Mitochondrial ATP-sensitive potassium channel plays a dominant role in ischemic preconditioning of rabbit heart

Redox Regulation of Mitochondrial Potassium Channels Activity

Redox reactions exert a profound influence on numerous cellular functions with mitochondria playing a central role in orchestrating these processes. This pivotal involvement arises from three primary factors: (1) the synthesis of reactive oxygen species (ROS) by mitochondria, (2) the presence of a substantial array of redox enzymes such as respiratory chain, and (3) the responsiveness of mitochondria to the cellular redox state. Within the inner mitochondrial membrane, a group of potassium channels, including ATP-regulated, large conductance calcium-activated, and voltage-regulated channels, is present. These channels play a crucial role in conditions such as cytoprotection, ischemia/reperfusion injury, and inflammation. Notably, the activity of mitochondrial potassium channels is intricately governed by redox reactions. Furthermore, the regulatory influence extends to other proteins, such as kinases, which undergo redox modifications. This review aims to offer a comprehensive exploration of the modulation of mitochondrial potassium channels through diverse redox reactions with a specific focus on the involvement of ROS.

Diazoxide Attenuates Postresuscitation Brain Injury in a Rat Model of Asphyxial Cardiac Arrest by Opening Mitochondrial ATP-Sensitive Potassium Channels

Objective. We investigated whether and how diazoxide can attenuate brain injury after cardiopulmonary resuscitation (CPR) by selective opening of mitochondrial ATP-sensitive potassium (mitoKATP) channels. Methods. Adult male Sprague-Dawley rats with induced cerebral ischemia (n = 10 per group) received an intraperitoneal injection of 0.1% dimethyl sulfoxide (1 mL; vehicle group), diazoxide (10 mg/kg; DZ group), or diazoxide (10 mg/kg) plus 5-hydroxydecanoate (5 mg/kg; DZ + 5-HD group) 30 min after CPR. The control group (sham group, n = 5) underwent sham operation, without cardiac arrest. Mitochondrial respiratory control rate (RCR) was determined. Brain cell apoptosis was assessed using TUNEL staining. Expression of Bcl-2, Bax, and protein kinase C epsilon (PKCε) in the cerebral cortex was determined by Western blotting and immunohistochemistry. Results. The neurological deficit scores (NDS) in the vehicle group decreased significantly at 24 h and 48 h after CPR. Diazoxide significantly improved NDS and mitochondrial RCR after CPR at both time points; 5-HD cotreatment abolished these effects. Diazoxide decreased TUNEL-positive cells following CPR, upregulated Bcl-2 and PKCε, downregulated Bax, and increased the Bcl-2/Bax ratio; 5-HD cotreatment reversed these effects. Conclusions. Diazoxide attenuates postresuscitation brain injury, protects mitochondrial function, inhibits brain cell apoptosis, and activates the PKC pathway by opening mitoKATP channels.

Landiolol Enhances Effect of Ischemic Preconditioning in Isolated Rabbit Hearts

The effect of the ultra-short-acting beta blocker, landiolol, on ischemic preconditioning was examined in isolated rabbit hearts. Ischemic preconditioned hearts received 2 episodes of 5 min each of global ischemia and reperfusion. The left anterior descending coronary artery was occluded for 1 hour and reperfused for 1 hour. Left ventricular end-systolic and end-diastolic pressures and infarct size were measured. Seven control hearts had no drug infused. Four groups of 6 hearts each were pretreated with 1 or 3 μM of landiolol or a combination of 1 or 3 μM landiolol and ischemic preconditioning. A further group of 6 hearts had ischemic preconditioning without landiolol. Ischemic preconditioning significantly reduced left ventricular end-diastolic pressure and infarct size compared to the controls. Landiolol alone did not change left ventricular end-diastolic pressure or infarct size, but landiolol 3 μM and ischemic preconditioning decreased left ventricular end-diastolic pressure more than preconditioning alone. These data suggest that pre-ischemic landiolol infusion may enhance the cardioprotective effect of ischemic preconditioning.

