Membrane fluidity changes are associated with the antiarrhythmic effects of docosahexaenoic acid in adult rat cardiomyocytes

Lipidome Atlas of the Developing Heart Uncovers Dynamic Membrane Lipid Attributes Underlying Cardiac Structural and Metabolic Maturation

Precise metabolic rewiring during heart organogenesis underlies normal cardiac development. Herein, we utilized high-coverage, quantitative lipidomic approaches to construct lipidomic atlases of whole hearts (861 lipids; 31 classes) and mitochondria (587 lipids; 27 classes) across prenatal and postnatal developmental stages in mice. We uncovered the progressive formation of docosahexaenoyl-phospholipids and enhanced remodeling of C18:2, C20:3, and C20:4 fatty acyl moieties into cardiolipins as cardiac development progresses. A preferential flow of ceramides toward sphingomyelin biosynthesis over complex glycosphingolipid formation was also noted. Using maSigPro and GPclust algorithms, we identified a repertoire of 448 developmentally dynamic lipids and mapped their expression patterns to a library of 550 biologically relevant developmentally dynamic genes. Our combinatorial transcriptomics and lipidomics approaches identified Hadha, Lclat1, and Lpcat3 as candidate molecular drivers governing the dynamic remodeling of cardiolipins and phospholipids, respectively, in heart development. Our analyses revealed that postnatal cardiolipin remodeling in the heart constitutes a biphasic process, which first accumulates polyunsaturated C78-cardiolipins prior to tetralinoleoyl cardiolipin forming the predominant species. Multiomics analyses supplemented with transmission electron microscopy imaging uncovered enhanced mitochondria-lipid droplet contacts mediated by perilipin-5. Our combinatorial analyses of multiomics data uncovered an association between mitochondrial-resident, docosahexaenoic acid-phospholipids and messenger RNA levels of proton-transporting adenosine triphosphate synthases on inner mitochondrial membranes, which adds credence to the membrane pacemaker theory of metabolism. The current findings offer lipid-centric biological insights potentially important to understanding the molecular basis of cardiac metabolic flexibility and disease pathology.

Ablation of fatty acid desaturase 2 (FADS2) exacerbates hepatic triacylglycerol and cholesterol accumulation in polyunsaturated fatty acid-depleted mice

Deficiency of polyunsaturated fatty acids (PUFAs) is known to induce hepatic steatosis. However, it is not clearly understood which type of PUFA is responsible for the worsening of steatosis. This study observed a marked accumulation of hepatic triacylglycerol and cholesterol in fatty acid desaturase 2 knockout (FADS2^-/- ) mice lacking both C18 and ≥ C20 PUFAs that were fed a PUFA-depleted diet. Hepatic triacylglycerol accumulation was associated with enhanced sterol regulatory element-binding protein (SREBP)-1-dependent lipogenesis and decreased triacylglycerol secretion into the plasma via very-low-density lipoprotein (VLDL). Furthermore, upregulation of cholesterol synthesis contributed to increased hepatic cholesterol content in FADS2^-/- mice. These results suggest that ≥ C20 PUFAs synthesized by FADS2 are important in regulating hepatic triacylglycerol and cholesterol accumulation during PUFA deficiency.

Thermal profiles reveal stark contrasts in properties of biological membranes from heart among Antarctic notothenioid fishes which vary in expression of hemoglobin and myoglobin

