Ketamine Preconditions Isolated Human Right Atrial Myocardium: Roles of Adenosine Triphosphate-sensitive Potassium Channels and Adrenoceptors

Background: The authors examined the effect of ketamine and its S(+) isomer on isolated human myocardium submitted to hypoxia-reoxygenation in vitro.

Methods: The authors studied isometric contraction of human right atrial trabeculae suspended in an oxygenated Tyrode's modified solution at 34[degrees]C. Ten minutes before a 30-min hypoxic period followed by a 60-min reoxygenation, muscles were exposed for 15 min to racemic ketamine and its S(+) isomer at 10-6, 10-5, and 10-4 m alone or in the presence of 8.10-4 m 5-hydroxydecanoate, 10-5 m HMR 1098 (sarcolemmal adenosine triphosphate-sensitive potassium channel antagonist), 10-6 m phentolamine ([alpha]-adrenoceptor antagonist), and 10-6 m propranolol ([beta]-adrenoceptor antagonist). Force of contraction at the end of the 60-min reoxygenation period was compared between groups (mean +/- SD).

Results: Ketamine (10-6 m: 85 +/- 4%; 10-5 m: 95 +/- 10%; 10-4 m: 94 +/- 14% of baseline) and S(+)-ketamine (10-6 m: 85 +/- 4%; 10-5 m: 91 +/- 16%; 10-4 m: 93 +/- 14% of baseline) enhanced recovery of force of contraction at the end of the reoxygenation period as compared with the control group (47 +/- 10% of baseline; P < 0.001). Ketamine-induced preconditioning at 10-4 m was inhibited by 5-hydroxydecanoate (60 +/- 16%; P < 0.001), HMR 1098 (60 +/- 14%; P < 0.001), phentolamine (56 +/- 12%; P < 0.001), and propranolol (60 +/- 7%; P < 0.001).     

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

Background: The authors examined the role of adenosine triphosphate-sensitive potassium channels and adenosine A1 receptors in sevoflurane-induced preconditioning on isolated human myocardium.

Methods: The authors recorded isometric contraction of human right atrial trabeculae suspended in oxygenated Tyrode's solution (34[degrees]C; stimulation frequency, 1 Hz). In all groups, a 30-min hypoxic period was followed by 60 min of reoxygenation. Seven minutes before hypoxia reoxygenation, muscles were exposed to 4 min of hypoxia and 7 min of reoxygenation or 15 min of sevoflurane at concentrations of 1, 2, and 3%. In separate groups, sevoflurane 2% was administered in the presence of 10 [mu]m HMR 1098, a sarcolemmal adenosine triphosphate-sensitive potassium channel antagonist; 800 [mu]m 5-hydroxy-decanoate, a mitochondrial adenosine triphosphate-sensitive potassium channel antagonist; and 100 nm 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A1 receptor antagonist. Recovery of force at the end of the 60-min reoxygenation period was compared between groups (mean +/- SD).

Results: Hypoxic preconditioning (90 +/- 4% of baseline) and sevoflurane 1% (82 +/- 3% of baseline), 2% (92 +/- 5% of baseline), and 3% (85 +/- 7% of baseline) enhanced the recovery of force after 60 min of reoxygenation compared with the control groups (52 +/- 9% of baseline). This effect was abolished in the presence of 5-hydroxy-decanoate (55 +/- 14% of baseline) and 8-cyclopentyl-1,3-dipropylxanthine (58 +/- 16% of baseline) but was attenuated in the presence of HMR 1098 (73 +/- 10% of baseline).     

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 sevoflurane-induced myocardial preconditioning in isolated human right atria in vitro

