Role of sarcolemmal ATP-sensitive potassium channel in oxidative stress-induced apoptosis: mitochondrial connection

The involvement of soluble epoxide hydrolase in the development of cardiovascular diseases through epoxyeicosatrienoic acids

Arachidonic acid (AA) has three main metabolic pathways: the cycloxygenases (COXs) pathway, the lipoxygenases (LOXs) pathway, and the cytochrome P450s (CYPs) pathway. AA produces epoxyeicosatrienoic acids (EETs) through the CYPs pathway. EETs are very unstable in vivo and can be degraded in seconds to minutes. EETs have multiple degradation pathways, but are mainly degraded in the presence of soluble epoxide hydrolase (sEH). sEH is an enzyme of bifunctional nature, and current research focuses on the activity of its C-terminal epoxide hydrolase (sEH-H), which hydrolyzes the EETs to the corresponding inactive or low activity diol. Previous studies have reported that EETs have cardiovascular protective effects, and the activity of sEH-H plays a role by degrading EETs and inhibiting their protective effects. The activity of sEH-H plays a different role in different cells, such as inhibiting endothelial cell proliferation and migration, but promoting vascular smooth muscle cell proliferation and migration. Therefore, it is of interest whether the activity of sEH-H is involved in the initiation and progression of cardiovascular diseases by affecting the function of different cells through EETs.

Modification of Ischemia/Reperfusion-Induced Alterations in Subcellular Organelles by Ischemic Preconditioning

It is now well established that ischemia/reperfusion (I/R) injury is associated with the compromised recovery of cardiac contractile function. Such an adverse effect of I/R injury in the heart is attributed to the development of oxidative stress and intracellular Ca²⁺-overload, which are known to induce remodeling of subcellular organelles such as sarcolemma, sarcoplasmic reticulum, mitochondria and myofibrils. However, repeated episodes of brief periods of ischemia followed by reperfusion or ischemic preconditioning (IP) have been shown to improve cardiac function and exert cardioprotective actions against the adverse effects of prolonged I/R injury. This protective action of IP in attenuating myocardial damage and subcellular remodeling is likely to be due to marked reductions in the occurrence of oxidative stress and intracellular Ca²⁺-overload in cardiomyocytes. In addition, the beneficial actions of IP have been attributed to the depression of proteolytic activities and inflammatory levels of cytokines as well as the activation of the nuclear factor erythroid factor 2-mediated signal transduction pathway. Accordingly, this review is intended to describe some of the changes in subcellular organelles, which are induced in cardiomyocytes by I/R for the occurrence of oxidative stress and intracellular Ca²⁺-overload and highlight some of the mechanisms for explaining the cardioprotective effects of IP.

Hearts lacking plasma membrane KATP channels display changes in basal aerobic metabolic substrate preference and AMPK activity

Cardiac ATP-sensitive K+ (KATP) channels couple changes in cellular metabolism to membrane excitability and are activated during metabolic stress, although under basal aerobic conditions, KATP channels are thought to be predominately closed. Despite intense research into the roles of KATP channels during metabolic stress, their contribution to aerobic basal cardiac metabolism has not been previously investigated. Hearts from Kir6.2+/+ and Kir6.2−/− mice were perfused in working mode, and rates of glycolysis, fatty acid oxidation, and glucose oxidation were measured. Changes in activation/expression of proteins regulating metabolism were probed by Western blot analysis. Despite cardiac mechanical function and metabolic efficiency being similar in both groups, hearts from Kir6.2−/− mice displayed an approximately twofold increase in fatty acid oxidation and a 0.45-fold reduction in glycolytic rates but similar glucose oxidation rates compared with hearts from Kir6.2+/+ mice. Kir6.2−/− hearts also possessed elevated levels of activated AMP-activated protein kinase (AMPK), higher glycogen content, and reduced mitochondrial density. Moreover, activation of AMPK by isoproterenol or diazoxide was significantly blunted in Kir6.2−/− hearts. These data indicate that KATP channel ablation alters aerobic basal cardiac metabolism. The observed increase in fatty acid oxidation and decreased glycolysis before any metabolic insult may contribute to the poor recovery observed in Kir6.2−/− hearts in response to exercise or ischemia-reperfusion injury. Therefore, KATP channels may play an important role in the regulation of cardiac metabolism through AMPK signaling.

