hmr-1098 and Disease-Models--Animal

The mechanisms responsible for anti-arrhythmic protection during ischemia-reperfusion (IR) in exercised hearts are not fully understood. The purpose of this investigation was to examine whether the ATP-sensitive potassium channels in the mitochondria (mito K(ATP)) and sarcolemma (sarc K(ATP)) provide anti-arrhythmic protection in exercised hearts during IR. Male Sprague-Dawley rats were randomly assigned to cardioprotective treadmill exercise or sedentary conditions before IR (I = 20 min, R = 30 min) in vivo. Subsets of exercised animals received pharmacological inhibitors for mito K(ATP) (5-hydroxydecanoate) or sarc K(ATP) (HMR1098) before IR. Blinded analysis of digital ECG tracings revealed that mito K(ATP) inhibition blunted the anti-arrhythmic effects of exercise, while sarc K(ATP) inhibition did not. Endogenous antioxidant enzyme activities for total, CuZn, and Mn superoxide dismutase, catalase, and glutathione peroxidase from ischemic and perfused ventricular tissue were not mitigated by IR, although oxidative stress was elevated in sedentary and mito K(ATP)-inhibited hearts from exercised animals. These findings suggest that the mito K(ATP) channel provides anti-arrhythmic protection as part of exercise-mediated cardioprotection against IR. Furthermore, these data suggest that the observed anti-arrhythmic protection may be associated with preservation of redox balance in exercised hearts.

Topics: Animals; Arrhythmias, Cardiac; Benzamides; Catalase; Decanoic Acids; Disease Models, Animal; Electrocardiography; Glutathione Peroxidase; Hydroxy Acids; KATP Channels; Male; Mitochondria, Heart; Myocardial Reperfusion Injury; Myocardium; Oxidation-Reduction; Oxidative Stress; Physical Exertion; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Sprague-Dawley; Sarcolemma; Superoxide Dismutase

Whether nicorandil is effective at preventing ventricular tachyarrhythmia (VT) during acute myocardial ischaemia is still controversial. We examined effects of nicorandil on the induction of VT during acute myocardial ischaemia. Optical action potentials were recorded from the entire transmural wall of arterially perfused canine left ventricular wedges. Ischaemia was produced by arterial occlusion for 20 min. During endocardial pacing, nicorandil shortened mean action potential duration (APD) in the transmural wall before ischaemia and further shortened it during ischaemia without increasing dispersion of APD. HMR1098, a selective blocker of sarcolemmal ATP-sensitive K(+) channels, inhibited the shortening of APD by nicorandil before and during ischaemia. Ischaemia decreased transmural conduction velocity (CV). Nicorandil partially restored CV to a similar extent in the absence and presence of HMR1098. In contrast, HMR1098 did not suppress the ischaemic conduction slowing in the absence of nicorandil. Nicorandil suppressed the increased dispersion of local CV during ischaemia. Isochrone maps on the initiation of VT showed that reentry in the transmural surface resulted from the excitation of the epicardial region of transmural surface. Nicorandil significantly increased the size of non-excited area in the epicardial region of the transmural wall, thereby significantly reducing the incidence of VT induced during ischaemia. HMR1098 inhibited this effect of nicorandil. These results suggest that nicorandil prevents VT during acute global ischaemia primarily by augmenting the inactivation of epicardial muscle through the activation of sarcolemmal K(ATP) channels.

Topics: Action Potentials; Animals; Anti-Arrhythmia Agents; Benzamides; Disease Models, Animal; Dogs; Drug Antagonism; Electric Stimulation; Heart Ventricles; Male; Myocardial Ischemia; Nicorandil; Organ Culture Techniques; Perfusion; Spectrometry, Fluorescence; Tachycardia; Ventricular Dysfunction, Left

The aim of this study was to investigate the effects of HMR1098, a selective blocker of sarcolemmal ATP-sensitive potassium channel (sarcK(ATP)), in Langendorff-perfused rat hearts submitted to ischemia and reperfusion. The recovery of heart hemodynamic and mitochondrial function, studied on skinned fibers, was analyzed after 30-min global ischemia followed by 20-min reperfusion. Infarct size was quantified on a regional ischemia model after 2-h reperfusion. We report that the perfusion of 10 microM HMR1098 before ischemia, delays the onset of ischemic contracture, improves recovery of cardiac function upon reperfusion, preserves the mitochondrial architecture, and finally decreases infarct size. This HMR1098-induced cardioprotection is prevented by 1 mM 2-mercaptopropionylglycine, an antioxidant, and by 100 nM nifedipine, an L-type calcium channel blocker. Concomitantly, it is shown that HMR1098 perfusion induces (i) a transient and specific inhibition of the respiratory chain complex I and, (ii) an increase in the averaged intracellular calcium concentration probed by the in situ measurement of indo-1 fluorescence. Finally, all the beneficial effects of HMR1098 were strongly inhibited by 5-hydroxydecanoate and abolished by glibenclamide, two mitoK(ATP) blockers. This study demonstrates that the HMR1098-induced cardioprotection occurs indirectly through extracellular calcium influx, respiratory chain complex inhibition, reactive oxygen species production and mitoK(ATP) opening. Taken together, these data suggest that a functional interaction between sarcK(ATP) and mitoK(ATP) exists in isolated rat heart ischemia model, which is mediated by extracellular calcium influx.

