Opening Of ATP-dependent Potassium Channels Research Articles

Ischemic Postconditioning Reduces NMDA Receptor Currents Through the Opening of the Mitochondrial Permeability Transition Pore and KATP Channel in Mouse Neurons.

Ischemic postconditioning (PostC) is known to reduce cerebral ischemia/reperfusion (I/R) injury; however, whether the opening of mitochondrial ATP-dependent potassium (mito-KATP) channels and mitochondrial permeability transition pore (mPTP) cause the depolarization of the mitochondrial membrane that remains unknown. We examined the involvement of the mito-KATP channel and the mPTP in the PostC mechanism. Ischemic PostC consisted of three cycles of 15s reperfusion and 15s re-ischemia, and was started 30s after the 7.5min ischemic load. We recorded N-methyl-D-aspartate receptors (NMDAR)-mediated currents and measured cytosolic Ca2+ concentrations, and mitochondrial membrane potentials in mouse hippocampal pyramidal neurons. Both ischemic PostC and the application of a mito-KATP channel opener, diazoxide, reduced NMDAR-mediated currents, and suppressed cytosolic Ca2+ elevations during the early reperfusion period. An mPTP blocker, cyclosporine A, abolished the reducing effect of PostC on NMDAR currents. Furthermore, both ischemic PostC and the application of diazoxide potentiated the depolarization of the mitochondrial membrane potential. These results indicate that ischemic PostC suppresses Ca2+ influx into the cytoplasm by reducing NMDAR-mediated currents through mPTP opening. The present study suggests that depolarization of the mitochondrial membrane potential by opening of the mito-KATP channel is essential to the mechanism of PostC in neuroprotection against anoxic injury.

Rationale, experimental data, and emerging clinical evidence on early and preventive use of levosimendan in patients with ventricular dysfunction.

Acute ventricular dysfunction (AVD) is a complex condition with substantial morbidity and mortality, still featuring unique therapeutic challenges. Levosimendan is a calcium sensitizer and ATP-dependent potassium channel opener that was developed as an inodilating drug for the treatment of acute heart failure and cardiogenic shock. Differently from other more widely used inotropic agents, levosimendan has some exclusive characteristics, in terms of mechanisms of action, pharmacodynamic profile, and haemodynamic effects. This may have important clinical implications. In particular, in patients with AVD or in patients with pre-existing severe ventricular impairment undergoing planned myocardial stress, the administration of levosimendan before the onset of overt symptoms or before cardiovascular therapeutic procedures may have the potential to bridge the patient through the critical phase. In this review, we will focus on the rationale, the existing experimental data, and the emerging clinical experience supporting an early, even preventive use of levosimendan in severe ventricular dysfunction, beyond its recognized indications.

Effects of Levosimendan on Inflammation and Oxidative Stress Pathways in a Lipopolysaccharide-Stimulated Human Endothelial Cell Model.

Levosimendan is a myocardial Ca2+ sensitizer and opener of ATP-dependent potassium channels with inotropic, vasodilating, and cardioprotective properties. It was originally developed for the treatment of acute decompensated heart failure, but its complex mechanism of action means that it could also play a role in organ protection in response to infection. Using an in vitro approach, we explored whether levosimendan administration influenced cell responses to lipopolysaccharide (LPS). Primary human umbilical vein endothelial cells were stimulated with 1 µg/ml LPS from Escherichia coli (E. coli). Cells were treated with levosimendan at 0, 0.1, 1, or 10 µM 3 hr later. Samples were taken 24 hr after treatment to measure cell necrosis, apoptosis, pro-inflammatory mediators (interleukin 6 [IL-6] and toll-like receptor 4 [TLR4]), and oxidative stress (total reactive oxygen species/reactive nitrogen species [ROS/RNS]). Levosimendan at 1 and 10 µM protected against LPS-induced endothelial cell death and reduced TLR4 expression (p < .05). All doses reduced levels of IL-6 and ROS/RNS (p < .05). Findings suggest that levosimendan may exert protective effects against endothelial cell death in this model via attenuation of inflammation and oxidative stress pathways. Future studies might explore the potential beneficial role of levosimendan in modulating molecular mechanisms triggered by infections.

Comparative effects of calcium and potassium channel modulators on ischemia/reperfusion injury in the isolated rat heart.