Role of ATP-dependent K channels in the effects of erythropoietin in renal ischaemia injury

Background & objectives:

Erythropoietin (EPO) has cytoprotective and anti-apoptotic effects in pathological conditions, including hypoxia and ischaemia-reperfusion injury. One of the targets to protect against injury is ATP-dependent potassium (KATP) channels. These channels could be involved in EPO induced ischaemic preconditoning like a protective effect. We evaluated the cell cytoprotective effects of EPO in relation to KATP channel activation in the renal tubular cell culture model under hypoxic/normoxic conditions.

Methods:

Dose and time dependent effects of EPO, KATP channel blocker glibenclamide and KATP channel opener diazoxide on cellular proliferation were evaluated by colorimetric assay MTT [3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide] under normoxic and hypoxic conditions in human renal proximal tubular cell line (CRL-2830). Evaluation of the dose and time dependent effects of EPO, glibenclamide and diazoxide on apoptosis was done by caspase-3 activity levels. Hypoxia inducible factor-1 alpha (HIF-1 α) mRNA levels were measured by semi-quantative reverse transcription polymerase chain reaction (RT)-PCR. Kir 6.1 protein expresion was evalutaed by Western blot.

Results:

Glibenclamide treatment decreased the number of living cells in a time and dose dependent manner, whereas EPO and diazoxide treatments increased. Glibenclamide (100 μM) treatment significantly blocked the anti-apoptotic effects of EPO (10 IU/ml) under both normoxic and hypoxic conditions. EPO (10 IU/ml) and diazoxide (100 μM) treatments significantly increased (P<0.01) whereas glibenclamide decreased (P<0.05) HIF-1 α mRNA expression. Glibenclamide significantly (P<0.01) decreased EPO induced HIF-1 α mRNA expression when compared with the EPO alone group.

Interpretation & conclusions:

Our results showed that the cell proliferative, cytoprotective and anti-apoptotic effects of EPO were associated with KATP channels in the renal tubular cell culture model under hypoxic/normal conditions.

KATP Channels in the Cardiovascular System

KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.

Is preconditioning by oxytocin administration mediated by iNOS and/or mitochondrial K(ATP) channel activation in the in vivo anesthetized rabbit heart?

AIMS

Oxytocin (OXT) pretreatment protects the heart during ischemia-reperfusion injury by activating ATP-dependent potassium (K(ATP)) channels. The aim of the current study was to elucidate the roles of nitric oxide synthaseNOS and myocardial biochemistry in the cardioprotective effects of OXT and ischemic preconditioning (IPC).

MAIN METHODS

Male New Zealand White anesthetized rabbits (13 groups) were subjected to 30 min of occlusion of the left coronary artery and 120 min of reperfusion with or without IPC.

KEY FINDINGS

IPC (1 cycle), OXT (0.03 μg/kg, i.p.) or IPC + OXT yield significant infarct size reductions (21.8±1.5%, 20.5±1.2% and 19.4±1.4%, respectively, versus 38.9±3.5% in the S-CONT group; P<0.01) and antiarrhythmic effects, including VF (0%, 0% and 0%, versus 50% in S-CONT group; P<0.05) sustained VT (13%, 13% and 13%, versus 100% in S-CONT group; P<0.005) and other arrhythmias (25%, 13% and 25%, versus 100% in S-CONT group; P<0.005, P<0.01 and P<0.005, respectively). Atosiban (ATO, a selective OXT receptor antagonist), 5-HD and L-NAME (a nonspecific NOS inhibitor) abolished the beneficial effects of IPC and OXT, suggesting that the benefits are achieved via selective activation of OXT receptors, mitochondrial K(ATP) channels and NO. An iNOS inhibitor (1400 W) blocked the beneficial effects of IPC but not OXT. The IPC, OXT, IPC + OXT and 1400 W + OXT interventions significantly preserved ATP levels in the heart.