Antarctic notothenioids are noted for extreme stenothermy, yet underpinnings of their thermal limits are not fully understood. We hypothesized that properties of ventricular membranes could explain previously observed differences among notothenioids in temperature onset of cardiac arrhythmias and persistent asystole. Microsomes were prepared using ventricles from six species of notothenioids, including four species from the hemoglobin-less (Hb-) family Channichthyidae (icefishes), which also differentially express cardiac myoglobin (Mb), and two species from the (Hb+) Nototheniidae. We determined membrane fluidity and structural integrity by quantifying fluorescence depolarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) and leakage of 5(6)-carboxyfluorescein, respectively, over a temperature range from ambient (0 °C) to 20 °C. Compositions of membrane phospholipids and cholesterol contents were also quantified. Membranes from all four species of icefishes exhibited greater fluidity than membranes from the red-blooded species N. coriiceps. Thermal sensitivity of fluidity did not vary among species. The greatest thermal sensitivity to leakage occurred between 0 and 5 °C for all species, while membranes from the icefish, Chaenocephalus aceratus (Hb-/Mb-) displayed leakage that was nearly 1.5-fold greater than leakage in N. coriiceps (Hb+/Mb+). Contents of phosphatidylethanolamine (PE) were approximately 1.5-fold greater in icefishes than in red-blooded fishes, and phospholipids had a higher degree of unsaturation in icefishes than in Hb + notothenioids. Cholesterol contents were lowest in Champsocephalus gunnari (Hb-/Mb-) and highest in the two Hb+/Mb + species, G. gibberifrons and N. coriiceps. Our results reveal marked differences in membrane properties and indicate a breach in membrane fluidity and structural integrity at a lower temperature in icefishes than in red-blooded notothenioids.

Does Supplementation with Omega-3 PUFAs Add to the Prevention of Cardiovascular Disease?

PURPOSE OF REVIEW

Omega-3 fatty acids are increasingly used for the protection of cardiovascular disease. The main but not the sole mechanism of action is the reduction of triglyceride levels. In this review, we summarize the effect of omega-3 supplements on all-cause and cardiovascular mortality, myocardial infarction, and stroke from the relevant randomized controlled trials.

RECENT FINDINGS

Twenty-one randomized controlled trials assessed omega-3 supplementation on mortality and cardiovascular-related outcomes. From these studies, as well as from the relevant meta-analyses, we found that omega-3 supplements do not exert a consistent benefit for cardiovascular protection. There is uncertainty of a clear profit from omega-3 supplementation in cardiovascular disease.

The pro- or antiarrhythmic actions of polyunsaturated fatty acids and of cholesterol

In this review, the pro- and anti-arrhythmic effects of a diet rich in fish oil fatty acids and of hypercholesterolemia will be discussed in relation to two major mechanisms of arrhythmogenesis (triggered activity and re-entry). Whereas a diet rich in fish oil is pro-arrhythmic in relation to re-entry based arrhythmias (as occur in acute myocardial ischemia) and anti-arrhythmic in relation to triggered activity based arrhythmias (as occur in heart failure), the reverse is true for hypercholesterolemia. Changing the lipid composition of cardiomyocytes likely has powerful pro- or anti-arrhythmic consequences, depending on the mechanism of arrhythmias, and has corresponding therapeutic potential.

Lipid Regulation of Sodium Channels

The lipid landscapes of cellular membranes are complex and dynamic, are tissue dependent, and can change with the age and the development of a variety of diseases. Researchers are now gaining new appreciation for the regulation of ion channel proteins by the membrane lipids in which they are embedded. Thus, as membrane lipids change, for example, during the development of disease, it is likely that the ionic currents that conduct through the ion channels embedded in these membranes will also be altered. This chapter provides an overview of the complex regulation of prokaryotic and eukaryotic voltage-dependent sodium (Nav) channels by fatty acids, sterols, glycerophospholipids, sphingolipids, and cannabinoids. The impact of lipid regulation on channel gating kinetics, voltage-dependence, trafficking, toxin binding, and structure are explored for Nav channels that have been examined in heterologous expression systems, native tissue, and reconstituted into artificial membranes. Putative mechanisms for Nav regulation by lipids are also discussed.

Effects of long-term thyroid hormone level alterations, n-3 polyunsaturated fatty acid supplementation and statin administration in rats

Thyroid hormones (THs) play multiple roles in the organism and alterations of their levels can result in many pathological changes. Currently, we use hyperthyroid and hypothyroid rats as "models of a diseased organism" and analyze whether n-3 polyunsaturated fatty acids (n-3 PUFA) administration can ameliorate TH-induced pathophysiological changes. We investigate myosin heavy chain composition, calsequestrin levels, changes in cardiac tissue remodeling and cell-to-cell communication, expression of protein kinases, mitochondrial functions, oxidative stress markers and cell death, changes in serum lipid levels, activities of key enzymes of thyroid hormone metabolism, activity of acetylcholine esterase and membrane anisotropy, as well as mobile behavior and thermal sensitivity. Additionally we also mention our pilot experiments dealing with the effect of statin administration on skeletal muscles and sensory functions. As THs and n-3 PUFA possess multiple sites of potential action, we hope that our complex research will contribute to a better understanding of their actions, which can be useful in the treatment of different pathophysiological events including cardiac insufficiency in humans.