The aim of this study was to examine and compare the effects of the acute administration of verapamil or amlodipine as representatives of the calcium channel blockers or nicorandil as a representative of the mitochondrial ATP-dependent potassium (KATP) channel opener to cardiac contractility, coronary flow, and oxidative stress markers on ischemia/reperfusion injury in the isolated rat heart. The hearts of adult male Wistar albino rats (n = 60 total, 12 per group) were divided into five groups, two controls (preconditioning with Krebs-Henseleit solution) and three experimental depending on acute administrated pharmacological agents (0,63µmol/L of verapamil, 0,1µmol/L of amlodipine, and 200µmol/L of nicorandil). After stabilization and 5min of preconditioning in experimental groups, hearts from I/R control and all experimental groups underwent global ischemia (20min) and reperfusion (30min). Hearts from sham group were continuously followed for 50min, after stabilization period. Cardiodynamic parameters and coronary flow were recorded at the end of stabilization (S), at the last minute of pharmacological preconditioning (P) and at intervals of 5min after global ischemia, during reperfusion, or in case of sham group during 20-50min after stabilization. At the same intervals, we collected coronary venous effluent from which we spectrophotometrically measured the parameters of oxidative stress: the index of lipid peroxidation, superoxide anion radical, hydrogen peroxide, and nitrite. In summary, our findings clearly indicate that the blocking of the calcium channel or the activation of KATP may mediate the protective effect of myocardial preconditioning. The ex vivo results showed that all examined drugs after ischemia and reperfusion have beneficial cardioprotective properties associated with lower values of major pro-oxidative molecules. Obtained effects seem to be the most convincible in case of nicorandil.

ATP-induced cardioprotection against myocardial ischemia/reperfusion injury is mediated through the RISK pathway.

The aim of the present study was to examine the post-infarct acute effect of adenosine-5′-triphosphate (ATP) on myocardial infarction (MI) size as well as its precise molecular mechanism. Sixty New Zealand white male rabbits were exposed to 40 min of ischemia followed by 180 min of reperfusion. The rabbits were intravenously administered 3 mg/kg of ATP (ATP group) or saline (control group) immediately after reperfusion and maintained throughout the first 30 min. The wortmannin+ATP, PD-98059+ATP, and 5-hydroxydecanoic acid (5-HD) sodium salt+ATP groups were separately injected with wortmannin (0.6 mg/kg), PD-98059 (0.3 mg/kg), and 5-HD (5 mg/kg) 5 min prior to ATP administration. MI size was calculated as the percentage of the risk area in the left ventricle. Myocardial apoptosis was determined using a TUNEL assay. Western blot analysis was performed to examine the levels of protein kinase B (Akt)/p-Akt and extracellular signal-regulated kinase (ERK)/p-ERK in the ischemic myocardium, 180 min after reperfusion. The infarct size was significantly smaller in the ATP group than in the control group (p<0.05). The infarct size-reducing effect of ATP was completely blocked by wortmannin, PD-98059 and 5-HD. Compared with the control group, cardiomyocyte apoptosis was significantly reduced in the ATP group, while this did not occur in the wortmannin+ATP, PD-98059+ATP and 5-HD+ATP groups. Western blot analysis revealed a higher myocardial expression of p-Akt and p-ERK 180 min following reperfusion in the ATP versus the control group. In conclusion, cardioprotection by postischemic ATP administration is mediated through activation of the reperfusion injury salvage kinase (RISK) pathway and opening of the mitochondrial ATP-dependent potassium channels.

The effects of ATP-dependent potassium channel opener; pinacidil, and blocker; glibenclamide, on the ischemia induced arrhythmia in partial and complete ligation of coronary artery in rats.

