infusion of levosimendan may produce cardioprotective effects while simultaneously enhancing ventricular contractile function.     

Isoflurane Preconditions Myocardium Against Infarction via Activation of Inhibitory Guanine Nucleotide Binding Proteins

Background: Isoflurane-induced myocardial protection during ischemia is mediated by adenosine triphosphate-regulated potassium (KATP) channels; however, the intracellular signal transduction cascade responsible for this process has been incompletely evaluated. The authors tested the hypothesis that isoflurane reduces myocardial infarct size through a Gi protein-mediated process.

Methods: Forty-eight hours after pretreatment with vehicle (0.9% saline) or the Gi protein inhibitor pertussis toxin (10 [mu]g/kg intravenously), barbiturate-anesthetized dogs (n = 43) were instrumented for measurement of aortic and left ventricular pressures and maximum rate of increase of left ventricular pressure. All dogs were subjected to a 60-min left anterior descending coronary artery occlusion followed by 3-h reperfusion. In four separate groups, vehicle- or pertussis toxin-pretreated dogs were studied with or without administration of 1 minimum alveolar concentration isoflurane. In two additional groups, dogs received the direct KATP channel agonist nicorandil (100 [mu]g/kg bolus and 10 [mu]g [middle dot] kg-1 [middle dot] min-1 intravenous infusion) in the presence or absence of pertussis toxin pretreatment. Myocardial perfusion and infarct size were measured with radioactive microspheres and triphenyltetrazolium staining, respectively.

Results: Isoflurane significantly (P < 0.05) decreased infarct size to 7 +/- 2% of the area at risk compared with control experiments (26 +/- 2%). Pertussis toxin pretreatment alone had no effects on myocardial infarct size (31 +/- 4%) but blocked the beneficial effects of isoflurane (21 +/- 3%). Nicorandil decreased infarct size (11 +/- 2%), but, in contrast to isoflurane, this effect was independent of pertussis toxin pretreatment (11 +/- 1%).     

Remifentanil preconditioning confers cardioprotection via cardiac kappa- and delta-opioid receptors

BACKGROUND: Remifentanil preconditioning (RPC) reduces the infarct size in anesthetized rat hearts, and this effect seems to be mediated by all three types of opioid receptors (ORs). Because there is evidence of only kappa- and delta- but not mu-ORs in the rat heart, the authors investigated whether RPC confers cardioprotection via cardiac kappa- and delta-OR as well as via extracardiac mu-OR agonist activity. The authors also investigated the involvement of signaling mechanisms, namely protein kinase C and mitochondrial adenosine triphosphate-sensitive potassium (KATP) channels. METHODS: The hearts of male Sprague-Dawley rats weighing 190-210 g were removed, mounted on a Langendorff apparatus, and perfused retrogradely at 100 cm H2O with Krebs-Ringer's solution. All hearts were subjected to 30 min of ischemia and 2 h of reperfusion. The study consisted of three series of experiments on the effect of ischemic preconditioning or RPC (10, 50, and 100 ng/ml remifentanil) after blockade of OR subtypes (delta-OR antagonist naltrindol, kappa-OR antagonist nor-binaltorphimine, and mu-OR antagonist CTOP). The involvement of protein kinase C or the KATP channel in the cardioprotection of RPC was also investigated using specific blockers in each group. RPC was produced by three cycles of 5-min perfusion of remifentanil in Krebs-Ringer's solution interspersed with a 5-min reperfusion with Krebs solution only. Infarct size, as a percentage of the area at risk, was determined by 2,3,5-triphenyltetrazolium staining. RESULTS: Infarct size as a percentage of the area at risk was significantly reduced after RPC from 51.9 +/- 5.0% (control, n = 8) to 36.2 +/- 10.0% (100 ng/ml RPC, n = 8, P < 0.01). This effect was stopped by pretreatment with naltrindol (52.3 +/- 5.2%) and nor-binaltorphimine (43.5 +/- 6.0%) but not CTOP (37.1 +/- 6.0%). Chelerythrine and GF109203X, both protein kinase C inhibitors, abolished the effects of RPC or ischemic preconditioning on infarct size as a percentage of area at risk. 5-Hydroxydecanoate (a selective mitochondrial KATP channel blocker) also abolished the cardioprotection of RPC and IPC, but HMR-1098 (a selective inhibitor of the sarcolemmal KATP channel) did not. CONCLUSION: Cardiac delta- and kappa- but not mu-ORs mediate the cardioprotection produced by RPC. Both protein kinase C and the mitochondrial KATP channel were involved in this effect.     

