thiourea and clamikalant

Sudden cardiac death resulting from ventricular tachyarrhythmias remains the leading cause of death in industrially developed countries, accounting for between 300,000 and 500,000 deaths each year in the United States. Yet, despite the enormity of this problem, the development of safe and effective anti-arrhythmic agents remains elusive. The identification of effective anti-arrhythmic agents is critically dependent upon the use of appropriate animal models of human disease. During the last 25 years, a canine model of sudden cardiac death has proven to be useful in both the identification of factors contributing to ventricular fibrillation (VF) and the evaluation of potential anti-arrhythmic therapies. The present review provides a detailed retrospective analysis of the data obtained with this model. Briefly, VF was reliably and reproducibly induced by the combination of acute myocardial ischemia at site distant from a previous myocardial infarction during submaximal exercise (to activate the autonomic nervous system). This exercise plus ischemia test identified 2 stable populations of dogs: those that development malignant arrhythmias (susceptible, n=303) and those that rarely developed even single premature ventricular activation (resistant, n=209). The susceptible animals exhibited an elevated sympathetic activation (due to an enhanced beta2-adrenoceptor responsiveness) and a subnormal parasympathetic regulation. Several interventions have proven to be particularly effective in preventing VF in the susceptible dogs; including calcium channel antagonists, left stellate ganglion disruption, ATP-sensitive potassium channel antagonists, beta-adrenoceptor antagonists, and non-pharmacological interventions (endurance exercise training and dietary omega-3 fatty acids).

Topics: Animals; Anti-Arrhythmia Agents; Autonomic Nervous System; Blood Pressure; Calcium; Death, Sudden, Cardiac; Disease Models, Animal; Dogs; Electrocardiography; Exercise; Fish Oils; Heart; Heart Rate; Humans; Sulfonamides; Thiourea; Ventricular Fibrillation

There is increasing evidence for a fatal interaction of myocardial ischemia, ventricular arrhythmias and sudden cardiac death in some patients with coronary artery disease. Evidence comes from autopsy studies, from the evaluation of patients who survived an episode of sudden cardiac death, from follow-up data of these patients either treated or not by revascularization therapy and/or an implantable cardioverter-defibrillator and indicate that reducing the individual ischemic burden will be beneficial to reduce the incidence of sudden cardiac death. Studies in patients with stable and especially with unstable angina using Holter monitoring could demonstrate that there is a close and causal relationship between myocardial ischemia inducing or aggravating life-threatening ventricular arrhythmias and sudden cardiac death particularly in patients with unstable and postinfarction status. This review summarizes some of our clinical knowledge on this topic and indicates that preventive strategies for myocardial ischemia are the antiarrhythmic treatment of choice in patients with severe coronary artery disease and patients with evidence or at risk for ischemic proarrhythmia.

Topics: Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; Atrial Fibrillation; Autopsy; Blood Coagulation; Coronary Disease; Death, Sudden, Cardiac; Defibrillators, Implantable; Electrocardiography; Humans; Ligation; Male; Middle Aged; Multivariate Analysis; Myocardial Ischemia; Myocardial Revascularization; Potassium Channel Blockers; Risk; Risk Factors; Sulfonamides; Tachycardia, Ventricular; Thiourea; Time Factors

Topics: Adenosine Triphosphate; Animals; Benzamides; Decanoic Acids; Humans; Hydroxy Acids; Ischemic Preconditioning; Mitochondria, Heart; Potassium Channels; Sulfonamides; Thiourea

ATP-dependent potassium (K(ATP)) channels exist in high density in the sarcolemmal membrane of heart muscle cells. Under normoxic conditions these channels are closed, but they become active when the intracellular ATP level falls. This leads to a shortening of the action potential duration, rendering the heart susceptible for life-threatening arrhythmias. Molecular biology has revealed that K(ATP) channels consist of heteromultimers of the inwardly rectifying channel Kir6.2 and the sulfonylurea receptor SUR. To date, three types of SURs were identified, representing the pancreatic (SUR1), the cardiac (SUR2A) and the smooth muscle (SUR2B) K(ATP) channel. In order to develop a novel therapeutic principle against ischemia-induced life-threatening arrhythmias leading to sudden cardiac death, the cardioselective K(ATP) channel blocker HMR 1883 was developed. This substance inhibits the sarcolemmal cardiac K(ATP) channel activated by the channel opener rilmakalim half-maximally at concentrations of 0.6-2.2 micromol/l, and substantially affects pancreatic K(ATP) channels at 9-50 times higher concentrations. K(ATP) channels of the coronary vascular system are only slightly blocked by HMR 1883 when activated by hypoxia. The substance was potently effective in preventing ventricular fibrillation in a conscious dog model, and thus can be considered to be a potential novel drug candidate against sudden cardiac death.

Topics: Adenosine Triphosphate; Animals; Dogs; Heart; Humans; Potassium Channel Blockers; Potassium Channels; Sulfonamides; Thiourea

Patients with sustained ventricular tachyarrhythmias are at high risk for sudden cardiac death. The mechanisms leading to multiple temporally related episodes of ventricular fibrillation (VF) are not yet fully elucidated, and treatment options are limited. We investigated whether K(ATP)-channels could be involved in triggering VF.. We determined postarrhythmic changes of monophasic action potentials (MAP) after repetitive induction of VF in 32 Langendorff-perfused rabbit hearts.. Postarrhythmic action potential duration (APD) was significantly shorter compared with baseline (100 +/- 12 ms vs. 140 +/- 8 ms, P < 0.05). With increasing numbers of VF and shortening of recovery intervals between VF episodes (2 min) inducibility of VF increased, and abbreviation of APD became more prominent (90 +/- 5 ms vs. 130 +/- 4 ms, P < 0.05). Pre-treatment with the selective K(ATP) blocking agent HMR 1883 led to a significant increase of postarrhythmic APDs compared with control hearts (100 +/- 12 ms vs. 118 +/- 3 ms, P = 0.0013). Moreover, HMR 1883 significantly reduced inducibility of VF and increased the rate of successful defibrillation.. Repetitive episodes of VF result in postarrhythmic abbreviation of APDs, a phenomenon thought to be of potential relevance for incessant tachyarrhythmias in patients. Prevention of postarrhythmic MAP-shortening by HMR 1883 might be useful in suppressing VF.

