The mitochondrial permeability transition pore and the Ca2+-activated K+ channel contribute to the cardioprotection conferred by tumor necrosis factor-alpha

A potent and selective activator of large-conductance Ca2+-activated K+ channels induces preservation of mitochondrial function after hypoxia and reoxygenation by handling of calcium and transmembrane potential

AIMS

Ischaemic heart disease remains a significant cause of mortality globally. A pharmacological agent that protects cardiac mitochondria against oxygen deprivation injuries is welcome in therapy against acute myocardial infarction. Here, we evaluate the effect of large-conductance Ca2+-activated K+ channels (BKCa) activator, Compound Z, in isolated mitochondria under hypoxia and reoxygenation.

METHODS

Mitochondria from mice hearts were obtained by differential centrifugation. The isolated mitochondria were incubated with a BKCa channel activator, Compound Z, and subjected to normoxia or hypoxia/reoxygenation. Mitochondrial function was evaluated by measurement of O2 consumption in the complexes I, II, and IV in the respiratory states 1, 2, 3, and by maximal uncoupled O2 uptake, ATP production, ROS production, transmembrane potential, and calcium retention capacity.

RESULTS

Incubation of isolated mitochondria with Compound Z under normoxia conditions reduced the mitochondrial functions and induced the production of a significant amount of ROS. However, under hypoxia/reoxygenation, the Compound Z prevented a profound reduction in mitochondrial functions, including reducing ROS production over the hypoxia/reoxygenation group. Furthermore, hypoxia/reoxygenation induced a large mitochondria depolarization, which Compound Z incubation prevented, but, even so, Compound Z created a small depolarization. The mitochondrial calcium uptake was prevented by the BKCa activator, extruding the mitochondrial calcium present before Compound Z incubation.

CONCLUSION

The Compound Z acts as a mitochondrial BKCa channel activator and can protect mitochondria function against hypoxia/reoxygenation injury, by handling mitochondrial calcium and transmembrane potential.

BKCa Channels as Targets for Cardioprotection

The large-conductance calcium- and voltage-activated K⁺ channel (BK_Ca) are encoded by the Kcnma1 gene. They are ubiquitously expressed in neuronal, smooth muscle, astrocytes, and neuroendocrine cells where they are known to play an important role in physiological and pathological processes. They are usually localized to the plasma membrane of the majority of the cells with an exception of adult cardiomyocytes, where BK_Ca is known to localize to mitochondria. BK_Ca channels couple calcium and voltage responses in the cell, which places them as unique targets for a rapid physiological response. The expression and activity of BK_Ca have been linked to several cardiovascular, muscular, and neurological defects, making them a key therapeutic target. Specifically in the heart muscle, pharmacological and genetic activation of BK_Ca channels protect the heart from ischemia-reperfusion injury and also facilitate cardioprotection rendered by ischemic preconditioning. The mechanism involved in cardioprotection is assigned to the modulation of mitochondrial functions, such as regulation of mitochondrial calcium, reactive oxygen species, and membrane potential. Here, we review the progress made on BK_Ca channels and cardioprotection and explore their potential roles as therapeutic targets for preventing acute myocardial infarction.

Mitigating effect of paxilline against injury produced by Cd2+ in rat pheochromocytoma PC12 and ascites hepatoma AS-30D cells

On two rat cell lines, pheochromocytoma PC12 and ascites hepatoma AS-30D, and on rat liver mitochondria we studied action of paxilline (lipophilic mycotoxin from fungus Penicillium paxilli which is blocker of large-conductance potassium channels) against harmful effects of Cd(II) - one of the most dangerous toxic metals and environmental pollutants. We investigated an influence of paxilline on cell viability and mitochondrial function in the presence and in the absence of Cd²⁺. As found, paxilline protected partially from the Cd²⁺-induced cytotoxicity, namely taken in concentration of 1 μM it decreased the Cd²⁺-induced cell necrosis in average by 10-14 or 13-23% for AS-30D and PC12 cells, respectively. Nevertheless, paxilline did not affect the Cd²⁺-induced apoptosis of AS-30D cells. The alleviating concentration of paxilline reduced an intracellular production of reactive oxygen species (ROS) in PC12 cells intoxicated by Cd²⁺ and enhanced the ROS production in control AS-30D cells; however, it weakly affected mitochondrial membrane potential of the cells in the absence and in the presence of Cd²⁺. The ameliorative concentration of paxilline decreased the maximal respiration rates of control cells of both types after short-term (3-5 h) treatment with it while the rates reached their control levels after long-term (24-48 h) incubation with the drug. Paxilline was not protective against the Cd²⁺-induced membrane permeability and respiration rate changes in isolated rat liver mitochondria. As result, the mitochondrial electron transport chain was concluded to contribute in the mitigating effect of paxilline against the Cd²⁺-produced cell injury.

