Myocardial distribution and biotransformation in vitro and in vivo of nicorandil in rats, with special reference to mitochondria

Doxorubicin-induced oxidative stress: The protective effect of nicorandil on HL-1 cardiomyocytes

The primary cardiotoxic action of doxorubicin when used as antitumor drug is attributed to the generation of reactive oxygen species (ROS) therefore effective cardioprotection therapies are needed. In this sense, the antianginal drug nicorandil has been shown to be effective in cardioprotection from ischemic conditions but the underlying molecular mechanism to cope with doxorubicin-induced ROS is unclear. Our in vitro study using the HL-1 cardiomyocyte cell line derived from mouse atria reveals that the endogenous nitric oxide (NO) production was stimulated by nicorandil and arrested by NO synthase inhibition. Moreover, while the NO synthase activity was inhibited by doxorubicin-induced ROS, the NO synthase inhibition did not affect doxorubicin-induced ROS. The inhibition of NO synthase activity by doxorubicin was totally prevented by preincubation with nicorandil. Nicorandil also concentration-dependently (10 to 100 μM) decreased doxorubicin-induced ROS and the effect was antagonized by 5-hydroxydecanoate. The inhibition profile of doxorubicin-induced ROS by nicorandil was unaltered when an L-arginine derivative or a protein kinase G inhibitor was present. Preincubation with pinacidil mimicked the effect of nicorandil and the protection was eliminated by glibenclamide. Quantitative colocalization of fluorescence indicated that the mitochondrion was the target organelle of nicorandil and the observed response was a decrease in the mitochondrial inner membrane potential. Interference with H⁺ movement across the mitochondrial inner membrane, leading to depolarization, also protected from doxorubicin-induced ROS. The data indicate that activation of the mitochondrial ATP-sensitive K⁺ channel by nicorandil causing mitochondrial depolarization, without participation of the NO donor activity, was responsible for inhibition of the mitochondrial NADPH oxidase that is the main contributor to ROS production in cardiomyocytes. Impairment of the cytosolic Ca²⁺ signal induced by caffeine and the increase in lipid peroxidation, both of which are indicators of doxorubicin-induced oxidative stress, were also prevented by nicorandil.

Nicorandil ameliorates mitochondrial dysfunction in doxorubicin-induced heart failure in rats: possible mechanism of cardioprotection

Despite of its known cardiotoxicity, doxorubicin is still a highly effective anti-neoplastic agent in the treatment of several cancers. In the present study, the cardioprotective effect of nicorandil was investigated on hemodynamic alterations and mitochondrial dysfunction induced by cumulative administration of doxorubicin in rats. Doxorubicin was injected i.p. over 2 weeks to obtain a cumulative dose of 18 mg/kg. Nicorandil (3 mg/kg/day) was given orally with or without doxorubicin treatment. Heart rate and aortic blood flow were recorded 24 h after receiving the last dose of doxorubicin. Rats were then sacrificed and hearts were rapidly excised for estimation of caspase-3 activity, phosphocreatine and adenine nucleotides contents in addition to cytochrome c, Bcl2, Bax and caspase 3 expression. Moreover, mitochondrial oxidative phosphorylation capacity, creatine kinase activity and oxidative stress markers were measured together with the examination of DNA fragmentation and ultrastructural changes. Nicorandil was effective in alleviating the decrement of heart rate and aortic blood flow and the state of mitochondrial oxidative stress induced by doxorubicin cardiotoxicity. Nicorandil also preserved phosphocreatine and adenine nucleotides contents by restoring mitochondrial oxidative phosphorylation capacity and creatine kinase activity. Moreover, nicorandil provided a significant cardioprotection via inhibition of apoptotic signaling pathway, DNA fragmentation and mitochondrial ultrastructural changes. Interestingly, nicorandil did not interfere with cytotoxic effect of doxorubicin against the growth of solid Ehrlich carcinoma. In conclusion, nicorandil was effective against the development of doxorubicin-induced heart failure in rats as indicated by improvement of hemodynamic perturbations, mitochondrial dysfunction and ultrastructural changes without affecting its antitumor activity.