Electrical inhomogeneity between ischemic and non ischemic myocardium is the basis of arrhythmia which occurs following coronary artery occlusion. The leakage of potassium from the ischemic region to the non ischemic region is very effective in the generation of these arrhythmias. The aim of this study is to research the effect of ATP-dependent potassium (KATP) channel blocker (glibenclamide) and opener (pinacidil) on ischemia induced arrhythmia in the presence of small and large infarct sizes. In this study Sprague-Dawley male rats of 8-9 months of age were used. Ischemia was produced by the partial ligation of left coronary artery ramus descending (PL) for smaller infarct and complete ligation of this artery (CL) for larger infarct for 30 min. The arrhythmia score which was calculated from the duration and type of arrhythmia was significantly higher in animals which had a larger infarct area than the animals which had a smaller infarct. Glibenclamide increased the rate of arrhythmia in animals having smaller infarct but not in animals having larger infarct. Pinacidil did not affect the occurrence of arrhythmia in either group. There was a significant difference in the infarct size and risk of infarct zone between animals which had small and large infarct sizes. The effect of glibenclamide and pinacidil on the arrhythmias differed depend on decrease of infarct size. Glibenclamide is not effective to decrease ischemia induced arrhythmia in the presence of small and pinacidil in large ischemic zone.

Effect of ATP-dependent channel modulators on ischemia-induced arrhythmia change depending on age and gender

The number of ATP-dependent potassium channels in myocardial cells has been previously shown to change depending on gender and age. Different effects of the ATP-dependent potassium channel blocker, glybenclamide and ATP-dependent potassium channel opener, pinacidil on ischemia or reperfusion-induced arrhythmia observed in various research might depend on different ages and genders of the animals used. The aim of this study is to research the effect of ATP-dependent potassium channel modulators on ischemia-induced arrhythmia in animals of different ages and genders. Sprague-Dawley rats of different ages and genders were used in this study. Ischemia was produced by the ligation of the left coronary artery for 30 min. Electrocardiogram (ECG), blood pressure, infarct area and blood glucose were determined during the 30 min of ischemia. An arrhythmia score from an ECG recorded during 30 min of ischemia was determined by examining the duration and type of arrhythmia. Different effects of glybenclamide and pinacidil on the arrhythmias were observed in male and female young and middle-age rats. Pinacidil decreased the infarct zone in younger female rats, but differences in the type and length of ischemia-induced arrhythmias between females and males disappeared in older age. The results of this study showed that the effect of ATP-dependent potassium channel modulators on ischemia-induced arrhythmia changed due to the age and gender of rats.

Potassium Channel Openers Increase Aortic Elastic Fiber Formation and Reverse the Genetically Determined Elastin Deficit in the BN Rat

Hypertension is a cardiovascular disorder that appears in more than half of the patients with Williams-Beuren syndrome, hemizygous for the elastin gene among 26 to 28 other genes. It was shown that the antihypertensive drug minoxidil, an ATP-dependent potassium channel opener, enhances elastic fiber formation; however, no wide clinical application was developed because of its adverse side effects. The Brown Norway rat was used here as an arterial elastin-deficient model. We tested 3 different potassium channel openers, minoxidil, diazoxide, and pinacidil, and 1 potassium channel blocker, glibenclamide, on cultured smooth muscle cells from Brown Norway rat aorta. All tested potassium channel openers increased mRNAs encoding proteins and enzymes involved in elastic fiber formation, whereas glibenclamide had the opposite effect. The higher steady-state level of tropoelastin mRNA in minoxidil-treated cells was attributable to an increase in both transcription and mRNA stability. Treatment of Brown Norway rats for 10 weeks with minoxidil or diazoxide increased elastic fiber content and decreased cell number in the aortic media, without changing collagen content. The minoxidil-induced cardiac hypertrophy was reduced when animals simultaneously received irbesartan, an angiotensin II-receptor antagonist. This side effect of minoxidil was not observed in diazoxide-treated animals. In conclusion, diazoxide, causing less undesirable side effects than minoxidil, or coadministration of minoxidil and irbesartan, increases elastic fiber content, decreases cell number in the aorta and, thus, could be suitable for treating vascular pathologies characterized by diminished arterial elastin content and simultaneous hypertension.

