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Myocytes
Kinds of Myocytes Terms modified by Myocytes Selected AbstractsComparative Pharmacology of Guinea Pig Cardiac Myocyte and Cloned hERG (IKr) ChannelJOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 11 2004CHRISTINA DAVIE Ph.D. Introduction: This study used whole-cell, patch clamp techniques on isolated guinea pig ventricular myocytes and HEK293 cells expressing cloned human ether-a-go-go-related gene (hERG) to examine the action of drugs causing QT interval prolongation and torsades de pointes (TdP) in man. Similarities and important differences in drug actions on cardiac myocytes and cloned hERG IKr channels were established. Qualitative actions of the drugs on cardiac myocytes corresponded with results obtained from Purkinje fibers and measurement of QT interval prolongation in animal and human telemetry studies. Methods and Results: Adult guinea pig ventricular myocytes were isolated by enzymatic digestion. Cells were continuously perfused with Tyrode's solution at 33,35°C. Recordings were made using the whole-cell, patch clamp technique. Action potentials (APs) were elicited under current clamp. Voltage clamp was used to study the effect of drugs on IKr (rapidly activating delayed rectifier potassium current), INa (sodium current), and ICa (L-type calcium current). Dofetilide increased the myocyte action potential duration (APD) in a concentration-dependent manner, with a pIC50 of 7.3. Dofetilide 1 ,M elicited early afterdepolarizations (EADs) but had little affect on ICa or INa. E-4031 increased APD in a concentration-dependent manner, with a pIC50 of 7.2. In contrast, 10 ,M loratadine, desloratadine, and cetirizine had little effect on APD or IKr. Interestingly, cisapride displayed a biphasic effect on myocyte APD and inhibited ICa at 1 ,M. Even at this high concentration, cisapride did not elicit EADs. A number of AstraZeneca compounds were tested on cardiac myocytes, revealing a mixture of drug actions that were not observed in hERG currents in HEK293 cells. One compound, particularly AR-C0X, was a potent blocker of myocyte AP (pIC50 of 8.4). AR-C0X also elicited EADs in cardiac myocytes. The potencies of the same set of drugs on the cloned hERG channel also were assessed. The pIC50 values for dofetilide, E-4031, terfenadine, loratadine, desloratadine, and cetirizine were 6.8, 7.1, 7.3, 5.1, 5.2, and <4, respectively. Elevation of temperature from 22 to 35°C significantly enhanced the current kinetics and amplitudes of hERG currents and resulted in approximately fivefold increase in E-4031 potency. Conclusion: Our study demonstrates the advantages of cardiac myocytes over heterologously expressed hERG channels in predicting QT interval prolongation and TdP in man. The potencies of some drugs in cardiac myocytes were similar to hERG, but only myocytes were able to detect important changes in APD characteristics and display EADs predictive of arrhythmia development. We observed similar qualitative drug profiles in cardiac myocytes, dog Purkinje fibers, and animal and human telemetry studies. Therefore, isolated native cardiac myocytes are a better predictor of drug-induced QT prolongation and TdP than heterologously expressed hERG channels. Isolated cardiac myocytes, when used with high-throughput patch clamp instruments, may have an important role in screening potential cardiotoxic compounds in the early phase of drug discovery. This would significantly reduce the attrition rate of drugs entering preclinical and/or clinical development. The current kinetics and amplitudes of the cloned hERG channel were profoundly affected by temperature, significantly altering the potency of one drug (E-4031). This finding cautions against routine drug testing at room temperature compared to physiologic temperature when using the cloned hERG channel. [source] Myocardial growth before and after birth: clinical implications,ACTA PAEDIATRICA, Issue 2 2000AM Rudolph Perinatal changes in myocardial growth have recently evoked considerable interest with regard to cardiac chamber development with congenital cardiac lesions and to myocardial development in