Mitochondrial Ca2+-activated K+ channels and their role in cell life and death pathways

Ca²⁺-activated K⁺ channels (K_Ca) are expressed at the plasma membrane and in cellular organelles. Expression of all K_Ca channel subtypes (BK, IK and SK) has been detected at the inner mitochondrial membrane of several cell types. Primary functions of these mitochondrial K_Ca channels include the regulation of mitochondrial ROS production, maintenance of the mitochondrial membrane potential and preservation of mitochondrial calcium homeostasis. These channels are therefore thought to contribute to cellular protection against oxidative stress through mitochondrial mechanisms of preconditioning. In this review, we summarize the current knowledge on mitochondrial KCa channels, and their role in mitochondrial function in relation to cell death and survival pathways. More specifically, we systematically discuss studies on the role of these mitochondrial K_Ca channels in pharmacological preconditioning, and according protective effects on ischemic insults to the brain and the heart.

Cardiomyocyte mitochondria as targets of humoral factors released by remote ischemic preconditioning

INTRODUCTION

Remote ischemic preconditioning (RIPC) reduces myocardial infarct size, and protection can be transferred with plasma to other individuals, even across species. Mitochondria are the end-effectors of cardioprotection by local ischemic conditioning maneuvers. We have now analyzed mitochondrial function in response to RIPC.

MATERIAL AND METHODS

Plasma from pigs undergoing placebo or RIPC (infarct size reduction by 67% in RIPC pigs compared to placebo) was transferred to isolated perfused rat hearts subjected to 30 min global ischemia followed by 120 min reperfusion for infarct size measurement. Additional experiments were terminated at 10 min reperfusion to isolate mitochondria for functional measurements. Effects of RIPC pig plasma were compared to local ischemic preconditioning (IPC) or to infusion of tumor necrosis factor α (TNF-α).

RESULTS

Ischemia/reperfusion (I/R) induced an infarct of 41 ±2% of total ventricular mass. Placebo pig plasma did not affect infarct size (38 ±1, p = 0.13). The RIPC pig plasma reduced infarct size (27 ±2, p < 0.001), as did IPC (20 ±1, p < 0.001) and TNF-α (28 ±2, p < 0.001). Associated with cardioprotection, reductions of mitochondrial adenosine diphosphate (ADP)-stimulated respiration, adenosine triphosphate (ATP) production and calcium retention capacity (CRC) by I/R and placebo pig plasma were prevented by RIPC pig plasma, as they were by IPC and TNF-α. Mitochondrial reactive oxygen species production (nmol H₂O₂/100 µg protein) induced by I/R (272 ±34) was comparable in response to placebo pig plasma (234 ±28, p = 0.37) and was reduced by RIPC pig plasma (83 ±15, p < 0.001) as well as by IPC (78 ±21, p < 0.001) and TNF-α (125 ±42, p = 0.002).

CONCLUSIONS

In rat myocardium, mitochondria are an intracellular target of protection induced by humoral factors retrieved from pigs undergoing RIPC.

Marine n-3 PUFA protects hearts from I/R injury via restoration of mitochondrial function

OBJECTIVES

Overwhelming evidence shows that dietary supplementation with n-3 polyunsaturated fatty acids (PUFAs) elicits protective effects on patients with cardiovascular disease. However, the detailed mechanisms underlying n-3 PUFA-mediated cardioprotection are unknown, and examined in the present study.

METHODS

We evaluated heart performances with Langendorff perfusion apparatus. Meanwhile, whole mitochondria were purified from non-perfused hearts for functional assessment, and lipid peroxidation level was measured as well.

RESULTS

Compared with control groups, hearts from n-3 PUFA-supplemented rats showed improved functional recovery and reduced tissue injury following ischemia/reperfusion (I/R). Furthermore, the mitochondrial function of PUFA-treated hearts was significantly enhanced, as demonstrated by biochemical analysis of respiratory chain activity. In addition, thiobarbituric acid-reactive substance or TBARS assay revealed that lipid peroxidation product, malondialdehyde or MDA, in the mitochondria was significantly reduced by PUFA treatment.