Cardioprotective Effects of Nicorandil, a Mitochondrial Potassium Channel Opener against Doxorubicin‐Induced Cardiotoxicity in Rats

Doxorubicin is a chemotherapeutic drug used to treat solid and haematopoietic tumours. Its use is limited by a major side effect of cardiotoxicity. It was reported that doxorubicin-induced cardiotoxicity is mediated through oxidative stress coupled with impaired NO bioavailability and NF-κB activation. Nicorandil, a mitochondrial ATP-dependent potassium (KATP ) channel opener, was reported to be cardioprotective on ischaemic myocardium. However, the effect of nicorandil against doxorubicin-induced cardiotoxicity has not yet been clarified. Accordingly, six groups of rats were used. The first three groups were injected with vehicle, nicorandil (3 mg/kg) orally and doxorubicin (a single intraperitoneal injection of 20 mg/kg), respectively. Group four was treated with nicorandil, whereas group five was treated with glibenclamide and then nicorandil starting 2 days before doxorubicin and continued for five consecutive days. Group six was treated with glibenclamide alone. At the end of the experiment, the rats were killed. Cardiac enzyme indexes were measured in serum. Heart tissues were processed for determination of nitrite/nitrate, NF-κB protein expression, glutathione (GSH), lipid peroxide (TBARS) levels and superoxide production. In addition to body-weight reduction, doxorubicin produced cardiotoxicity as indicated from the increase in lactate dehydrogenase (LDH), creatine kinase (CK) activities, TBARS, superoxide production, NF-κB expression and caspase-3 activity. Moreover, doxorubicin decreased GSH and nitrite/nitrate levels. Histopathological examination of doxorubicin-treated hearts revealed degenerative changes. On the other hand, nicorandil protected cardiac tissues against doxorubicin cardiotoxicity as demonstrated from normalization of cardiac biochemical and oxidative stress parameters and amelioration of histopathological changes. Glibenclamide, a blocker of the KATP channel, reversed most of the cardiac effects of nicorandil.

The clinical effects of levosimendan are not attenuated by sulfonylureas

Objectives. Levosimendan is an inodilator indicated for acute heart failure (AHF). Its vasodilatory and anti-ischemic effects are mediated by the opening of ATP-dependent potassium channels (KATP channels). Diabetes mellitus is common in AHF patients and sulfonylureas are often prescribed. Sulfonylureas act by blocking the KATP channels. An interaction between levosimendan and sulfonylureas has been shown in preclinical models and could be hypothesized in clinical practice. Design. We produced a pooled analysis of six randomized levosimendan trials (in total of 3004 patients of which 1700 were treated with levosimendan and 226 both with levosimendan and sulfonylureas) with the aim to study the influence of concurrent sulfonylurea treatment to the levosimendan effects. Invasive and non-invasive hemodynamics, biomarkers (BNP), adverse events related to myocardial ischemia, and survival were evaluated. Results. In our relatively small data set, we could not detect any clinically relevant interactions between the sulfonylureas and levosimendan. Similar decreases in systolic and diastolic blood pressure, pulmonary capillary wedge pressure and BNP, and similar survival and adverse event profiles were seen in sulfonylurea users and non-users exposed to levosimendan. Conclusions. Concomitant use of sulfonylureas with levosimendan does not attenuate the hemodynamic or other effects of levosimendan.

Levosimendan improves cardiac function and survival in rats with angiotensin II-induced hypertensive heart failure

Calcium-sensitizing agents improve cardiac function in acute heart failure; however, their long-term effects on cardiovascular mortality are unknown. We tested the hypothesis that levosimendan, an inodilator that acts through calcium sensitization, opening of ATP-dependent potassium channels and phosphodiesterase III inhibition, improves cardiac function and survival in double transgenic rats harboring human renin and angiotensinogen genes (dTGRs), a model of angiotensin II (Ang II)-induced hypertensive heart failure. Levosimendan (1 mg kg(-1)) was administered orally to 4-week-old dTGRs and normotensive Sprague-Dawley rats for 4 weeks. Untreated dTGRs developed severe hypertension, cardiac hypertrophy, heart failure with impaired diastolic relaxation, and exhibited a high mortality rate at the age of 8 weeks. Levosimendan did not decrease blood pressure and did not prevent cardiac hypertrophy. However, levosimendan improved systolic function, decreased cardiac atrial natriuretic peptide mRNA expression, ameliorated Ang II-induced cardiac damage and decreased mortality. Levosimendan did not correct Ang II-induced diastolic dysfunction and did not influence heart rate. In a separate survival study, levosimendan increased dTGR survival by 58% and median survival time by 27% (P=0.004). Our findings suggest that levosimendan ameliorates Ang II-induced hypertensive heart failure and reduces mortality. The results also support the notion that the effects of levosimendan in dTGRs are mediated by blood pressure-independent mechanisms and include improved systolic function and amelioration of Ang II-induced coronary and cardiomyocyte damage.