Pharmacological preconditioning with nicorandil and pioglitazone attenuates myocardial ischemia/reperfusion injury in rats

The present investigation was designed to study the cardioprotective effects of nicorandil and pioglitazone preconditioning in myocardial ischemia/reperfusion-induced hemodynamic, biochemical and histological changes in rats. Oral doses of nicorandil (3 or 6 mg/kg) and pioglitazone (10 or 20mg/kg) were administered once daily for 5 consecutive days. Rats were then subjected to myocardial ischemia/reperfusion (40 min/10 min). Heart rate and ventricular arrhythmias were recorded during ischemia/reperfusion progress. At the end of reperfusion, plasma creatine kinase-MB activity and total nitrate/nitrite were determined. In addition, lactate, adenine nucleotides, thiobarbituric acid reactive substances, reduced glutathione and myeloperoxidase activity were estimated in the heart left ventricle. Finally, histological examination was performed to visualize the protective cellular effects of different pretreatments. Nicorandil (3 or 6 mg/kg) was effective in attenuating the ischemia/reperfusion-induced ventricular arrhythmias, creatine kinase-MB release, lactate accumulation and oxidative stress. Nicorandil (3 mg/kg) was more effective in improving the energy production and lowering the elevated myeloperoxidase activity. Both doses of pioglitazone (10 or 20 mg/kg) were equally effective in reducing lactate accumulation and completely counteracting the oxidative stress. Pioglitazone (10 mg/kg) was more effective in improving energy production and reducing ventricular arrhythmias, plasma creatine kinase-MB release and total nitrate/nitrite. It seems that selective mitochondrial K(ATP) channel opening by lower doses of nicorandil and pioglitazone in the present study provided more cardioprotection against ventricular arrhythmias and biochemical changes induced by ischemia/reperfusion. Histological examination revealed also better improvement by the lower dose of nicorandil than that of pioglitazone.

Effects of nicorandil on the cAMP-dependent Cl- current in guinea-pig ventricular cells

In guinea-pig cardiomyocytes, a cAMP-dependent Cl(-) current (I(Cl,cAMP)) flows through a cardiac isoform of the cystic fibrosis transmembrane conductance regulator (CFTR), which belongs to a family of the ATP-binding cassette (ABC) proteins. Although several K(+)-channel openers and sulfonylurea ATP-sensitive K(+) (K(ATP))-channel blockers reportedly inhibit I(Cl,cAMP), effects of nicorandil on the Cl(-) current have not been evaluated. This study was conducted to examine the effects of nicorandil on I(Cl,cAMP) in isolated guinea-pig ventricular cells using patch clamp techniques. Nicorandil in concentrations higher than 300 microM enhanced the I(Cl,cAMP) preactivated by 0.1 microM isoproterenol. The isoproterenol-induced I(Cl,cAMP) was inhibited by 100 microM glibenclamide, but not by 100 microM pinacidil. SNAP (S-nitroso-N-acetyl-D,L-penicillamine, 10 microM), a nitric oxide (NO) donor, similarly enhanced the isoproterenol-induced I(Cl,cAMP). However, SG-86, a denitrated metabolite possessing K(+ )channel-opening action, failed to enhance the Cl(-) current. When the I(Cl,cAMP) was activated by 3-isobutyl-1-methylxanthine (IBMX, 30 microM), either nicorandil or SNAP failed to enhance the isoproterenol-induced I(Cl,cAMP). Thus, nicorandil enhances I(Cl,cAMP) in guinea-pig cardiomyocytes through an increase in intracellular cGMP, although direct modulation of I(Cl,cAMP) by NO cannot be completely excluded.

Nicorandil opens mitochondrial K(ATP) channels not only directly but also through a NO-PKG-dependent pathway

Nicorandil, a hybrid of nitrate generator and potassium channel opener, protects ischemic myocardium by opening mitochondrial ATP sensitive potassium (mitoK(ATP)) channels. We recently found that nitric oxide (NO) opened K(ATP) channels in rabbit hearts by a protein kinase G (PKG) mechanism. This study examined whether the NO-donor property of nicorandil also contributes to opening of mitoK(ATP) channels through PKG. MitoK(ATP) channel opening was monitored in adult rabbit cardiomyocytes by measuring reactive oxygen species (ROS) production, an established marker of channel opening. Nicorandil increased ROS production in a dose-dependent manner. The selective mitoK(ATP) channel inhibitor 5-hydroxydecanoate (200 microM) completely blocked ROS production by nicorandil at all doses. The PKG inhibitor 8-bromoguanosine-3',5'-cyclic monophosphorothioate, Rpisomer (Rp-8-Br-cGMPs, 50 microM) shifted the dose-ROS production curve to the right with an increase of the EC(50) from 2.4 x 10(-5) M to 6.9 x 10(-5) M. Rp- 8-Br-cGMPs did not affect the increase in ROS production by the selective mitoK(ATP) channel opener diazoxide while it completely blocked increased ROS production from the NO donor S-nitroso-N-acetylpenicillamine (1 microM). Furthermore ODQ, an antagonist of soluble guanylyl cyclase, blocked nicorandil's ability to increase ROS generation. These results indicate that nicorandil, in addition to its direct effect on the channels, opens mitoK(ATP) channels indirectly via a NO-PKG signaling pathway.

