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Isolated Cardiomyocytes (isolated + cardiomyocyte)
Selected AbstractsReduced calcium tolerance in rat cardiomyocytes after myocardial infarctionACTA PHYSIOLOGICA, Issue 4 2002I. Sjaastad ABSTRACT During ischaemia and reperfusion the intracellular Na+ concentration is elevated in the cardiomyocytes and the cells are depolarized, both favouring reverse mode Na,Ca-exchange loading of the cell with Ca2+. We examined whether cardiomyocytes from rats with congestive heart failure (CHF) and younger rats (HINCX) which both have a high expression of the Na,Ca-exchanger protein (NCX) showed reduced tolerance to extracellular Ca2+. The CHF was induced in Isofluran anaesthetized rats by left coronary artery ligation. Isolated cardiomyocytes were loaded with Fura-2AM and 140 mm Na+ and exposed to 0.05 mm Ca2+. Expression of the Na,Ca-exchanger protein was analysed. Fura-2 340/380 ratio rose more rapidly in HINCX and CHF than in SHAM, and the rise was abolished by Ni2+. Hypercontracture developed more frequently in HINCX and CHF than in SHAM cells. The amount of NCX was 54% higher in HINCX and 76% higher in CHF compared with SHAM. Na+ -loaded cardiomyocytes from CHF and HINCX rats are more susceptible to Ca2+ overload than SHAM cells because of the increased capacity for Na,Ca-exchange. [source] Thyroid hormone receptor , can control action potential duration in mouse ventricular myocytes through the KCNE1 ion channel subunitACTA PHYSIOLOGICA, Issue 2 2010A. Mansén Abstract Aims:, The reduced heart rate and prolonged QTend duration in mice deficient in thyroid hormone receptor (TR) ,1 may involve aberrant expression of the K+ channel ,-subunit KCNQ1 and its regulatory ,-subunit KCNE1. Here we focus on KCNE1 and study whether increased KCNE1 expression can explain changes in cardiac function observed in TR,1-deficient mice. Methods:, TR-deficient, KCNE1-overexpressing and their respective wildtype (wt) mice were used. mRNA and protein expression were assessed with Northern and Western blot respectively. Telemetry was used to record electrocardiogram and temperature in freely moving mice. Patch-clamp was used to measure action potentials (APs) in isolated cardiomyocytes and ion currents in Chinese hamster ovary (CHO) cells. Results:, KCNE1 was four to 10-fold overexpressed in mice deficient in TR,1. Overexpression of KCNE1 with a heart-specific promoter in transgenic mice resulted in a cardiac phenotype similar to that in TR,1-deficient mice, including a lower heart rate and prolonged QTend time. Cardiomyocytes from KCNE1-overexpressing mice displayed increased AP duration. CHO cells transfected with expression plasmids for KCNQ1 and KCNE1 showed an outward rectifying current that was maximal at equimolar plasmids for KCNQ1-KCNE1 and decreased at higher KCNE1 levels. Conclusion:, The bradycardia and prolonged QTend time in hypothyroid states can be explained by altered K+ channel function due to decreased TR,1-dependent repression of KCNE1 expression. [source] Cardiac L-type calcium current is increased in a model of hyperaldosteronism in the ratEXPERIMENTAL PHYSIOLOGY, Issue 6 2009Beatriz Martin-Fernandez Accumulating evidence supports the importance of aldosterone as an independent risk factor in the pathophysiology of cardiovascular disease. It has been postulated that aldosterone could contribute to ventricular arrhythmogeneity by modulation of cardiac ionic channels. The aim of this study was to analyse ex vivo the electrophysiological characteristics of the L-type cardiac calcium current (ICaL) in a model of hyperaldosteronism in the rat. Aldosterone was administered for 3 weeks, and cardiac collagen deposition and haemodynamic parameters were analysed. In addition, RT-PCR and patch-clamp techniques were applied to study cardiac L-type Ca2+ channels in isolated cardiomyocytes. Administration of aldosterone induced maladaptive cardiac remodelling that was related to increased collagen deposition, diastolic dysfunction and cardiac hypertrophy. In addition, ventricular myocytes isolated from the aldosterone-treated group showed increased ICaL density and conductance and prolongation of the action potential duration. No changes in kinetics or in voltage dependence of activation and inactivation of ICaL were observed, but relative expression of CaV1.2 mRNA levels was higher in cardiomyocytes isolated from the aldosterone-treated group. The present study demonstrates that aldosterone treatment induces myocardial fibrosis, cardiac hypertrophy, increase of ICaL density, upregulation of L-type Ca2+ channels and prolongation of action potential duration. It could be proposed that aldosterone, through these mechanisms, might exert pro-arrhythmic effects in the