Endothelium-Derived Nitric Oxide Inhibits the Relaxation of the Porcine Coronary Artery to Natriuretic Peptides by Desensitizing Big Conductance Calcium-Activated Potassium Channels of Vascular Smooth Muscle

The present experiments investigated whether endothelium-derived mediators modulate the effect of natriuretic peptides in porcine coronary arteries. Rings with and without endothelium were suspended in organ chambers for isometric tension recording. Concentration-relaxation curves to C-type natriuretic peptide (CNP) and atrial natriuretic peptide (ANP) were obtained during contractions to endothelin-1. Removal of the endothelium potentiated relaxations to both CNP and ANP. N(omega)-nitro-L-arginine methyl ester potentiated relaxations to natriuretic peptides only in arteries with endothelium. Sodium nitroprusside (SNP) inhibited the response to the natriuretic peptides only in the absence of the endothelium. In rings with endothelium, 1H-[1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one (ODQ) and 4H-8-bromo-1,2,4-oxadiazolo[3,4-d]benz[b][1,4]oxazin-1-one (NS2028) potentiated CNP-mediated relaxations. Iberiotoxin (IBTX) reduced the response only in rings without endothelium. Glybenclamide inhibited the relaxations in both the presence and absence of endothelium. CNP-induced relaxations were reduced by 8-bromoguanosine 3',5'-cGMP (8-bromo-cGMP) to the same extent in rings with and without endothelium. There was no significant difference between the increased cGMP content caused by CNP in porcine coronary arteries with or without endothelium. In patch-clamp studies in porcine coronary arterial smooth muscle cells, the natriuretic peptide-mediated enhancement of the IBTX-sensitive big conductance calcium-activated potassium channel (BK(Ca)) amplitude was reversed by SNP and 8-bromo-cGMP. These findings demonstrate that, in the porcine coronary artery, the opening of BK(Ca) and ATP-dependent potassium channels of the vascular smooth muscle contributes to CNP-mediated relaxations. Endothelium-derived and exogenous NO inhibit the direct relaxing effect of natriuretic peptides by desensitizing the response of the BK(Ca)s of the vascular smooth muscle to the generation of cGMP.

Endothelium-Independent Vasorelaxation by Ligusticum wallichii in Isolated Rat Aorta: Comparison of a Butanolic Fraction and Tetramethylpyrazine, the Main Active Component of Ligusticum wallichii

Ligusticum wallichii is an herb widely used to treat vascular disorders in Asian countries, and tetramethylpyrazine (TMP) has been identified as one of its vasorelaxant active components. This study was performed to examine the endothelium-independent relaxation produced by the butanol-soluble fraction of L. wallichii extract (LwBt) and its possible mechanisms of action in isolated rat aortic rings. The effects were compared with those of TMP. LwBt produced vasorelaxation that increased gradually after 2-3 min of LwBt administration and reached a maximum within 30 min. LwBt-induced relaxation was significantly attenuated by pretreatment with 4-aminopyridine and apamin. Additionally, LwBt attenuated CaCl(2)-induced vasoconstriction in high-potassium depolarized medium. Thus, LwBt-induced vasorelaxation apparently involved inhibition of calcium influx, mediated by the opening of voltage-dependent and/or Ca(2+)-activated potassium channels. On the other hand, the effect of TMP was significantly attenuated by pretreatment with glibenclamide, and 4-aminopyridine had no effect. In conclusion, LwBt-induced endothelium-independent vasorelaxation was mediated by the opening of voltage-dependent potassium channels, while TMP-induced relaxation was mediated by the opening of ATP-dependent potassium channels. These effects of LwBt may be due to a substance other than TMP.

Drug-induced QT interval shortening: potential harbinger of proarrhythmia and regulatory perspectives.