BACKGROUND: The authors examined the role of adenosine triphosphate-sensitive potassium channels and adenosine A(1) receptors in sevoflurane-induced preconditioning on isolated human myocardium. METHODS: The authors recorded isometric contraction of human right atrial trabeculae suspended in oxygenated Tyrode's solution (34 degrees C; stimulation frequency, 1 Hz). In all groups, a 30-min hypoxic period was followed by 60 min of reoxygenation. Seven minutes before hypoxia reoxygenation, muscles were exposed to 4 min of hypoxia and 7 min of reoxygenation or 15 min of sevoflurane at concentrations of 1, 2, and 3%. In separate groups, sevoflurane 2% was administered in the presence of 10 microm HMR 1098, a sarcolemmal adenosine triphosphate-sensitive potassium channel antagonist; 800 microm 5-hydroxy-decanoate, a mitochondrial adenosine triphosphate-sensitive potassium channel antagonist; and 100 nm 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A(1) receptor antagonist. Recovery of force at the end of the 60-min reoxygenation period was compared between groups (mean +/- SD). RESULTS: Hypoxic preconditioning (90 +/- 4% of baseline) and sevoflurane 1% (82 +/- 3% of baseline), 2% (92 +/- 5% of baseline), and 3% (85 +/- 7% of baseline) enhanced the recovery of force after 60 min of reoxygenation compared with the control groups (52 +/- 9% of baseline). This effect was abolished in the presence of 5-hydroxy-decanoate (55 +/- 14% of baseline) and 8-cyclopentyl-1,3-dipropylxanthine (58 +/- 16% of baseline) but was attenuated in the presence of HMR 1098 (73 +/- 10% of baseline). CONCLUSIONS: In vitro, sevoflurane preconditions human myocardium against hypoxia through activation of adenosine triphosphate-sensitive potassium channels and stimulation of adenosine A(1) receptors.     

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.     

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).     

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 microg. kg-1. min-1) or mitochondrial (5-hydroxydecanoate [5-HD]; 150 microg. kg-1. 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). CONCLUSION: Desflurane reduces myocardial infarct size in vivo, and the results further suggest that both sarcolemmal and mitochondrial KATP channels could be involved.     

The inotropic and lusitropic effects of ketamine in isolated human atrial myocardium: the effect of adrenoceptor blockade

We studied the direct myocardial effects of racemic ketamine, in the presence of alpha- and beta-adrenoceptor blockade, on isolated human right atrial myocardium. Isometric force of contraction (FoC), its first derivative with time (+dF/dt), the contraction relaxation coupling parameter R2 = (+dF/dt) / (-dF/dt), and time to half relaxation (T(1/2)) were recorded before and after addition of 10(-6), 10(-5) and 10(-4) M racemic ketamine alone and in the presence of alpha-adrenoceptor blockade (phentolamine 10(-6) M) and beta-adrenoceptor blockade (propranolol at 10(-6) M). Ketamine had a moderate positive inotropic effect at 10(-5) M (FoC, 104% +/- 5% of baseline value; P = 0.03) and 10(-4) M (FoC, 107% +/- 11% of baseline value; P = 0.09). Racemic ketamine had a negative inotropic effect in the presence of propranolol (FoC, ketamine 10(-6) M, 77% +/- 11%; ketamine 10(-5) M, 63% +/- 16%; ketamine 10(-4) M, 62% +/- 17% of baseline; P < 0.001) but not phentolamine (FoC, ketamine at 10(-6) M, 94% +/- 6%; ketamine 10(-5) M, 96% +/- 5%; and ketamine 10(-4) M, 98% +/- 15% of baseline). Ketamine decreased T(1/2) (ketamine 10(-5) M, 94% +/- 3% of baseline value; P < 0.001 and ketamine 10(-4) M, 90% +/- 9% of baseline value; P = 0.007) but did not modify R2. In human right atrial myocardium, racemic ketamine induced a moderate positive inotropic effect and hastened isometric relaxation. In the presence of beta-adrenoceptor blockade it induced a direct negative inotropic effect.     