CONCLUSION

Taken together, our data indicate that marine n-3 PUFA could improve cardiac performance after I/R injury by restoring mitochondrial respiratory activities and attenuating lipid peroxidation.

Calpeptin, not calpain, directly inhibits an ion channel of the inner mitochondrial membrane

The permeability transition pore (PTP) of inner mitochondrial membranes is a large conductance pathway for ions up to 1500 Da which opening is responsible for ion equilibration and loss of membrane potential in apoptosis and thus in several neurodegenerative diseases. The PTP can be regulated by the Ca(2+)-activated mitochondrial K channel (BK). Calpains are Ca(2+)-activated cystein proteases; calpeptin is an inhibitor of calpains. We wondered whether calpain or calpeptin can modulate activity of PTP or BK. Patch clamp experiments were performed on mitoplasts of rat liver (PTP) and of an astrocytoma cell line (BK). Channel-independent open probability (P(o)) was determined (PTP) and, taking into account the number of open levels, NP(o) by single channel analysis (BK). We find that PTP in the presence of Ca(2+) (200 μM) is uninfluenced by calpain (13 nM) and shows insignificant decrease by the calpain inhibitor calpeptin (1 μM). The NP(o) of the BK is insensitive to calpain (54 nM), too. However, it is significantly and reversibly inhibited by the calpain inhibitor calpeptin (IC50 = 42 μM). The results agree with calpeptin-induced activation of the PTP via inhibition of the BK. Screening experiments with respirometry show calpeptin effects, fitting to inhibition of the BK by calpeptin, and strong inhibition of state 3 respiration.

Calcium-Activated Potassium Channels: Potential Target for Cardiovascular Diseases

Ca(2+)-activated K(+) channels (KCa) are classified into three subtypes: big conductance (BKCa), intermediate conductance (IKCa), and small conductance (SKCa) KCa channels. The three types of KCa channels have distinct physiological or pathological functions in cardiovascular system. BKCa channels are mainly expressed in vascular smooth muscle cells (VSMCs) and inner mitochondrial membrane of cardiomyocytes, activation of BKCa channels in these locations results in vasodilation and cardioprotection against cardiac ischemia. IKCa channels are expressed in VSMCs, endothelial cells, and cardiac fibroblasts and involved in vascular smooth muscle proliferation, migration, vessel dilation, and cardiac fibrosis. SKCa channels are widely expressed in nervous and cardiovascular system, and activation of SKCa channels mainly contributes membrane hyperpolarization. In this chapter, we summarize the physiological and pathological roles of the three types of KCa channels in cardiovascular system and put forward the possibility of KCa channels as potential target for cardiovascular diseases.

CaM and TNF-α mediate myocardial damage in acute necrotizing pancreatitis in rats

AIM: To investigate the role of calmodulin (CaM) and tumor necrosis factor (TNF)-α in myocardial injury associated with acute necrotizing pancreatitis (ANP) in rats.

METHODS: Thirty-six male Sprague-Dawley (SD) rats were randomly divided into a sham-operation (SO) group and an ANP group. ANP was induced by retrograde injection of sodium taurocholate into the biliopancreatic duct. Rats were sacrificed at 1, 4 and 8 h after operation. HE staining was used to observe the pathological changes of pancreatic and myocardial tissues. Fluorescence monitoring method was used to determine the free Ca²⁺ concentration in rat myocardial cells. The expression of CaM and TNF-α in myocardial cells was analyzed by real-time PCR.

RESULTS: Rats in the ANP all had pathological damage in pancreatic and myocardial tissues, which was progressively exacerbated. Compared with the SO group, the free Ca²⁺ concentration in rat myocardial cells was significantly reduced in the ANP group, and the free Ca²⁺ concentration decreased as the severity of the disease increased (P < 0.05). Compared with the SO group, the expression of CaM and TNF-α in myocardial cells was markedly up-regulated in the ANP group. The expression of CaM and TNF-α was negatively correlated with the calcium ion concentration in myocardial cells.

CONCLUSION: CaM and TNF-α mediate myocardial damage in ANP through inhibiting calcium channels.

BK channel activators and their therapeutic perspectives

The large conductance calcium- and voltage-activated K⁺ channel (KCa1.1, BK, MaxiK) is ubiquitously expressed in the body, and holds the ability to integrate changes in intracellular calcium and membrane potential. This makes the BK channel an important negative feedback system linking increases in intracellular calcium to outward hyperpolarizing potassium currents. Consequently, the channel has many important physiological roles including regulation of smooth muscle tone, neurotransmitter release and neuronal excitability. Additionally, cardioprotective roles have been revealed in recent years. After a short introduction to the structure, function and regulation of BK channels, we review the small organic molecules activating BK channels and how these tool compounds have helped delineate the roles of BK channels in health and disease.