Topics: Adenosine Triphosphate; Animals; Benzamides; Disease Models, Animal; Electron Transport Complex I; Male; Mitochondria, Heart; Myocardial Ischemia; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Sarcolemma

Both glycogen synthase kinase 3beta (GSK3beta) and the ATP-dependant potassium channel (K(ATP)) mediate opioid-induced cardioprotection (OIC). However, whether direct K(ATP) channel openers induce cardioprotection prior to reperfusion and their signaling cascade position with respect to GSK3beta inhibition is unknown. Therefore, we investigated the role of K(ATP) channel opening at reperfusion in OIC, and the interaction between the GSK signaling axis and K(ATP) channels in cardioprotection.Male Sprague-Dawley rats underwent 30 minutes ischemia with 2 hours of reperfusion and infarct size was determined. Rats given the nonselective opioid agonist, morphine (0.3 mg/kg), or the selective delta opioid agonist, BW373U86 (1.0 mg/kg), 5 minutes prior to reperfusion reduced infarct size (40.3+/-1.6*, 39.7+/-1.9* versus 60.0+/-1.1%, respectively, * P<0.001%). This protection was abrogated with prior administration of the putative sarcolemmal K(ATP) antagonist, HMR-1098 (6 mg/kg), or the putative mitochondrial K(ATP) antagonist, 5-HD (10 mg/kg). The putative sK(ATP) channel opener, P-1075 (1microg/kg) or the putative mK(ATP) channel opener, BMS-191095 (1 mg/kg) given 5 minutes prior to reperfusion also reduced infarct size (41.8+/-2.4*, 43.4+/-1.4*) and protection was abrogated by prior administration of the PI3k inhibitor wortmannin (60.0+/-1.7, 64.0+/-2.6%, respectively, * P<0.001). Cardioprotection afforded by the GSK inhibitor SB216763 (0.6 mg/kg) given 5 minutes prior to reperfusion was also partially blocked by either HMR or 5-HD and completely blocked when HMR and 5-HD were given in combination (40.8+/-1.6*, 50.4+/-1.6;; 49.4+/-1.7;, 61.6+/-1.6%, respectively, * or ; P<0.001). These data indicate that both the sK(ATP) and mK(ATP) channel are involved in acute OIC and the GSK signaling axis regulates cardioprotection via K(ATP) channel opening.

Topics: Analgesics, Opioid; Androstadienes; Animals; Benzamides; Benzopyrans; Blood Pressure; Cardiotonic Agents; Disease Models, Animal; Glycogen Synthase Kinase 3; Glycogen Synthase Kinase 3 beta; Guanidines; Heart Rate; Imidazoles; Indoles; Ion Channel Gating; Male; Maleimides; Morphine; Myocardial Infarction; Myocardial Reperfusion Injury; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Piperazines; Potassium Channel Blockers; Potassium Channels; Protein Kinase Inhibitors; Pyridines; Rats; Rats, Sprague-Dawley; Sarcolemma; Signal Transduction; Time Factors; Wortmannin

The blockade of myocardial K(ATP) channels may be antiarrhythmic for ischemic arrhythmias. A new sulfonylthiourea, HMR1098 (1-[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenylsulfonyl]-3-methylthiourea, sodium salt), was demonstrated to be a cardioselective K(ATP)-channel antagonist and to suppress arrhythmias during acute ischemia. We investigated effects of HMR1098 on the arrhythmias induced by programmed electrical stimulation (PES) in a canine old myocardial infarction model. HMR1098 (3 mg/kg, i.v.) significantly improved the scores of PES-induced ventricular arrhythmias, without changing the blood glucose concentrations. A classical sulfonylurea, glibenclamide (1 mg/kg, i.v.), had no significant effects on these arrhythmias, but reduced the blood glucose and increased the plasma insulin concentrations.

Topics: Adenosine Triphosphate; Animals; Arrhythmias, Cardiac; Benzamides; Disease Models, Animal; Dogs; Electric Stimulation; Female; Glyburide; Male; Myocardial Infarction; Potassium Channel Blockers; Potassium Channels; Sarcolemma

ST elevation is a classical hallmark of acute transmural myocardial ischemia. Indeed, ST elevation is the major clinical criterion for committing patients with chest pain to emergent coronary revascularization. Despite its clinical importance, the mechanism of ST elevation remains unclear. Various studies have suggested that activation of sarcolemmal ATP-sensitive potassium (K(ATP)) channels by ischemic ATP depletion may play a role, but little direct evidence is available. We studied mice with homozygous knockout (KO) of the Kir6.2 gene, which encodes the pore-forming subunit of cardiac surface K(ATP) channels. Patch-clamp studies in cardiomyocytes confirmed that surface K(ATP) current was indeed absent in KO, but robust in cells from wild-type mice (WT). We then measured continuous electrocardiograms in anesthetized adult mice before and after open-chest ligation of the left anterior descending artery (LAD). Whereas ST elevation was readily evident in WT after LAD ligation, it was markedly suppressed in KO. Such qualitative differences persisted for the rest of the 60-minute observation period of ischemia. In support of the concept that K(ATP) channels are responsible for ST elevation, the surface K(ATP)channel blocker HMR1098 (5 mg/kg IP) suppressed early ST elevation in WT. Thus, the opening of sarcolemmal K(ATP)channels underlies ST elevation during ischemia. These data are the first to link a specific gene product with a common electrocardiographic phenomenon.

Topics: Adenosine Triphosphate; Animals; Benzamides; Disease Models, Animal; Electrocardiography; Heart Conduction System; In Vitro Techniques; Mice; Mice, Knockout; Myocardial Ischemia; Patch-Clamp Techniques; Potassium; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Inwardly Rectifying; Sarcolemma