NEW & NOTEWORTHY In this study, we show that genetic ablation of plasma membrane ATP-sensitive K+ channels results in pronounced changes in cardiac metabolic substrate preference and AMP-activated protein kinase activity. These results suggest that ATP-sensitive K+ channels may play a novel role in regulating metabolism in addition to their well-documented effects on ionic homeostasis during periods of stress.

Sarcolemmal ATP-sensitive potassium channel protects cardiac myocytes against lipopolysaccharide-induced apoptosis

The sarcolemmal ATP-sensitive K⁺ (sarcK_ATP) channel plays a cardioprotective role during stress. However, the role of the sarcK_ATP channel in the apoptosis of cardiomyocytes and association with mitochondrial calcium remains unclear. For this purpose, we developed a model of LPS-induced sepsis in neonatal rat cardiomyocytes (NRCs). The TUNEL assay was performed in order to detect the apoptosis of cardiac myocytes and the MTT assay was performed to determine cellular viability. Exposure to LPS significantly decreased the viability of the NRCs as well as the expression of Bcl-2, whereas it enhanced the activity and expression of the apoptosis-related proteins caspase-3 and Bax, respectively. The sarcK_ATP channel blocker, HMR-1098, increased the apoptosis of NRCs, whereas the specific sarcK_ATP channel opener, P-1075, reduced the apoptosis of NRCs. The mitochondrial calcium uniporter inhibitor ruthenium red (RR) partially inhibited the pro-apoptotic effect of HMR-1098. In order to confirm the role of the sarcK_ATP channel, we constructed a recombinant adenovirus vector carrying the sarcK_ATP channel mutant subunit Kir6.2AAA to inhibit the channel activity. Kir6.2AAA adenovirus infection in NRCs significantly aggravated the apoptosis of myocytes induced by LPS. Elucidating the regulatory mechanisms of the sarcK_ATP channel in apoptosis may facilitate the development of novel therapeutic targets and strategies for the management of sepsis and cardiac dysfunction.

Adenosine triphosphate-sensitive potassium channels and cardiomyopathies (Review)

Cardiomyopathies have been indicated to be one of the leading causes of heart failure. Though it was indicated that genetic defects, viral infection and trace element deficiency were among the causes of cardiomyopathy, the etiology has remained to be fully elucidated. Cardiomyocytes require large amounts of energy to maintain their normal biological functions. Adenosine triphosphate-sensitive potassium channels (KATP), composed of inward-rectifier potassium ion channel and sulfonylurea receptor subunits, are present on the cell surface and mitochondrial membrane of cardiac muscle cells. As metabolic sensors sensitive to changes in intracellular energy levels, KATP adapt electrical activities to metabolic challenges, maintaining normal biological functions of myocytes. It is implied that malfunctions, mutations and altered expression of KATP are associated with the pathogenesis of conditions including c hypertrophy, diabetes as well as dilated, ischemic and endemic cardiomyopathy. However, the current knowledge is only the tip of the iceberg and the roles of KATP in cardiomyopathies largely remain to be elucidated in future studies.

Impact of hypoglycemic agents on myocardial ischemic preconditioning

Murry et al in 1986 discovered the intrinsic mechanism of profound protection called ischemic preconditioning. The complex cellular signaling cascades underlying this phenomenon remain controversial and are only partially understood. However, evidence suggests that adenosine, released during the initial ischemic insult, activates a variety of G protein-coupled agonists, such as opioids, bradykinin, and catecholamines, resulting in the activation of protein kinases, especially protein kinase C (PKC). This leads to the translocation of PKC from the cytoplasm to the sarcolemma, where it stimulates the opening of the ATP-sensitive K⁺ channel, which confers resistance to ischemia. It is known that a range of different hypoglycemic agents that activate the same signaling cascades at various cellular levels can interfere with protection from ischemic preconditioning. This review examines the effects of several hypoglycemic agents on myocardial ischemic preconditioning in animal studies and clinical trials.