ATP-dependent potassium channel openers such as pinacidil and levcromakalim have long been known to shorten action potential duration and to be profibrillatory in non-clinical models, raising concerns on the clinical safety of drugs that shorten QT interval. Routine non-clinical evaluation of new drugs for their potential to affect cardiac repolarization has revealed that drugs may also shorten QT interval. The description of congenital short QT syndrome in 2000, together with the associated arrhythmias, suggests that drug-induced short QT interval may be proarrhythmic, and an uncanny parallel is evolving between our appreciation of the short and the long QT intervals. Epidemiological studies report an over-representation of short QT interval values in patients with idiopathic ventricular fibrillation. Therefore, as new compounds that shorten QT interval are progressed further into clinical development, questions will inevitably arise on their safety. Arising from the current risk-averse clinical and regulatory environment and concerns on proarrhythmic safety of drugs, together with our lack of a better understanding of the clinical significance of short QT interval, new drugs that substantially shorten QT interval will likely receive an unfavourable regulatory review unless these drugs fulfil an unmet clinical need. This review provides estimates of parameters of QT shortening that may be of potential clinical significance. Rufinamide, a recently approved anticonvulsant, illustrates the current regulatory approach to drugs that shorten QT interval. However, to further substantiate or confirm the safety of these drugs, their approval may well be conditional upon large-scale post-marketing studies with a focus on cardiac safety.

Oral levosimendan prevents postinfarct heart failure and cardiac remodeling in diabetic Goto-Kakizaki rats

Diabetes increases the risk for fatal myocardial infarction and development of heart failure. Levosimendan, an inodilator acting both via calcium sensitization and opening of ATP-dependent potassium channels, is used intravenously for acute decompensated heart failure. The long-term effects of oral levosimendan on postinfarct heart failure are largely unknown. To examine whether oral treatment with levosimendan could improve cardiac functions and prevent cardiac remodeling after myocardial infarction in a rodent model of type 2 diabetes, the Goto-Kakizaki rat. Myocardial infarction (MI) was induced to diabetic Goto-Kakizaki and nondiabetic Wistar rats by coronary ligation. Twenty-four hours after surgery, Goto-Kakizaki and Wistar rats were randomized into four groups: MI group without treatment, MI group with levosimendan for 12 weeks (1 mg/kg per day), sham-operated group, sham-operated group with levosimendan. Blood pressure, cardiac functions as wells as markers of cardiac remodeling were determined. In Goto-Kakizaki rats, MI induced systolic heart failure, pronounced cardiac hypertrophy in the remote area, and sustained cardiomyocyte apoptosis. Postinfarct cardiac remodeling was associated with increased atrial natriuretic peptide, interleukin-6 and connective tissue growth factor mRNA expressions, as well as three-fold increased cardiomyocyte senescence, measured as cardiac p16 mRNA expression. Levosimendan improved cardiac function and prevented postinfarct cardiomyocyte hypertrophy, cardiomyocyte apoptosis, and cellular senescence. Levosimendan also ameliorated MI-induced atrial natriuretic peptide, IL-6, and connective tissue growth factor overexpression as well as MI-induced disturbances in calcium-handling proteins (SERCA2, Na-Ca exchanger) without changes in diabetic status or systemic blood pressure. In nondiabetic Wistar rats, MI induced systolic heart failure; however, the postinfarct cardiac remodeling was associated with less pronounced cardiac hypertrophy, cardiomyocyte apoptosis, inflammatory reaction, and induction of cellular senescence. Levosimendan only partially prevented postinfarct heart failure and cardiac remodeling in Wistar rats. Our findings suggest a therapeutic role for oral levosimendan in prevention of postinfarct heart failure and cardiac remodeling in type 2 diabetes and underscore the importance of sustained cardiomyocyte apoptosis and induction of cellular senescence in the pathogenesis.

The Ceiling Effect of Pharmacological Postconditioning with the Phytoestrogen Genistein Is Reversed by the GSK3β Inhibitor SB 216763 [3-(2,4-Dichlorophenyl)-4(1-methyl-1H-indol-3-yl)-1H-pyrrole-2,5-dione] through Mitochondrial ATP-Dependent Potassium Channel Opening