Atorvastatin-induced cardioprotection of human myocardium is mediated by the inhibition of mitochondrial permeability transition pore opening via tumor necrosis factor-α and Janus kinase/signal transducers and activators of transcription pathway

BACKGROUND

The role of tumor necrosis factor-α (TNF-α), Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway, and mitochondrial Permeability Transition Pore in atorvastatin-induced cardioprotection were examined in human myocardium, in vitro.

METHODS

Isometric force of contraction of human right atrial trabeculae was recorded during 30-min hypoxia and 60-min reoxygenation (control) and in the presence of atorvastatin (0.1 µM, 1 µM, 10 µM). In early reoxygenation, the TNF-α inhibitor, AG490 (inhibitor of JAK/STAT), or atractyloside (mitochondrial Permeability Transition Pore opener), were administered. Cyclosporine A (inhibitor of mitochondrial Permeability Transition Pore opening) was administered during the first minute of reoxygenation alone or in presence of atorvastatin and TNF-α inhibitor or AG490. The force of contraction (percentage of baseline) at the end of reoxygenation period was compared (mean ± SD; n = 6 in each group). Protein expression of JAK/STAT pathway was measured using Western immunoblotting.

RESULTS

Atorvastatin 0.1 µM (70 ± 9%), 1 µM (85 ± 5%), 10 µM (89 ± 5%), and Cyclosporine A (87 ± 10%) improved the recovery of force of contraction at the end of reoxygenation, as compared with control (50 ± 3%). Atorvastatin 1 µM (4.64 ± 2.90 ng · ml(-1) · g(-1) of tissue) decreased the release of troponin Ic after hypoxia-reoxygenation (control: 26.34 ± 19.30 ng · ml(-1) · g(-1); P < 0.001). The enhanced recovery of force of contraction after atorvastatin administration was abolished by TNF-α inhibitor (53 ± 8%), AG490 (56 ± 7%), atractyloside (48 ± 8%). Cyclosporine A restored the atorvastatin-induced cardioprotection abolished by TNF-α inhibitor (87 ± 6%) and AG490 (83 ± 9%). Atorvastatin significantly increased the phosphorylation of JAK-2 and STAT-3, TNF-α inhibitor abolished the enhanced phosphorylation of JAK-2 and STAT-3 by atorvastatin.

CONCLUSIONS

Atorvastatin-induced cardioprotection involved the inhibition of the mitochondrial Permeability Transition Pore opening via the activation of TNF-α and the JAK/STAT pathway in early reoxygenation.

The protective effect of fasudil on the structure and function of cardiac mitochondria from rats with type 2 diabetes induced by streptozotocin with a high-fat diet is mediated by the attenuation of oxidative stress

Dysfunction of cardiac mitochondria appears to play a substantial role in cardiomyopathy or myocardial dysfunction and is a promising therapeutic target for many cardiovascular diseases. We investigated the effect of the Rho/Rho-associated protein kinase (ROCK) inhibitor fasudil on cardiac mitochondria from rats in which diabetes was induced by a combination of streptozotocin (STZ) and a sustained high-fat diet. Eight weeks after diabetes was induced by a single intraperitoneal injection of 50 mg/kg STZ followed by a sustained high-fat diet, either fasudil (5 mg/kg bid) or equivalent volumes of saline (control) were administered over four weeks. Fasudil significantly protected against the histopathologic changes of cardiac mitochondria in diabetic rats. Fasudil significantly reduced the abundances of the Rho A, ROCK 1, and ROCK 2 proteins, restored the activities of succinate dehydrogenase (SDH) and monoamine oxidase (MAO) in cardiac mitochondria, inhibited the opening of the mitochondrial permeability transition pore, and decreased the total antioxidant capacity, as well as levels of malonyldialdehyde, hydroxy radical, reduced glutathione, and superoxide dismutase in heart. Fasudil improved the structures of cardiac mitochondria and increased both SDH and MAO activities in cardiac mitochondria. These beneficial effects may be associated with the attenuation of oxidative stress caused by fasudil treatment.