Current evidence and future perspectives of omega-3 polyunsaturated fatty acids for the prevention of cardiovascular disease

Omega-3 fatty acids have been traditionally used for the prevention of major cardiovascular events in patients with or without a history of cardiovascular disease. Their main mechanism of action is to lower triglyceride levels, but they also exert anti-arrythmic and anti-inflammatory properties, they reduce blood pressure levels and stabilize the atherosclerotic plaques. There is a vast amount of evidence derived from randomized studies that seems to question their benefit for the prevention of major cardiovascular events. Upcoming trials will help to better clarify their use in certain indications.

The effects of supplementation with omega-3 polyunsaturated Fatty acids on cardiac rhythm: anti-arrhythmic, pro-arrhythmic, both or neither? It depends…

Supplementation of omega-3 fatty acids (Ω-3) has been associated with a decreased cardiovascular risk, thereby concentrating attention on a potentially preventive effect regarding tachyarrhythmias and sudden cardiac death. However, recent randomized controlled trials challenge the efficacy of the additional application of Ω-3 and its anti-arrhythmic effect under certain clinical conditions. The present paper reflects the results of earlier and recent clinical studies with respect to the individual background conditions that may determine the clinical outcome of Ω-3 supplementation and thereby explain apparently conflicting clinical results. It is concluded that the efficacy of Ω-3 supplementation to prevent cardiac arrhythmias strongly depends on the underlying clinical and pharmacological conditions, a hypothesis that also is supported by data from experimental animal studies and by molecular interactions of Ω-3 at the cellular level.

Polyunsaturated fatty acids and their effects on cardiovascular disease

Dietary polyunsaturated fatty acids (PUFAs) affect a wide variety of physiological processes. Much attention has been given to the n-3 PUFAs and their role in the prevention and treatment of cardiovascular disease, stemming from evidence obtained through a number of epidemiological studies and clinical trials. Investigators are now focused on elucidating the pathways and mechanisms for the biological action of n-3 PUFAs. Dietary intervention is recognized as a key measure in patient therapy and in the maintenance of human health in general. This review provides a summary of several important clinical trials, and while the exact modes of action of n-3 PUFA are not known, current viewpoints regarding the mechanisms of these fatty acids on atherosclerosis, circulating lipid profile, cell membranes, cell proliferation, platelet aggregation and cardiac arrhythmias are discussed.

Cardiovascular effects of marine omega-3 fatty acids

Much evidence shows that the marine omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid have beneficial effects in various cardiac disorders, and their use is recommended in guidelines for management of patients after myocardial infarction. However, questions have been raised about their usefulness alongside optimum medical therapies with agents proven to reduce risk of cardiac events in high-risk patients. Additionally, there is some evidence for a possible pro-arrhythmic effect in subsets of cardiac patients. Some uncertainly exists about the optimum dose needed to obtain beneficial effects and the relative merit of dietary intake of omega-3 polyunsaturated fatty acids versus supplements. We review evidence for the effects of omega-3 polyunsaturated fatty acids on various cardiac disorders and the risk factors for cardiac disease. We also assess areas of uncertainty needing further research.

Maternal dietary fat intake during gestation and lactation alters tissue fatty acid composition in the adult offspring of C57Bl/6 mice

We investigated the effects of maternal dietary fat intake during gestation and lactation on the tissue fatty acid composition of the adult offspring. Female C57Bl/6 mice were fed high fat diets enriched with lard or safflower oil or chow during mating, gestation and lactation. The offspring obtained from each group of mothers were continued on diets rich in lard, safflower oil or chow post-weaning until 11 weeks of age. Livers and hearts were collected for fatty acid analysis. A maternal diet rich in safflower oil was associated with enrichment of hepatic tissue with n-3 polyunsaturated fatty acids in the offspring fed chow post-weaning compared to the offspring fed chow throughout. However, a continuous exposure to a safflower oil- as well as lard-rich diet during the pre- and post-weaning time periods was associated with reduced content of docosahexaenoic acid in both liver and heart tissues compared to the offspring fed chow throughout. In conclusion, this study demonstrated lasting effects of maternal dietary fat intake, as well as an interaction between pre- and post-weaning diets, on the tissue fatty composition in adult offspring.