pathological heart. [source] Nuclear factor-,B inhibition improves myocardial contractility in rats with cirrhotic cardiomyopathyLIVER INTERNATIONAL, Issue 5 2008Hongqun Liu Abstract Background/Aims: Cytokines such as tumour necrosis factor (TNF-,) contribute to the pathogenesis of cirrhotic cardiomyopathy. Nuclear factor-,B (NF-,B) is crucial for cytokine regulation, and induces cardiac dysfunction in several heart disease models. We aimed to elucidate possible NF-,B involvement in cirrhotic cardiomyopathy. Methods: Rats were bile duct ligated (BDL) to produce cirrhosis; controls received sham operation. Animals were studied 4 weeks later. Two NF-,B inhibitors were used: pyrrolidine dithiocarbamate (PDTC) and Bay 11-7082. Four groups were studied in most protocols: sham control, sham+PDTC, BDL and BDL+PDTC. Additional contractility studies were performed with Bay 11-7082. Myocardial NF-,B and TNF-, expression was measured by Western blot and ELISA. The contractility of isolated cardiomyocytes was observed under direct microscopy. Results: Nuclear factor-,B and TNF-, levels were increased in cirrhotic hearts compared with controls. PDTC significantly reduced NF-,B activity and TNF-, expression in cirrhotic hearts; controls were unaffected. Cirrhotic cardiomyocytes showed decreased systolic and diatolic velocity compared with sham controls. Both PDTC and Bay 11-7082 restored contractile function in cirrhotic cardiomyocytes, but did not affect controls. Conclusions: Inhibition of the increased NF-,B activity in cirrhotic hearts was associated with improvement of attenuated cardiomyocyte contractility. NF-,B, via effects on cytokine expression, may contribute to the pathogenesis of cirrhotic cardiomyopathy. [source] Expression pattern of neuronal and skeletal muscle voltage-gated Na+ channels in the developing mouse heartTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Volker Haufe In the mammalian heart, a variety of voltage-gated Na+ channel transcripts and proteins have been detected. However, little quantitative information is available on the abundance of each transcript during development, or the contribution of TTX-sensitive Na+ channels to the cardiac sodium current (INa). Using competitive and real-time RT-PCR we investigated the transcription of six Na+ channels (Nav1.1,Nav1.6) and the ,1 subunit during mouse heart development. Nav1.5 was predominantly expressed in the adult heart, whereas the splice variant Nav1.5a was the major Na+ channel isoform in embryonic hearts. The TTX-resistant Na+ channel transcripts (Nav1.5 and Nav1.5a) increased 1.7-fold during postnatal development. Transcripts encoding TTX-sensitive Na+ channels (Nav1.1,Nav1.4) and the ,1 subunit gradually increased up to fourfold from postnatal day (P)1 to P126, while the Nav1.6 transcript level remained low and constant over the same period. In adults, TTX-sensitive channel mRNA accounted for 30,40% of the channel pool in whole-heart preparations (Nav1.3 > Nav1.4 > Nav1.2 , Nav1.1 , Nav1.6), and 16% in mRNA from isolated cardiomyocytes (Nav1.4 > Nav1.3 > Nav1.2 > Nav1.1 > Nav1.6). Confocal immunofluorescence on ventricular myocytes suggested that Nav1.1 and Nav1.2 were localized at the intercalated disks and in the t tubules. Nav1.3 labelling predominantly produced a diffuse but strong intracellular signal. Nav1.6 fluorescence was detected only along the Z lines. Electrophysiological recordings showed that TTX-sensitive and TTX-resistant Na+ channels, respectively, accounted for 8% and 92% of the INa in adult ventricular cardiomyocytes. Our data suggest that neuronal and skeletal muscle Na+ channels contribute to the action potential of cardiomyocytes in the adult mammalian heart. [source] The Novel Antiarrhythmic Drug Dronedarone: Comparison with AmiodaroneCARDIOVASCULAR THERAPEUTICS, Issue 3 2005Sven Kathofer ABSTRACT Dronedarone is a noniodinated benzofuran derivative that has been developed to overcome the limiting iodine-associated adverse effects of the commonly used antiarrhythmic drug, amiodarone. It displays a wide cellular electrophysiological spectrum largely similar to amiodarone, inhibiting the potassium currents Ikr, IKs, IKI, IKACh, and Isus, as well as sodium currents and L-type calcium currents in isolated cardiomyocytes. In addition, dronedarone exhibits antiadrenergic properties. In vivo, dronedarone has been shown to be more effective than amiodarone in several arrhythmia models, particularly in preventing ischemia- and reperfusion-induced ventricular fibrillation and in reducing mortality. However, an increased incidence of torsades de pointes with dronedarone in dogs shows that possible proarrhythmic effects of dronedarone require further evaluation. The clinical trails DAFNE, EURIDIS, and ADONIS