Intracellular BK(Ca) (iBK(Ca)) channels

The large conductance calcium- and voltage-activated potassium channel (BK(Ca)) is widely expressed at the plasma membrane. This channel is involved in a variety of fundamental cellular functions including excitability, smooth muscle contractility, and Ca(2+) homeostasis, as well as in pathological situations like proinflammatory responses in rheumatoid arthritis, and cancer cell proliferation. Immunochemical, biochemical and pharmacological studies from over a decade have intermittently shown the presence of BK(Ca) in intracellular organelles. To date, intracellular BK(Ca) (iBK(Ca)) has been localized in the mitochondria, endoplasmic reticulum, nucleus and Golgi apparatus but its functional role remains largely unknown except for the mitochondrial BK(Ca) whose opening is thought to play a role in protecting the heart from ischaemic injury. In the nucleus, pharmacology suggests a role in regulating nuclear Ca(2+), membrane potential and eNOS expression. Establishing the molecular correlates of iBK(Ca), the mechanisms defining iBK(Ca) organelle-specific targeting, and their modulation are challenging questions. This review summarizes iBK(Ca) channels, their possible functions, and efforts to identify their molecular correlates.

Desflurane-induced post-conditioning against myocardial infarction is mediated by calcium-activated potassium channels: role of the mitochondrial permeability transition pore

BACKGROUND

Desflurane (DES)-induced preconditioning is mediated by large-conductance calcium-activated potassium channels (BK(Ca)). Whether BK(Ca) are involved in anaesthetic-induced post-conditioning is unknown. We tested the hypothesis that DES-induced post-conditioning is mediated by BK(Ca) upstream of the mitochondrial permeability transition pore (mPTP).

METHODS

Pentobarbital-anaesthetized male C57Black/6 mice were subjected to 45 min coronary artery occlusion (CAO) and 3 h reperfusion. Animals received either no intervention or dimethylsulphoxide (DMSO, 10 µl g(-1)). DES (1.0 MAC, 7.5 vol%) was administered for 18 min, starting 3 min before the end of CAO. The following agents were given either alone or in combination with DES: the BK(Ca) activator NS1619 (1 µg g(-1)), the BK(Ca) inhibitor iberiotoxin (IbTx, 0.05 µg g(-1)), the mPTP opener atractyloside (ATRA, 25 µg g(-1)), and the mPTP inhibitor cyclosporine A (CYC A, 10 µg g(-1)). Infarct size (IS) was determined with triphenyltetrazolium chloride and the area at risk with Evans Blue, respectively.

RESULTS

IS in control animals was 48(6)%. Neither DMSO, IbTx nor ATRA affected myocardial IS. DES alone or NS1619 alone or the combination reduced IS (P<0.05), CYC A alone or in combination with IbTx or DES also reduced IS (P<0.05). DES-induced reduction of myocardial IS was completely abolished by IbTx and was partially blocked by ATRA and ATRA partially blocked IS reduction by NS1619.

CONCLUSIONS

These data suggest that DES-induced post-conditioning against myocardial infarction is mediated by BK(Ca) and mPTP. Cardioprotection by BK(Ca) activator NS1619 might occur, at least in part, independently of mPTP.

Role of large-conductance Ca²+-activated K+ channels in adenosine A₁ receptor-mediated pharmacological postconditioning in H9c2 cells

Ischaemic postconditioning is a phenomenon whereby short periods of ischaemia applied during the start of reperfusion protect the myocardium from the damaging consequences of reperfusion. As such, pharmacological-induced postconditioning represents an attractive therapeutic strategy for reducing reperfusion injury during cardiac surgery and following myocardial infarction. The primary aim of this study was to determine the role of large-conductance Ca²(+)-activated potassium channels (BK(Ca) channels) in adenosine A₁ receptor-induced pharmacological postconditioning in the rat embryonic cardiomyoblast-derived cell line H9c2. H9c2 cells were exposed to 6 h hypoxia (0.5% O₂) followed by 18 h reoxygenation (H/R) after which cell viability was assessed by monitoring lactate dehydrogenase (LDH) release and caspase-3 activation. The adenosine A₁ receptor agonist N⁶-cyclopentyladenosine (CPA; 100 nmol/L) or the BK(Ca) channel opener NS1619 (10 µmol/L) were added for 30 min at the start of reoxygenation following 6 h hypoxic exposure. Where appropriate, cells were treated (15 min) before pharmacological postconditioning with the BK(Ca) channel blockers paxilline (1 µmol/L) or iberiotoxin (100 nmol/L). Pharmacological postconditioning with CPA or NS1619 significantly reduced H/R-induced LDH release. Treatment with paxilline or iberiotoxin attenuated adenosine A₁ receptor and NS1619-induced pharmacological postconditioning. These results have shown for the first time that BK(Ca) channels are involved in adenosine A₁ receptor-induced pharmacological postconditioning in a cell model system.