Late preconditioning is blocked by racemic ketamine, but not by S(+)-ketamine

Racemic ketamine blocks K(ATP) channels in isolated cells and abolishes short-term cardioprotection against prolonged ischemia. We investigated the effects of racemic ketamine and S(+)-ketamine on ischemic late preconditioning (LPC) in the rabbit heart in vivo. A coronary occluder was chronically implanted in 36 rabbits. After recovery, the rabbits divided into four groups (each n = 9). LPC was induced in conscious rabbits by a 5-min coronary occlusion. Twenty-four hours later, the animals were instrumented for measurement of left ventricular systolic pressure (LVSP, tip manometer), cardiac output (CO, ultrasonic flowprobe) and myocardial infarct size (triphenyltetrazolium staining). All rabbits were then subjected to 30-min coronary occlusion and 2 h reperfusion. Controls underwent the ischemia-reperfusion program without LPC. To test whether racemic ketamine or S(+)-ketamine blocks the cardioprotection induced by LPC, the drugs (10 mg/kg) were given 10 min before the 30-min ischemia. Hemodynamic values were not significantly different between groups during the experiments (baseline: LVSP, 94 +/- 3 mm Hg [mean +/- SEM] and CO, 243 +/- 9 mL/min; coronary occlusion: LVSP, 93% +/- 4% of baseline and CO, 84% +/- 4%; after 2 h of reperfusion: LVSP, 85% +/- 4% and CO, 83% +/- 4%). LPC reduced infarct size from 44% +/- 3% of the area at risk in controls to 22% +/- 3% (P = 0.002). Administration of racemic ketamine abolished the cardioprotective effects of LPC (44 +/- 4%, P = 0.002). S(+)-ketamine did not affect the infarct size reduction induced by LPC (26 +/- 6%, P = 0.88). IMPLICATIONS: Racemic ketamine, but not S(+)-ketamine, blocks the cardioprotection induced by ischemic late preconditioning in rabbit hearts in vivo. Thus, the influence of ketamine on ischemic late preconditioning is most likely enantiomer specific, and the use of S(+)-ketamine may be preferable in patients with coronary artery disease.     

Signal Transduction of Opioid-induced Cardioprotection in Ischemia-Reperfusion

Background: Morphine reduces myocardial ischemia-reperfusion injury in vivo and in vitro. The authors tried to determine the role of opioid [delta]1 receptors, oxygen radicals, and adenosine triphosphate-sensitive potassium (KATP) channels in mediating this effect.

Methods: Chick cardiomyocytes were studied in a flow-through chamber while pH, flow rate, oxygen, and carbon dioxide tension were controlled. Cell viability was quantified by nuclear stain propidium iodide, and oxygen radicals were quantified using molecular probe 2',7'-dichlorofluorescin diacetate.

Results: Morphine (1 [mu]m) or the selective [delta]-opioid receptor agonist BW373U86 (10 pm) given for 10 min before 1 h of ischemia and 3 h of reoxygenation reduced cell death (31 +/- 5%, n = 6, and 28 +/- 5%, n = 6 [P < 0.05], respectively, 53 +/- 6%, n = 6, in controls) and generated oxygen radicals before ischemia (724 +/- 53, n = 8, and 742 +/- 75, n = 8 [P < 0.05], respectively, vs. 384 +/- 42, n = 6, in controls, arbitrary units). The protection of morphine was abolished by naloxone, or the selective [delta]1-opioid receptor antagonist 7-benzylidenenaltrexone. Reduction in cell death and increase in oxygen radicals with BW373U86 were blocked by the selective mitochondrial KATP channel antagonist 5-hydroxydecanoate or diethyldithiocarbamic acid (1000 [mu]m), which inhibited conversion of O2- to H2O2. The increase in oxygen radicals was abolished by the mitochondrial electron transport inhibitor myxothiazol. Reduction in cell death was associated with attenuated oxidant stress at reperfusion.     

Prevention of Isoflurane-induced Preconditioning by 5-Hydroxydecanoate and Gadolinium: Possible Involvement of Mitochondrial Adenosine Triphosphate-sensitive Potassium and Stretch-activated Channels

Background: Both mitochondrial adenosine triphosphate-sensitive potassium (MKATP) channels (selectively blocked by 5-hydroxydecanoate) and stretch-activated channels (blocked by gadolinium) have been involved in the mechanism of ischemic preconditioning. Isoflurane can reproduce the protection afforded by ischemic preconditioning. We sought to determine whether isoflurane-induced preconditioning may involve MKATP and stretch-activated channels.

Methods: Anesthetized open-chest rabbits underwent 30 min of coronary occlusion followed by 3 h of reperfusion. Before this, rabbits were randomized into one of six groups and underwent a treatment period consisting of either no intervention for 40 min (control group; n = 9) or 15 min of isoflurane inhalation (1.1% end tidal) followed by a 15-min washout period (isoflurane group; n = 9). The two groups received an intravenous bolus dose of either 5-hydroxydecanoate (5 mg/kg) or gadolinium (40 [mu]mol/kg) before coronary occlusion and reperfusion (5-hydroxydecanoate, n = 9; gadolinium, n = 7). Two additional groups received 5-hydroxydecanoate or gadolinium before isoflurane exposure (isoflurane-5-hydroxydecanoate, n = 10; isoflurane-gadolinium, n = 8). Area at risk and infarct size were assessed by blue dye injection and tetrazolium chloride staining.