SIGNIFICANCE

This study demonstrates similarities between acute OXT pretreatment and IPC in terms of infarct size reduction, antiarrhythmic activity, and metabolic status.

The A3 adenosine receptor: an enigmatic player in cell biology

Adenosine is a primordial signaling molecule present in every cell of the human body that mediates its physiological functions by interacting with 4 subtypes of G-protein-coupled receptors, termed A1, A2A, A2B and A3. The A3 subtype is perhaps the most enigmatic among adenosine receptors since, although several studies have been performed in the years to elucidate its physiological function, it still presents in several cases a double nature in different pathophysiological conditions. The 2 personalities of A3 often come into direct conflict, e.g., in ischemia, inflammation and cancer, rendering this receptor as a single entity behaving in 2 different ways. This review focuses on the most relevant aspects of A3 adenosine subtype activation and summarizes the pharmacological evidence as the basis of the dichotomy of this receptor in different therapeutic fields. Although much is still to be learned about the function of the A3 receptor and in spite of its duality, at the present time it can be speculated that A3 receptor selective ligands might show utility in the treatment of ischemic conditions, glaucoma, asthma, arthritis, cancer and other disorders in which inflammation is a feature. The biggest and most intriguing challenge for the future is therefore to understand whether and where selective A3 agonists or antagonists are the best choice.

Pharmacological preconditioning by levosimendan is mediated by inducible nitric oxide synthase and mitochondrial KATP 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 micromol/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(omega)-nitro-L-arginine methyl ester (L-NAME, a nonspecific NOS inhibitor) and the specific iNOS inhibitor 1400 W [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.

Improvement of ventricular mechanical properties by puerarin involves mitochondrial permeability transition in isolated rat heart during ischemia and reperfusion

The aim of the present study was to determine whether the clinically effective cardioprotection conferred by puerarin (Pue) against ischemia and reperfusion is mediated by mitochondrial transmembrane pores and/or channels. In isolated rat hearts subjected to 30 min regional ischemia and 120 min reperfusion, pretreatment with Pue at 0.24 mmol/L for 5 min before ischemia increased myocardial formazan content, an index of myocardial viability, reduced lactate dehydrogenase release, improved recovery of the maximal rise/fall rate of left ventricular pressure, left ventricular end-diastolic pressure and rate-pressure product (left ventricular developed pressure multiplied by heart rate) during reperfusion. Administration of atractyloside (20 micromol/L), an opener of the mitochondrial permeability transition pore, for the first 20 min of reperfusion and 5-hydroxydecanoate (100 micromol/L), the mitochondrial specific ATP-sensitive potassium channel blocker, for 20 min before ischemia, attenuated the protective effects of Pue. In mitochondria isolated from hearts pretreated with 0.24 mmol/L Pue for 5 min, a significant inhibition of Ca²⁺-induced swelling was observed, and this inhibition was attenuated by 5-hydroxydecanoate. These findings indicate that Pue protects the myocardium against ischemia and reperfusion injury via inhibiting mitochondrial permeability transition pore opening and activating the mitochondrial ATP-sensitive potassium channel.

Similarities between ischemic preconditioning and 17beta-estradiol mediated cardiomyocyte KATP channel activation leading to cardioprotective and antiarrhythmic effects during ischemia/reperfusion in the intact rabbit heart