Kir6.2 limits Ca(2+) overload and mitochondrial oscillations of ventricular myocytes in response to metabolic stress

ATP-sensitive K(+) (KATP) channels are abundant membrane proteins in cardiac myocytes that are directly gated by intracellular ATP and form a signaling complex with metabolic enzymes, such as creatine kinase. KATP channels are known to be essential for adaption to cardiac stress, such as ischemia; however, how all the molecular components of the stress response interact is not fully understood. We examined the effects of decreasing the KATP current density on Ca(2+) and mitochondrial homeostasis and ischemic preconditioning. Acute knockdown of the pore-forming subunit, Kir6.2, was achieved using adenoviral delivery of short hairpin RNA targeted to Kir6.2. The acute nature of the knockdown of Kir6.2 accurately shows the effects of Kir6.2 depletion without any compensatory effects that may arise in transgenic studies. We also investigated the effect of reducing the KATP current while maintaining KATP channel protein in the sarcolemmal membrane using a nonconducting Kir6.2 construct. Only 50% KATP current remained after Kir6.2 knockdown, yet there were profound effects on myocyte responses to metabolic stress. Kir6.2 was essential for cardiac myocyte Ca(2+) homeostasis under both baseline conditions before any metabolic stress and after metabolic stress. Expression of nonconducting Kir6.2 also resulted in increased Ca(2+) overload, showing the importance of K(+) conductance in the protective response. Both ischemic preconditioning and protection during ischemia were lost when Kir6.2 was knocked down. KATP current density was also important for the mitochondrial membrane potential at rest and prevented mitochondrial membrane potential oscillations during oxidative stress. KATP channel density is important for adaption to metabolic stress.

Novel soluble epoxide hydrolase inhibitor protects mitochondrial function following stress

Epoxyeicosatrienoic acids (EETs) are active metabolites of arachidonic acid that are inactivated by soluble epoxide hydrolase enzyme (sEH) to dihydroxyeicosatrienoic acid. EETs are known to render cardioprotection against ischemia reperfusion (IR) injury by maintaining mitochondrial function. We investigated the effect of a novel sEH inhibitor (sEHi) in limiting IR injury. Mouse hearts were perfused in Langendorff mode for 40 min and subjected to 20 min of global no-flow ischemia followed by 40 min of reperfusion. Hearts were perfused with 0.0, 0.1, 1.0 and 10.0 µmol·L–1 of the sEHi N-(2-chloro-4-methanesulfonyl-benzyl)-6-(2,2,2-trifluoro-ethoxy)-nicotinamide (BI00611953). Inhibition of sEH by BI00611953 significantly improved postischemic left-ventricular-developed pressure and reduced infarct size following IR compared with control hearts, and similar to hearts perfused with 11,12-EETs (1 µmol·L–1) and sEH–/– mice. Perfusion with the putative EET receptor antagonist 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE, 10 µmol·L–1), or the plasma membrane KATP channels (pmKATP) inhibitor (glibenclamide, 10 µmol·L–1) abolished the improved recovery by BI00611953 (1 µmol·L–1). Mechanistic studies in H9c2 cells demonstrated that BI0611953 decreased ROS generation, caspase-3 activity, proteasome activity, increased HIF-1∝ DNA binding, and delayed the loss of mitochondrial membrane potential (ΔΨm) caused by anoxia–reoxygenation. Together, our data demonstrate that the novel sEHi BI00611953, a nicotinamide-based compound, provides significant cardioprotection against ischemia reperfusion injury.

Role of PI3Kα and sarcolemmal ATP-sensitive potassium channels in epoxyeicosatrienoic acid mediated cardioprotection

AIMS

Epoxyeicosatrienoic acids (EETs) are cytochrome P450 epoxygenase metabolites of arachidonic acid that have known cardioprotective properties. While the mechanism(s) remains unknown, evidence suggests that phosphoinositide 3-kinase (PI3K) and sarcolemmal ATP-sensitive potassium channels (pmK(ATP)) are important. However the role of specific PI3K isoforms and corresponding intracellular mechanisms remains unknown.

METHODS AND RESULTS

To study this, mice hearts were perfused in Langendorff mode for 40 min of baseline and subjected to 20 or 30 min of global no-flow ischemia followed by 40 min of reperfusion. C57BL6 mice perfused with 11,12-EET (1 μM) had improved postischemic recovery, whereas co-perfusion with PI3Kα inhibitor, PI-103 (0.1 μM), abolished the EET-mediated effect. In contrast, blocking of PI3Kβ or PI3Kγ isoforms failed to inhibit EET-mediated cardioprotection. In addition to the improved post-ischemic recovery, increased levels of p-Akt, decreased calcineurin activity and decreased translocation of proapoptotic protein BAD to mitochondria were noted in EET-treated hearts. Perfusion of 11,12-EET to Kir6.2 deficient mice (pmK(ATP)) failed to improve postischemic recovery, decrease calcineurin activity and translocation of proapoptotic protein BAD, however increased levels of p-Akt were still observed. Patch-clamp experiments demonstrated that 11,12-EET could not activate pmK(ATP) currents in myocytes pre-treated with PI-103. Mechanistic studies in H9c2 cells demonstrate that 11,12-EET limits anoxia-reoxygenation triggered Ca(2+) accumulation and maintains mitochondrial ΔΨm compared to controls. Both PI-103 and glibenclamide (10 μM, pmK(ATP) inhibitor) abolished EET cytoprotection.