preterm infants. It is suggested that cardiac chamber development is influenced by blood flow. Experimental pulmonary stenosis in fetal lambs may induce either greatly reduced or markedly increased right ventricular volume. Ventricular enlargement appears to be associated with a large ventricular volume load resulting from tricuspid valve regurgitation. A small competent tricuspid valve is associated with reduced flow through the ventricle due to outflow obstruction and a small right ventricle. Postnatal growth of the ventricles in congenital heart disease is discussed. Increase in myocardial mass prenatally is achieved by hyperplasia, both during normal development and when myocardial mass is increased by right ventricular outflow obstruction. Postnatally, increases in myocardial mass with normal growth, as well as with ventricular outflow obstruction, are largely due to hypertrophy of myocytes. Myocardial capillary numbers do not increase in proportion with myocyte numbers in ventricular myocardium in association with outflow obstruction. The postnatal effects of these changes in congenital heart lesions are considered. Studies in fetal lambs suggest that the late gestational increase in blood cortisol concentrations is responsible for the change in the pattern of myocardial growth after birth. The concern is raised that prenatal exposure of the premature infant to glucocorticoids, administered to the mother to attempt to prevent hyaline membrane disease in the infant, may inhibit myocyte proliferation and result in a heart with fewer than normal myocytes. This would necessitate that each myocyte would have to hypertrophy abnormally to achieve a normal cardiac mass postnatally. [source] Quantification of myoglobin deoxygenation and intracellular partial pressure of O2 during muscle contraction during haemoglobin-free medium perfusionEXPERIMENTAL PHYSIOLOGY, Issue 5 2010Hisashi Takakura Although the O2 gradient regulates O2 flux from the capillary into the myocyte to meet the energy demands of contracting muscle, intracellular O2 dynamics during muscle contraction remain unclear. Our hindlimb perfusion model allows the determination of intracellular myoglobin (Mb) saturation () and intracellular oxygen tension of myoglobin () in contracting muscle using near infrared spectroscopy (NIRS). The hindlimb of male Wistar rats was perfused from the abdominal aorta with a well-oxygenated haemoglobin-free Krebs,Henseleit buffer. The deoxygenated Mb (,[deoxy-Mb]) signal was monitored by NIRS. Based on the value of ,[deoxy-Mb],,,and,,were calculated, and the time course was evaluated by an exponential function model. Both,,and,,started to decrease immediately after the onset of contraction. The steady-state values of,,and,,progressively decreased with relative work intensity or muscle oxygen consumption. At the maximal twitch rate,,,and,,were 49% and 2.4 mmHg, respectively. Moreover, the rate of release of O2 from Mb at the onset of contraction increased with muscle oxygen consumption. These results suggest that at the onset of muscle contraction, Mb supplies O2 during the steep decline in,, which expands the O2 gradient to increase the O2 flux to meet the increased energy demands. [source] Molecular cloning, genomic organization and functional characterization of a new short-chain potassium channel toxin-like peptide BmTxKS4 from Buthus martensii Karsch(BmK)JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 4 2004Sheng Jiqun Abstract Scorpion venom contains many small polypeptide toxins, which can modulate Na+, K+, Cl,, and Ca2+ ion,channel conductance in the cell membrane. A full-length cDNA sequence encoding a novel type of K+ -channel toxin (named BmTxKS4) was first isolated and identified from a venom gland cDNA library of Buthus martensii Karsch (BmK). The encoded precursor contains 78 amino acid residues including a putative signal peptide of 21 residues, propeptide of 11 residues, and a mature peptide of 43 residues with three disulfide bridges. BmTxKS4 shares the identical organization of disulfide bridges with all the other short-chain K+ -channel scorpion toxins. By PCR amplification of the genomic