Results: Area at risk was comparable among the six groups (29 +/- 7, 30 +/- 5, 27 +/- 6, 35 +/- 7, 31 +/- 7, and 27 +/- 4% of the left ventricle in the control, isoflurane, isoflurane-5-hydroxydecanoate, 5-hydroxydecanoate, isoflurane-gadolinium, and gadolinium groups, respectively). Infarct size averaged 60 +/- 20% (SD) in untreated controls versus 54 +/- 27 and 65 +/- 15% of the risk zone in 5-hydroxydecanoate- and gadolinium-treated controls (P = nonsignificant). In contrast, infarct size in the isoflurane group was significantly reduced to 26 +/- 11% of the risk zone (P < 0.05 vs. control). Both 5-hydroxydecanoate and gadolinium prevented this attenuation: infarct size averaged 68 +/- 23 and 56 +/- 21% of risk zone in the isoflurane-5-hydroxydecanoate and isoflurane-gadolinium groups, respectively (P = nonsignificant vs. control).     

Prevention of isoflurane-induced preconditioning by 5-hydroxydecanoate and gadolinium: possible involvement of mitochondrial adenosine triphosphate-sensitive potassium and stretch-activated channels

BACKGROUND: Both mitochondrial adenosine triphosphate-sensitive potassium (MKATP) channels (selectively blocked by 5-hydroxydecanoate) and stretch-activated channels (blocked by gadolinium) have been involved in the mechanism of ischemic preconditioning. Isoflurane can reproduce the protection afforded by ischemic preconditioning. We sought to determine whether isoflurane-induced preconditioning may involve MKATP and stretch-activated channels. METHODS: Anesthetized open-chest rabbits underwent 30 min of coronary occlusion followed by 3 h of reperfusion. Before this, rabbits were randomized into one of six groups and underwent a treatment period consisting of either no intervention for 40 min (control group; n = 9) or 15 min of isoflurane inhalation (1.1% end tidal) followed by a 15-min washout period (isoflurane group; n = 9). The two groups received an intravenous bolus dose of either 5-hydroxydecanoate (5 mg/kg) or gadolinium (40 micromol/kg) before coronary occlusion and reperfusion (5-hydroxydecanoate, n = 9; gadolinium, n = 7). Two additional groups received 5-hydroxydecanoate or gadolinium before isoflurane exposure (isoflurane-5-hydroxydecanoate, n = 10; isoflurane-gadolinium, n = 8). Area at risk and infarct size were assessed by blue dye injection and tetrazolium chloride staining. RESULTS: Area at risk was comparable among the six groups (29 +/- 7, 30 +/- 5, 27 +/- 6, 35 +/- 7, 31 +/- 7, and 27 +/- 4% of the left ventricle in the control, isoflurane, isoflurane-5-hydroxydecanoate, 5-hydroxydecanoate, isoflurane-gadolinium, and gadolinium groups, respectively). Infarct size averaged 60 +/- 20% (SD) in untreated controls versus 54 +/- 27 and 65 +/- 15% of the risk zone in 5-hydroxydecanoate- and gadolinium-treated controls (P = nonsignificant). In contrast, infarct size in the isoflurane group was significantly reduced to 26 +/- 11% of the risk zone (P < 0.05 vs.control). Both 5-hydroxydecanoate and gadolinium prevented this attenuation: infarct size averaged 68 +/- 23 and 56 +/- 21% of risk zone in the isoflurane-5-hydroxydecanoate and isoflurane-gadolinium groups, respectively (P = nonsignificant vs.control). CONCLUSION: 5-Hydroxydecanoate and gadolinium inhibited pharmacologic preconditioning by isoflurane. This result suggests that MKATP channels and mechanogated channels are probably involved in this protective mechanism.     