TNFα in myocardial ischemia/reperfusion, remodeling and heart failure

TNFα is crucially involved in the pathogenesis and progression of myocardial ischemia/reperfusion injury and heart failure. The formation and release of TNFα and its downstream signal transduction cascade following activation of its two receptor subtypes are characterized. Myocardial TNFα and TNF receptor activation have an ambivalent role in myocardial ischemia/reperfusion injury and protection from it. Excessive TNFα expression and subsequent cardiomyocyte TNF receptor type 1 stimulation induce contractile dysfunction, hypertrophy, fibrosis and cell death, while a lower TNFα concentration and subsequent cardiomyocyte TNF receptor type 2 stimulation are protective. Apart from its concentration and receptor subtype, the myocardial action of TNFα depends on the duration of its exposure and its localization. While detrimental during sustained ischemia, TNFα contributes to ischemic preconditioning protection, no matter whether it is the first, second or third window of protection, and both TNF receptors are involved in the protective signal transduction cascade. Finally, the available clinical attempts to antagonize TNFα in cardiovascular disease, notably heart failure, are critically discussed.

Antecedent ethanol attenuates cerebral ischemia/reperfusion-induced leukocyte-endothelial adhesive interactions and delayed neuronal death: role of large conductance, Ca2+-activated K+ channels

EtOH-PC reduces postischemic neuronal injury in response to cerebral (I/R). We examined the mechanism underlying this protective effect by determining (i) whether it was associated with a decrease in I/R-induced leukocyte-endothelial adhesive interactions in postcapillary venules, and (ii) whether the protective effects were mediated by activation of large conductance, calcium-activated potassium (BK(Ca)) channels. Mice were administered ethanol by gavage or treated with the BK(Ca) channel opener, NS1619, 24 hours prior to I/R with or without prior treatment with the BK(Ca) channel blocker, PX. Both CCA were occluded for 20 minutes followed by two and three hours of reperfusion, and rolling (LR) and adherent (LA) leukocytes were quantified in pial venules using intravital microscopy. The extent of DND, apoptosis and glial activation in hippocampus were assessed four days after I/R. Compared with sham, I/R elicited increases in LR and LA in pial venules and DND and apoptosis as well as glial activation in the hippocampus. These effects were attenuated by EtOH-PC or antecedent NS1619 administration, and this protection was reversed by prior treatment with PX. Our results support a role for BK(Ca) channel activation in the neuroprotective effects of EtOH-PC in cerebral I/R.

Gadolinium decreases inflammation related to myocardial ischemia and reperfusion injury

BACKGROUND

The lanthanide cation, gadolinium (GdCl3) protects the myocardium against infarction following ischemia and reperfusion. Neutrophils and macrophages are the main leukocytes responsible for infarct expansion after reperfusion. GdCl3 interferes with macrophage and neutrophil function in the liver by decreasing macrophage secretion of inflammatory cytokines and neutrophil infiltration. We hypothesized that GdCl3 protects against ischemia and reperfusion injury by decreasing inflammation. We determined the impact of GdCl3 treatment for reperfusion injury on 1) circulating monoctye and neutrophil counts, 2) secretion of inflammatory cytokines, and 3) influx of monocytes and neutrophils into the myocardium.

METHODS

Rats (n = 3-6/gp) were treated with saline or GdCl3 (20 mumol/kg) 15 min prior to a 30 min period of regional ischemia and 120 min reperfusion. Sham rats were not subject to ischemia. Blood was collected either after 30 min ischemia or 120 min reperfusion and hearts were harvested at 120 min reperfusion for tissue analysis. Blood was analyzed for leukocytes counts and cytokines. Tissue was analyzed for cytokines and markers of neutrophil and monocyte infiltration by measuring myeloperoxidase (MPO) and alpha-naphthyl acetate esterase (ANAE).