Prevention of atrial fibrillation following cardiac surgery: basis for a novel therapeutic strategy based on non-hypoxic myocardial preconditioning

Atrial fibrillation is the most common complication of cardiac surgical procedures performed with cardiopulmonary bypass. It contributes to increased hospital length of stay and treatment costs. At present, preventive strategies offer only suboptimal benefits, despite improvements in anesthesia, surgical technique, and medical therapy. The pathogenesis of postoperative atrial fibrillation is considered to be multifactorial. However oxidative stress is a major contributory factor representing the unavoidable consequences of ischemia/reperfusion cycle occurring in this setting. Considerable evidence suggests the involvement of reactive oxygen species (ROS) in the pathogenic mechanism of this arrhythmia. Interestingly, the deleterious consequences of high ROS exposure, such as inflammation, cell death (apoptosis/necrosis) or fibrosis, may be abrogated by a myocardial preconditioning process caused by previous exposure to moderate ROS concentration known to trigger survival response mechanisms. The latter condition may be created by n-3 PUFA supplementation that could give rise to an adaptive response characterized by increased expression of myocardial antioxidant enzymes and/or anti-apoptotic pathways. In addition, a further reinforcement of myocardial antioxidant defenses could be obtained through vitamins C and E supplementation, an intervention also known to diminish enzymatic ROS production. Based on this paradigm, this review presents clinical and experimental evidence supporting the pathophysiological and molecular basis for a novel therapeutic approach aimed to diminish the incidence of postoperative atrial fibrillation through a non-hypoxic preconditioning plus a reinforcement of the antioxidant defense system in the myocardial tissue.

Differential cerebral cortex transcriptomes of baboon neonates consuming moderate and high docosahexaenoic acid formulas

BACKGROUND

Docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (ARA, 20:4n-6) are the major long chain polyunsaturated fatty acids (LCPUFA) of the central nervous system (CNS). These nutrients are present in most infant formulas at modest levels, intended to support visual and neural development. There are no investigations in primates of the biological consequences of dietary DHA at levels above those present in formulas but within normal breastmilk levels.

METHODS AND FINDINGS

Twelve baboons were divided into three formula groups: Control, with no DHA-ARA; "L", LCPUFA, with 0.33%DHA-0.67%ARA; "L3", LCPUFA, with 1.00%DHA-0.67%ARA. All the samples are from the precentral gyrus of cerebral cortex brain regions. At 12 weeks of age, changes in gene expression were detected in 1,108 of 54,000 probe sets (2.05%), with most showing <2-fold change. Gene ontology analysis assigns them to diverse biological functions, notably lipid metabolism and transport, G-protein and signal transduction, development, visual perception, cytoskeleton, peptidases, stress response, transcription regulation, and 400 transcripts having no defined function. PLA2G6, a phospholipase recently associated with infantile neuroaxonal dystrophy, was downregulated in both LCPUFA groups. ELOVL5, a PUFA elongase, was the only LCPUFA biosynthetic enzyme that was differentially expressed. Mitochondrial fatty acid carrier, CPT2, was among several genes associated with mitochondrial fatty acid oxidation to be downregulated by high DHA, while the mitochondrial proton carrier, UCP2, was upregulated. TIMM8A, also known as deafness/dystonia peptide 1, was among several differentially expressed neural development genes. LUM and TIMP3, associated with corneal structure and age-related macular degeneration, respectively, were among visual perception genes influenced by LCPUFA. TIA1, a silencer of COX2 gene translation, is upregulated by high DHA. Ingenuity pathway analysis identified a highly significant nervous system network, with epidermal growth factor receptor (EGFR) as the outstanding interaction partner.

CONCLUSIONS

These data indicate that LCPUFA concentrations within the normal range of human breastmilk induce global changes in gene expression across a wide array of processes, in addition to changes in visual and neural function normally associated with formula LCPUFA.