Distinct Roles for Sarcolemmal and Mitochondrial Adenosine Triphosphate-sensitive Potassium Channels in Isoflurane-induced Protection against Oxidative Stress

Background: Cardiac preconditioning, including that induced by halogenated anesthetics, is an innate protective mechanism against ischemia-reperfusion injury. The adenosine triphosphate-sensitive potassium (KATP) channels are considered essential in preconditioning mechanism. However, it is unclear whether KATP channels are triggers initiating the preconditioning signaling, and/or effectors responsible for the cardioprotective memory and activated during ischemia-reperfusion.

Methods: Adult rat cardiomyocytes were exposed to oxidative stress with 200 [mu]m H2O2 and 100 [mu]m FeSO4. Myocyte survival was determined based on morphologic characteristics and trypan blue exclusion. To induce preconditioning, the myocytes were pretreated with isoflurane. The involvement of sarcolemmal and mitochondrial KATP channels was investigated using specific inhibitors HMR-1098 and 5-hydroxydecanoic acid. Data are expressed as mean +/- SD.

Results: Oxidative stress induced cell death in 47 +/- 14% of myocytes. Pretreatment with isoflurane attenuated this effect to 26 +/- 8%. Blockade of the sarcolemmal KATP channels abolished the protection by isoflurane pretreatment when HMR-1098 was applied throughout the experiment (50 +/- 21%) or only during oxidative stress (50 +/- 12%), but not when applied during isoflurane pretreatment (29 +/- 13%). Inhibition of the mitochondrial KATP channels abolished cardioprotection irrespective of the timing of 5-hydroxydecanoic acid application. Cell death was 42 +/- 23, 45 +/- 23, and 46 +/- 22% when 5-hydroxydecanoic acid was applied throughout the experiment, only during isoflurane pretreatment, or only during oxidative stress, respectively.     

Contractile recovery of heart muscle after hypothermic hypoxia is improved by nicorandil via mitochondrial K(ATP) channels.

BACKGROUND: The ATP-sensitive potassium channel (K(ATP)) opener nicorandil used instead of potassium in hypothermic cardioplegia significantly improves preservation of cardiac function and energetics in the in situ heart preparation. The present study, therefore, examines the effect of nicorandil at different temperatures and the role of sarcolemmal and mitochondrial K(ATP) channels under ex vivo conditions using contractile force (CF) and action potential duration (APD) as end points. METHODS: Guinea-pig papillary muscles at 37, 27, or 22 degrees C (1Hz) were exposed to nicorandil 0.2-1.1 mM. The contributions of K(ATP) channel subtypes in cardioprotection were examined using mitochondrial (mito) (0.1 mM) or non-selective (1.0 mM) concentrations of nicorandil, mito K(ATP) blocker 5-hydroxyl decanoate (5HD, 300 microM) or sarcolemmal (sarc) K(ATP) blocker HMR1098 (30 microM) before and during 140 min of hypothermic (22 degrees C) glucose-free hypoxia. RESULTS: Nicorandil >0.5 mM shortened the APD, and this was abolished by hypothermia and HMR1098 but not by 5HD. Nicorandil in both tested concentrations preserved contractile force after hypoxia-reoxygenation significantly better than control (73.7+/-4.4% and 75.8+/-3.9% vs 40.6+/-2.6%, n=6 in each group). Protection was blocked by 5HD but not by HMR1098. 5HD and HMR1098 alone did not change recovery of contractile force compared to control. CONCLUSION: Shortening of APD and activation of sarc K(ATP) by nicorandil were not related to myocardial protection. Thus, the mito K(ATP) seems to play a significant role in cardioprotection compared to the sarc K(ATP) also when substrate depletion and hypoxia are combined with hypothermia.     

Opening of mitochondrial ATP-sensitive potassium channels enhances cardioplegic protection

