Effects of epoxyeicosatrienoic acids on isolated hearts and ventricular myocytes

Redox Regulation of Soluble Epoxide Hydrolase-Implications for Cardiovascular Health and Disease

Cell responses to changes in their redox state are significantly mediated by reversible oxido-reductive post-translational modifications of proteins, potentially altering their activities or interactions. These modifications are important for the homeostatic responses of cells to environmental changes that alter their redox state. Such redox regulatory mechanisms not only operate to maintain health, but can become dysregulated and contribute to pathophysiology. In this review, we focus on the redox control of soluble epoxide hydrolase (sEH), which is widely expressed, including in blood vessels and cardiomyocytes. We review the different types of oxidative modifications that regulate sEH and how they may alter cardiovascular physiology and affect disease progression during stress.

Epoxides and soluble epoxide hydrolase in cardiovascular physiology

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites that importantly contribute to vascular and cardiac physiology. The contribution of EETs to vascular and cardiac function is further influenced by soluble epoxide hydrolase (sEH) that degrades EETs to diols. Vascular actions of EETs include dilation and angiogenesis. EETs also decrease inflammation and platelet aggregation and in general act to maintain vascular homeostasis. Myocyte contraction and increased coronary blood flow are the two primary EET actions in the heart. EET cell signaling mechanisms are tissue and organ specific and provide significant evidence for the existence of EET receptors. Additionally, pharmacological and genetic manipulations of EETs and sEH have demonstrated a contribution for this metabolic pathway to cardiovascular diseases. Given the impact of EETs to cardiovascular physiology, there is emerging evidence that development of EET-based therapeutics will be beneficial for cardiovascular diseases.

Stable EET urea agonist and soluble epoxide hydrolase inhibitor regulate rat pulmonary arteries through TRPCs

Epoxyeicosatrienoic acids (EETs), cytochrome P450-derived metabolites of arachidonic acid, have been reported to increase intracellular calcium concentration in aortic vascular smooth muscle cells (SMCs). As EETs are labile, we synthesized a new stable urea EET analog with agonist and soluble epoxide hydrolase (sEH) inhibitor properties. We refer to this analog, 12-(3-hexylureido)dodec-8-enoic acid, as 8-HUDE. Measuring tension of vascular rings, intracellular calcium signaling by confocal laser scanning microscopy and gene expression by reverse-transcription-PCR and western blots, we examined the effects of 8-HUDE on pulmonary vascular tone and calcium signaling in rat pulmonary artery (PA) SMCs (PASMCs). 8-HUDE increased the tension of rat PAs to 145% baseline, whereas it had no effect on the tension of mesenteric arteries (MAs). The 8-HUDE-induced increase in vascular tone was abolished by removal of extracellular Ca(2+) or by pretreatment with either La(3+) or SKF96365, which are inhibitors of canonical transient receptor potential channels (TRPCs). Furthermore, 8-HUDE-evoked increases in [Ca(2+)](i) in PASMCs could be blunted by inhibition of TRPC with SKF96365, removal of extracellular calcium or depletion of intracellular calcium stores with caffeine, cyclopiazonic acid or 2-aminoethoxydiphenyl borate, but not by the voltage-activated calcium channel blocker nifedipine. In addition to immediate effects on calcium signaling, 8-HUDE upregulated the expression of TRPC1 and TRPC6 at both mRNA and protein levels in rat PASMCs, whereas it suppressed the expression of sEH. Our observations suggest that 8-HUDE increases PA vascular tone through increased release of calcium from intracellular stores, enhanced [Ca(2+)](i) influx in PASMCs through store-operated Ca(2+) channels and modulated the expression of TRPC and sEH proteins in a proconstrictive manner.