The aims of our present work were to assess whether treatment with either ischemic preconditioning (IPC) or 17beta-estradiol or both combined produce proarrhythmic or antiarrhythmic effects, and whether opening of the sarcolemmal or mitochondrial KATP channels is relatable to this effect; to assess biochemically the effects of IPC and/or 17beta-estradiol on oxidant stress and antioxidant defenses in the myocardium; to examine the effects of nitric oxide (NO) synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) pretreatment in rabbits treated with either IPC or 17beta-estradiol (because 17beta-estradiol evoked NO release has been implicated in KATP activation and IPC); and examine the effects of ischemic preconditioning and 17beta-estradiol on myocardial energy metabolism during ischemia and reperfusion in a well-standardized model of reperfusion arrhythmias in anesthetized adult male New Zealand White rabbits (n = 124) subjected to 30 minutes occlusion of the left coronary artery followed by 120 minutes of reperfusion. Pretreatment with either 17beta-estradiol (10 microg/kg, i.v.) or one cycle of ischemic preconditioning prior to the period of coronary occlusion offers significant infarct size reduction (18.6 +/- 2.2% and 19.4 +/- 1.9%, respectively versus 40.1 +/- 3.9% in saline control and 39.2 +/- 3.2% in vehicle control groups; P < 0.01) and antiarrhythmic effects. Both 17beta-estradiol and ischemic preconditioning treatment significantly attenuated the incidence of life-threatening arrhythmias like sustained VT (13% and 13%, respectively versus 100% in saline control and 100% in vehicle control groups; P < 0.001) and other arrhythmias (25% and 25%, respectively versus 100% in saline control and 100% in vehicle control groups; P < 0.001), and were quite effective in increasing the number of animals that survived without developing any arrhythmia during ischemia and reperfusion. 5-hydroxydecanoate(5-HD; 5 mg/kg, i.v.) alone offered no cardioprotective and antiarrhythmic activities. Pretreatment with 5-HD but not HMR 1883 (3 mg/kg, i.v.) abolished the beneficial effects of 17beta-estradiol and ischemia preconditioning on reperfusion-induced arrhythmias and cardioprotection suggesting that such effects have been achieved via the selective activation of cardiomyocyte mitochondrial KATP channels rather than sarcolemmal KATP channels. The reduced reperfusion arrhythmic incidence and durations induced by estrogen was not significantly altered by ICI 182 720 (2.5 mg/kg, i.v.). The lack of effect of ICI 182 720 on antiarrhythmic and infarct-limiting effects of 17beta-estradiol and ischemic preconditioning suggest that these favorable effects are rapid, direct, and non-genomic effects. This study demonstrates similarities between 17beta-estradiol and ischemic preconditioning of the rabbit myocardium in terms of cardioprotection, antiarrhythmic, and metabolic activities. Ischemic preconditioning and 17beta-estradiol appear to share a final common effector; the mitochondrial KATP channel.

Atractyloside and 5-hydroxydecanoate block the protective effect of puerarin in isolated rat heart

The aim of the present study was to determine whether the clinically effective cardioprotection conferred by puerarin (Pue) against ischemia and reperfusion is mediated by mitochondrial transmembrane pores and/or channels. Hearts isolated from male Sprague-Dawley rats were perfused on a Langendorff apparatus and subjected to 30 min of global ischemia followed by 120 min of reperfusion. The production of formazan, which provides an index of myocardial viability, was measured by absorbance at 550 nm, and the level of lactate dehydrogenase (LDH) in the coronary effluent was determined. In this model, Pue (0.0024-2.4 mmol/l) had a dose-dependent, negatively inotropic effect. Pretreatment with Pue at 0.24 mmol/l for 5 min before ischemia increased myocardial formazan content, reduced LDH release, improved recovery of left ventricular end-diastolic pressure and rate-pressure product (left ventricular developed pressure multiplied by heart rate) during reperfusion. Administration of atractyloside (20 micromol/l), an opener of the mitochondrial permeability transition pore, for the first 20 min of reperfusion, and 5-hydroxydecanoate (100 micromol/l), the mitochondrial-specific ATP-sensitive potassium channel blocker, for 20 min before ischemia, attenuated the protective effects of Pue. In mitochondria isolated from hearts pretreated with 0.24 mmol/l Pue for 5 min, a significant inhibition of Ca(2+)-induced swelling was observed, and this inhibition was attenuated by 5-hydroxydecanoate. In isolated ventricular myocytes, pretreatment with Pue prevented ischemia-induced cell death and depolarization of the mitochondrial membrane, and atractyloside and 5-hydroxydecanoate attenuated the effects of Pue. These findings indicate that puerarin protects the myocardium against ischemia and reperfusion injury via inhibiting mitochondrial permeability transition pore opening and activating the mitochondrial ATP-sensitive potassium channel.