region encoding BmTxKS4, it was shown that BmTxKS4 composed of two exons is disrupted by an intron of 87 bp inserted between the first and the second codes of Phe (F) in the encoding signal peptide region, which is completely identical with that of the characterized scorpion K+ -channel ligands in the size, position, consensus junctions, putative branch point, and A+T content. The GST-BmTxKS4 fusion protein was successfully expressed in BL21 (DE3) and purified with affinity chromatography. About 2.5 mg purified recombinant BmTxKS4 (rBmTxKS4) protein was obtained by treating GST-BmTxKS4 with enterokinase and sephadex chromatography from 1 L bacterial culture. The electrophysiological activity of 1.0,M rBmTxKS4 was measured and compared by whole cell patch-clamp technique. The results indicated that rBmTxKS4 reversibly inhibited the transient outward K+ current (Ito), delayed inward rectifier K+ current (Ik1), and prolonged the action potential duration of ventricular myocyte, but it has no effect on the action potential amplitude. Taken together, BmTxKS4 is a novel subfamily member of short-strain K+ -channel scorpion toxin. © 2004 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:187,195, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20026 [source] Influence of cardiac-specific overexpression of insulin-like growth factor 1 on lifespan and aging-associated changes in cardiac intracellular Ca2+ homeostasis, protein damage and apoptotic protein expressionAGING CELL, Issue 6 2007Qun Li Summary A fall in circulating levels of cardiac survival factor insulin-like growth factor 1 (IGF-1) contributes to cardiac aging. To better understand the role of IGF-1 in cardiac aging, we examined the influence of cardiac IGF-1 overexpression on lifespan, cardiomyocyte intracellular Ca2+ homeostasis, protein damage, apoptosis and expression of pro- and anti-apoptotic proteins in young and old mice. Mouse survival rate was constructed by the Kaplan,Meier curve. Intracellular Ca2+ was evaluated by fura-2 fluorescence. Protein damage was determined by protein carbonyl formation. Apoptosis was assessed by caspase-8 expression, caspase-3 and TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) assay. Pro- and anti-apoptotic proteins including Bax, p53, pp53, Bcl2, Omi/HtrA2, apoptosis repressor with caspase recruitment domain (ARC) and X-linked inhibitor of apoptosis protein (XIAP) were assessed by Western blot. Aging decreased plasma in IGF-1 levels, elevated myocyte resting intracellular Ca2+ levels, reduced electrically stimulated rise in intracellular Ca2+ and delayed intracellular Ca2+ decay associated with enhanced protein carbonyl formation, caspase-8 expression and caspase-3 activity in FVB mice, all of which with the exception of elevated resting intracellular Ca2+ were attenuated by IGF-1. Aging up-regulated expression of Bax, Bcl2 and ARC, down-regulated XIAP expression and did not affect p53, pp53 and Omi/HtrA2. The IGF-1 transgene attenuated or nullified aging-induced changes in Bax, Bcl2 and XIAP. Our data suggest a beneficial role for IGF-1 in aging-induced survival, cardiac intracellular Ca2+ homeostasis, protein damage and apoptosis possibly related to pro- and anti-apoptotic proteins. [source] Up-Regulation and Functional Effect of Cardiac ,3 -Adrenoreceptors in Alcoholic MonkeysALCOHOLISM, Issue 7 2010Heng-Jie Cheng Background:, Recent studies link altered cardiac ,-adrenergic receptor (AR) signaling to the pathology of alcoholic cardiomyopathy (ACM). However, the alteration and functional effect of ,3 -AR activation in ACM are unknown. We tested the hypothesis that chronic alcohol intake causes an up-regulation of cardiac ,3 -AR, which exacerbates myocyte dysfunction and impairs calcium regulation, thereby directly contributing to the progression of ACM. Methods:, We compared myocyte ,3 - and ,1 -AR expression and myocyte contractile ([Ca2+]i), transient ([Ca2+]iT), and Ca2+ current (ICa,L) responses to ,- and ,3 -AR stimulation in myocytes obtained from left ventricle (LV) tissue samples obtained from 10 normal control (C) and 16 monkeys with self-administered alcohol for 12 months prior to