Platelets and cardiac arrhythmia

Sudden cardiac death (SCD) remains one of the most prevalent modes of death in industrialized countries, and myocardial ischemia due to thrombotic coronary occlusion is its primary cause. The role of platelets in the occurrence of SCD extends beyond coronary flow impairment by clot formation. Here we review the substances released by platelets during clot formation and their arrhythmic properties. Platelet products are released from three types of platelet granules: dense core granules, alpha-granules, and platelet lysosomes. The physiologic properties of dense granule products are of special interest as a potential source of arrhythmic substances. They are released readily upon activation and contain high concentrations of serotonin, histamine, purines, pyrimidines, and ions such as calcium and magnesium. Potential arrhythmic mechanisms of these substances, e.g., serotonin and high energy phosphates, include induction of coronary constriction, calcium overloading, and induction of delayed after-depolarizations. Alpha-granules produce thromboxanes and other arachidonic-acid products with many potential arrhythmic effects mediated by interference with cardiac sodium, calcium, and potassium channels. Alpha-granules also contain hundreds of proteins that could potentially serve as ligands to receptors on cardiomyocytes. Lysosomal products probably do not have an important arrhythmic effect. Platelet products and ischemia can induce coronary permeability, thereby enhancing interaction with surrounding cardiomyocytes. Antiplatelet therapy is known to improve survival after myocardial infarction. Although an important part of this effect results from prevention of coronary clot formation, there is evidence to suggest that antiplatelet therapy also induces anti-arrhythmic effects during ischemia by preventing the release of platelet activation products.

Review article: epoxyeicosatrienoic acids: novel mediators of cardioprotection

Recent evidence from a number of in vitro and in vivo studies in isolated cells and animal models has suggested that the cytochrome P450 (CYP450) pathway of arachidonic acid (AA) metabolism produces potent cardioprotective metabolites that markedly reduce reversible (myocardial stunning) and irreversible (infarct size [IS]) injury in the ischemic/reperfused heart. The major players in this protective response appear to be the AA metabolites including the regioisomers of 5,6-, 8,9-, 11,12-, and 14,15-epoxyeicosatrienoic acids (EETs). The present review article will discuss the beneficial effects of the EETs on myocardial stunning and IS reduction and consider some of the signaling pathways and cellular mechanisms by which the EETs produce their beneficial effects and the possible therapeutic benefits that may result from activation of this pathway. The results discussed in this review are taken from experiments obtained from 3 diverse species in different laboratories: the mouse, rat, and dog, in which the results were nearly identical qualitatively and quantitatively, suggesting that these findings are likely to be extrapolated to man as well.

Overexpression of CYP2J2 provides protection against doxorubicin-induced cardiotoxicity

Human cytochrome P-450 (CYP)2J2 is abundant in heart and active in biosynthesis of epoxyeicosatrienoic acids (EETs). Recently, we demonstrated that these eicosanoid products protect myocardium from ischemia-reperfusion injury. The present study utilized transgenic (Tr) mice with cardiomyocyte-specific overexpression of human CYP2J2 to investigate protection toward toxicity resulting from acute (0, 5, or 15 mg/kg daily for 3 days, followed by 24-h recovery) or chronic (0, 1.5, or 3.0 mg/kg biweekly for 5 wk, followed by 2-wk recovery) doxorubicin (Dox) administration. Acute treatment resulted in marked elevations of serum lactate dehydrogenase and creatine kinase levels that were significantly greater in wild-type (WT) than CYP2J2 Tr mice. Acute treatment also resulted in less activation of stress response enzymes in CYP2J2 Tr mice (catalase 750% vs. 300% of baseline, caspase-3 235% vs. 165% of baseline in WT vs. CYP2J2 Tr mice). Moreover, CYP2J2 Tr hearts exhibited less Dox-induced cardiomyocytes apoptosis (measured by TUNEL) compared with WT hearts. After chronic treatment, comparable decreases in body weight were observed in WT and CYP2J2 Tr mice. However, cardiac function, assessed by measurement of fractional shortening with M-mode transthoracic echocardiography, was significantly higher in CYP2J2 Tr than WT hearts after chronic Dox treatment (WT 37 +/- 2%, CYP2J2 Tr 47 +/- 1%). WT mice also had larger increases in beta-myosin heavy chain and cardiac ankryin repeat protein compared with CYP2J2 Tr mice. CYP2J2 Tr hearts had a significantly higher rate of Dox metabolism than WT hearts (2.2 +/- 0.25 vs. 1.6 +/- 0.50 ng.min(-1).100 microg protein(-1)). In vitro data from H9c2 cells demonstrated that EETs attenuated Dox-induced mitochondrial damage. Together, these data suggest that cardiac-specific overexpression of CYP2J2 limited Dox-induced toxicity.