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

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

Reactive oxygen species mediate the neuroprotection conferred by a mitochondrial ATP-sensitive potassium channel opener during ischemia in the rat hippocampal slice

Reactive oxygen species (ROS) are known to mediate the protection conferred by the opening of mitochondrial ATP-sensitive potassium channels (mitoK(ATP)) during ischemia in heart, but this has not been demonstrated in brain. The present study examined whether ROS mediate the neuroprotection conferred by a mitoK(ATP) opener during ischemia in rat hippocampal slices. Ischemia was simulated by oxygen and glucose deprivation. The direct current potential and population spike were recorded in the stratum pyramidale of the CA1 region, and lactate dehydrogenase (LDH) efflux into the medium was assayed. ROS generation was measured spectrophotofluorometrically. Pretreatment of slices with diazoxide (DIA, 300 microM), a mitoK(ATP) opener, (i) prolonged the latency to ischemic depolarization and decreased its amplitude, (ii) delayed the onset of population spike disappearance and enhanced its recovery after reperfusion, (iii) decreased LDH efflux and (iv) increased ROS levels. The effects induced by DIA were attenuated by 5-hydroxydecanoic acid (200 microM), a mitoK(ATP) blocker. Pretreatment with N-2-mercaptopropionyl glycine (MPG, 500 microM), a ROS scavenger, also abrogated the effects induced by DIA, while treatment with MPG alone had no effect during normoxia and ischemia. These results indicate that ROS participate in the neuroprotection conferred by a mitoK(ATP) opener during ischemia.

BMS-191095, a cardioselective mitochondrial K(ATP) opener, inhibits human platelet aggregation by opening mitochondrial K(ATP) channels

We evaluated the antiplatelet effects of two classes of ATP-sensitive potassium channel openers (K(ATP) openers) on washed human platelets, and the study's emphasis was on the role of mitochondrial K(ATP) in platelet aggregation. Collagen-induced platelet aggregation was inhibited in a dose dependent manner by lemakalim and SKP-450, which are potent cardio-nonselective K(ATP) openers, and also by cardioselective BMS-180448 and BMS-191095 (IC50: 1,130, >1,500, 305.3 and 63.9 microM, respectively), but a significantly greater potency was noted for the cardioselective K(ATP) openers. The latter two K(ATP) openers also inhibited platelet aggregation induced by thrombin, another important blood-borne platelet activator, with similar rank order of potency (IC50: 498.0 and 104.8 microM for BMS-180448 and BMS-191095, respectively). The inhibitory effects of BMS-191095 on collagen-induced platelet aggregation were significantly blocked by a 30-min pretreatment of platelets with glyburide (1 microM) or sodium 5-hydroxydecanoate (5-HD, 100 microM), a nonselective and selective mitochondrial K(ATP) antagonist, respectively, at similar magnitudes; this indicates the role of mitochondrial K(ATP) in the antiplatelet activity of BMS-191095. However, glyburide and 5-HD had no effect when they were added to the platelet cuvette immediately prior to the addition of BMS-191095. These findings indicate that cardioselective mitochondrial K(ATP) openers like BMS-191095 are able to exert cardioprotective effects in cardiac ischemia/reperfusion injury via dual mechanisms directed at the inhibition of platelet aggregation and the protection of cardiomyocytes, and both these mechanisms are mediated by mitochondrial K(ATP).