Topics: Action Potentials; Animals; Cardiac Pacing, Artificial; Disease Models, Animal; Female; In Vitro Techniques; Male; Potassium Channel Blockers; Potassium Channels; Rabbits; Recurrence; Sulfonamides; Thiourea; Ventricular Fibrillation

ATP-dependent potassium channels (K(ATP)) have been implicated in cardioprotection both during myocardial ischemia and reperfusion. We compared the effect of a non-selective K(ATP) inhibitor glibenclamide, a selective mitochondrial K(ATP) inhibitor 5-hydroxy-decanoate (5-HD) and a selective sarcolemmal K(ATP) blocker HMR 1883, on survival and incidence of arrhythmias during myocardial ischemia in conscious, and during ischemia-reperfusion in pentobarbitone anesthetized rats. Glibenclamide (5 mg/kg i.p.) or HMR 1883 (3 mg/kg i.v.) reduced ischemia-induced irreversible ventricular fibrillation and improved survival during myocardial ischemia (64% and 61% vs. 23% in controls, respectively). 5-HD (5 mg/kg i.v.) did not influence survival and the incidence of ventricular arrhythmias. The incidence of reperfusion-induced arrhythmias was reduced by both glibenclamide and HMR 1883 (3 or 10 mg/kg) resulting in improved survival during reperfusion (81%, 82% and 96% vs. 24% in controls, respectively) in anesthetized rats. 5-HD did not reduce the incidence of lethal reperfusion arrhythmias. Glibenclamide and HMR 1883 prolonged (89+/-4.6 and 89+/-4.9 ms vs. 60+/-2.4 ms in controls), while 5-HD did not change the QT interval. In conclusion, inhibition of sarcolemmal K(ATP) reduces the incidence of lethal ventricular arrhythmias and improves survival both during acute myocardial ischemia and reperfusion in rats. This beneficial effect correlates with the prolongation of repolarization. Inhibition of mitochondrial K(ATP) does not improve survival or reduce the occurrence of ischemia and/or reperfusion-induced arrhythmias and does not prolong the QT interval. The present results also suggest that the antiarrhythmic effect of K(ATP) inhibitors is not influenced by pentobarbitone anesthesia.

Topics: Acute Disease; Anesthesia; Animals; Anti-Arrhythmia Agents; Autonomic Nervous System; Blood Pressure; Cell Membrane; Decanoic Acids; Electrocardiography; Glyburide; Heart; Hydroxy Acids; KATP Channels; Male; Organ Specificity; Potassium Channel Blockers; Rats; Rats, Sprague-Dawley; Reperfusion Injury; Sarcolemma; Sulfonamides; Survival; Thiourea; Ventricular Fibrillation

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 di

Topics: Anesthesia; Animals; Anti-Arrhythmia Agents; Antioxidants; Arrhythmias, Cardiac; ATP-Binding Cassette Transporters; Blood Gas Analysis; Cardiotonic Agents; Decanoic Acids; Electrocardiography; Glutathione; Hemodynamics; Hydroxy Acids; KATP Channels; Malondialdehyde; Minoxidil; Mitochondria, Heart; Myocardial Reperfusion Injury; Myocardium; Nicorandil; Oxidative Stress; Potassium Channel Blockers; Potassium Channels, Inwardly Rectifying; Rabbits; Sarcolemma; Sulfonamides; Superoxide Dismutase; Survival; Thiourea; Vasodilator Agents

In this study, we investigated whether a novel anti-ischemic KATP opener KR-31378 [(2S,3S,4R)-N"-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methly-2-dimethoxymethly-2H-benzopyran-4-yl)-N'-benzylguanidine] has protective effect against oxidative stress-induced death in heart-derived H9c2 cells. Cell death was induced by BSO, butionine sulfoximine, which inhibits GSH synthesis and subsequently increases reactive oxygen species (ROS) level. Cell death was quantitatively determined by measuring lactate dehydrogenase (LDH) activity and stained by Hoechst 33258. BSO-induced ROS production and mitochondrial membrane potential (MMP) were measured using 2',7'-dichlorofluorescein diacetate oxidation and rhodamine 123, respectively. Both the LDH release and the ROS elevation induced by treatment of H9c2 cells with 10 mM BSO, were significantly decreased by KR-31378. These protective effect and antioxidant effect of KR-31378 appeared to be independent on KATP channel opening. Cells exposed to BSO showed an early reduction in MMP, and this reduction in MMP was significantly reversed by treatment with KR-31378. Caspase-3 activity in BSO treated H9c2 cells was remarkably increased, and this increased caspase-3 activity was significantly reversed by KR-31378. In conclusion, our results suggest that KR-31378 can produce cardioprotective effect against oxidative stress-induced cell death through antioxidant mechanism.

Topics: Animals; Apoptosis; Benzimidazoles; Buthionine Sulfoximine; Caspase 3; Caspase Inhibitors; Caspases; Cell Line; Decanoic Acids; Dose-Response Relationship, Drug; Fluoresceins; Guanidines; Hydroxy Acids; L-Lactate Dehydrogenase; Membrane Potentials; Microscopy, Fluorescence; Mitochondrial Membranes; Myocytes, Cardiac; Oxidative Stress; Potassium Channel Blockers; Pyrans; Reactive Oxygen Species; Sulfonamides; Thiourea; Time Factors

We have used isolated myocytes to investigate the effects of diazoxide on sarcolemmal KATP channel (sarcoKATP) activity and action potential failure during metabolic inhibition, and the role of these channels in protection of functional recovery on reperfusion.. Isolated adult rat ventricular myocytes were exposed to metabolic inhibition (NaCN and iodoacetate) and reperfusion. Functional recovery was assessed from the ability of cells to contract on electrical stimulation and to recover calcium homeostasis, measured with fura-2. Action potentials and KATP currents were measured using patch clamp.. Pretreatment with diazoxide (100 microM, 5 min) increased the proportion of cells that recovered contractile function after MI and reperfusion from 16.8 +/- 2.4% to 65.0 +/- 2.2% (p<0.001) and the proportion of cells in which [Ca2+]i recovered to <250 nM. Pretreatment also accelerated action potential and contractile failure during MI. In cell-attached patches, MI activated sarcoKATP channels after 224 +/- 11 s, and diazoxide pretreatment decreased this to 145 +/- 24 s (p<0.01). However, diazoxide present in the patch pipette did not accelerate sarcoKATP channel activation. Intracellular Mg2+ rose earlier in diazoxide-pretreated cells. The sarcoKATP blocker HMR 1883 delayed action potential failure and reduced diazoxide protection.. Diazoxide pretreatment increases recovery of function and [Ca2+]i following reperfusion. Protection is coupled with early action potential failure, due to early activation of sarcoKATP channels during metabolic inhibition (MI), which is likely to involve an indirect effect of diazoxide.