Eicosanoid signalling pathways in the heart

Myocardial phospholipids serve as primary reservoirs of arachidonic acid (AA), which is liberated through the rate-determining hydrolytic action of cardiac phospholipases A2 (PLA2s). A predominant PLA2 in myocardium is calcium-independent phospholipase A2beta (iPLA2beta), which, through its calmodulin (CaM) and ATP-binding domains, is regulated by alterations in local cellular Ca2+ concentrations and cardiac bioenergetic status, respectively. Importantly, iPLA2beta has been demonstrated to be activated by ischaemia through elevation of the concentration of myocardial fatty acyl-CoA, which abrogates Ca2+/CaM-mediated inhibition of iPLA2beta. AA released by PLA2-catalysed hydrolysis of phospholipids serves as a precursor for eicosanoids generated by pathways dependent on cyclooxygenases (COX), lipoxygenases (LOX), and cytochromes P450 (CYP). Eicosanoids initiate and propagate diverse signalling cascades, primarily through their interaction with cellular receptors and ion channels. However, during pathologic states such as ischaemia or congestive heart failure, eicosanoids contribute to multiple maladaptive changes including inflammation, alterations of cellular growth programmes, and activation of multiple transcriptional events leading to the deleterious sequelae of these pathologic states. This review summarizes the central roles of myocardial PLA(2)s in eicosanoid signalling in the heart, the major COX, LOX, and CYP pathways of eicosanoid generation in the myocardium, and the effects of important eicosanoids on receptor-, ion channel-, and transcription-mediated processes that facilitate cardiac hypertrophy, mediate ischaemic preconditioning, and precipitate arrhythmogenesis in response to pathologic stimuli.

Roles of epoxyeicosatrienoic acids in vascular regulation and cardiac preconditioning

Continuing investigations of the roles of cytochrome P450 (CYP) arachidonic acid epoxygenase metabolites in the regulation of cardiovascular physiology and pathophysiology have revealed their complex and diverse biological effects. Often these metabolites demonstrate protective properties that are revealed during cardiovascular disease. In this regard, the epoxyeicosatrienoic acids (EETs) are an emerging target for pharmacological manipulation aimed at enhancing their cardiac and vascular protective mechanisms. This review will focus on the role of EETs in the regulation of vascular tone, with emphasis on the coronary circulation, their role in limiting platelet aggregation, vascular inflammation and EET contribution to preconditioning of the ischemic myocardium. Production and metabolism of EETs as well as their specific cellular signaling mechanisms are discussed.

Epoxygenases and peroxisome proliferator-activated receptors in mammalian vascular biology

Epoxygenases, particularly of the CYP2C and CYP2J families, are important lipid-metabolizing enzymes. Epoxygenases are found throughout the cardiovascular system where their lipid products, particularly the epoxyeicosatrienoic acids (EETs), which are arachidonic acid metabolites, have the potential to regulate vascular tone, cellular proliferation, migration, inflammation and cardiac function. The receptors for EETs are, however, poorly understood. The peroxisome proliferator-activated receptors (PPARs) are a family of three (alpha, beta/delta and gamma) nuclear receptors that are activated by lipid metabolites. Activation of PPAR alpha and PPAR gamma, similar to the longer term effects of EETs, causes the inhibition of vascular cell proliferation, migration and inflammation. Interestingly, EETs and their metabolites have recently been found to active both PPAR alpha and PPAR gamma. The epoxygenase-EET-PPAR pathway may therefore represent a novel endogenous protective pathway by which short-lived lipid mediators control vascular cell activation.