necropsy: 6 moderate (M) and 10 heavy (H) drinkers with group average alcohol intakes of 1.5 ± 0.2 and 3.3 ± 0.2 g/kg/d, respectively. Results:, Compared with control myocytes (C), in alcoholic cardiomyocytes, basal cell contraction (dL/dtmax, ,39%, H: 69.8 vs. C: 114.6 ,m/s), relaxation (dR/dtmax, ,37%, 58.2 vs. 92.9 ,m/s), [Ca2+]iT (,34%, 0.23 vs. 0.35), and ICa,L (,25%, 4.8 vs. 6.4pA/pF) were all significantly reduced. Compared with controls, in moderate and heavy drinkers, ,1 -AR protein levels decreased by 23% and 42%, but ,3 -AR protein increased by 46% and 85%, respectively. These changes were associated with altered myocyte functional responses to ,-AR agonist, isoproterenol (ISO), and ,3 -AR agonist, BRL-37344 (BRL). Compared with controls, in alcoholic myocytes, ISO (10,8 M) produced significantly smaller increases in dL/dtmax (H: 40% vs. C: 71%), dR/dtmax (37% vs. 52%), [Ca2+]iT (17% vs. 37%), and ICa,L (17% vs. 27%), but BRL (10,8 M) produced a significantly greater decrease in dL/dtmax (H: ,23% vs. C: ,11%), [Ca2+]iT (,30% vs. ,11%), and ICa,L (,28% vs. ,17%). Conclusions:, Chronic alcohol consumption down-regulates cardiac ,1 - and up-regulates ,3 -ARs, contributing to the abnormal response to catecholamines in ACM. The up-regulation of cardiac ,3 -AR signaling enhances inhibition of LV myocyte contraction and relaxation and exacerbates the dysfunctional [Ca2+]i regulation and, thus, may precede the development of ACM. [source] Melatonin and its analogs potentiate the nifedipine-sensitive high-voltage-activated calcium current in the chick embryonic heart cellsJOURNAL OF PINEAL RESEARCH, Issue 1 2001Y.A. Mei Effects of melatonin and its analogs on the voltage-activated calcium current of embryonic chick ventricular cardiomyocytes were investigated. Myocytes were dissociated from 14- to 16-day-old chicks (yellow Red Rob) embryonic hearts and cultured for 2,3 days. Calcium currents were studied by the patch-clamp technique. Whole-cell current recording showed nifedipine-sensitive, high-voltage-activated L-type calcium current inactivated in 70,100 ms during the voltage step period of 200 ms. There was no evidence of low-voltage-activated T-type calcium channels. Melatonin (ejected solution: 50 ,mol/L melatonin; concentration at the vicinity of recording cell: about 1,5 ,mol/L melatonin) and its analogs, 2-iodomelatonin and 2-iodo-n-butanol-5-methoxytryptamine, significantly increased the amplitude of the calcium current by 42,62%. The effect of melatonin on the L-type calcium current was not desensitised by repeated melatonin treatment. Our results suggest a specific melatonin receptor-mediated action on the calcium channel of the embryonic chick myocyte. The melatonin-induced increase in high-voltage calcium current may increase myocyte contractility and enhance cardiac output. A regulatory role of melatonin on the chick cardiac function should be further considered. [source] Microvascular Perfusion and Transport in the Diabetic HeartMICROCIRCULATION, Issue 3 2000PAUL F. McDONAGH ABSTRACT Diabetes is a chronic disease of metabolic dysfunction that is increasing worldwide. The hyperglycemia associated with diabetes causes significant protein alterations and an oxidative stress. In the heart, all cell types are affected by diabetes; the myocyte, the vasculature and the blood cells. Four out of five diabetics die from ischemic heart disease and stroke, suggesting that the diabetic is quite vulnerable to ischemic injury. It is important to understand the pathophysiologic changes that occur in the diabetic heart in order to develop thoughtful treatments to limit this serious complication. This review focuses on the anatomical and functional alterations that occur in the diabetic circulation of the heart, with emphasis on the coronary microcirculation. Coronary microvascular dysfunction combined with blood cellular alterations are presented to explain the amplified oxidative stress that occurs in the diabetic heart under ischemic conditions. [source] Endothelin-1 activates a Ca2+ -permeable cation channel with TRPC3 and TRPC7 properties in rabbit coronary artery myocytesTHE JOURNAL OF PHYSIOLOGY, Issue 