Ketamine, but not S(+)-ketamine, blocks ischemic preconditioning in rabbit hearts in vivo

BACKGROUND: Ketamine blocks KATP channels in isolated cells and abolishes the cardioprotective effect of ischemic preconditioning in vitro. The authors investigated the effects of ketamine and S(+)-ketamine on ischemic preconditioning in the rabbit heart in vivo. METHODS: In 46 alpha-chloralose-anesthetized rabbits, left ventricular pressure (tip manometer), cardiac output (ultrasonic flow probe), and myocardial infarct size (triphenyltetrazolium staining) at the end of the experiment were measured. All rabbits were subjected to 30 min of occlusion of a major coronary artery and 2 h of subsequent reperfusion. The control group underwent the ischemia-reperfusion program without preconditioning. Ischemic preconditioning was elicited by 5-min coronary artery occlusion followed by 10 min of reperfusion before the 30 min period of myocardial ischemia (preconditioning group). To test whether ketamine or S(+)-ketamine blocks the preconditioning-induced cardioprotection, each (10 mg kg(-1)) was administered 5 min before the preconditioning ischemia. To test any effect of ketamine itself, ketamine was also administered without preconditioning at the corresponding time point. RESULTS: Hemodynamic baseline values were not significantly different between groups [left ventricular pressure, 107 +/- 13 mmHg (mean +/- SD); cardiac output, 183 +/- 28 ml/min]. During coronary artery occlusion, left ventricular pressure was reduced to 83 +/- 14% of baseline and cardiac output to 84 +/- 19%. After 2 h of reperfusion, functional recovery was not significantly different among groups (left ventricular pressure, 77 +/- 19%; cardiac output, 86 +/- 18%). Infarct size was reduced from 45 +/- 16% of the area at risk in controls to 24 +/- 17% in the preconditioning group (P = 0.03). The administration of ketamine had no effect on infarct size in animals without preconditioning (48 +/- 18%), but abolished the cardioprotective effects of ischemic preconditioning (45 +/- 19%, P = 0.03). S(+)-ketamine did not affect ischemic preconditioning (25 +/- 11%, P = 1.0). CONCLUSIONS: Ketamine, but not S(+)-ketamine blocks the cardioprotective effect of ischemic preconditioning in vivo.     

Ketamine, but Not S (+)-ketamine, Blocks Ischemic Preconditioning in Rabbit Hearts In Vivo

Background: Ketamine blocks KATP channels in isolated cells and abolishes the cardioprotective effect of ischemic preconditioning in vitro. The authors investigated the effects of ketamine and S (+)-ketamine on ischemic preconditioning in the rabbit heart in vivo.

Methods: In 46 [alpha]-chloralose-anesthetized rabbits, left ventricular pressure (tip manometer), cardiac output (ultrasonic flow probe), and myocardial infarct size (triphenyltetrazolium staining) at the end of the experiment were measured. All rabbits were subjected to 30 min of occlusion of a major coronary artery and 2 h of subsequent reperfusion. The control group underwent the ischemia-reperfusion program without preconditioning. Ischemic preconditioning was elicited by 5-min coronary artery occlusion followed by 10 min of reperfusion before the 30 min period of myocardial ischemia (preconditioning group). To test whether ketamine or S (+)-ketamine blocks the preconditioning-induced cardioprotection, each (10 mg kg-1) was administered 5 min before the preconditioning ischemia. To test any effect of ketamine itself, ketamine was also administered without preconditioning at the corresponding time point.

Results: Hemodynamic baseline values were not significantly different between groups [left ventricular pressure, 107 +/- 13 mmHg (mean +/- SD); cardiac output, 183 +/- 28 ml/min]. During coronary artery occlusion, left ventricular pressure was reduced to 83 +/- 14% of baseline and cardiac output to 84 +/- 19%. After 2 h of reperfusion, functional recovery was not significantly different among groups (left ventricular pressure, 77 +/- 19%; cardiac output, 86 +/- 18%). Infarct size was reduced from 45 +/- 16% of the area at risk in controls to 24 +/- 17% in the preconditioning group (P = 0.03). The administration of ketamine had no effect on infarct size in animals without preconditioning (48 +/- 18%), but abolished the cardioprotective effects of ischemic preconditioning (45 +/- 19%, P = 0.03). S (+)-ketamine did not affect ischemic preconditioning (25 +/- 11%, P = 1.0).     