BACKGROUND: Mitochondrial and sarcolemmal ATP-sensitive potassium channels have been implicated in cardioprotection; however, the role of these channels in magnesium-supplemented potassium (K/Mg) cardioplegia during ischemia or reperfusion is unknown. METHODS: Rabbit hearts (n = 76) were used for Langendorff perfusion. Sham hearts were perfused for 180 minutes. Global ischemia hearts received 30 minutes of global ischemia and 120 minutes of reperfusion. K/Mg hearts received cardioplegia before ischemia. The role of ATP-sensitive potassium channels in K/Mg cardioprotection during ischemia and reperfusion was investigated, separately using the selective mitochondrial ATP sensitive potassium and channel blocker, 5-hydroxydecanoate, and the selective sarcolemmal ATP-sensitive potassium channel blocker HMR1883. Separate studies were performed using the selective mitochondrial ATP-sensitive potassium channel opener, diazoxide, and the nonselective ATP-sensitive potassium channel opener pinacidil. RESULTS: Infarct size was 1.9%+/-0.4% in sham, 3.7%+/-0.5% in K/Mg, and 27.8%+/-2.4% in global ischemia hearts (p < 0.05 versus K/Mg). Left ventricular peak-developed pressure (percent of equilibrium) at the end of 120 minutes of reperfusion was 91%+/-6% in sham, 92% +/-2% in K/Mg, and 47%+/-6% in global ischemia (p < 0.05 versus K/Mg). Blockade of sarcolemmal ATP-sensitive potassium channels in K/Mg hearts had no effect on infarct size or left ventricular peak-developed pressure. However, blockade of mitochondrial ATP-sensitive potassium channels before ischemia significantly increased infarct size to 23%+/-2% in K/Mg hearts (p < 0.05 versus K/Mg; no statistical significance [NS] as compared to global ischemia) and significantly decreased left ventricular peak-developed pressure to 69%+/-4% (p < 0.05 versus K/Mg). Diazoxide when added to K/Mg cardioplegia significantly decreased infarct size to 1.5%+/-0.4% (p < 0.05 versus K/Mg). CONCLUSIONS: The cardioprotection afforded by K/Mg cardioplegia is modulated by mitochondrial ATP-sensitive potassium channels. Diazoxide when added to K/Mg cardioplegia significantly reduces infarct size, suggesting that the opening of mitochondrial ATP-sensitive potassium channels with K/Mg cardioplegic protection would allow for enhanced myocardial protection in cardiac operations.     

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

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

Remifentanil Preconditioning Confers Cardioprotection via Cardiac κ- and δ-Opioid Receptors

Background: Remifentanil preconditioning (RPC) reduces the infarct size in anesthetized rat hearts, and this effect seems to be mediated by all three types of opioid receptors (ORs). Because there is evidence of only [kappa]- and [delta]- but not [mu]-ORs in the rat heart, the authors investigated whether RPC confers cardioprotection via cardiac [kappa]- and [delta]-OR as well as via extracardiac [mu]-OR agonist activity. The authors also investigated the involvement of signaling mechanisms, namely protein kinase C and mitochondrial adenosine triphosphate-sensitive potassium (KATP) channels.

Methods: The hearts of male Sprague-Dawley rats weighing 190-210 g were removed, mounted on a Langendorff apparatus, and perfused retrogradely at 100 cm H2O with Krebs-Ringer's solution. All hearts were subjected to 30 min of ischemia and 2 h of reperfusion. The study consisted of three series of experiments on the effect of ischemic preconditioning or RPC (10, 50, and 100 ng/ml remifentanil) after blockade of OR subtypes ([delta]-OR antagonist naltrindol, [kappa]-OR antagonist nor-binaltorphimine, and [mu]-OR antagonist CTOP). The involvement of protein kinase C or the KATP channel in the cardioprotection of RPC was also investigated using specific blockers in each group. RPC was produced by three cycles of 5-min perfusion of remifentanil in Krebs-Ringer's solution interspersed with a 5-min reperfusion with Krebs solution only. Infarct size, as a percentage of the area at risk, was determined by 2,3,5-triphenyltetrazolium staining.

Results: Infarct size as a percentage of the area at risk was significantly reduced after RPC from 51.9 +/- 5.0% (control, n = 8) to 36.2 +/- 10.0% (100 ng/ml RPC, n = 8, P < 0.01). This effect was stopped by pretreatment with naltrindol (52.3 +/- 5.2%) and nor-binaltorphimine (43.5 +/- 6.0%) but not CTOP (37.1 +/- 6.0%). Chelerythrine and GF109203X, both protein kinase C inhibitors, abolished the effects of RPC or ischemic preconditioning on infarct size as a percentage of area at risk. 5-Hydroxydecanoate (a selective mitochondrial KATP channel blocker) also abolished the cardioprotection of RPC and IPC, but HMR-1098 (a selective inhibitor of the sarcolemmal KATP channel) did not.     