Electrophysiological properties of cardiomyocytes isolated from CYP2J2 transgenic mice

CYP2J2 is abundant in cardiac tissue and active in the biosynthesis of eicosanoids such as epoxyeicosatrienoic acids (EETs). To determine the effects of CYP2J2 and its eicosanoid products in the heart, we characterized the electrophysiology of single cardiomyocytes isolated from adult transgenic (Tr) mice with cardiac-specific overexpression of CYP2J2. CYP2J2 Tr cardiomyocytes had a shortened action potential. At 90% repolarization, the action potential duration (APD) was 30.6 +/- 3.0 ms (n = 22) in wild-type (Wt) cells and 20.2 +/- 2.3 ms (n = 19) in CYP2J2 Tr cells (p < 0.005). This shortening was probably due to enhanced maximal peak transient outward K(+) currents (I(to,peak)), which were 38.6 +/- 2.8 and 54.4 +/- 4.9 pA/pF in Wt and CYP2J2 Tr cells, respectively (p < 0.05). In contrast, the late portion of the transient outward K(+) current (I(to,280ms)), the slowly inactivating outward K(+) current (I(K,slow)), and the voltage-gated Na(+) current (I(Na)) were not significantly altered in CYP2J2 Tr cells. N-Methylsulphonyl-6-(2-proparglyloxy-phenyl)hexanamide (MS-PPOH), a specific inhibitor of EET biosynthesis, significantly reduced I(to,peak) and increased APD in CYP2J2 Tr cardiomyocytes but not in Wt cells. Intracellular dialysis with a monoclonal antibody against CYP2J2 also significantly reduced I(to,peak) and increased APD in CYP2J2 Tr cardiomyocytes. Addition of 11,12-EET or 8-bromo-cAMP significantly reversed the MS-PPOH- or monoclonal antibody-induced changes in I(to,peak) and APD in CYP2J2 Tr cells. Together, our data demonstrate that shortening of the action potential in CYP2J2 Tr cardiomyocytes is associated with enhanced I(to,peak) via an EET-dependent, cAMP-mediated mechanism.

Mechanisms by which epoxyeicosatrienoic acids (EETs) elicit cardioprotection in rat hearts

Cytochrome P450 (CYP) epoxygenases and their arachidonic acid (AA) metabolites, the epoxyeicosatrienoic acids (EETs), have been shown to produce reductions in infarct size in canine myocardium following ischemia-reperfusion injury via opening of either the sarcolemmal K(ATP) (sarcK(ATP)) or mitochondrial K(ATP) (mitoK(ATP)) channel. In the present study, we subjected intact rat hearts to 30 min of left coronary artery occlusion and 2 h of reperfusion followed by tetrazolium staining to determine infarct size as a percent of the area at risk (IS/AAR, %). The results demonstrate that the two major regioisomers of the CYP epoxygenase pathway, 11,12-EET (2.5 mg/kg, iv) and 14,15-EET (2.5 mg/kg, iv) significantly reduced myocardial infarct size (IS/AAR, %) in rats as compared with control (41.9+/-2.3%, 40.9+/-1.2% versus 61.5+/-1.6%, respectively), whereas, a third regioisomer, 8,9-EET (2.5 mg/kg, iv) had no effect (55.2+/-1.4). The protective effect of pretreatment with 11,12- and 14,15-EETs was completely abolished (61.9+/-0.7%, 58.6+/-3.1%, HMR; 63.3+/-1.2%, 63.2+/-2.5%, 5-HD) in the presence of the selective sarcK(ATP) channel antagonist, HMR 1098 (6 mg/kg, iv) or the selective mitoK(ATP) channel antagonist, 5-HD (10 mg/kg, iv) given 10 min after 11,12- or 14,15-EET administration but 5 min prior to index ischemia. Furthermore, concomitant pretreatment with 11,12- or 14,15-EET in combination with the free radical scavenger, 2-mercaptopropionyl glycine (2-MPG), at a dose (20 mg/kg, iv) that had no effect on IS/AAR (57.7+/-1.3%), completely abolished the cardioprotective effect of 11,12- and 14,15-EETs (58.2+/-1.6%, 61.4+/-1.0%), respectively. These data suggest that part of the cardioprotective effects of EETs in rat hearts against infarction is the result of an initial burst of reactive oxygen species (ROS) and subsequent activation of both the sarcK(ATP) and mitoK(ATP) channel.