indicated safety, antiarrhythmic efficacy and low proarrhythmic potential of the drug in low-risk patients. In contrast, the increased incidence of death in the dronedarone group of the discontinued ANDROMEDA trial raises safety concerns for patients with congestive heart failure and moderate to severe left ventricular dysfunction. Dronedarone appears to be effective in preventing relapses of atrial fibrillation and atrial flutter. Torsades de pointes, the most severe adverse effect associated with amiodarone, has not yet been reported in humans with dronedarone. Unlike amiodarone, dronedarone had little effect on thyroid function and hormone levels in animal models and had no significant effects on human thyroid function in clinical trials. In conclusion, dronedarone could be a useful drug for prevention of atrial fibrillation and atrial flutter relapses in low-risk patients. However, further experimental studies and long-term clinical trials are required to provide additional evidence of efficacy and safety of dronedarone. [source] The Transcriptional Coactivator p300 Plays a Critical Role in the Hypertrophic and Protective Pathways Induced by Phenylephrine in Cardiac Cells but Is Specific to the Hypertrophic Effect of UrocortinCHEMBIOCHEM, Issue 1 2005Sean M. Davidson Dr. Abstract Anacardic acid is an alkylsalicylic acid obtained from cashew-nut-shell liquid, and is a potent inhibitor of p300 histone acetyl-transferase (HAT) activity. We have used anacardic acid to prevent the induction of hypertrophy in isolated neonatal rat cardiomyocytes. Hypertrophy was detected as an increase in cell size, the rearrangement of sarcomeres into a striated pattern, and the induction of embryonic genes ,-MHC and ANF. p300 inhibition was equally effective at preventing hypertrophy whether it was induced by treatment with the ,1-adrenergic agonist, phenylephrine, or by treatment with urocortin, a member of the corticotrophin-releasing-factor family, which stimulates specific G protein-coupled receptors. Spiruchostatin A is a natural-product inhibitor of histone deacetylases (HDAC) similar to the depsipeptide FK228 molecule. We have recently synthesized spiruchostatin A and now show that, although HDACs act in opposition to HATs, spiruchostatin A has the same effect as anacardic acid, that is, it prevents the induction of hypertrophy in response to phenylephrine or urocortin. Pretreatment with either phenylephrine or urocortin reduced the extent of death observed after the exposure of isolated cardiomyocytes to simulated ischaemia and reoxygenation. Inhibition of p300 or HDAC activity eliminated the protection conferred by phenylephrine; however, it did not affect the protection conferred by urocortin. Therefore, it might eventually be possible to use chemical inhibitors such as these in a therapeutic setting to dissociate the protective effect and hypertrophic effect of urocortin, enhancing the survival of cardiomyocytes exposed to transient ischemia, while inhibiting the hypertrophic pathway that would otherwise be induced concurrently. [source] CALCIUM ANTAGONIST PROPERTY OF CPU228, A DOFETILIDE DERIVATIVE, CONTRIBUTES TO ITS LOW INCIDENCE OF TORSADES DE POINTES IN RABBITSCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2007Zhi-Jiang Huang SUMMARY 1Torsades de pointes (TDP) is a severe adverse effect during the clinical use of dofetilide, a selective blocker of the rapid component of the delayed rectifier potassium channel (IKr). The present study was designed to test whether CPU228, a derivative of dofetilide with calcium (Ca2+) antagonist properties, could reduce TDP without reducing the blockade of IKr. 2The incidence of TDP in a rabbit model and the effective refractory period (ERP) were measured and compared for dofetilide and CPU228. Suppression of IKr and the L-type Ca2+ current (ICa,L) and the Ca2+ transients of isolated cardiomyocytes were investigated by whole-cell patch-clamp and Fluo-3 dye spectrophotometry. 3The incidence of TDP was greatly reduced by CPU228 relative to dofetilide, occurring in only one of six rabbits compared with five of six rabbits following dofetilide (P < 0.05). In isolated atria, prolongation of ERP by CPU228 was less than that of dofetilide and no reverse frequency dependence was observed. Negative inotropism by CPU228 was significant against positive inotropism by dofetilide. CPU228 inhibited both IKr and ICa,L currents and the IC50 for ICa,L inhibition was 0.909 µmol/L. At 3 µmol/L, CPU228 significantly suppressed the Ca2+ transients. 4CPU228 is able to block ICa,L, contributing to decreased TDP, while also blocking IKr activity. By combined blockade of IKr and ICa,L, CPU228 shares the property of complex Class III anti-arrhythmic agents. [source] | |||||||||||||