Sevoflurane confers additional cardioprotection after ischemic late preconditioning in rabbits

BACKGROUND: Sevoflurane exerts cardioprotective effects that mimic the early ischemic preconditioning phenomenon (EPC) by activating adenosine triphosphate-sensitive potassium (KATP) channels. Ischemic late preconditioning (LPC) is an important cardioprotective mechanism in patients with coronary artery disease. The authors investigated whether the combination of LPC and sevoflurane-induced preconditioning results in enhanced cardioprotection and whether opening of KATP channels plays a role in this new setting. METHODS: Seventy-three rabbits were instrumented with a coronary artery occluder. After recovery for 10 days, they were subjected to 30 min of coronary artery occlusion and 120 min of reperfusion (I/R). Controls (n = 14) were not preconditioned. LPC was induced in conscious animals by a 5-min period of coronary artery occlusion 24 h before I/R (LPC, n = 15). Additional EPC was induced by a 5-min period of myocardial ischemia 10 min before I/R (LPC+EPC, n = 9). Animals of the sevoflurane (SEVO) groups inhaled 1 minimum alveolar concentration of sevoflurane for 5 min at 10 min before I/R with (LPC+SEVO, n = 10) or without (SEVO, n = 15) additional LPC. The KATP channel blocker 5-hydroxydecanoate (5-HD, 5 mg/kg) was given intravenously 10 min before sevoflurane administration (LPC+SEVO+5-HD, n = 10). RESULTS: Infarct size of the area at risk (triphenyltetrazolium staining) was reduced from 45 +/- 16% (mean+/-SD, control) to 27 +/- 11% by LPC (P < 0.001) and to 27 +/- 17% by sevoflurane (P = 0.001). Additional sevoflurane administration after LPC led to a further infarct size reduction to 14 +/- 8% (LPC+SEVO, P = 0.003 vs. LPC; P = 0.032 vs. SEVO), similar to the combination of LPC and EPC (12 +/- 8%; P = 0.55 vs. LPC+SEVO). Cardioprotection induced by LPC+SEVO was abolished by 5-HD (LPC+SEVO+5-HD, 41 +/- 19%, P = 0.001 vs. LPC+SEVO). CONCLUSIONS: Sevoflurane administration confers additional cardioprotection after LPC by opening of KATP channels.     

Desflurane-induced preconditioning alters calcium-induced mitochondrial permeability transition

BACKGROUND: Recent investigations have focused on the pivotal role of the mitochondria in the underlying mechanisms volatile anesthetic-induced myocardial preconditioning. This study aimed at examining the effect of anesthetic preconditioning on mitochondrial permeability transition (MPT) pore opening. METHODS: Anesthetized open chest rabbits were randomized to one of four groups and underwent 10 min of ischemia, except for the sham 1 group (n = 12). Before this, they underwent a treatment period consisting of (1) no intervention (ischemic group; n = 12), (2) 30 min of desflurane inhalation (8.9% end-tidal concentration) followed by a 15-min washout period (desflurane group; n = 12), or (3) ischemic preconditioning (IPC group; n = 12). A second set of experiments was performed to evaluate the effect of a putative mitochondrial adenosine triphosphate-sensitive potassium channel antagonist, 5-hydroxydecanoate (5-HD). The animals underwent the same protocol as previously, plus pretreatment with 5 mg/kg 5-HD. They were randomized to one of five groups: the sham 2 group, receiving no 5-HD (n = 12); the sham 5-HD group (n = 12); the ischemic 5-HD group (n = 12), the desflurane 5-HD group (n = 12), and the IPC 5-HD group (n = 12). At the end of the protocol, the hearts were excised, and mitochondria were isolated. MPT pore opening was assessed by measuring the amount of calcium required to trigger a massive calcium release indicative of MPT pore opening. RESULTS: Desflurane and IPC group mitochondria needed a higher calcium load than ischemic group mitochondria (362 +/- 84, 372 +/- 74, and 268 +/- 110 microM calcium, respectively; P < 0.05) to induce MPT pore opening. The sham 1 and sham 2 groups needed a similar amount of calcium to trigger mitochondrial calcium release (472 +/- 70 and 458 +/- 90 microM calcium, respectively). 5-HD preadministration had no effect on sham animals (458 +/- 90 and 440 +/- 128 microM calcium without and with 5-HD, respectively) and ischemic group animals (268 +/- 110 and 292 +/- 102 microM calcium without and with 5-HD, respectively) but abolished the effects of desflurane on calcium-induced MPT pore opening (362 +/- 84 microM calcium without 5-HD vs. 238 +/- 96 microM calcium with 5-HD; P < 0.05) and IPC (372 +/- 74 microM calcium without 5-HD vs. 270 +/- 104 microM calcium with 5-HD; P < 0.05). CONCLUSION: Like ischemic preconditioning, desflurane improved the resistance of the transition pore to calcium-induced opening. This effect was inhibited by 5-HD, suggesting a link between mitochondrial adenosine triphosphate-sensitive potassium and MPT.