Topics: Action Potentials; Animals; Antihypertensive Agents; Calcium; Diazoxide; Magnesium; Male; Myocardial Contraction; Myocardial Reperfusion Injury; Myocytes, Cardiac; Patch-Clamp Techniques; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Wistar; Sarcolemma; Sulfonamides; Thiourea

A novel compound KR-31378 [(2S,3S,4R)-N''-cyano-N-(6-amino-3,4-dihydro-3-hydroxy-2-methly-2-dimethoxy-methly-2H-benzo-pyran-4-yl)-N-benzylguanidine] has been demonstrated as an anti-ischemic agent in rat heart and brain. Here, we report the effects of this compound on hypoxia-induced cell death and possible signaling pathways in heart-derived H9c2 cells. Treatment with KR-31378 (3-30 microM) 1 h before and during hypoxia significantly reduced hypoxia-induced cell death in a concentration-dependent manner. In addition, increase in hypoxia-induced transferase UTP nick end labeling (TUNEL)-positive cells was reduced by KR-31378, suggesting its antiapoptotic potential in H9c2 cells. The protective effect conferred by KR-31378 (10 microM) was abolished by cotreatment with 5-hydroxydecanoate (5HD), a specific blocker of the mitochondrial KATP (mtKATP) channel, but not by HMR-1883 (1-[[5-[2-(5-chloro-o-anisamido)ethyl]-methoxyphenyl]sulfonyl]-3-methylthiourea), a specific blocker of the sarcolemmal KATP channel. We observed that the treatment with KR-31378 could increase the expression of protein kinase C (PKC)-epsilon protein, but not other PKC isotypes (-alpha, -beta, -delta, -zeta), in the particulate fraction. This increased level of PKC-epsilon was sustained during the hypoxic period up to 8 h. In addition, our results showed that treatment with KR-31378 induced the expression of PKC-epsilon mRNA as early as 15 min after the treatment. A specific inhibitor for PKC-epsilon isoform, epsilonV1-2, completely blocked the protective effect of KR-31378 against hypoxia-induced cell death. In conclusion, our results suggest that KR-31378 can protect cultured H9c2 cells from hypoxia-induced death via the mtKATP channel and PKC-epsilon.

Topics: Animals; Apoptosis; Blotting, Western; Cell Hypoxia; Cell Line; Decanoic Acids; Dose-Response Relationship, Drug; Guanidines; Hydroxy Acids; In Situ Nick-End Labeling; Membrane Proteins; Mitochondria, Heart; Myocytes, Cardiac; Potassium Channels; Protein Kinase C; Protein Kinase C-epsilon; Pyrans; Sulfonamides; Thiourea; Time Factors

The roles of cardiomyocyte sarcolemmal ATP-sensitive K+ (KATP) and mitochondrial KATP channels in cardioprotection and antiarrhythmic activity induced by KATP channel openers remain obscure. However, it has been suggested that the mitochondrial KATP channels are involved as a subcellular mediator in cardioprotection afforded by ischemic preconditioning. In the present study, we investigated the effects of the administration of non-hypotensive doses of ATP-sensitive K+ channel (KATP) openers (nicorandil and 3-pyridyl pinacidil), a specific mitochondrial KATP channel blocker (5-hydroxydecanoate) and a specific sarcolemmal KATP channel blocker (HMR 1883; 1-[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3- methylthiourea) prior to and during coronary occlusion, as well as prior to and during 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 = 80), occlusion of the left main coronary artery and hence, myocardial ischemia-induced arrhythmias were achieved by tightening a previously placed loose silk ligature for 30 min. In Group II (n = 186), arrhythmias were induced by reperfusion following a 20 min ligation of the left main coronary artery. In both Group I and Group II, early intravenous infusion of nicorandil (100 micrograms/kg bolus + 10 micrograms/kg/min), 3-pyridyl pinacidil (3.0 micrograms/kg bolus + 1.0 microgram/kg/min), HMR 1883 (3 mg/kg)/nicorandil and HMR 1883 (3 mg/kg)/3-pyridyl pinacidil, just prior to and during ischemia, increased survival rate (75%, 67%, 86% and 75% vs. 60% in the control subgroup in Group I; 67%, 75%, 75% and 67% vs. 43% in the control subgroup in Group II), significantly decreased the incidence and severity of life-threatening arrhythmias and significantly decreased myocardial infarct size. However, late intravenous administration of nicorandil or 3-pyridyl pinacidil at the onset of and during reperfusion did not increase survival rate nor confer any antiarrhythmic or cardioprotective effects. The antiarrhythmic and cardioprotective effects of both nicorandil and 3-pyridyl pinacidil were abolished by pretreating the rabbits with 5-hydroxydecanoate (5 mg/kg, i.v. bolus), a selective mitochondrial KATP channel blocker, but not by pretreatment with HMR 1883 (3 mg/kg). In the present study, high

Topics: Animals; Anti-Arrhythmia Agents; Antioxidants; Arrhythmias, Cardiac; Blood Pressure; Decanoic Acids; Electrocardiography; Heart Rate; Hydroxy Acids; Ion Channel Gating; Male; Membrane Proteins; Myocardial Ischemia; Myocardial Reperfusion Injury; Myocardium; Nicorandil; Oxidative Stress; Pinacidil; Potassium Channel Blockers; Potassium Channels; Rabbits; Sarcolemma; Sulfonamides; Survival Rate; Thiourea

The roles 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 investigated the effects of administration of non-hypotensive doses of ATP-sensitive K(+) channel (K(ATP)) openers (nicorandil and cromakalim), 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 and during coronary occlusion as well as prior to and during 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=80), occlusion of the left main coronary artery and hence, myocardial ischemia-induced arrhythmias were achieved by tightening a previously placed loose silk ligature for 30min. In Group II (n=184), arrhythmias were induced by reperfusion following a 20 min ligation of the left main coronary artery. Both in Groups I and II, early intravenous infusion of nicorandil (100 micro g/kg bolus+10 micro g/kg/min), cromakalim (0.2 micro g/kg/min), HMR 1883 (3mg/kg)/nicorandil and HMR 1883 (3mg/kg)/cromakalim just prior to and during ischemia increased survival rate (75%, 67%, 86% and 75% versus 60% in the control subgroup in Group I; 75%, 75%, 75% and 67% versus 50% in the control subgroup in Group II), significantly decreased the incidence and severity of life-threatening arrhythmias and significantly decreased myocardial infarct size. However, late intravenous administration of nicorandil or cromakalim at the onset and during reperfusion did neither increase survival rate nor confer any antiarrhythmic or cardioprotective effects. The antiarrhythmic and cardioprotective effects of both nicorandil and cromakalim were abolished by pretreating the rabbits with 5-HD (5mg/kg, i.v. bolus), a selective mitochondrial K(ATP) channel blocker but not by HMR 1883 (3mg/kg). In the present study, higher levels of malondialdehyde (MDA) and lower levels of reduced glutathione (GSH) and superoxide dismutase

Topics: Analysis of Variance; Animals; Anti-Arrhythmia Agents; Antihypertensive Agents; Arrhythmias, Cardiac; Blood Pressure; Cromakalim; Decanoic Acids; Disease Models, Animal; Glutathione; Heart Rate; Hydroxy Acids; Male; Malondialdehyde; Membrane Proteins; Myocardial Infarction; Myocardial Reperfusion Injury; Nicorandil; Oxidative Stress; Potassium Channels; Rabbits; Sarcolemma; Sulfonamides; Superoxide Dismutase; Survival Rate; Thiourea