Role of adenosine A1 and A3 receptors in regulation of cardiomyocyte homeostasis after mitochondrial respiratory chain injury

Activation of either the A(1) or the A(3) adenosine receptor (A(1)R or A(3)R, respectively) elicits delayed cardioprotection against infarction, ischemia, and hypoxia. Mitochondrial contribution to the progression of cardiomyocyte injury is well known; however, the protective effects of adenosine receptor activation in cardiac cells with a respiratory chain deficiency are poorly elucidated. The aim of our study was to further define the role of A(1)R and A(3)R activation on functional tolerance after inhibition of the terminal link of the mitochondrial respiratory chain with sodium azide, in a state of normoxia or hypoxia, compared with the effects of the mitochondrial ATP-sensitive K(+) channel opener diazoxide. Treatment with 10 mM sodium azide for 2 h in normoxia caused a considerable decrease in the total ATP level; however, activation of adenosine receptors significantly attenuated this decrease. Diazoxide (100 muM) was less effective in protection. During treatment of cultured cardiomyocytes with hypoxia in the presence of 1 mM sodium azide, the A(1)R agonist 2-chloro-N(6)-cyclopentyladenosine was ineffective, whereas the A(3)R agonist 2-chloro-N(6)-iodobenzyl-5'-N-methylcarboxamidoadenosine (Cl-IB-MECA) attenuated the decrease in ATP level and prevented cell injury. Cl-IB-MECA delayed the dissipation in the mitochondrial membrane potential during hypoxia in cells impaired in the mitochondrial respiratory chain. In cells with elevated intracellular Ca(2+) concentration after hypoxia and treatment with NaN(3) or after application of high doses of NaN(3), Cl-IB-MECA immediately decreased the elevated intracellular Ca(2+) concentration toward the diastolic control level. The A(1)R agonist was ineffective. This may be especially important for the development of effective pharmacological agents, because mitochondrial dysfunction is a leading factor in the pathophysiological cascade of heart disease.

Resident cardiac mast cells and ischemia-reperfusion injury

BACKGROUND

The intense inflammatory reaction following reperfusion of ischemic myocardium has been implicated as a factor in the extension of myocardial injury. One of the therapeutic goals of modern cardiology is to design strategies to limit the infarct size following myocardial infarction. A sound understanding of the inflammatory cascade that involves the release of various proinflammatory mediators from cardiac cells is necessary before a specific intervention is pursued.

OBSERVATION

Summarized is the role of resident cardiac mast cells, which are noted to release inflammatory mediators, in ischemia-reperfusion-induced myocardial injury. Various pharmacologic interventions, such as disodium cromoglycate and ketotifen, that stabilize cardiac mast cells, or agents such as chlorpheniramine and cetirizine that prevent their degranulation during ischemia and reperfusion, may prove to be potential therapeutic agents to limit or salvage ischemia-reperfusion-induced injury.

CONCLUSION

On the basis of the effects of histamine H1 antagonists, adrenoceptor blockers, cellular calcium and nitric oxide modulators, as well as inhibitors of phosphodiesterase and mitogen-activated protein kinase on mast cells, cardiac resident mast cells may represent a novel target for the development of cardioprotective agents.

Preischemic infusion of alpha-human atrial natriuretic peptide elicits myoprotective effects against ischemia reperfusion in isolated rat hearts

Carperitide, a synthetic alpha-human atrial natriuretic peptide (ANP) is a newly developed drug for the treatment of heart failure. However, effects of carperitide on susceptibility to ischemia reperfusion injury are left to be determined. Isolated rat hearts were subjected to Langendorff perfusion. Six hearts received 0.1 microM of carperitide for 10 min, 6 hearts received 1 mM of a NO synthetase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) for 5 min before the infusion of carperitide, 6 hearts received 0.02 microM of a PKC synthetase inhibitor chelerythrine chloride for 5 min before the infusion of carperitide, 6 hearts received 100 microM of a selective mitochondrial ATP-sensitive potassium (KATP) channel blocker 5-dehydroxydecanoate (5HD) before the infusion of carperitide, 6 hearts received 10 microM of a soluble guanylate cyclase inhibitor methylene blue for 5 min before the infusion of carperitide, and 6 hearts served as a control with no drug infusion. All hearts were then subjected to 20 min of global ischemia followed by 120 min of reperfusion. Left ventricular pressures and coronary flow were measured throughout the experiment and infarct size was detected at the end of experiment. Both plasma and tissue cGMP levels were also determined. The results showed: (1) Carperitide significantly reduced infarct size compared to control (26.1 +/- 2.8 vs. 42.7 +/- 2.3%, carperitide vs. control, p < 0.05). This effect was reversed by L-NAME, chelerythrine and 5HD, but not methylene blue. (2) Plasma cGMP levels were increased in carperitide-treated group. This effect was reversed by L-NAME (0.16 +/- 0.03 vs. 1.04 +/- 0.09* vs. 0.28 +/- 0.02 nmol/L, control vs. carperitide vs. L-NAME, *p < 0.01 vs. control). We conclude that preischemic infusion of carperitide exerts cardioprotective effects possibly through NO-PKC dependent pathway followed by mitochondrial KATP channel activation.