3 2007C. M. Peppiatt-Wildman In the present work we used patch pipette techniques to study the properties of a novel Ca2+ -permeable cation channel activated by the potent coronary vasoconstrictor endothelin-1 (ET-1) in freshly dispersed rabbit coronary artery myocytes. With cell-attached recording bath application of 10 nm ET-1 evoked cation channel currents (Icat) with subconductance states of about 18, 34 and 51 and 68 pS, and a reversal potential of 0 mV. ET-1 evoked channel activity when extracellular Ca2+ was the charge carrier, illustrating significant Ca2+ permeability. ET-1-induced responses were inhibited by the ETA receptor antagonist BQ123 and the phospholipase C (PLC) inhibitor U73122. The diacylglycerol analogue 1-oleoyl-2-acetyl- sn -glycerol (OAG) also stimulated Icat, but the protein kinase C (PKC) inhibitor chelerythrine did not inhibit either the OAG- or ET-1-induced Icat. Inositol 1,4,5-trisphosphate (IP3) did not activate Icat, but greatly potentiated the response to OAG and this effect was blocked by heparin. Bath application of anti-TRPC3 and anti-TRPC7 antibodies to inside-out patches markedly inhibited ET-1-evoked Icat, but antibodies to TRPC1, C4, C5 and C6 had no effect. Immunocytochemical studies demonstrated preferential TRPC7 expression in the plasmalemma, whereas TRPC3 was distributed throughout the myocyte, and moreover co-localization of TRPC3 and TRPC7 signals was observed at, or close to, the plasma membrane. Flufenamic acid, Gd3+, La3+ and extracellular Ca2+ inhibited Icat with IC50 values of 2.45 ,m, 3.8 ,m, 7.36 ,m and 22 ,m, respectively. These results suggest that in rabbit coronary artery myocytes ET-1 evokes a Ca2+ -permeable non-selective cation channel with properties similar to TRPC3 and TRPC7, and indicates that these proteins may be important components of this conductance. [source] The Molecular Phenotype of Heart Transplant Biopsies: Relationship to Histopathological and Clinical VariablesAMERICAN JOURNAL OF TRANSPLANTATION, Issue 9 2010M. Mengel Histopathology of endomyocardial biopsies (EMB) is the standard rejection surveillance for heart transplants. However, ISHLT consensus criteria for interpreting biopsies are arbitrarily defined. Gene expression offers an independent re-evaluation of existing diagnostic systems. We performed histologic and microarray analysis on 105 EMB from 45 heart allograft recipients. Histologic lesions, diagnosis and transcripts were compared to one another, time posttransplantation, indication for biopsy and left ventricular ejection fraction (LVEF). Histologic lesions presented in two groups: myocyte,interstitial and microcirculation lesions. Expression of transcript sets reflecting T cell and macrophage infiltration, and ,-interferon effects correlated strongly with each other and with transcripts indicating tissue/myocardium injury. This molecular phenotype correlated with Quilty (p < 0.005), microcirculation lesions (p < 0.05) and decreased LVEF (p < 0.007), but not with the histologic diagnosis of rejection. In multivariate analysis, LVEF was associated (p < 0.03) with ,-interferon inducible transcripts, time posttransplantation, ischemic injury and clinically indicated biopsies, but not the diagnosis of rejection. The results indicate that (a) the current ISHLT system for diagnosing rejection does not reflect the molecular phenotype in EMB and lacks clinical relevance; (b) the interpretation of Quilty lesions has to be revisited; (c) the assessment of molecules in heart biopsy can guide improvements of current diagnostics. [source] A Metabolic Mechanism For Cardiac K+ Channel RemodellingCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 1-2 2002George J Rozanski SUMMARY 1. Electrical remodelling of the ventricle is a common pathogenic feature of cardiovascular disease states that lead to heart failure. Experimental data suggest this change in electrophysiological phenotype is largely due to downregulation of K+ channels involved in repolarization of the action potential. 