The effects of K(ATP) channel blockers (glibenclamide, HMR 1883, HMR 1372) and openers (cromakalim, pinacidil, diazoxide) on the electrically-evoked (5 Hz) release of [(3)H]acetylcholine were studied in isolated guinea-pig atria and myenteric plexus-longitudinal muscle preparations which had been preincubated with [(3)H]choline. Atria: Cromakalim (0.3 microM and 1 microM), pinacidil (10 microM) and diazoxide (30 microM) significantly reduced the stimulation-evoked release of [(3)H]acetylcholine. The inhibition produced by cromakalim and pinacidil was prevented by 1 microM of either HMR 1883, HMR 1372 or glibenclamide. The blockers alone significantly increased the release at concentrations of 30 microM, whereas 1 microM and 10 microM had no effect. Myenteric plexus-longitudinal muscle preparation: The electrically-evoked release of [(3)H]acetylcholine was not affected by K(ATP) channel blockers or openers. In contrast, the contractions of the longitudinal muscle caused by electrical stimulation or by carbachol were strongly inhibited by 1 microM cromakalim which suggests that the relaxant effect of the K(ATP) channel openers is exclusively a direct effect on intestinal smooth muscle. The findings suggest that blockade of activated K(ATP) channels in vagal nerves of guinea-pig atria stimulates acetylcholine release, and that this effect may contribute to the antiarrhythmic actions of K(ATP) channel blockers. By contrast, release of acetylcholine from guinea-pig myenteric plexus is not modulated by K(ATP) channels which suggests heterogeneity of K(ATP) channel distribution in peripheral autonomic nerves.

Topics: Acetylcholine; Animals; Atrial Function; Cromakalim; Diazoxide; Female; Glyburide; Guinea Pigs; Heart Atria; In Vitro Techniques; Intestine, Small; Male; Muscle, Smooth; Myenteric Plexus; Myocardial Contraction; Neuromuscular Junction; Pinacidil; Potassium Channel Blockers; Potassium Channels; Sulfonamides; Thiourea

HMR 1883 (the free acid form of HMR 1098) selectively inactivates myocardial ATP sensitive potassium channels, which may be a potential important therapeutic approach to prevent life-threatening arrhythmias. This study was designed to assess the effects of HMR 1883 combined with adrenaline on haemodynamic variables, blood gases, and cardiac arrhythmias in a porcine cardiac arrest model.. After 8 min of untreated cardiac arrest, followed by 1 min of cardiopulmonary resuscitation (CPR), 12 pigs weighing 30-40 kg were assigned randomly to receive either 45 microg/kg adrenaline alone (n=6), or 45 microg/kg adrenaline combined with 3 mg/kg HMR 1883 (n=6), followed by up to three defibrillation attempts 2 min later. Five minutes after return of spontaneous circulation, cardiac arrest was induced for 1 min, with the CPR protocol following as described above. All animals subsequently underwent four cardiac arrest intervals of 1, 2, 3, and 4 min duration which were separated by four episodes of 5 min of return of spontaneous circulation.. Haemodynamic variables, cardiac arrhythmias in the acute resuscitation phase between termination of chest compressions and return of spontaneous circulation, and after return of spontaneous circulation in both groups were comparable throughout the experiment. Survival rates throughout the experiment were comparable between groups. Arterial blood gases, electrolyte, glucose, and lactate levels in both groups during the experiment indicated comparable severe metabolic acidosis, with increasing levels after each episode of simulated refibrillation, and subsequent return of spontaneous circulation.. Combining HMR 1883 with adrenaline during CPR resulted in comparable haemodynamic variables, return of spontaneous circulation rates, cardiac arrhythmias, lactate and glucose levels compared with adrenaline alone. This indicates that injection of HMR 1883 was safe under these conditions.

Topics: Animals; Blood Gas Analysis; Cardiopulmonary Resuscitation; Drug Therapy, Combination; Epinephrine; Heart Arrest; Hemodynamics; Models, Animal; Potassium Channel Blockers; Sulfonamides; Swine; Thiourea; Ventricular Fibrillation

Sulfonylthioureas exhibiting cardioselective blockade of ATP-sensitive potassium channels (K(ATP) channels) were discovered by stepwise structural variations of the antidiabetic sulfonylurea glibenclamide. As screening assays, reversal of rilmakalim-induced shortening of the cardiac action potential in guinea pig papillary muscles was used to probe for activity on cardiac K(ATP) channels as the target, and membrane depolarization in CHO cells stably transfected with hSUR1/hKir6.2 was used to probe for unwanted side effects on pancreatic K(ATP) channels. Changing glibenclamide's para-arrangement of substituents in the central aromatic ring to a meta-pattern associated with size reduction of the substituent at the terminal nitrogen atom of the sulfonylurea moiety was found to achieve cardioselectivity. An additional change from a sulfonylurea moiety to a sulfonylthiourea moiety along with an appropriate substituent in the ortho-position of the central aromatic system was a successful strategy to further improve potency on the cardiac K(ATP) channel. Among this series of sulfonylthioureas HMR1883, 1-[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea, and its sodium salt HMR1098 were selected for development and represent a completely new therapeutic approach toward the prevention of life-threatening arrhythmias and sudden cardiac death in patients with coronary heart disease.

Topics: Action Potentials; Adenosine Triphosphate; Animals; Anti-Arrhythmia Agents; Arrhythmias, Cardiac; ATP-Binding Cassette Transporters; CHO Cells; Cricetinae; Death, Sudden; Electric Stimulation; Female; Guinea Pigs; Heart; In Vitro Techniques; Male; Myocardial Contraction; Potassium Channel Blockers; Potassium Channels; Potassium Channels, Inwardly Rectifying; Receptors, Drug; Structure-Activity Relationship; Sulfonamides; Sulfonylurea Receptors; Thiourea