CONCLUSION

Together our data suggest that EET-mediated cardioprotection involves activation of PI3Kα, upstream of pmK(ATP), which prevents Ca(2+) overload and maintains mitochondrial function.

Activation of mitochondrial calcium-independent phospholipase A2γ (iPLA2γ) by divalent cations mediating arachidonate release and production of downstream eicosanoids

Calcium-independent phospholipase A(2)γ (iPLA(2)γ) (PNPLA8) is the predominant phospholipase activity in mammalian mitochondria. However, the chemical mechanisms that regulate its activity are unknown. Here, we utilize iPLA(2)γ gain of function and loss of function genetic models to demonstrate the robust activation of iPLA(2)γ in murine myocardial mitochondria by Ca(2+) or Mg(2+) ions. Calcium ion stimulated the production of 2-arachidonoyl-lysophosphatidylcholine (2-AA-LPC) from 1-palmitoyl-2-[(14)C]arachidonoyl-sn-glycero-3-phosphocholine during incubations with wild-type heart mitochondrial homogenates. Furthermore, incubation of mitochondrial homogenates from transgenic myocardium expressing iPLA(2)γ resulted in 13- and 25-fold increases in the initial rate of radiolabeled 2-AA-LPC and arachidonic acid (AA) production, respectively, in the presence of calcium ion. Mass spectrometric analysis of the products of calcium-activated hydrolysis of endogenous mitochondrial phospholipids in transgenic iPLA(2)γ mitochondria revealed the robust production of AA, 2-AA-LPC, and 2-docosahexaenoyl-LPC that was over 10-fold greater than wild-type mitochondria. The mechanism-based inhibitor (R)-(E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one (BEL) (iPLA(2)γ selective), but not its enantiomer, (S)-BEL (iPLA(2)β selective) or pyrrolidine (cytosolic PLA(2)α selective), markedly attenuated Ca(2+)-dependent fatty acid release and polyunsaturated LPC production. Moreover, Ca(2+)-induced iPLA(2)γ activation was accompanied by the production of downstream eicosanoid metabolites that were nearly completely ablated by (R)-BEL or by genetic ablation of iPLA(2)γ. Intriguingly, Ca(2+)-induced iPLA(2)γ activation was completely inhibited by long-chain acyl-CoA (IC(50) ∼20 μm) as well as by a nonhydrolyzable acyl-CoA thioether analog. Collectively, these results demonstrate that mitochondrial iPLA(2)γ is activated by divalent cations and inhibited by acyl-CoA modulating the generation of biologically active metabolites that regulate mitochondrial bioenergetic and signaling functions.

Mechanisms of the beneficial actions of ischemic preconditioning on subcellular remodeling in ischemic-reperfused heart

Cardiac function is compromised by oxidative stress which occurs upon exposing the heart to ischemia reperfusion (I/R) for a prolonged period. The reactive oxygen species (ROS) that are generated during I/R incur extensive damage to the myocardium and result in subcellular organelle remodeling. The cardiac nucleus, glycocalyx, myofilaments, sarcoplasmic reticulum, sarcolemma, and mitochondria are affected by ROS during I/R injury. On the other hand, brief periods of ischemia followed by reperfusion, or ischemic preconditioning (IPC), have been shown to be cardioprotective against oxidative stress by attenuating the cellular damage and alterations of subcellular organelles caused by subsequent I/R injury. Endogenous defense mechanisms, such as antioxidant enzymes and heat shock proteins, are activated by IPC and thus prevent damage caused by oxidative stress. Although these cardioprotective effects of IPC against I/R injury are considered to be a consequence of changes in the redox state of cardiomyocytes, IPC is considered to promote the production of NO which may protect subcellular organelles from the deleterious actions of oxidative stress. The article is intended to focus on the I/R-induced oxidative damage to subcellular organelles and to highlight the cardioprotective effects of IPC. In addition, the actions of various endogenous cardioprotective interventions are discussed to illustrate that changes in the redox state due to IPC are cardioprotective against I/R injury to the heart.