2. Voltage-clamp studies of the transient outward current (Ito) in diabetic cardiomyopathy support a metabolic mechanism for K+ channel downregulation. In particular, Ito density is significantly increased in diabetic rat isolated ventricular myocytes treated in vitro with insulin or agents that activate pyruvate dehydrogenase. Recent data suggest this mechanism is not limited to diabetic conditions, because metabolic stimuli that upregulate Ito in diabetic rat myocytes act similarly in non- diabetic models of heart failure. 3. Depressed Ito channel activity is also reversed by experimental conditions that increase myocyte levels of reduced glutathione, indicating that oxidative stress is involved in electrical remodelling. Moreover, upregulation of Ito density by activators of glucose utilization is blocked by inhibitors of glutathione metabolism, supporting the premise that there is a functional link between glucose utilization and the glutathione system. 4. Electrophysiological studies of diabetic and non-diabetic disease conditions affecting the heart suggest Ito channels are regulated by a redox-sensitive mechanism, where glucose utilization plays an essential role in maintaining a normally reduced state of the myocyte. This hypothesis has implications for clinical approaches aimed at reversing pathogenic electrical remodelling in a variety of cardiovascular disease states. [source] Myocardial growth before and after birth: clinical implications,ACTA PAEDIATRICA, Issue 2 2000AM Rudolph Perinatal changes in myocardial growth have recently evoked considerable interest with regard to cardiac chamber development with congenital cardiac lesions and to myocardial development in preterm infants. It is suggested that cardiac chamber development is influenced by blood flow. Experimental pulmonary stenosis in fetal lambs may induce either greatly reduced or markedly increased right ventricular volume. Ventricular enlargement appears to be associated with a large ventricular volume load resulting from tricuspid valve regurgitation. A small competent tricuspid valve is associated with reduced flow through the ventricle due to outflow obstruction and a small right ventricle. Postnatal growth of the ventricles in congenital heart disease is discussed. Increase in myocardial mass prenatally is achieved by hyperplasia, both during normal development and when myocardial mass is increased by right ventricular outflow obstruction. Postnatally, increases in myocardial mass with normal growth, as well as with ventricular outflow obstruction, are largely due to hypertrophy of myocytes. Myocardial capillary numbers do not increase in proportion with myocyte numbers in ventricular myocardium in association with outflow obstruction. The postnatal effects of these changes in congenital heart lesions are considered. Studies in fetal lambs suggest that the late gestational increase in blood cortisol concentrations is responsible for the change in the pattern of myocardial growth after birth. The concern is raised that prenatal exposure of the premature infant to glucocorticoids, administered to the mother to attempt to prevent hyaline membrane disease in the infant, may inhibit myocyte proliferation and result in a heart with fewer than normal myocytes. This would necessitate that each myocyte would have to hypertrophy abnormally to achieve a normal cardiac mass postnatally. [source] Increased Expression of p53 Protein Correlates With the Extent of Myocyte Damage in Cardiac Allograft RejectionCONGESTIVE HEART FAILURE, Issue 6 2008Bernadette K. McLaren MD Acute cardiac allograft rejection (ACAR) has been associated with a poor prognosis. The early diagnosis of ACAR necessitates the accurate detection of myocyte damage. Nuclear damage activates p53, a transcription factor that initiates apoptosis and repair. Endomyocardial biopsies (n=25) from 10 cardiac allograft recipients were stained for nuclear p53. The biopsies were divided into rejection groups based on the grading of ACAR: group 1, grade 0; group 2, grade Ia and Ib; group 3, grades II and III. While clinical indices did not correlate with myocyte damage, significantly more myocytes in group 3 stained for nuclear p53 (2.48±0.60/mm2) compared with group 1 (0.22±0.12/mm2) and group 2 (0.43±0.18/mm2). Increased expression