Arachidonic acid preserves hippocampal neuron membrane fluidity in senescent rats

Previous studies indicate that long-term dietary supplementation with arachidonic acid (AA) in 20-month-old rats (OA) effectively restores performance in a memory task and the induction of long-term potentiation in the hippocampus to the level of young control animals (YC). The present study examined protein mobility using the live cell imaging technique "Fluorescent Recovery After Photobleaching (FRAP)" in YC, old control (OC) and OA neurons in hippocampal slice preparations. Three measures; mobile fraction (M(f)), diffusion constant (D) and time constant (tau), were estimated among YC, OC and OA. Each of these parameters was significantly different between OC and YC, suggesting that membrane fluidity is lower in OC than in YC. In contrast, D and tau were comparable in OA and YC, indicating that hippocampal neuronal membranes supplemented with AA were more fluid than those in OC, whereas the fraction of diffusible protein in the bleached region remained smaller than in YC. Long-term administration of AA to senescent rats might help to preserve membrane fluidity and maintain hippocampal plasticity.

Dietary fish oil alters cardiomyocyte Ca2+ dynamics and antioxidant status

The n-3 polyunsaturated fatty acids (PUFAs) found in fish oil (FO) have been shown to protect against reperfusion arrhythmias, a manifestation of reperfusion injury, which is believed to be induced by the formation of reactive oxygen species (ROS) and intracellular calcium (Ca2+) overload. Adult rats fed a diet supplemented with 10% FO had a higher proportion of myocardial n-3 PUFAs and increased expression of antioxidant enzymes compared with the saturated fat (SF)-supplemented group. Addition of hydrogen peroxide (H2O2) to cardiomyocytes isolated from rats in the SF-supplemented group increased the proportions of cardiomyocytes contracting in an asynchronous manner, increased the rate of Ca2+ influx, and increased the diastolic and systolic [Ca2+]i compared with the FO group. H2O2 exposure increased the membrane fluidity of cardiomyocytes from the FO group. These results demonstrate that dietary FO supplementation is associated with a reduction in the susceptibility of myocytes to ROS-induced injury and this may be related to membrane incorporation of n-3 PUFAs, increased antioxidant defenses, changes in cardiomyocyte membrane fluidity, and the ability to prevent rises in cellular Ca2+ in response to ROS.

Membrane basis for fish oil effects on the heart: linking natural hibernators to prevention of human sudden cardiac death

The concept that diet-induced changes in membrane lipids could modify heart function partly arose from observations that membrane composition and physical properties were closely associated with the capacity of the heart to respond appropriately to torpor and hibernation. Observations of natural hibernators further revealed that behavior of key membrane-bound enzymes could be influenced through the lipid composition of the cell membrane, either by changing the surrounding fatty acids through reconstitution into a foreign lipid milieu of different composition, or by alteration through diet. Myocardial responsiveness to beta-adrenoceptor stimulation, including initiation of spontaneous dysrhythmic contractions, was altered by both hibernation and dietary modulation of membrane fatty acids, suggesting modified vulnerability to cardiac arrhythmia. Subsequent studies using whole-animal models recognized that vulnerability to ventricular fibrillation decreased as the polyunsaturated: saturated fat (P:S) ratio of the diet increased. However, dietary fish oils, which typically contain at least 30% saturated fatty acids and only 30% long-chain n-3 (omega-3) polyunsaturated fatty acids (PUFA), exhibit antiarrhythmic effects that exceed the predicted influence of the P:S ratio, suggesting properties unique to the long-chain n-3 PUFA. Large-scale clinical trials and epidemiology have confirmed the arrhythmia prevention observed in vitro in myocytes, papillary muscles, and isolated hearts and in whole-animal models of sudden cardiac death. Some progress has been made towards a biologically plausible mechanism. These developments highlight nature's ability to provide guidance for the most unexpected applications.