Role of epoxyeicosatrienoic acids in protecting the myocardium following ischemia/reperfusion injury

Cardiomyocyte injury following ischemia-reperfusion can lead to cell death and result in cardiac dysfunction. A wide range of cardioprotective factors have been studied to date, but only recently has the cardioprotective role of fatty acids, specifically arachidonic acid (AA), been investigated. This fatty acid can be found in the membranes of cells in an inactive state and can be released by phospholipases in response to several stimuli, such as ischemia. The metabolism of AA involves the cycloxygenase (COX) and lipoxygenase (LOX) pathways, as well as the less well characterized cytochrome P450 (CYP) monooxygenase pathway. Current research suggests important differences with respect to the cardiovascular actions of specific CYP mediated arachidonic acid metabolites. For example, CYP mediated hydroxylation of AA produces 20-hydroxyeicosatetraenoic acid (20-HETE) which has detrimental effects in the heart during ischemia, pro-inflammatory effects during reperfusion and potent vasoconstrictor effects in the coronary circulation. Conversely, epoxidation of AA by CYP enzymes generates 5,6-, 8,9-, 11,12- and 14,15-epoxyeicosatrienoic acids (EETs) that have been shown to reduce ischemia-reperfusion injury, have potent anti-inflammatory effects within the vasculature, and are potent vasodilators in the coronary circulation. This review aims to provide an overview of current data on the role of these CYP pathways in the heart with an emphasis on their involvement as mediators of ischemia-reperfusion injury. A better understanding of these relationships will facilitate identification of novel targets for the prevention and/or treatment of ischemic heart disease, a major worldwide public health problem.

Reduction of ischemia and reperfusion-induced myocardial damage by cytochrome P450 inhibitors

Ischemia and reperfusion both contribute to tissue damage after myocardial infarction. Although many drugs have been shown to reduce infarct size when administered before ischemia, few have been shown to be effective when administered at reperfusion. Moreover, although it is generally accepted that a burst of reactive oxygen species (ROS) occurs at the onset of reperfusion and contributes to tissue damage, the source of ROS and the mechanism of injury is unclear. We now report the finding that chloramphenicol administered at reperfusion reduced infarct size by 60% in a Langendorff isolated perfused rat heart model, and that ROS production was also substantially reduced. Chloramphenicol is an inhibitor of mitochondrial protein synthesis and is also an inhibitor of a subset of cytochrome P450 monooxygenases (CYPs). We could not detect any effect on mitochondrial encoded proteins or mitochondrial respiration in chloramphenicol-perfused hearts, and hypothesized that the effect was caused by inhibition of CYPs. We tested additional CYP inhibitors and found that cimetidine and sulfaphenazole, two CYP inhibitors that have no effect on mitochondrial protein synthesis, were also able to reduce creatine kinase release and infarct size in the Langendorff model. We also showed that chloramphenicol reduced infarct size in an open chest rabbit model of regional ischemia. Taken together, these findings implicate CYPs in myocardial ischemia/reperfusion injury.

P-450 metabolites of arachidonic acid in the control of cardiovascular function

Recent studies have indicated that arachidonic acid is primarily metabolized by cytochrome P-450 (CYP) enzymes in the brain, lung, kidney, and peripheral vasculature to 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) and that these compounds play critical roles in the regulation of renal, pulmonary, and cardiac function and vascular tone. EETs are endothelium-derived vasodilators that hyperpolarize vascular smooth muscle (VSM) cells by activating K(+) channels. 20-HETE is a vasoconstrictor produced in VSM cells that reduces the open-state probability of Ca(2+)-activated K(+) channels. Inhibitors of the formation of 20-HETE block the myogenic response of renal, cerebral, and skeletal muscle arterioles in vitro and autoregulation of renal and cerebral blood flow in vivo. They also block tubuloglomerular feedback responses in vivo and the vasoconstrictor response to elevations in tissue PO(2) both in vivo and in vitro. The formation of 20-HETE in VSM is stimulated by angiotensin II and endothelin and is inhibited by nitric oxide (NO) and carbon monoxide (CO). Blockade of the formation of 20-HETE attenuates the vascular responses to angiotensin II, endothelin, norepinephrine, NO, and CO. In the kidney, EETs and 20-HETE are produced in the proximal tubule and the thick ascending loop of Henle. They regulate Na(+) transport in these nephron segments. 20-HETE also contributes to the mitogenic effects of a variety of growth factors in VSM, renal epithelial, and mesangial cells. The production of EETs and 20-HETE is altered in experimental and genetic models of hypertension, diabetes, uremia, toxemia of pregnancy, and hepatorenal syndrome. Given the importance of this pathway in the control of cardiovascular function, it is likely that CYP metabolites of arachidonic acid contribute to the changes in renal function and vascular tone associated with some of these conditions and that drugs that modify the formation and/or actions of EETs and 20-HETE may have therapeutic benefits.