The protective roles of mitochondrial ATP-sensitive potassium channels during hypoxia-ischemia-reperfusion in brain

The role of ATP-sensitive potassium (K(ATP)) channels in cerebral ischemia-reperfusion has been well documented. K(ATP) channel openers protect neuron by mimicking ischemic preconditioning. However, the different protection between the mitochondrial and sarcolemma K(ATP) openers has been seldom studied. In the experiment, we investigated the effects of K(ATP) channel openers diazoxide and pinacidil on the hypoxia-ischemia-reperfusion in cultured hippocampal neurons and gerbil brain. The cultured hippocampal neurons and gerbil brain were pretreated with diazoxide or pinacidil before oxygen-glucose deprivation (OGD) and cerebral ischemia-reperfusion, respectively. Survival rate, apoptosis rate and lactate dehydrogenase (LDH) releasing after the reperfusion were subsequently detected. Then the subunits mRNA was detected by RT-PCR. The survival rate and LDH content in diazoxide group increased more than that in pinacidil group (86.21±2.73% vs. 78.59±1.94%, P<0.05; 133.29±15.00 U/L vs. 193.47±3.39 U/L, P<0.01). The apoptosis rate in diazoxide group decreased significantly more than that in pinacidil group (23.82±0.14% vs. 37.05±0.67%, P<0.01). Diazoxide pretreatment increased the expression of Kir6.1 mRNA obviously. The results suggested that mitoK(ATP) channels opener diazoxide played a major protective role on cerebral ischemia-reperfusion. Furthermore, diazoxide might become a new treatment for cerebral ischemia diseases through increasing the expression of Kir6.1 mRNA.

Inward rectifier potassium channels in the HL-1 cardiomyocyte-derived cell line

HL-1 is a line of immortalized cells of cardiomyocyte origin that are a useful complement to native cardiomyocytes in studies of cardiac gene regulation. Several types of ion channel have been identified in these cells, but not the physiologically important inward rectifier K(+) channels. Our aim was to identify and characterize inward rectifier K(+) channels in HL-1 cells. External Ba(2+) (100 µM) inhibited 44 ± 0.05% (mean ± s.e.m., n = 11) of inward current in whole-cell patch-clamp recordings. The reversal potential of the Ba(2+)-sensitive current shifted with external [K(+)] as expected for K(+)-selective channels. The slope conductance of the inward Ba(2+)-sensitive current increased with external [K(+)]. The apparent Kd for Ba(2+) was voltage dependent, ranging from 15 µM at -150  mV to 148 µM at -75  mV in 120  mM external K(+). This current was insensitive to 10 µM glybenclamide. A component of whole-cell current was sensitive to 150 µM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), although it did not correspond to the Ba(2+)-sensitive component. The effect of external 1 mM Cs(+) was similar to that of Ba(2+). Polymerase chain reaction using HL-1 cDNA as template and primers specific for the cardiac inward rectifier K(ir)2.1 produced a fragment of the expected size that was confirmed to be K(ir)2.1 by DNA sequencing. In conclusion, HL-1 cells express a current that is characteristic of cardiac inward rectifier K(+) channels, and express K(ir)2.1 mRNA. This cell line may have use as a system for studying inward rectifier gene regulation in a cardiomyocyte phenotype.

Protective actions of epoxyeicosatrienoic acid: dual targeting of cardiovascular PI3K and KATP channels