It has been argued that activation of KATP channels in the sarcolemmal membrane of heart muscle cells during ischemia provides an endogenous cardioprotective mechanism. In order to test whether the novel cardioselective KATP channel blocker HMR 1098 affects cardiac function during ischemia, experiments were performed in rat hearts during ischemia and reperfusion. Isolated perfused working rat hearts were subjected to 30 min of low-flow ischemia in which the coronary flow was reduced to 10% of its control value, followed by 30-min reperfusion. In the first set of experiments the hearts were electrically paced at 5 Hz throughout the entire protocol. At the end of the 30-min ischemic period the aortic flow had fallen to 44 +/- 2% (n=8) of its nonischemic value in vehicle-treated hearts, whereas in the presence of 0.3 micromol/l and 3 micromol/l HMR 1098 it had fallen to 29 +/- 7% (n=5, not significant) and 8 +/- 2% (n=12, P<0.05), respectively. Glibenclamide (3 micromol/l) reduced the aortic flow to 9.5 +/- 7% (n=4, P<0.05). In control hearts the QT interval in the electrocardiogram shortened from 63 +/- 6 ms to 36 +/- 4 ms (n=10, P<0.05) within 4-6 min of low-flow ischemia. This shortening was completely prevented by 3 micromol/l HMR 1098 (60 +/- 5 ms before ischemia, 67 +/- 6 ms during ischemia, n=9, not significant). When rat hearts were not paced, the heart rate fell spontaneously during ischemia, and HMR 1,098 (3 micromol/l) caused only a slight, statistically non-significant reduction in aortic flow during the ischemic period. In order to investigate whether HMR 1098 shows cardiodepressant effects in a more pathophysiological model, the left descending coronary artery was occluded for 30 min followed by reperfusion for 60 min in anesthetized rats. Treatment with HMR 1098 (10 mg/kg i.v.) had no statistically significant effects on mean arterial blood pressure and heart rate during the control, ischemia and reperfusion periods. At the end of the reperfusion period, aortic blood flow was slightly reduced by HMR 1098, without reaching statistical significance (two-way analysis of ANOVA, P=0.15). Myocardial infarct size as a percentage of area at risk was not affected by HMR 1098 (vehicle: 75 +/- 3%, HMR 1098: 72 +/- 2%, n=7 in each group). In conclusion, cardiodepressant effects of HMR 1098 were observed only in isolated perfused working rat hearts which were continuously paced during global low-flow ischemia. In the model of anesthetized rats subjected to

Topics: Anesthesia; Animals; Anti-Arrhythmia Agents; Benzamides; Glyburide; Heart; Hemodynamics; In Vitro Techniques; Male; Models, Animal; Myocardial Contraction; Myocardial Infarction; Myocardial Ischemia; Myocardial Reperfusion; Potassium; Potassium Channel Blockers; Rats; Rats, Wistar; Sulfonamides; Thiourea

The novel sulfonylthiourea 1-[[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl]-3-methylthiourea (HMR 1883), a blocker of ATP-sensitive K(+) channels (K(ATP) channels), has potential against ischemia-induced arrhythmias. Here, the interaction of HMR 1883 with sulfonylurea receptor (SUR) subtypes and recombinant K(ATP) channels is compared with that of the standard sulfonylurea, glibenclamide, in radioligand receptor binding and electrophysiological experiments. HMR 1883 and glibenclamide inhibited [(3)H]glibenclamide binding to SUR1 with K(i) values of 63 microM and 1.5 nM, and [(3)H]opener binding to SUR2A/2B with K(i) values of 14/44 microM and 0.5/2.8 microM, respectively (values at 1 mM MgATP). The interaction of HMR 1883 with the SUR2 subtypes was more sensitive to inhibition by MgATP and MgADP than that of glibenclamide. In inside-out patches and in the absence of nucleotides, HMR 1883 inhibited the recombinant K(ATP) channels from heart (Kir6.2/SUR2A) and nonvascular smooth muscle (Kir6.2/SUR2B) with IC(50) values of 0.38 and 1.2 microM, respectively; glibenclamide did not discriminate between these channels (IC(50) approximately 0.026 microM). In whole cells, the recombinant vascular K(ATP) channel, Kir6.1/SUR2B, was inhibited by HMR 1883 and glibenclamide with IC(50) values of 5.3 and 0.043 microM, respectively. The data show that the sulfonylthiourea exhibits a selectivity profile quite different from that of glibenclamide with a major loss of affinity toward SUR1 and slight preference for SUR2A. The stronger inhibition by nucleotides of HMR 1883 binding to SUR2 (as compared with glibenclamide) makes the sulfonylthiourea an interesting tool for further investigation.

Topics: ATP-Binding Cassette Transporters; Binding Sites; Cells, Cultured; Glyburide; Humans; Membrane Proteins; Patch-Clamp Techniques; Potassium Channels; Potassium Channels, Inwardly Rectifying; Radioligand Assay; Receptors, Drug; Recombinant Proteins; Sulfonamides; Sulfonylurea Receptors; Thiourea

ATP-sensitive potassium channels (KATP) open during myocardial ischemia. The ensuing repolarising potassium efflux shortens the action potential. Accumulation of extracellular potassium is able to partially depolarise the membrane, reducing the upstroke velocity of the action potential and thereby impairing impulse conduction. Both mechanisms are believed to be involved in the development of reentrant arrhythmias during cardiac ischemia. The sulfonylthiourea HMR 1883 (1-[[5-[2-(5-chloro-O-anisamido)ethyl]-methoxyphenyl]sulfonyl]-3-m ethylthiourea) was designed as a cardioselective KATP channel blocker for the prevention of arrhythmic sudden death in patients with ischemic heart disease. The aim of this study was to show that this compound, which has already shown antifibrillatory efficacy in dogs and rats, is able to inhibit ischemic changes of the action potential induced by coronary artery occlusion in anesthetised pigs. Action potentials were taken in situ with the technique of monophasic action potential (MAP) recording. In a control group (n=7), three consecutive occlusions of a small branch of the left circumflex coronary artery resulted in reproducible reductions in MAP duration and a decrease in upstroke velocity. In a separate group (n=7), HMR 1883 (3 mg/kg i.v.) significantly (P<0.05) reduced the ischemia-induced shortening of the MAP: during the first and second control occlusion of the coronary artery in the HMR 1883-group, MAP50 duration shortened from 218.5 +/- 3.0 ms to 166.7 +/- 3.3 ms and from 219.7 +/- 4.5 ms to 164.9 +/- 1.8 ms, respectively. After HMR 1883, during the third occlusion, MAP duration decreased from 226.9 +/- 3.6 ms to 205.3 +/- 4.3 ms only corresponding to 59% inhibition. HMR 1883 also improved the upstroke velocity of the MAP, which was depressed by ischemia: in the two preceding control occlusions ischemia prolonged the time to peak of the MAP, an index for upstroke velocity, from 10.83 +/- 0.43 ms to 39.42 +/- 1.60 ms and from 12.97 +/- 0.40 ms to 37.17 +/- 2.98 ms, respectively. With HMR 1883, time to peak during ischemia rose from 12.42 +/- 0.51 ms to 25.53+/-2.51 ms only, corresponding to an average inhibitory effect of 53.4%. The irregular repolarisation contour of the ischemic MAP was also improved. In conclusion, the present results indicate that HMR 1883 effectively blocks myocardial KATP channels during coronary ischemia in anesthetised pigs, preventing an excessive shortening of the action potential and improv

Topics: Action Potentials; Anesthesia; Animals; Anti-Arrhythmia Agents; Glyburide; Guinea Pigs; Heart; Male; Myocardial Ischemia; Myocardial Reperfusion; Potassium Channel Blockers; Sulfonamides; Swine; Thiourea