Is the sarcolemmal or mitochondrial K(ATP) channel activation important in the antiarrhythmic and cardioprotective effects during acute ischemia/reperfusion in the intact anesthetized rabbit model?

The relative contributions of cardiomyocyte sarcolemmal ATP-sensitive K(+) (K(ATP)) and mitochondrial K(ATP) channels in the cardioprotection and antiarrhythmic activity induced by K(ATP) channel openers remain obscure, though the mitochondrial K(ATP) channels have been proposed to be involved as a subcellular mediator in cardioprotection afforded by ischemic preconditioning. In the present study, we sought to investigate the effects of administration of ATP-sensitive K(+) channel (K(ATP)) openers (nicorandil and minoxidil), a specific mitochondrial K(ATP) channel blocker (5-hydroxydecanoate (5-HD)) and a specific sarcolemmal K(ATP) channel blocker (HMR 1883; (1-[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea) prior to coronary occlusion as well as prior to post-ischemic reperfusion on survival rate, ischemia-induced and reperfusion-induced arrhythmias and myocardial infarct size in anesthetized albino rabbits. The thorax was opened in the left 4th intercostal space and after pericardiotomy the heart was exposed. In Group I (n=88), occlusion of the left main coronary artery and hence, myocardial ischemia-induced arrhythmias was achieved by tightening a previously placed loose silk ligature for 30 min. In Group II (n=206), arrhythmias were induced by reperfusion following a 20-min ligation of the left main coronary artery. Both in Group I and Group II, intravenous (i.v.) administration of nicorandil (0.47 mg/kg), minoxidil (0.5 mg/kg), HMR 1883 (3 mg/kg)/nicorandil and HMR 1883 (3 mg/kg)/minoxidil before coronary artery occlusion increased survival rate (86%, 75%, 75% and 86% vs. 55% in the control subgroup in Group I; 75%, 67%, 67% and 75% vs. 46% in the control subgroup in Group II), significantly decreased the incidence and severity of life-threatening arrhythmias. In Group II, i.v. administration of nicorandil and minoxidil before coronary artery occlusion significantly decreased myocardial infarct size. However, i.v. administration of nicorandil or minoxidil before reperfusion did neither increase survival rate nor confer any antiarrhythmic or cardioprotective effects. The antiarrhythmic and cardioprotective effects of both nicorandil and minoxidil were abolished by pretreating the rabbits with 5-HD (5 mg/kg, i.v. bolus), a selective mitochondrial K(ATP) channel blocker but not by HMR 1883 (3 mg/kg). In the present study, higher levels of malondialdehyde (MDA) and lower levels of reduced glutathione (GSH) and superoxide dismutase (SOD) in necrotic zone of myocardium in all the 16 subgroups in Group II suggest little anti-free radical property of nicorandil and minoxidil. We conclude that intervention by intravenous administration of nicorandil and minoxidil (through the selective activation of mitochondrial K(ATP) channels) increased survival rate and exhibited antiarrhythmic and cardioprotective effects during coronary occlusion and reperfusion in anesthetized rabbits when administered prior to coronary occlusion. The cardiomyocyte mitochondrial K(ATP) channel may be a pharmacologically modulable target of cardioprotection and antiarrhythmic activity.