In the present study, we investigated the efficacy of pharmacological postconditioning induced by 17beta-estradiol and the phytoestrogen, genistein, against myocardial infarction induced by increasing durations of coronary artery occlusion (CAO). Anesthetized rabbits underwent either 20-min (protocol A) or 30-min (protocol B) CAO, followed by 4 h of coronary artery reperfusion (CAR). Before CAR, they randomly received an intravenous injection of either vehicle (control), 100 or 1000 microg/kg genistein (Geni(100) and Geni(1000), respectively), or 100 microg/kg 17beta-estradiol (17beta-E(100)). In protocol A, infarct size was significantly reduced in Geni(100) (n = 6), Geni(1000) (n = 6), and 17beta-E(100) (n = 6) versus control (n = 9) (6 +/- 2, 15 +/- 4, and 11 +/- 3 versus 35 +/- 5%, respectively). In protocol B, none of these drugs reduced infarct size versus control. Western blots demonstrated an increase of Akt phosphorylation in the Geni(100) and 17beta-E(100) hearts submitted to 20-min CAO but not to 30-min CAO. The selective GSK3beta inhibitor SB 216763 (0.2 mg/kg) [3-(2,4)-dichlorophenyl)-4(1-methyl-1H-indol-3-yl)-1H-pyrrole-2,5-dione] did not exhibit cardioprotection at this dose, but its administration restored the cardioprotective effect of genistein and 17beta-estradiol with 30-min CAO. Administration of 5-hydroxydecanoate (5 mg/kg) abolished the cardioprotective effects of Geni(100) and 17beta-E(100) alone with 20-min CAO and also those observed when combined to SB 216763 with 30-min CAO. Thus, pharmacological postconditioning with genistein and 17beta-estradiol is limited by a "ceiling effect of protection" along with a loss of Akt phosphorylation. However, this ceiling effect is reversed by concomitant inhibition of GSK3beta by SB 216763 through opening of mitochondrial ATP-dependent potassium channels.

Pharmacological preconditioning by levosimendan is mediated by inducible nitric oxide synthase and mitochondrial K ATP channel activation in the in vivo anesthetized rabbit heart model

Background Provocation of fatal cardiac arrhythmias has limited the use of inotropic agents as heart failure therapy. Levosimendan (LEV) is a new inodilator, whose mechanism of action includes calcium sensitization of contractile proteins and the opening of ATP-dependent potassium channels. Objectives and methods The aim of this investigation was to test whether the administration of LEV has cardioprotective and antiarrhythmic effects against ischemia and reperfusion injury in a manner similar to ischemic preconditioning (IPC) in a well-standardized model of reperfusion arrhythmias in anesthetized adult male rabbits ( n = 122) subjected to 30 min occlusion of the left coronary artery followed by 120 min of reperfusion. Results Pretreatment with either 1 cycle of IPC, LEV (0.1 μmol/kg, i.v.), or IPC + LEV prior to the period of coronary occlusion offers significant infarct size reduction (21.6 ± 1.6%, 22.1 ± 2.2%, and 21.4 ± 1.4%, respectively vs 38.7 ± 3.6% in saline control group; P < 0.01) and antiarrhythmic effects. IPC, LEV and IPC + LEV treatment significantly attenuated the incidence of life-threatening arrhythmias like sustained VT (13%, 13% and 13%, respectively vs 100% in saline control group; P < 0.005) and other arrhythmias (25%, 25% and 13%, respectively vs 100% in saline control group; P < 0.005), and increased the number of surviving animals without arrhythmias. Pretreatment with 5-HD, N ω-nitro- l-arginine methyl ester ( l-NAME, a nonspecific NOS inhibitor) and the specific iNOS inhibitor 1400W [ N-(-3-(aminomethyl)benzyl) acetamidine] abolished the beneficial effects of IPC, and LEV on reperfusion induced arrhythmias and cardioprotection suggesting that benefits have been achieved via both the selective activation of cardiomyocyte mitochondrial K ATP channels and NO. One cycle of IPC and LEV pretreatment significantly preserved the level of ATP in the 30 min ischemic heart and 120 min reperfused heart. Conclusions The present study demonstrates similarities between acute LEV treatment and IPC of the rabbit myocardium in terms of survival, cardioprotection, antiarrhythmic activity, and metabolic status.