Sublethal periods of ischemia preceding a prolonged interval of ischaemia protect the myocardium. This myocardial preconditioning (PC) appears to be effected by KATP channels. These channels occur both in the sarcolemma and the mitochondrial membrane. We investigated whether mitochondrial KATP channels are the end-effector of PC in the human myocardium.. Right atrium specimens obtained from patients undergoing cardiac surgery were prepared and incubated in buffer solution at 37 degrees C. After 30-min stabilisation, the muscles were made ischemic for 90 min and then reperfused for 120 min. The preparations were randomised into eight experimental groups (n = 6/group): (1) Aerobic control--incubated in oxygenated buffer for 210 min, (2) ischemia alone--90 min ischemia followed by 120 min reperfusion, (3) PC--preconditioned with 5 min ischemia/5 min reperfusion, (4) Glibenclamide (10 microM) in the incubation media for 10 min before PC, (5) 5-hydroxydecanoate (5-HD, MitoKATP blocker, 1 mM) in the incubation media for 10 min before PC, (6) HMR 1883 (SarcKATP blocker, 10 microM) in the incubation media for 10 min before PC, (7) Pinacidil (0.5 mM) in the incubation media for 10 min before ischemia, and (8) Diazoxide (MitoKATP opener, 0.1 mM) in the incubation media for 10 min before ischemia. Creatinine kinase leakage into the medium (CK, IU/g wet wt) and MTT reduction (OD/mg wet wt.), an index of cell viability, were assessed at the end of the experiment.. Ischemia alone resulted in a significant increase in CK leakage (8.01 +/- 0.35) and decrease in MTT (0.15 +/- 0.01) from the values seen in the aerobic control (2.24 +/- 0.52 and 0.78 +/- 0.10 respectively, P < 0.05 in both instances). PC fully reversed the effect of ischemia (CK = 2.97 +/- 0.31 and MTT = 0.61 +/- 0.05; P < 0.05 vs. ischemia alone group but P = NS vs. aerobic control group). Both Glibenclamide and 5-HD abolished the protection induced by PC (CK = 6.23 +/- 0.5 and 7.84 +/- 0.64; MTT = 0.18 +/- 0.03 and 0.13 +/- 0.02, respectively, P < 0.05 vs. PC), but interestingly, the protective effect of PC was not abolished by HMR 1883 (CK = 2.85 +/- 0.24 and MTT = 0.58 +/- 0.05, P = NS vs. PC). Diazoxide mimicked the protective effect of PC (CK = 3.56 +/- 0.32 and MTT = 0.58 +/- 0.02, P = NS vs. PC), however pinacidil exhibited less protection than PC (CK = 4.02 +/- 0.16 and MTT = 0.30 +/- 0.02, P < 0.05 vs. PC).. These studies demonstrate that KATP channels are the end-effectors of ischemic preconditioning and that protection is mediated by mitochondrial KATP channels in human right atrial myocardium.

Topics: Analysis of Variance; Cell Membrane; Decanoic Acids; Diazoxide; Dose-Response Relationship, Drug; Glyburide; Heart; Humans; Hydroxy Acids; Hypoglycemic Agents; In Vitro Techniques; Ischemic Preconditioning, Myocardial; Mitochondria, Heart; Myocardial Ischemia; Pinacidil; Potassium Channel Blockers; Potassium Channels; Random Allocation; Sarcolemma; Sulfonamides; Thiourea

Previous experimental studies showed that the benefit of ischemic preconditioning (IPC) is abolished by K(ATP) channel blockade with glibenclamide. However, the newly discovered K(ATP) channel blocker HMR 1883 (1-[[5-[2-(5-chloro-o-anisamido)ethyl]-methoxyphenyl]sulfonyl]-3-m ethylthiourea) shows marked antifibrillatory activity in the dose range of 3 mg/kg to 10 mg/kg i.v. in various experimental models without affecting blood glucose levels. In order to investigate in a head to head comparison glibenclamide and HMR 1883 with respect to their influence on IPC, experiments were performed in rabbits with ischemia-reperfusion using myocardial infarct mass as final read out. Male New Zealand White rabbits (2.6-3.0 kg) were subjected to 30-min occlusion of a branch of the left descending coronary artery (LAD) followed by 2-h reperfusion. For IPC experiments the LAD was additionally occluded for two periods of 5 min, each followed by 10-min reperfusion, before the long-term ischemia. Infarct mass was evaluated by TTC staining and expressed as a percentage of area at risk. Rabbits (n=7/group) were randomly selected to receive (i.v.) saline vehicle 5 min prior to the 30-min occlusion period in infarct studies without IPC or to receive glibenclamide (0.3 mg/kg) or HMR 1883 (3 mg/kg) in IPC experiments, these substances being given 5 min prior to the first preconditioning or 5 min prior to the long-term ischemia of 30 min. Myocardial risk mass as a percentage of left ventricular mass did not differ between groups. The same was true for the ratio of left ventricular mass to 100 g body weight. Myocardial infarct mass as a percentage of the area at risk in the saline vehicle group without IPC was 41+/-3%. Whereas glibenclamide significantly increased infarct mass (from 41+/-3% to 55+/-4%), HMR 1883 did not affect it. IPC reduced infarct mass from 41+/-3% to 21+/-4% (P<0.05 vs. control without IPC). Glibenclamide given prior to IPC or prior to the long-term ischemia totally abolished the IPC effect (42+/-2% and 55+/-4%, respectively; P<0.05 vs. control). In contrast, HMR 1883 under the same conditions did not affect infarct size when given prior to IPC or prior to the long-term ischemia (21+/-3% and 26+/-2%, respectively). The monophasic action potential duration (MAP50) was reduced from 103+/-3 ms under normoxic conditions to 82+/-2 ms, 5 min after ischemia in the absence of drugs. This ischemia-induced shortening of the MAP was prevented by both HMR 1883 (MAP50 103+

Topics: Action Potentials; Adenosine Triphosphate; Animals; Blood Glucose; Glyburide; Heart; Ischemic Preconditioning, Myocardial; Male; Myocardial Infarction; Potassium Channel Blockers; Rabbits; Sulfonamides; Thiourea