Mitochondrial KATP channel opener prevents ischemia-reperfusion injury in rat liver

Ischemia-reperfusion injury is responsible for the morbidity associated with liver surgery under total vascular exclusion or after liver transplantation. Recently, it has been reported that mitochondrial K(ATP) channel openers have an effect on myocardial protection via a pharmacological preconditioning action. However, it remains unclear as to whether K(ATP) channel openers can reduce ischemia-reperfusion injury in the liver. The aim of this study was to determine the effects of the mitochondrial K(ATP) channel opener, nicorandil, on ischemia-reperfusion injury in the rat liver. Male Wistar rats were subjected to 73% ischemia for 45 minutes followed by 120 minutes of reperfusion. Nicorandil (3 mg/kg) was orally administered 60 minutes before hepatic ischemia. Nicorandil significantly decreased plasma levels of alanine aminotransferase and lactate dehydrogenase by about 50% and inhibited the remarkably increased TUNEL-positive hepatocytes after reperfusion. Some mediators associated with apoptosis were analyzed by Western blotting. Cytochrome-c and caspase-3 levels in the cytosol increased after reperfusion; nicorandil inhibited the release of cytochrome-c and activation of caspase-3. The expression of Bax and Bcl-2 was significantly increased after reperfusion, being slightly inhibited by the administration of nicorandil. These results suggest that the protective effects of nicorandil against hepatic ischemia-reperfusion injury correlate with the inhibition of mitochondrial cytochrome-c release and caspase-3 activation. These findings demonstrate that nicorandil may become a therapeutic drug for ischemia reperfusion-related liver injury.

Infarct size limitation by nicorandil: roles of mitochondrial K(ATP) channels, sarcolemmal K(ATP) channels, and protein kinase C

OBJECTIVES

This study aimed to examine:1) whether nicorandil protects the ischemic myocardium by activating sarcolemmal adenosine triphosphate (ATP)-sensitive K(+) (sarcK(ATP)) channels or the mitochondrial K(ATP) (mitoK(ATP)) channels, and 2) whether protein kinase C (PKC) activity is necessary for cardioprotection afforded by nicorandil.

BACKGROUND

Nicorandil is a hybrid of nitrate and a K(ATP) channel opener that activates the sarcK(ATP) and mitoK(ATP) channels. Both of these K(ATP) channels are regulated by PKC, and this kinase may be activated by nitric oxide and also by oxygen free radicals (OFR) generated after mitoK(ATP) channel opening.

METHODS

In isolated rabbit hearts, infarction was induced by 30-min global ischemia/2-h reperfusion with monitoring of the activation recovery interval (ARI), an index of action potential duration. Protein kinase C translocation was assessed by Western blotting.

RESULTS

Nicorandil did not change ARI before ischemia, but it accelerated ARI shortening after the onset of ischemia and reduced infarct size by 90%. A sarcK(ATP) channel selective blocker, HMR1098, abolished acceleration of ischemia-induced ARI-shortening by nicorandil and eliminated 40% of nicorandil-induced infarct size limitation. A mitoK(ATP) channel selective blocker, 5-hydroxydecanoate, abolished the protection afforded by nicorandil without affecting ARI. Cardioprotection by nicorandil was inhibited neither by an OFR scavenger, N-2-mercaptopropionylglycine nor by a PKC inhibitor, calphostin C, at a dose that was capable of inhibiting PKC- epsilon translocation after preconditioning.

CONCLUSIONS

Both the sarcK(ATP) and mitoK(ATP) channels are involved in anti-infarct tolerance afforded by nicorandil, but PKC activation induced by nitric oxide or OFR generation, if any, does not play a crucial role.

Left ventricular remodeling after infarction: sequential MR imaging with oral nicorandil therapy in rat model

PURPOSE

To use magnetic resonance (MR) imaging in quantification of the short- and long-term effects of therapy with orally administered nicorandil on left ventricular (LV) geometry and function independent of infarction size.

MATERIALS AND METHODS

Forty-six rats were subjected to reperfused infarction and randomly divided into two groups. Group 1 rats (n = 21) were treated with nicorandil (3 mg/kg/day in drinking water) for 4 days before infarction and 8 weeks after infarction (hereafter, the nicorandil group). Group 2 rats (n = 25) received tap water for the same period and served as the control group. Mesoporphyrin- (as a necrosis-specific agent) enhanced MR imaging was used to define necrotic myocardium on day 2 after infarction in all 46 animals. Contrast material-enhanced MR images showed large but identical infarction size in 11 control and 11 nicorandil rats. Only these 22 rats underwent repeat MR imaging at 8 weeks after infarction. The following variables were measured: LV volumes, ejection fraction, mass, wall thickness, and infarction size. Student t test and analysis of variance for repeated measurements were used for statistical analysis.