Signal transduction of opioid-induced cardioprotection in ischemia-reperfusion

BACKGROUND: Morphine reduces myocardial ischemia-reperfusion injury in vivo and in vitro. The authors tried to determine the role of opioid delta1 receptors, oxygen radicals, and adenosine triphosphate-sensitive potassium (KATP) channels in mediating this effect. METHODS: Chick cardiomyocytes were studied in a flow-through chamber while pH, flow rate, oxygen, and carbon dioxide tension were controlled. Cell viability was quantified by nuclear stain propidium iodide, and oxygen radicals were quantified using molecular probe 2',7'-dichlorofluorescin diacetate. RESULTS: Morphine (1 microM) or the selective delta-opioid receptor agonist BW373U86 (10 pM) given for 10 min before 1 h of ischemia and 3 h of reoxygenation reduced cell death (31 +/- 5%, n = 6, and 28 +/- 5%, n = 6 [P < 0.05], respectively, 53 +/- 6%, n = 6, in controls) and generated oxygen radicals before ischemia (724 +/- 53, n = 8, and 742 +/- 75, n = 8 [P < 0.05], respectively, vs. 384 +/- 42, n = 6, in controls, arbitrary units). The protection of morphine was abolished by naloxone, or the selective delta1-opioid receptor antagonist 7-benzylidenenaltrexone. Reduction in cell death and increase in oxygen radicals with BW373U86 were blocked by the selective mitochondrial KATP channel antagonist 5-hydroxydecanoate or diethyldithiocarbamic acid (1,000 microM), which inhibited conversion of O2- to H2O2. The increase in oxygen radicals was abolished by the mitochondrial electron transport inhibitor myxothiazoL Reduction in cell death was associated with attenuated oxidant stress at reperfusion. CONCLUSION: Stimulation of delta1-opioid receptors generates oxygen radicals via mitochondrial KATP channels. This signaling pathway attenuates oxidant stress and cell death in cardiomyocytes.     

Lidocaine attenuates cytokine-induced cell injury in endothelial and vascular smooth muscle cells

Local anesthetics have been reported to attenuate the inflammatory response and ischemia/reperfusion injury. Therefore, we hypothesized that pretreatment with local anesthetics may protect endothelial and vascular smooth muscle (VSM) cells from cytokine-induced injury. Human microvascular endothelial cells and rat VSM cells were pretreated with lidocaine or tetracaine (5-100 microM for 30 min) and then exposed to the cytokines tumor necrosis factor-alpha, interferon-gamma, and interleukin-1beta for 72 h. Cell survival and integrity were evaluated by trypan blue exclusion and lactate dehydrogenase release. The role of adenosine triphosphate-sensitive potassium (KATP) channels, protein kinase C, or both in modulating local anesthetic-induced protection was evaluated with the mitochondrial KATP antagonist 5-hydroxydecanoate, the cell-surface KATP antagonist 1-[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea (HMR-1098), and the protein kinase C inhibitor staurosporine. Lidocaine attenuated cytokine-induced cell injury in a dose-dependent manner. Lidocaine (5 microM) increased cell survival by approximately 10%, whereas lidocaine (100 microM) increased cell survival by approximately 60% and induced a threefold decrease in lactate dehydrogenase release in both cell types. In contrast, tetracaine did not attenuate cytokine-induced cell injury. 5-hydroxydecanoate abolished the protective effects of lidocaine, but staurosporine and HMR-1098 had no effect on the lidocaine-induced protection. This study showed that lidocaine, but not tetracaine, attenuates cytokine-induced injury in endothelial and VSM cells. Lidocaine-induced protection appears to be modulated by mitochondrial KATP channels. IMPLICATIONS: This study demonstrates that lidocaine attenuates cytokine-induced injury of endothelial and vascular smooth muscle cells via mechanisms involving adenosine triphosphate-sensitive potassium channels. Protection of the vasculature from cytokine-induced inflammation may preserve important physiological endothelial and vascular smooth muscle functions.     

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.     

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).     

Effects of ketamine and its isomers on ischemic preconditioning in the isolated rat heart