Cytochrome P-450 metabolite of arachidonic acid mediates bradykinin-induced negative inotropic effect

This study focused on the mechanisms of the negative inotropic response to bradykinin (BK) in isolated rat hearts perfused at constant flow. BK (100 nM) significantly reduced developed left ventricular pressure (LVP) and the maximal derivative of systolic LVP by 20-22%. The cytochrome P-450 (CYP) inhibitors 1-aminobenzotriazole (1 mM and 100 microM) or proadifen (5 microM) abolished the cardiodepression by BK, which was not affected by nitric oxide and cyclooxygenase inhibitors (35 microM NG-nitro-L-arginine methyl ester and 10 microM indomethacin, respectively). The CYP metabolite 14,15-epoxyeicosatrienoic acid (14,15-EET; 50 ng/ml) produced effects similar to those of BK in terms of the reduction in contractility. After the coronary endothelium was made dysfunctional by Triton X-100 (0.5 microl), the BK-induced negative inotropic effect was completely abolished, whereas the 14,15-EET-induced cardiodepression was not affected. In hearts with normal endothelium, after recovery from 14,15-EET effects, BK reduced developed LVP to a 35% greater extent than BK in the control. In conclusion, CYP inhibition or endothelial dysfunction prevents BK from causing cardiodepression, suggesting that, in the rat heart, endothelial CYP products mediate the negative inotropic effect of BK. One of these mediators appears to be 14,15-EET.

Effects of epoxyeicosatrienoic acids on the cardiac sodium channels in isolated rat ventricular myocytes

1. Whole-cell Na+ currents (holding potential, -80 mV; test potential, -30 mV) in rat myocytes were inhibited by 8, 9-epoxyeicosatrienoic acid (8,9-EET) in a dose-dependent manner with 22+/-4% inhibition at 0.5 microM, 48+/-5% at 1 microM, and 73+/-5% at 5 microM (mean +/- S.E.M., n = 10, P<0.05 for each dose vs. control). Similar results were obtained with 5,6-, 11,12-, and 14,15-EETs, while 8,9-dihydroxyeicosatrienoic acid (DHET) was 3-fold less potent and arachidonic acid was 10- to 20-fold less potent. 2. 8,9-EET produced a dose-dependent, hyperpolarized shift in the steady-state membrane potential at half-maximum inactivation (V ), without changing the slope factor. 8,9-EET had no effect on the steady-state activation of Na+ currents. 3. Inhibition of Na+ currents by 8,9-EET was use dependent, and channel recovery was slowed. The effects of 8,9-EET were greater at depolarized potentials. 4. Single channel recordings showed 8,9-EET did not change the conductance or the number of active Na+ channels, but markedly decreased the probability of Na+ channel opening. These results were associated with a decrease in the channel open time and an increase in the channel closed times. 5. Incubation of cultured cardiac myocytes with 1 microM [3H]8,9-EET showed that 25% of the radioactivity was taken up by the cells over a 2 h period, and most of the uptake was incorporated into phospholipids, principally phosphatidylcholine. Analysis of the medium after a 2 h incubation indicated that 86% of the radioactivity remained as [3H]8,9-EET while 13% was converted into [3H]8,9-DHET. After a 30 min incubation, 1-2% of the [3H]8,9-EET uptake by cells remained as unesterified EET. 6. These results demonstrate that cardiac cells have a high capacity to take up and metabolize 8,9-EET. 8,9-EET is a potent use- and voltage-dependent inhibitor of the cardiac Na+ channels through modulation of the channel gating behaviour.