Docosahexaenoic acid (omega−3) blocks voltage-gated sodium channel activity and migration of MDA-MB-231 human breast cancer cells

Omega-3 polyunsaturated fatty acids have been suggested to play an important role in cancer prevention/progression, on the one hand, and in modulation of membrane ion channels on the other. We investigated whether docosahexaenoic acid would influence the in vitro migration of MDA-MB-231 human breast cancer cells. An important follow-up question was whether any effect would involve voltage-gated Na(+) channels, shown previously to occur in human breast cancer in vitro and in vivo and to correlate with metastatic potential. Short-term (acute) and long-term (24-72 h) application of docosahexaenoic acid suppressed the activity of the channel activity in a dose-dependent manner. At the working concentrations of docosahexaenoic acid used (0.05-0.5 microM), there was no effect on proliferation. Long-term treatment with docosahexaenoic acid down-regulated mRNA and protein (total and plasma membrane) levels of neonatal Nav1.5 voltage-gated Na(+) channel, known to be predominant in these cells. Docosahexaenoic acid suppressed migration of the MDA-MB-231 cells to the same extent as tetrodotoxin, a highly specific blocker of voltage-gated Na(+) channels, but the two effects were not additive. It was concluded that the docosahexaenoic acid-induced suppression of cellular migration occurred primarily via down-regulation of voltage-gated Na(+) channel (neonatal Nav1.5) mRNA and functional protein expression.

A systematic review and meta-analysis of the impact of omega-3 fatty acids on selected arrhythmia outcomes in animal models

Epidemiological studies and clinical trials report the beneficial effects of fish or fish oil consumption on cardiovascular disease outcomes including sudden death. We performed a systematic review of the literature on controlled animal studies that assessed the effects of omega-3 fatty acids on selected arrhythmia outcomes. On the basis of predetermined criteria, 27 relevant animal studies were identified; 23 of these were feeding studies, and 4 were infusion studies. Across species, fish oil, eicosapentaenoic acid, and/or docosahexaenoic acid appear to have beneficial effects on ventricular tachycardia (VT) and fibrillation (VF) in ischemia- but not reperfusion-induced arrhythmia models; no effect on the incidence of death and infarct size; and inconsistent results with regard to arrhythmia score, VF threshold, ventricular premature beats or length of time in normal sinus rhythm, compared to omega-6, monounsaturated, or saturated fatty acids, and no treatment controls. In a meta-analysis of 13 studies using rat models, fish oil but not alpha-linolenic acid supplementation showed a significant protective effect for ischemia- and reperfusion-induced arrhythmias by reducing the incidence of VT and VF. It is not known whether omega-3 fatty-acid supplementation has antiarrhythmic effects in other disease settings not related to ischemia.

Docosahexaenoic acid and eicosapentaenoic acid antagonize the proinflammatory interactions of pneumolysin with human neutrophils

Pneumolysin (4.18 ng/ml)-mediated influx of Ca(2+) and augmentation of the chemoattractant-activated generation of reactive oxidants was antagonized by pretreatment of human neutrophils with the omega-3 polyunsaturated fatty acids docosahexaenoic acid and eicosapentaenoic acid (1.25 to 5 microg/ml). These agents may have potential in attenuating the proinflammatory properties of this pneumococcal toxin.

Dietary fish oil prevents asynchronous contractility and alters Ca(2+) handling in adult rat cardiomyocytes

This study examined the effects of dietary incorporation of n-3 polyunsaturated fatty acids (PUFAs) into cardiac membrane phospholipids on Ca(2+) handling (using Fura-2) and arrhythmic contractility in electrically-stimulated, adult rat ventricular cardiomyocytes. Dietary lipid supplementation with fish oil (FO) for 3 weeks significantly increased the proportion of total n-3 polyunsaturated fatty acids (in particular, docosahexaenoic acid) in ventricular membrane phospholipids compared with a saturated fat (SF) supplemented diet (26.2 +/- 0.9% vs 6.9 +/- 0.9%, respectively, P < 0.001). Cardiomyocytes isolated from the FO group were significantly (P < 0.001) less susceptible to isoproterenol-induced arrhythmic contractile activity compared with the SF group over a range of isoproterenol concentrations. Isoproterenol (0.5 &mgr;M) stimulation increased end-diastolic and systolic [Ca(2+)](i) to a similar extent in both groups. The time constant of Ca(2+) transient decay was significantly increased in the FO group compared with the SF group (98.4 +/- 2.8 ms, n = 8 and 86.9 +/- 2.1 ms, n = 8, P < 0.01, respectively). The effect of dietary n-3 PUFA incorporation into membrane phospholipids was not associated with changes in sarcoplasmic reticulum Ca(2+) content (measured by rapid application of caffeine) or membrane fluidity. The increase in the time constant of decay of Ca(2+) transients following dietary supplementation with FO may indicate altered functioning of the sarcolemmal Na(+)-Ca(2+) exchanger by n-3 PUFA incorporation into membrane phospholipids.