An overview of potassium channel activators for the treatment of overactive bladder: a survey of new structures 2000 – 2005

For over 25 years, the muscarinic receptor antagonists have been the first-line treatment for overactive bladder (OAB). However, severe dry mouth and exacerbation of disease symptoms with prolonged use can result in compliance rates as low as 30%. Approximately 10 years ago, investigators began to look for alternative approaches to the treatment of overactive bladder. In the recent past, it was demonstrated that ATP-dependent potassium channel openers designed as antihypertensive agents inhibited the hyperactivity associated with the symptoms of overactive bladder. Newer agents targeting other bladder potassium channels and/or bladder-specific channel subtypes represent an exciting new frontier for the effective treatment of OAB, with the potential of having an improved side effect profile compared to the antimuscarinic agents. In this review the authors examine the patent literature surrounding the discovery and development of several novel classes of compounds targeting the various potassium channels associated with urinary bladder activity and excitability. When appropriate, the primary literature is also touched upon to highlight pertinent structure–activity relationships (SAR) associated with these newly disclosed chemotypes.

European Experience on the Practical Use of Levosimendan in Patients with Acute Heart Failure Syndromes

The novel calcium sensitizer and ATP-dependent potassium channel opener levosimendan has been introduced for routine use in several European countries. Recent reports on clinical experience confirm the positive hemodynamic results and beneficial clinical effects described in the initial dose-finding and randomized comparative therapeutic trials in patients with severe low-output heart failure. In addition, studies in small series of patients with cardiogenic shock after myocardial infarction and/or surgical interventions and post-interventional myocardial dysfunction (stunning) indicate that the inotropic and vasodilating actions of levosimendan may be of value in a wider range of indications. Dose recommendations, combination with other drugs, and potential side effects are discussed in this overview.

Levosimendan: A New Inodilatory Drug for the Treatment of Decompensated Heart Failure

Levosimendan is a new calcium sensitizer developed for the treatment of congestive heart failure. Experimental studies indicate that levosimendan increases myocardial contractility and dilates both the peripheral and coronary vessels. Its positive inotropic effect is based on calcium-dependent binding of the drug to cardiac troponin C. It also acts as an opener of ATP-dependent potassium channels in vascular smooth muscle, thus inducing vasodilation. Although levosimendan acts preferentially as a calcium sensitizer it has also demonstrated selective phosphodiesterase III inhibitory effects in vitro. However, this selective inhibition does not seem to contribute to the positive action at pharmacologically relevant concentrations. Levosimendan has an active metabolite, OR-1896. Similarly to levosimendan, the metabolite exerts its positive inotropic and vasodilatory effects on myocardium and vasculature. The elimination half-life of levosimendan is about 1 hour. Thus, with intravenous administration, the parent drug rapidly disappears from the circulation after the infusion is stopped. The active metabolite, however, has a half-life of approximately 80 hours, and can be detected in circulation up to 2 weeks after stopping a 24-hour infusion of levosimendan. The intravenous formulation of levosimendan has been studied in several randomized comparative studies in patients with decompensated heart failure. Both patients with ischemic and non-ischemic etiology have participated in the studies. Levosimendan produces significant, dose-dependent increases in cardiac output, stroke volume and heart rate, and decreases in PCWP, mean blood pressure, mean pulmonary artery pressure, mean right atrial pressure and total peripheral resistance. With a loading dose, the effects on PCWP and cardiac ouput are seen within few minutes. There is no sign of development of tolerance even with a prolonged infusion up to 48 hours. Cardiac performance is improved with no significant increases in oxygen consumption or potentially malignant rhythm disorders. Due to the formation of an active metabolite, the hemodynamic effects are maintained up to several days after stopping levosimendan infusion. Compared to dobutamine, levosimendan produces similar increase in cardiac output but profoundly greater decrease in pulmonary capillary wedge pressure. On the contrary to dobutamine, the hemodynamic effects are not attenuated with concomitant beta-blocker use. Levosimendan has been shown to have favourable effects on symptoms of heart failure superior to placebo and at least comparable to dobutamine. Mortality and morbidity in levosimendan treated patients has been shown to be significantly lower when compared to dobutamine or placebo treated patients. The most common adverse events associated with levosimendan treatment are headache and hypotension, as a likely consequence of the vasodilating properties of the compound. In conclusion, levosimendan offers a new effective option for the treatment of acutely decompensated heart failure. Unlike traditional inotropes, levosimendan seems also to be safe in terms of morbidity and mortality.