Epoxyeicosatrienoic acid(s) (EETs) have been shown to protect cardiovascular tissue against apoptosis dependent on activation of targets such as ATP-sensitive K+ (KATP) channels (sarcolemmal and mitochondrial), calcium-activated K+ channels, extracellular signal-regulated kinase or phosphoinositide 3-kinase (PI3K). We tested if EETs protect human atrial tissue ex vivo from hypoxia/reoxygenation (H/R) injury, and compared our results with myocardium from two rodent species, rats and mice. EETs reduced myocardial caspase 3 activity in all three species and protected against loss of mitochondrial membrane potential in primary cultures of neonatal rat ventricular myocytes submitted to H/R. In addition, EETs protected mouse pulmonary arteries ex vivo exposed to H/R. Myocardium and pulmonary arteries from genetically engineered mice having elevated plasma levels of EETs (Ephx2-/-) exhibited protection from H/R-induced injury over that of wild type controls, suggesting that endogenously produced EETs may have pro-survival effects. Electrophysiological studies in myocytes demonstrated that EETs can stimulate KATP currents even when PI3K is inhibited. Similarly, activation of PI3K/Akt occurred in the presence of the KATP channel blocker glibenclamide. Based upon loss of protection with EETs in the presence of either wortmannin (a PI3K inhibitor) or glibenclamide, simultaneous activation of at least 2 pathways, PI3K and KATP channels respectively, appears to be required for protection. In conclusion, we demonstrate that exogenous and endogenous EETs have powerful pro-survival effects in cardiovascular tissues including diseased human myocardium, mediated by activation of not only one but at least two pathways, PI3K and KATP channels.

Clinical cardioprotection and the value of conditioning responses

Adjunctive cardioprotective strategies for ameliorating the reversible and irreversible injuries with ischemia-reperfusion (I/R) are highly desirable. However, after decades of research, the promise of clinical cardioprotection from I/R injury remains poorly realized. This may arise from the challenges of trialing and effectively translating experimental findings from laboratory models to patients. One can additionally consider whether features of the more heavily focused upon candidates could limit or preclude therapeutic utility and thus whether we might shift attention to alternate strategies. The phenomena of preconditioning and postconditioning have proven fertile in identification of experimental means of cardioprotection and are the most intensely interrogated responses in the field. However, there is evidence these processes, which share common molecular signaling elements and end effectors, may be poor choices for clinical exploitation. This includes evidence of age dependence, limiting efficacy in target aged or senescent hearts; refractoriness to conditioning stimuli in diseased myocardium; interference from a variety of relevant pharmaceuticals; inadvertent induction of these responses by prior ischemia or commonly used drugs, precluding further benefit; and sex dependence of protective signaling. This review focuses on these features, raising questions about current research strategies, and the suitability of these widely studied phenomena as rational candidates for clinical translation.

Epoxyeicosatrienoic acid prevents postischemic electrocardiogram abnormalities in an isolated heart model

Cytochrome P450 epoxygenases metabolize arachidonic acid (AA) to epoxyeicosatrienoic acids (EETs) which are in turn converted to dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH). The main objective of this study was to investigate the protective effects of EETs following ischemic injury using an ex vivo electrocardiogram (EKG) model. Hearts from C57Bl/6, transgenic mice with cardiomyocyte-specific overexpression of CYP2J2 (Tr) and wildtype (WT) littermates were excised and perfused with constant pressure in a Langendorff apparatus. Electrodes were placed superficially at the right atrium and left ventricle to assess EKG waveforms. In ischemic reperfusion experiments hearts were subjected to 20 min of global no-flow ischemia followed by 20 min of reperfusion (R20). The EKG from C57Bl/6 hearts perfused with 1 microM 14,15-EET showed less QT prolongation (QTc) and ST elevation (STE) (QTc=41+/-3, STE=2.3+/-0.3; R20: QTc=42+/-2 ms, STE=1.2+/-0.2mv) than control hearts (QTc=36+/-2, STE=2.3+/-0.2; R20: QTc=53+/-3 ms; STE=3.6+/-0.4mv). Similar results of reduced QT prolongation and ST elevation were observed in EKG recording from CYP2J2 Tr mice (QTc=35+/-1, STE=1.9+/-0.1; R20: QTc=38+/-4 ms, STE=1.3+/-0.2mv) compared to WT hearts. The putative epoxygenase inhibitor MS-PPOH (50 microM) and EET antagonist 14,15-EEZE (10 microM) both abolished the cardioprotective response, implicating EETs in this process. In addition, separate exposure to the K(ATP) channel blockers glibenclamide (1 microM) and HMR1098 (10 microM), or the PKA protein inhibitor H89 (50 nM) during reperfusion abolished the improved repolarization in both the models. Consistent with a role of PKA, CYP2J2 Tr mice had an enhanced activation of the PKAalpha regulatory II subunit in plasma membrane following IR injury. The present data demonstrate that EETs can enhance the recovery of ventricular repolarization following ischemia, potentially by facilitating activation of K(+) channels and PKA-dependent signaling.