Changes in tissue polyunsaturated fatty acids with age, in spontaneously hypertensive rats

The relationship between the biosynthesis of long-chain fatty acids and their distribution in the key organs of hypertension is of considerable interest because of their role in the production of vasoactive eicosanoids and their effects on membrane properties. The present study analyzed the fatty acid compositions of the total lipids in the kidney, aorta, heart, and hepatocytes of 1-, 3-, and 6-mon-old spontaneously hypertensive rats (SHR) and their normotensive controls, Wistar Kyoto rats (WKY) by capillary gas chromatography . The major changes concerned the polyunsaturated fatty acids (PUFA). The percentage of arachidonic acid (AA) was significantly greater in the 1-mon-old SHR kidney than in the WKY kidney, but it was lower at 3 and 6 mon. The percentage of eicosapentaenoic acid was very low in the SHR kidney. The results for the aorta were similar, with marked decreases in 18:2n-6 and 18:3n-3 in SHR aged 1 and 6 mon. Despite a higher proportion of 18:2n-6 and AA at 6 mon, there was no major change in the SHR heart lipids. The fatty acid spectrum in the liver provides additional evidence for the previously reported inhibition of desaturase activities in SHR. Thus, this study shows that the PUFA composition is modified differently in different tissues in SHR, and this may be related to the pathogenesis of hypertension in these animals.

Cytochrome P450: a novel system modulating Ca2+ channels and contraction in mammalian heart cells

1. Cytochrome P450 (P450) is a ubiquitous enzyme system that catalyses oxidative reactions of numerous endogenous and exogenous compounds. The modulatory effects of P450 on the L-type Ca2+ current (ICa), intracellular free Ca2+ signals and cell shortening were assessed in adult rat single ventricular myocytes. 2. Bath administration of the imidazole antimycotics, clotrimazole, econazole and miconazole, which are potent P450 inhibitors, significantly suppressed cardiac ICa. While the Ca2+ channel antagonist nifedipine blocked ICa within 30 s, clotrimazole-induced suppression of ICa required 5.1 +/- 0.4 min (n = 14) to reach a steady low level. The suppression of ICa was dose dependent and recovered after washout of clotrimazole. Intracellular dialysis with the P450 antibody anti-rat CYP1A2 also significantly reduced cardiac ICa. 3. Additional administration of the beta-adrenergic agonist isoprenaline (1 microM) or the membrane-permeable 8-bromo-cAMP (2 mM) completely reversed the suppressant effects of clotrimazole and NaCN on ICa. In addition, intracellular dialysis with 2 mM cAMP abolished the P450 inhibitor-induced suppression of ICa. Phosphorylation of the channel with hydrolysis-resistant ATPgammaS prevented the suppressant effect of clotrimazole on ICa. Furthermore, dephosphorylation of the Ca2+ channel with intracellular dialysis with phosphatase types I and II reduced ICa by 85 +/- 3 % and abolished clotrimazole-induced suppression of ICa. 4. Extracellular administration of the phospholipase A2 inhibitors mepacrine and 4-bromophenacyl bromide significantly suppressed ICa. 5. Clotrimazole, econazole, miconazole and CN- also significantly inhibited intracellular free Ca2+ signals and cell shortening in rat single ventricular myocytes. 6. Intracellular cAMP content was significantly reduced in isolated ventricular myocytes incubated with clotrimazole or CN-. Extracellular administration of 11, 12-epoxyeicosatrienoic acid, one of the P450-mediated metabolites of arachidonic acid, enhanced ICa and intracellular cAMP content. The epoxyeicosatrienoic acid also restored the amplitude of the reduced ICa in P450 antibody-dialysed myocytes. 7. The present data suggest that cytochrome P450 modulates cardiac ICa and cell contraction, and the modulation may result from changes in intracellular levels of cAMP by P450- mediated metabolites of arachidonic acid.