In vivo characterization of the mitochondrial selective K(ATP) opener (3R)-trans-4-((4-chlorophenyl)-N-(1H-imidazol-2-ylmethyl)dimethyl-2H-1-benzopyran-6-carbonitril monohydrochloride (BMS-191095): cardioprotective, hemodynamic, and electrophysiological effects

Recent studies have shown the importance of mitochondrial ATP-sensitive potassium channels (K(ATP)) in cardioprotection, and studies in vitro have shown that the benzopyran analog (3R)-trans- 4-((4-chlorophenyl)-N-(1H-imidazol-2-ylmethyl)dimethyl-2H-1-benzopyran-6-carbonitril monohydrochloride (BMS-191095) is a selective mitochondrial K(ATP) opener with cardioprotective activity. The goal of this study was to show selective cardioprotection for BMS-191095 in vivo without hemodynamic or cardiac electrophysiological effects expected for nonselective K(ATP) openers. BMS-191095 reduced infarct size in anesthetized dogs (90-min ischemia + 5-h reperfusion) in a dose-dependent manner (ED(25) = 0.4 mg/kg i.v.) with efficacious plasma concentrations of 0.3 to 1.0 microM, which were consistent with potency in vitro. None of the doses of BMS-191095 tested caused any effect on peripheral or coronary hemodynamic status. Further studies in dogs showed no effects of BMS-191095 on cardiac conduction or action potential configuration within the cardioprotective dose range. In a programmed electrical stimulation model, BMS-191095 showed no proarrhythmic effects, which is consistent with its lack of effects on cardiac electrophysiological status. BMS-191095 is a potent and efficacious cardioprotectant that is devoid of hemodynamic and cardiac electrophysiological side effects of first generation K(ATP) openers, which open both sarcolemmal and mitochondrial K(ATP). Selective opening or activation of mitochondrial K(ATP) seems to be a potentially effective strategy for developing well tolerated and efficacious K(ATP) openers.

Activation of mitochondrial ATP-sensitive potassium channels prevents neuronal cell death after ischemia in neonatal rats

Activation of mitochondrial ATP-sensitive potassium channels (mK(ATP)) has been shown to protect against cell death following ischemia/reperfusion in the heart but not in brain. We examined whether mK(ATP) activation with diazoxide (DIZ) prevents neuronal cell death following hypoxia-ischemia (HI) in 7-day-old rat pups. Rat pups were subjected to HI (left carotid ligation; 8% O(2); 2.5 h), following administration of vehicle, 1.9 mg/kg DIZ, 3.8 mg/kg DIZ or DIZ plus 10 mg/kg 5-hydroxydecanoic acid (mK(ATP) antagonist). Total infarct volume was reduced from 99.8+/-2.7% in vehicle animals to 80.6+/-4.2% in 3.8 mg/kg DIZ treated animals (n=85, P<0.05). Western blotting showed K(ATP) subunits concentrated in mitochondria. Fluorescent studies indicated DIZ directly depolarized the mitochondria. In conclusion, selective opening of mK(ATP) prior to HI results in neuroprotection in immature rats.