Clinical evidence indicates an antiarrhythmic effect of sulfonylureas, which might be blunted by their vascular action. We wanted to investigate the effect of glibenclamide and the new sulfonylthiourea compound 1-[[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]-sulfonyl]-3 -me thylthiourea (HMR1883) on cardiac electrophysiology in the course of regional ischemia and reperfusion. Isolated rabbit hearts (Langendorff-technique) were pretreated with either vehicle (n=14), 3 micromol/l glibenclamide (n=7) or 3 micromol/l HMR1883 (n=7) before regional ischemia was induced by left coronary artery branch occlusion (45 min) followed by 45 min reperfusion. Unipolar epicardial electrocardiograms were recorded from 256 epicardial AgCl electrodes. Coronary ligation resulted in a decrease in coronary flow (CF) by 35% and in left ventricular pressure (LVP) by 40% in all series. The occluded zone was 23+/-3% in all series. Ischemia led to shortening of the epicardial activation-recovery interval (ARI) in the ischemic area, which was inhibited by both drugs especially in the early phase. In the non-ischemic area, ARIs remained stable and there was no effect of the drugs. Ischemia led to an increase in the regional difference in ARI between ischemic center and border zone. This increase was significantly inhibited by both substances during late ischemia and early reperfusion (until 15 min reperfusion). In addition, the dispersion of ARIs was reduced by both drugs during late ischemia and reperfusion. Ventricular fibrillation was observed in 7/14 (control), 0/7 (glibenclamide), and 0/7 (HMR1883). All ventricular fibrillation occurred during reperfusion. In glibenclamide but not in HMR1883-treated hearts recovery of CF upon reperfusion was significantly depressed (control: 25.5+/-4; HMR1883: 23+/-2.5; glibenclamide: 16+/-1 ml/min, values at 2 min reperfusion), while the elevation of ST-segments of the electrograms in early ischemia was fully prevented by both treatments. We conclude that both glibenclamide and HMR1883 exert an antiarrhythmic effect in this model, and reduce the shortening of the ARIs in the ischemic area, thus attenuating regional differences in ARIs between ischemic and non-ischemic area. Furthermore, unlike glibenclamide HMR1883 does not interfere with postischemic hyperemia.

Topics: Animals; Arrhythmias, Cardiac; Electrocardiography; Electrophysiology; Glyburide; Heart; In Vitro Techniques; Male; Myocardial Ischemia; Myocardial Reperfusion; Potassium Channel Blockers; Potassium Channels, Inwardly Rectifying; Rabbits; Sulfonamides; Thiourea; Ventricular Fibrillation

Adenosine-enhanced ischemic preconditioning (APC) extends the protection afforded by ischemic preconditioning (IPC) by both significantly decreasing infarct size and significantly enhancing postischemic functional recovery. The purpose of this study was to determine whether APC is modulated by ATP-sensitive potassium (K(ATP)) channels and to determine whether this modulation occurs before ischemia or during reperfusion. The role of K(ATP) channels before ischemia (I), during reperfusion (R), or during ischemia and reperfusion (IR) was investigated using the nonspecific K(ATP) blocker glibenclamide (Glb), the mitochondrial (mito) K(ATP) channel blocker 5-hydroxydecanoate (5-HD), and the sarcolemmal (sarc) K(ATP) channel blocker HMR-1883 (HMR). Infarct size was significantly increased (P < 0.05) in APC hearts with Glb-I, Glb-R, and 5-HD-I treatment and partially with 5-HD-R. Glb-I and Glb-R treatment significantly decreased APC functional recovery (P < 0.05 vs. APC), whereas 5-HD-I and 5-HD-R had no effect on APC functional recovery. HMR-IR significantly decreased postischemic functional recovery (P < 0.05 vs. APC) but had no effect on infarct size. These data indicate that APC infarct size reduction is modulated by mitoK(ATP) channels primarily during ischemia and suggest that functional recovery is modulated by sarcK(ATP) channels during ischemia and reperfusion.

Topics: Adenosine; Animals; Anti-Arrhythmia Agents; Calcium; Decanoic Acids; Glyburide; Hydroxy Acids; Hypoglycemic Agents; In Vitro Techniques; Ischemic Preconditioning, Myocardial; Mitochondria; Myocardial Stunning; Potassium Channel Blockers; Potassium Channels; Rabbits; Sarcolemma; Sulfonamides; Thiourea; Vasodilator Agents

ATP-sensitive potassium (K(ATP)) channels are activated during myocardial ischemia. The ensuing potassium efflux leads to a shortening of the action potential duration and depolarization of the membrane by accumulation of extracellular potassium favoring the development of reentrant arrhythmias, including ventricular fibrillation. The sulfonylthiourea HMR 1883 was designed as a cardioselective blocker of myocardial K(ATP) channels for the prevention of arrhythmic sudden death in patients with ischemic heart disease. We investigated the effect of HMR 1883 on sudden cardiac arrhythmic death and electrocardiography (ECG) changes induced by 20 min of left anterior descending coronary artery occlusion in pentobarbital-anesthetized pigs. HMR 1883 (3 mg/kg i.v.) protected pigs from arrhythmic death (91% survival rate versus 33% in control animals; n = 12; p<.05). Ischemic areas were of a similar size. The compound had no effect on hemodynamics and ECG, including Q-T interval, under baseline conditions and no effect on hemodynamics during occlusion. In control animals, left anterior descending coronary artery occlusion lead to a prompt and significant depression of the S-T segment (-0.35 mV) and a prolongation of the Q-J time (+46 ms), the former reflecting heterogeneity in the plateau phase of the action potentials and the latter reflecting irregular impulse propagation and delayed ventricular activation. Both ischemic ECG changes were significantly attenuated by HMR 1883 (S-T segment, -0.14 mV; Q-J time, +15 ms), indicating the importance of K(ATP) channels in the genesis of these changes. In conclusion, the K(ATP) channel blocker HMR 1883, which had no effect on hemodynamics and ECG under baseline conditions, reduced the extent of ischemic ECG changes and sudden death due to ventricular fibrillation during coronary occlusion.

Topics: Anesthesia; Animals; Arrhythmias, Cardiac; Coronary Disease; Death, Sudden, Cardiac; Electrocardiography; Hemodynamics; Myocardial Ischemia; Potassium; Sulfonamides; Swine; Thiourea

Ventricular fibrillation (VF) is a major cause of sudden cardiac death in which myocardial ischemia plays a leading role. During ischaemia activation of ATP-sensitive potassium channels (K(ATP)) occurs, leading to potassium efflux from cardiomyocytes and shortening of the action potential favoring the genesis of ventricular fibrillation. In confirmation of this concept the sulfonylurea glibenclamide, which stimulates insulin release by inhibition of pancreatic K(ATP) channels, has been shown to inhibit VF in different models of ischaemia by inhibition of myocardial K(ATP) channels. HMR 1883 (1-[15-12-(5-chloro-o-anisamido)ethyl]-methoxyphenyl]sulfonyl]-3-m ethylthiourea) was designed as a cardioselective K(ATP) channel blocker. The aim of this study was to show that with this compound it is possible to separate the antifibrillatory from the insulin-releasing effect for the treatment of patients at risk of ischaemia-induced arrhythmias and sudden death. In the present study HMR 1883 reduced VF in Sprague-Dawley rats during prolonged ischaemia and also diminished mortality and the duration of VF in a separate reperfusion experiment at 3 mg/kg and 10 mg/kg with no effect on blood glucose or insulin. Glibenclamide, which was antifibrillatory at 0.3 mg/kg and 1 mg/kg, increased plasma insulin and lowered blood glucose already at a dose as low as 0.01 mg/kg. In conclusion, based on its antifibrillatory action and the absence of significant pancreatic effects at therapeutic doses, HMR 1883 is of potential clinical utility for the prevention of severe arrhythmias in patients with ischaemic heart disease.