BACKGROUND: Ischemic preconditioning protects the heart against subsequent ischemia. Opening of the adenosine triphosphate-sensitive potassium (KATP) channel is a key mechanism of preconditioning. Ketamine blocks KATP channels of isolated cardiomyocytes. The authors investigated the effects of ketamine and its stereoisomers on preconditioning. METHODS: Isolated rat hearts (n = 80) underwent 30 min of no-flow ischemia and 60 min of reperfusion. Two groups with eight hearts each underwent the protocol without intervention (control-1 and control-2), and, in eight hearts, preconditioning was elicited by two 5-min periods of ischemia before the 30 min ischemia. In the six treatment groups (each n = 8), ketamine, R(-)- or S(+)-ketamine were administered at concentrations of 2 or 20 microg/ml before preconditioning. Eight hearts received 20 microg/ml R(-)-ketamine before ischemia. Left ventricular (LV) developed pressure and creatine kinase (CK) release during reperfusion were determined as variables of ventricular function and cellular injury. RESULTS: Baseline LV developed pressure was similar in all groups: 104 +/- 28 mmHg (mean +/- SD). Controls showed a poor recovery of LV developed pressure (17 +/- 8% of baseline) and a high CK release (70 +/- 17 IU/g). Ischemic preconditioning improved recovery of LV developed pressure (46 +/- 14%) and reduced CK release (47 +/- 17 IU/g, both P < 0.05 vs. control-1). Ketamine (2 microg/ml) and 2 or 20 microg/ml S(+)-ketamine had no influence on recovery of LV developed pressure compared with preconditioning (47 +/- 18, 43 +/- 8, 49 +/- 36%) and CK release (39 +/- 8, 30 +/- 14, 41 +/- 25 IU/g). After administration of 20 microg/ml ketamine and 2 or 20 microg/ml R(-)-ketamine, the protective effects of preconditioning were abolished (LV developed pressure-recovery, 16 +/- 14, 22 +/- 21, 18 +/- 11%; CK release, 67 +/- 11, 80 +/- 21, 82 +/- 41 IU/g; each P < 0.05 vs. preconditioning). Preischemic treatment with R(-)-ketamine had no effect on CK release (74 +/- 8 vs. 69 +/- 9 IU/g in control-2, P = 0.6) and functional recovery (LV developed pressure 12 +/- 4 vs. 9 +/- 2 mmHg in control-2, P = 0.5). CONCLUSION: Ketamine can block the cardioprotective effects of ischemic preconditioning. This effect is caused by the R(-)-isomer.     

Effects of Ketamine and Its Isomers on Ischemic Preconditioning in the Isolated Rat Heart

Background: Ischemic preconditioning protects the heart against subsequent ischemia. Opening of the adenosine triphosphate-sensitive potassium (KATP) channel is a key mechanism of preconditioning. Ketamine blocks KATP channels of isolated cardiomyocytes. The authors investigated the effects of ketamine and its stereoisomers on preconditioning.

Methods: Isolated rat hearts (n = 80) underwent 30 min of no-flow ischemia and 60 min of reperfusion. Two groups with eight hearts each underwent the protocol without intervention (control-1 and control-2), and, in eight hearts, preconditioning was elicited by two 5-min periods of ischemia before the 30 min ischemia. In the six treatment groups (each n = 8), ketamine, R (-)- or S (+)-ketamine were administered at concentrations of 2 or 20 [mu]g/ml before preconditioning. Eight hearts received 20 [mu]g/ml R (-)-ketamine before ischemia. Left ventricular (LV) developed pressure and creatine kinase (CK) release during reperfusion were determined as variables of ventricular function and cellular injury.

Results: Baseline LV developed pressure was similar in all groups: 104 +/- 28 mmHg (mean +/- SD). Controls showed a poor recovery of LV developed pressure (17 +/- 8% of baseline) and a high CK release (70 +/- 17 IU/g). Ischemic preconditioning improved recovery of LV developed pressure (46 +/- 14%) and reduced CK release (47 +/- 17 IU/g, both P < 0.05 vs. control-1). Ketamine (2 [mu]g/ml) and 2 or 20 [mu]g/ml S (+)-ketamine had no influence on recovery of LV developed pressure compared with preconditioning (47 +/- 18, 43 +/- 8, 49 +/- 36%) and CK release (39 +/- 8, 30 +/- 14, 41 +/- 25 IU/g). After administration of 20 [mu]g/ml ketamine and 2 or 20 [mu]g/ml R (-)-ketamine, the protective effects of preconditioning were abolished (LV developed pressure-recovery, 16 +/- 14, 22 +/- 21, 18 +/- 11%; CK release, 67 +/- 11, 80 +/- 21, 82 +/- 41 IU/g; each P < 0.05 vs. preconditioning). Preischemic treatment with R (-)-ketamine had no effect on CK release (74 +/- 8 vs. 69 +/- 9 IU/g in control-2, P = 0.6) and functional recovery (LV developed pressure 12 +/- 4 vs. 9 +/- 2 mmHg in control-2, P = 0.5).