RESULTS

The size of the necrotic region on mesoporphyrin-enhanced MR images was 39% +/- 3 of the size of the left ventricle in the control group and 41% +/- 2 in the nicorandil group (difference not significant, unpaired Student t test). Pretreatment with nicorandil for 6 days before imaging did not reduce LV dilation or improve function compared with those in control animals with identical infarction size. Eight weeks after infarction, control animals showed deterioration in LV function, wall thinning, and gradient in regional dysfunction (analysis of variance test). Nicorandil produced significant salutary effects on LV ejection fraction (37% +/- 3 in the nicorandil group vs 24% +/- 3 in the control group), end-diastolic volume (0.53 mL +/- 0.03 vs 0.65 mL +/- 0.04), end-systolic volume (0.36 mL +/- 0.03 vs 0.49 mL +/- 0.05), LV wall thickening in remote noninfarcted myocardium (28% +/- 2 vs 19% +/- 1), and a rim of infarction (16% +/- 2 vs 8% +/- 1) (P <.05 for all parameters). The increase in LV mass was reduced in the nicorandil group (0.73 g +/- 0.03) compared with that in the control group (0.89 g +/- 0.04) (P <.05).

CONCLUSION

In animals studied longitudinally, MR imaging demonstrated the deleterious changes in LV geometry and function in the period after infarction and the salutary effects of medical therapy.

Nicorandil preserves mitochondrial function during ischemia in perfused rat heart

A possible mechanism for the action of nicorandil on the improvement of energy metabolism of ischemic/reperfused hearts was examined. Perfused rat hearts were subjected to 35-min ischemia/60-min reperfusion. The heart was treated with nicorandil at concentrations of 10 to 100 microM for the last 30-min of pre-ischemia. Nicorandil preserved the mitochondrial oxygen consumption rate during ischemia and attenuated the decrease in mitochondrial function during reperfusion in association with the enhanced post-ischemic recovery of the left ventricular developed pressure. To assess the direct effect on mitochondria, myocardial saponin-skinned bundles were incubated under hypoxic conditions in vitro. Hypoxia-induced decrease in the mitochondrial oxygen consumption rate was attenuated by treatment of the bundles with 100 microM nicorandil. This attenuation was abolished by the combined treatment with the K(ATP) channel blocker, 5-hydroxydecanoate (5-HD). These results suggest that nicorandil is capable of attenuating ischemia/reperfusion injury of isolated perfused hearts through preservation of mitochondrial function during ischemia.

Selective mitochondrial K(ATP) channel activation results in antiarrhythmic effect during experimental myocardial ischemia/reperfusion in anesthetized rabbits

We investigated the effects of administration of non-hypotensive doses of ATP-sensitive K+ channel (K(ATP)) openers (nicorandil and aprikalim), and a specific mitochondrial K(ATP) channel blocker (5-hydroxydecanoate) prior to and during coronary occlusion as well as prior to and during post-ischemic reperfusion on survival rate, ischemia/reperfusion-induced arrhythmias and myocardial infarct size in anesthetized albino rabbits. Arrhythmias were induced by reperfusion following a 20 min ligation of the left main coronary artery with a releaseable silk ligature. Early intervention by intravenous infusion of nicorandil (100 microg/kg bolus+10 microg/kg/min) or aprikalim (10 microg/kg bolus+0.1 microg/kg/min) just before and during ischemia increased survival rate (86% and 75% vs. 55% in the control group), significantly decreased the incidence and severity of life-threatening arrhythmias and myocardial infarct size. The antiarrhythmic and cardioprotective effects of both nicorandil and aprikalim were abolished by pretreating the rabbits with 5-hydroxydecanoate (5 mg/kg, i.v. bolus). In conclusion, intervention by intravenous administration of nicorandil and aprikalim (through the selective activation of mitochondrial K(ATP) channels) increased survival rate and exhibited antiarrhythmic and cardioprotective effects during coronary occlusion and reperfusion in anesthetized rabbits when administered prior to and during coronary occlusion.

Effects of nicorandil administration on survival rate and arrhythmias during reperfusion in anesthetized rabbits