RESULTS

GdCl3 did not affect the number of circulating neutrophils prior to ischemia. Two hours reperfusion resulted in a 2- and 3- fold increase in circulating monocytes and neutrophils, respectively. GdCl3 decreased the number of circulating monocytes and neutrophils during reperfusion to levels below those present prior to ischemia. Furthermore, after 120 min of reperfusion, GdCl3 decreased ANAE and MPO activity in the myocardium by 1.9-fold and 6.5-fold respectively. GdCl3 decreased MPO activity to levels below those measured in the Sham group. Serum levels of the major neutrophil chemoattractant cytokine, IL-8 were increased from pre-ischemic levels during ischemia and reperfusion in both control and GdCl3 treated rats. Likewise, IL-8 levels increased throughout the 3 hour time period in the Sham group. There was no difference in IL-8 detected in the myocardium after 120 min reperfusion between groups. In contrast, after 120 min reperfusion GdCl3 decreased the myocardial tissue levels of macrophage secreted cytokines, GM-CSF and IL-1.

CONCLUSION

GdCl3 treatment prior to ischemia and reperfusion injury decreased circulating monocytes and neutrophils, macrophage secreted cytokines, and leukocyte infiltration into injured myocardium. These results suggest GdCl3 decreased monoctye and neutrophil migration and activation and may be a novel treatment for inflammation during ischemia and reperfusion.

Role of large-conductance Ca(2+) -activated potassium channels in adenosine A(1) receptor-mediated pharmacological preconditioning in H9c2 cells

Large-conductance Ca(2+)-activated potassium channels, located on the inner mitochondrial membrane, have recently been implicated in cytoprotection. Therefore, the primary aim of this study was to determine the role of large-conductance Ca(2+)-activated potassium channels in adenosine A(1) receptor-induced pharmacological preconditioning in the rat embryonic cardiomyoblast-derived cell line H9c2. For pharmacological preconditioning, H9c2 cells were exposed to the adenosine A(1) receptor agonist N(6)-cyclopentyladenosine (100 nM) or the Ca(2+)-activated potassium channel opener NS1619 (10 microM) for 30 min prior to 6 h hypoxia (0.5% O(2)) in glucose-free and serum-free media. Where appropriate cells were treated (15 min) before pharmacological preconditioning with the Ca(2+)-activated potassium channels blockers paxilline (1 microM) or iberiotoxin (100 nM). Cell viability following 6 h hypoxia was assessed by monitoring lactate dehydrogenase (LDH) release and caspase-3 activation. Ca(2+)-activated potassium channel subunit protein expression and cell survival protein kinase (ERK1/2 and PKB/Akt) activation were assessed by Western blotting. The results demonstrate that the adenosine A(1) receptor is functionally expressed in H9c2 cells and when activated protects against hypoxia-induced LDH release and caspase-3 activation. Treatment with paxilline or iberiotoxin attenuated adenosine A(1) receptor and NS1619-induced pharmacological preconditioning. Large-conductance Ca(2+)-activated potassium channel alpha and beta4 protein subunits were detected in mitochondrial fractions isolated from H9c2 cells. NS1619 (10 microM) induced no significant changes in ERK1/2 or PKB phosphorylation. These results have shown for the first time that large-conductance Ca(2+)-activated potassium channels are involved in adenosine A(1) receptor-induced pharmacological preconditioning in a cell model system.

Activation of the protective Survivor Activating Factor Enhancement (SAFE) pathway against reperfusion injury: Does it go beyond the RISK pathway?

Lethal reperfusion injury is now recognized as a major limitation of current reperfusion therapy by primary percutaneous coronary intervention for acute myocardial infarction. Interestingly, the heart itself is capable of activating an intrinsic protective signaling programme to limit cell death during reperfusion. Tumor necrosis factor alpha (TNFalpha) is a cytokine generally thought to contribute to myocardial dysfunction in ischemia/reperfusion or heart failure. We review evidence that TNFalpha can paradoxically initiate the activation of a novel protective pathway against reperfusion injuries that we have named the Survivor Activating Factor Enhancement (SAFE) pathway. This path requires the activation of the signal transducer and activator of transcription 3 (STAT-3) and it can successfully lessen cardiomyocyte death at the time of reperfusion, independently of the activation of the already well-described Reperfusion Injury Salvage Kinase (RISK) pathway (which includes activation of Akt and Erk 1/2). Emerging knowledge on this novel protective path is presented here with the aim of unravelling its interaction with the RISK pathway and its potential human application to protect against lethal reperfusion injury.

Activation of mitochondrial large-conductance calcium-activated K+ channels via protein kinase A mediates desflurane-induced preconditioning

BACKGROUND

ATP-regulated K+ channels are involved in anesthetic-induced preconditioning (APC). The role of other K+ channels in APC is unclear. We tested the hypothesis that APC is mediated by large-conductance calcium-activated K+ channels (K(Ca)).