Topics: Adenosine Triphosphate; Administration, Oral; Animals; Arrhythmias, Cardiac; Arterial Occlusive Diseases; Blood Glucose; Blood Pressure; Dose-Response Relationship, Drug; Glyburide; Heart Rate; Injections, Intravenous; Insulin; Male; Myocardial Ischemia; Myocardial Reperfusion; Potassium Channel Blockers; Rats; Rats, Sprague-Dawley; Sulfonamides; Thiourea; Time Factors; Ventricular Fibrillation

During coronary angioplasty, a stair-step decrease in peak S-T segment elevation from the first to the second coronary occlusion has been assumed to indicate a preconditioning (PC) effect. This association was evaluated with myocardial electrograms in rabbits, which revealed that two sequential 5-min coronary occlusions resulted in a marked decrease in the area under the S-T segment voltage-time curve (P < 0.05) with no change during a third occlusion. Pretreatment with either 5-hydroxydecanoate, a mitochondrial ATP-sensitive potassium (K(ATP)) channel blocker, or anisomycin, an activator of stress-activated protein kinases, had no effect on the stair-step decline in the S-T segment voltage between the first two occlusions. HMR-1883, a potent closer of sarcolemmal K(ATP) channels, abolished changes in S-T segment elevation after brief coronary occlusions but had no effect on the infarct-sparing property of the two preconditioning 5-min occlusions. Interestingly, HMR-1883 blocked myocardial protection from diazoxide, raising doubt that the latter opens only mitochondrial channels. Therefore, myocardial protection and S-T segment changes during ischemia are dissociated. These data suggest that it is the mitochondrial K(ATP) channel that protects the myocardium, and it is the sarcolemmal channel that is responsible for changes in S-T elevation. Therefore, it cannot always be inferred that changes in S-T segment elevation reflect the state of myocardial protection.

Topics: Adenosine Triphosphate; Animals; Anisomycin; Anti-Arrhythmia Agents; Blood Pressure; Coronary Vessels; Decanoic Acids; Diazoxide; Electrocardiography; Heart; Heart Rate; Hydroxy Acids; Ion Channel Gating; Ischemic Preconditioning; Mitochondria; Potassium Channel Blockers; Potassium Channels; Rabbits; Sarcolemma; Sulfonamides; Thiourea

The novel sulfonylthiourea HMR 1883 was investigated in in vitro systems. The rilmakalim-induced shortening of the APD90 in guinea pig right papillary muscle at pHo = 6.0 was antagonized half-maximally by glibenclamide and HMR 1883 with 0.14 microM and 0. 6 microM, respectively. Hypoxia-induced shortening of the APD90 was significantly attenuated by the sulfonylureas when applied 60 min after induction of hypoxia. In isolated guinea pig ventricular myocytes the APD90 as well as the whole-cell current was measured with the patch-clamp technique. The rilmakalim-induced shortening of the APD90 was half-maximally antagonized by glibenclamide and HMR 1883 with 10 nM and 0.4 microM, respectively (pHo = 6.5). The rilmakalim-induced whole-cell current (at 0 mV clamp-potential) was inhibited by glibenclamide and HMR 1883 half-maximally with 20 nM and 0.8 microM, respectively (pHo = 7.4). In isolated perfused guinea pig hearts, the coronary flow (CF) was increased by perfusion with hypoxic solution (20% O2). Whereas 1 microM glibenclamide completely inhibited the hypoxia-induced increase in CF, 10 microM HMR 1883 reduced it by only 18%. Pancreatic effects were investigated in rat insulinoma cells (RINm5F), which were hyperpolarized with 100 microM diazoxide. Addition of glibenclamide or HMR 1883 depolarized the cell potential half-maximally with concentrations of 9 nM and approximately 20 microM, respectively. In conclusion, the sulfonylthiourea HMR 1883 blocks KATPs in cardiac muscle cells with 10-50 fold higher potency than in pancreatic beta-cells and has little effect on the coronary vascular system. Therefore, HMR 1883 has pharmacological selectivity for cardiac myocytes and thereby may be a promising substance for the prevention of ischemia-induced ventricular fibrillation.

Topics: Action Potentials; Adenosine Triphosphate; Animals; Chromans; Coronary Circulation; Deoxyglucose; Dose-Response Relationship, Drug; Female; Guinea Pigs; Heart; Islets of Langerhans; Male; Papillary Muscles; Perfusion; Potassium Channel Blockers; Pyrrolidines; Rats; Sulfonamides; Thiourea

The activation of the ATP-sensitive potassium channel (KATP) during myocardial ischemia leads to potassium efflux, reductions in action potential duration and the formation of ventricular fibrillation (VF). Drugs that inactivate KATP should prevent these changes and thereby prevent VF. However, most KATP antagonists also alter pancreatic channels, which promote insulin release and hypoglycemia. Recently, a cardioselective KATP antagonist, HMR 1883, has been developed that may offer cardioprotection without the untoward side effects of existing compounds. Therefore, VF was induced in 13 mongrel dogs with healed myocardial infarctions by a 2-min coronary artery occlusion during the last minute of a submaximal exercise test. On subsequent days, the exercise-plus-ischemia test was repeated after pretreatment with HMR 1883 (3.0 mg/kg i.v., n = 13) or glibenclamide (1.0 mg/kg i.v., n = 7). HMR 1883 (P < .001) and glibenclamide (P < .01) prevented VF in 11 of 13 and 6 of 7 animals, respectively. Glibenclamide, but not HMR 1883, elicited increases in plasma insulin and reductions in blood glucose. Glibenclamide also reduced (P < .01) both mean coronary blood flow and left ventricular dP/dt maximum as well as the reactive hyperemia induced by 15-sec coronary occlusions (-30.3 +/- 11%), whereas HMR 1883 did not alter this increase in coronary flow (-3.0 +/- 4.7%). Finally, myocardial ischemia (n = 10) significantly (P < .01) reduced refractory period (control, 121 +/- 2 msec; occlusion, 115 +/- 2 msec), which was prevented by either glibenclamide or HMR 1883. Thus, the cardioselective KATP antagonist HMR 1883 can prevent ischemically induced reductions in refractory period and VF without major hemodynamic effects or alterations in blood glucose levels. These data further suggest that the activation of KATPs may play a particularly important role in both the reductions in refractory period and lethal arrhythmia formation associated with myocardial ischemia.

Topics: Adenosine Triphosphate; Animals; Dogs; Glyburide; Heart; Hemodynamics; Myocardial Ischemia; Potassium Channel Blockers; Refractory Period, Electrophysiological; Sulfonamides; Thiourea; Ventricular Fibrillation