The aim was to study the effects of nicorandil (an ATP-sensitive K+ channel opener) and tolbutamide (an ATP-sensitive K+ channel blocker) on reperfusion-induced arrhythmias in pentobarbitone and ketamine anesthetized rabbits. Arrhythmias were induced by reperfusion for 20 min following a 15-min ligation of the left main coronary artery with a silk ligature. Rabbits were pretreated with nicorandil (0.47, 0.93 or 1.86 mg/kg i.v.) or tolbutamide (180 mg/kg i.p.) or vehicle (dimethylsulfoxide/saline) before the coronary artery occlusion. In the control group (n = 10), only 60% of the animals survived during reperfusion. Intravenous pretreatment with 0.47, 0.93 or 1.86 mg/kg of nicorandil increased the survival rate to 86% (n = 7), 75% (n = 8) and 86% (n = 7), respectively. Nicorandil pretreatment significantly decreased the incidence and duration of reperfusion-induced life-threatening arrhythmias and increased the number of animals that survived without developing any arrhythmia. Tolbutamide pretreatment was associated with a decreased survival rate of 50% (n = 12) and an increase in the incidence and duration of reperfusion-induced arrhythmias. Pretreatment with nicorandil may result in protection against reperfusion-induced arrhythmias and increased survival in anesthetized rabbits.

Synergistic effect of nicorandil and amlodipine on mitochondrial function during isoproterenol-induced myocardial infarction in rats

The synergistic effects of nicorandil (KATP-channel opener) and amlodipine (calcium-channel blocker) on heart mitochondrial enzymes and the mitochondrial antioxidant defence system was examined on isoproterenol-induced myocardial infarction in rats. The rats given isoproterenol (150 mg kg(-1) daily, i.p.) for two days showed significant changes in marker enzymes, mitochondrial enzymes and the mitochondrial defence system. Pre-co-treatment with nicorandil (2.5 mg kg(-1) daily, p.o.) and amlodipine (5.0 mg kg(-1) daily, p.o.) for 3 days significantly prevented these alterations and restored enzyme activity to near normal. These findings demonstrate the protective and synergistic effect of nicorandil and amlodipine in combination against isoproterenol-induced cardiac damage.

Nicorandil metabolism in rat myocardial mitochondria

The in vitro study using rats was carried out to clarify the hypothesis that nicorandil is denitrated and then may produce nitric oxide (NO) in myocardial mitochondria. In the presence of a NADPH-generating system, [14C]nicorandil, which was incubated in mitochondrial and microsomal fractions of the lung, heart, or liver, was converted to its main denitrated metabolite, SG-86 and other metabolites. Apparent Km and Vmax for nicorandil in mitochondrial and microsomal fractions of the heart were considerably similar to those of the lung, but completely different from those of the liver. It seems that glutathione-S-transferases (GSTs) are not primarily involved in the conversion of nicorandil to SG-86, because a known GST inhibitor, indomethacin, did not affect the nicorandil degradation in the mitochondrial fraction. Nitrite, the stable metabolite of NO, was measured by the Griess reaction. In the presence of an NADPH-generating system, nicorandil significantly increased nitrite production in myocardial mitochondria, but SG-86 did not. These data strongly indicate that nicorandil is metabolized to SG-86 in myocardial mitochondria, then releasing NO, and that GSTs are not primarily responsible for the conversion of nicorandil to SG-86.

Nicorandil, a potent cardioprotective agent, acts by opening mitochondrial ATP-dependent potassium channels

OBJECTIVES

To determine the mechanism of cardioprotection afforded by nicorandil, an orally efficacious antianginal drug, we examined its effects on ATP-dependent potassium (K(ATP)) channels.

BACKGROUND

Nicorandil can mimic ischemic preconditioning, while mitochondrial K(ATP) (mitoK(ATP)) channels rather than sarcolemmal K(ATP) (surfaceK(ATP)) channels have emerged as the likely effectors.

METHODS

Flavoprotein fluorescence and membrane current in intact rabbit ventricular myocytes were measured simultaneously to assay mitoK(ATP) channel and surface K(ATP) channel activities, respectively. In a cell-pelleting model of ischemia, cells permeable to trypan blue were counted as killed by 60 and 120 min of ischemia.

RESULTS

Nicorandil (100 micromol/liter) increased flavoprotein oxidation but not membrane current; a 10-fold higher concentration recruits both mitoK(ATP) and surfaceK(ATP) channels. Pooled dose-response data confirm that nicorandil concentrations as low as 10 micromol/liter turn on mitoK(ATP) channels, while surfaceK(ATP) current requires exposure to millimolar concentrations. Nicorandil blunted the rate of cell death in a pelleting model of ischemia; this cardioprotective effect was prevented by the mitoK(ATP) channel blocker 5-hydroxydecanoate but was unaffected by the surfaceK(ATP) channel blocker HMR1098.

CONCLUSIONS

Nicorandil exerts a direct cardioprotective effect on heart muscle cells, an effect mediated by selective activation of mitoK(ATP) channels.