METHODS

Pentobarbital-anesthetized male C57BL/6 mice were subjected to 45 min of coronary artery occlusion and 3 h reperfusion. Thirty minutes before coronary artery occlusion, 1.0 MAC desflurane was administered for 15 min alone or in combination with the large-conductance K(Ca) channel activator NS1619 (1 microg/g i.p.), its respective vehicle dimethylsulfoxide (10 microL/g i.p.), the large-conductance K(Ca) channel blocker iberiotoxin (0.05 microg/g i.p.), or the protein kinase A (PKA) inhibitor H-89 (0.5 microg/g intraventricular). Infarct size was determined with triphenyltetrazolium chloride and area at risk with Evans blue. Mitochondrial and sarcolemmal localization of large-conductance K(Ca) channels in cardiac myocytes was investigated with immunocytochemical staining of isolated cardiac myocytes.

RESULTS

Desflurane significantly reduced infarct size compared with control animals (7.4% +/- 0.8% vs 51.3% +/- 6.1%; P < 0.05). Activation of large-conductance K(Ca) channels by NS1619 (7.5% +/- 1.8%; P < 0.05) mimicked and blockade of large-conductance K(Ca) channels by iberiotoxin (49.1% +/- 7.5%) abrogated desflurane-induced preconditioning. PKA blockade by H-89 abolished desflurane-induced (45.1% +/- 4.0%) but not NS1619-induced (9.0% +/- 2.4%, P < 0.05) preconditioning. Immunocytochemical staining revealed that large-conductance K(Ca) channels were localized in the mitochondria but not in the sarcolemma of cardiac myocytes.

CONCLUSION

These data suggest that desflurane-induced APC is mediated in part by activation of mitochondrial large-conductance K(Ca) channels, and that activation of these channels by desflurane is mediated by PKA.

Opening the calcium-activated potassium channel participates in the cardioprotective effect of puerarin

The aim of the present study was to determine whether the effective cardioprotection conferred by puerarin against ischemia and reperfusion is mediated by the calcium-activated potassium channel. 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. Pretreatment with puerarin at 0.24 mmol/l for 5 min before ischemia increased myocardial formazan content and reduced LDH release during reperfusion. Administration of paxilline (1 micromol/l), an antagonist of the calcium-activated potassium channel, attenuated the protective effects of puerarin. In isolated ventricular myocytes, pretreatment with puerarin prevented simulated ischemia and reperfusion injury, hydrogen peroxide-induced cell death and the release of reactive oxygen species. Paxilline and chelerythrine (a protein kinase C inhibitor) both attenuated the effects of puerarin. These findings indicate that puerarin protects the myocardium against ischemia and reperfusion injury via opening the calcium-activated potassium channel and activating protein kinase C.

Mitochondrial ion channels

In work spanning more than a century, mitochondria have been recognized for their multifunctional roles in metabolism, energy transduction, ion transport, inheritance, signaling, and cell death. Foremost among these tasks is the continuous production of ATP through oxidative phosphorylation, which requires a large electrochemical driving force for protons across the mitochondrial inner membrane. This process requires a membrane with relatively low permeability to ions to minimize energy dissipation. However, a wealth of evidence now indicates that both selective and nonselective ion channels are present in the mitochondrial inner membrane, along with several known channels on the outer membrane. Some of these channels are active under physiological conditions, and others may be activated under pathophysiological conditions to act as the major determinants of cell life and death. This review summarizes research on mitochondrial ion channels and efforts to identify their molecular correlates. Except in a few cases, our understanding of the structure of mitochondrial ion channels is limited, indicating the need for focused discovery in this area.

Bongkrekic acid and atractyloside inhibits chloride channels from mitochondrial membranes of rat heart

The aim of this work was to characterize the effect of bongkrekic acid (BKA), atractyloside (ATR) and carboxyatractyloside (CAT) on single channel properties of chloride channels from mitochondria. Mitochondrial membranes isolated from a rat heart muscle were incorporated into a bilayer lipid membrane (BLM) and single chloride channel currents were measured in 250/50 mM KCl cis/trans solutions. BKA (1-100 microM), ATR and CAT (5-100 microM) inhibited the chloride channels in dose-dependent manner. The inhibitory effect of the BKA, ATR and CAT was pronounced from the trans side of a BLM and it increased with time and at negative voltages (trans-cis). These compounds did not influence the single channel amplitude, but decreased open dwell time of channels. The inhibitory effect of BKA, ATR and CAT on the mitochondrial chloride channel may help to explain some of their cellular and/or subcellular effects.