Effects of dietary n-3 fatty acids on contractility, Na+ and K+ currents in a rat cardiomyocyte model of arrhythmia

The n-3 polyunsaturated fatty acids (PUFAs) have been reported to prevent ventricular fibrillation in human clinical studies and in studies involving experimental animals and isolated cardiomyocytes. This study aimed to determine whether dietary n-3 PUFAs could prevent isoproterenol and free radical-induced arrhythmic (asynchronous) contractile activity in adult rat cardiomyocytes and whether whole-cell Na(+) and K(+) currents measured by patch-clamp techniques were affected. Dietary supplementation with fish oil for 3 weeks significantly increased the proportion of total n-3 PUFAs in ventricular membrane phospholipids compared with saturated fat supplementation (18.8 +/- 0.6% vs. 8.1 +/- 1.0%, respectively). Cardiomyocytes from the fish oil group were less susceptible to isoproterenol-induced asynchronous contractile activity than were those from the saturated fat group [EC(50) values: 892 +/- 130 nM, n = 6 and 347 +/- 91 nM, n = 6 (P < 0.05), respectively]. Fish oil supplementation also prolonged the time taken to develop asynchronous contractile activity induced by superoxide and hydrogen peroxide. The voltage dependence of inactivation of Na(+) currents were significantly altered (-73.5 +/- 1.2 mV, n = 5 vs. -76.7 +/- 0.7 mV, n = 5, P < 0.05, for saturated fat and fish oil treated groups, respectively). The voltage dependence of activation of Na(+) and K(+) currents was not significantly affected by the dietary fish oil treatment. These results demonstrate the antiarrhythmic effects of dietary fish oil in a cardiomyocyte model of arrhythmia.

Termination of asynchronous contractile activity in rat atrial myocytes by n-3 polyunsaturated fatty acids

A protective effect of the n-3 polyunsaturated fatty acids (PUFAs) in preventing ventricular fibrillation in experimental animals and cultured cardiomyocytes has been demonstrated in a number of studies. In this study, a possible role for the n-3 PUFAs in the treatment of atrial fibrillation (AF) was investigated at the cellular level using atrial myocytes isolated from young adult rats as the experimental model. Electrically-stimulated, synchronously-contracting myocytes were induced to contract asynchronously by the addition of 10 microM isoproterenol. Asynchronous contractile activity was reduced following acute addition of the n-3 PUFAs docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) at 10 microM, compared with no fatty acid addition (from 99.0+/-1.0% to 30.7+/-5.2% (p < 0.05) for DHA and 23.8+/-2.8% (p < 0.01) for EPA), while the saturated fatty acid, docosanoic acid (DA) and the methyl ester of DHA (DHA m.e.) did not exert a significant effect on asynchronous contractile activity. Asynchronous contractile activity was also reduced to 1.7+/-1.7% in the presence of the membrane fluidising agent, benzyl alcohol (p < 0.001 vs no fatty acid addition). Cell membrane fluidity was determined by steady state fluorescence anisotropy using the fluorescent probe, TMAP-DPH. Addition of DHA, EPA or benzyl alcohol significantly increased sarcolemmal membrane fluidity (decreased anisotropy, r(ss)) of atrial myocytes compared with no addition of fatty acid (control) (from r(ss) = 0.203+/-0.004 to 0.159+/-0.004 (p < 0.01) for DHA, 0.166+/-0.001 (p < 0.01) for EPA and 0.186+/-0.003 (p < 0.05) for benzyl alcohol, while DA and DHA m.e. were without effect. It is concluded that the n-3 PUFAs exert anti-asynchronous effects in rat atrial myocytes by a mechanism which may involve changes in membrane fluidity.