of p53 in cardiac myocytes with grade II or grade III rejection provides an objective quantification as an aid in the diagnosis of ACAR. [source] Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor Fn14 during cardiac remodelling in ratsACTA PHYSIOLOGICA, Issue 1 2010E. Mustonen Abstract Aim:, Accumulating evidence supports the concept that proinflammatory cytokines play an essential role in the failing heart. We examined the concomitant tumour necrosis factor-like weak inducer of apoptosis (TWEAK)/Fn14 expression in myocytes in vitro as well as in vivo in cardiac remodelling. Methods:, We assessed TWEAK and its receptor Fn14 expression in response to angiotensin (Ang) II, myocardial infarction (MI) as well as to local adenovirus-mediated p38 gene transfer in vivo. The effect of various hypertrophic factors and mechanical stretch was studied in neonatal rat ventricular myocyte cell culture. Results:, Ang II increased Fn14 levels from 6 h to 2 weeks, the greatest increase in mRNA levels being observed at 6 h (6.3-fold, P < 0.001) and protein levels at 12 h (4.9-fold, P < 0.01). TWEAK mRNA and protein levels remained almost unchanged during Ang II infusion. Likewise, a rapid and sustained elevation of Fn14 mRNA and protein levels in the left ventricle was observed after experimental MI. Moreover, local p38 gene transfer increased Fn14 mRNA and protein but not TWEAK levels. Fn14 immunoreactive cells were mainly proliferating non-myocytes in the inflammation area while TWEAK immunoreactivity localized to cardiomyocytes and endothelial cells of the coronary arteries. Hypertrophic agonists and lipopolysaccharide increased Fn14 but not TWEAK gene expression in neonatal rat myocytes, while mechanical stretch upregulated Fn14 and downregulated TWEAK gene expression. Conclusions:, In conclusion, the cardiac TWEAK/Fn14 pathway is modified in response to myocardial injury, inflammation and pressure overload. Furthermore, our findings underscore the importance of Fn14 as a mediator of TWEAK/Fn14 signalling in the heart and a potential target for therapeutic interventions. [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] Acute atrial arrhythmogenesis in murine hearts following enhanced extracellular Ca2+ entry depends on intracellular Ca2+ storesACTA PHYSIOLOGICA, Issue 2 2010Y. Zhang Abstract Aim:, To investigate the effect of increases in extracellular Ca2+ entry produced by the L-type Ca2+ channel agonist FPL-64176 (FPL) upon acute atrial arrhythmogenesis in intact Langendorff-perfused mouse hearts and its dependence upon diastolic Ca2+ release from sarcoplasmic reticular Ca2+ stores. Methods:, Confocal microscope studies of Fluo-3 fluorescence in isolated atrial myocytes were performed in parallel with electrophysiological examination of Langendorff-perfused mouse hearts. Results:, Atrial myocytes stimulated at 1 Hz and exposed to FPL (0.1 ,m) initially showed (<10 min) frequent, often multiple, diastolic peaks following the evoked Ca2+ transients whose amplitudes remained close to control values. With continued pacing (>10 min) this reverted to a regular pattern of evoked transients with increased amplitudes but in which diastolic peaks were absent. Higher FPL concentrations (1.0 ,m) produced sustained and irregular patterns of cytosolic Ca2+ activity, independent of pacing. Nifedipine (0.5 ,m), and caffeine (1.0 mm) and cyclopiazonic acid (CPA) (0.15 ,m) pre-treatments respectively produced immediate and gradual reductions in the F/F0 peaks. Such nifedipine and caffeine, or CPA pre-treatments, abolished, or reduced, the effects of 0.1 and 1.0 ,m FPL on cytosolic Ca2+ signals. FPL (1.0 ,m) increased the incidence of atrial tachycardia and fibrillation in intact Langendorff-perfused hearts without altering atrial effective refractory periods. These effects were inhibited by nifedipine and caffeine, and reduced by CPA. Conclusion:, Enhanced extracellular Ca2+ entry exerts acute atrial arrhythmogenic effects that is nevertheless dependent upon diastolic Ca2+ release. These findings complement reports that associate established, chronic, atrial arrhythmogenesis with decreased overall inward Ca2+ current. [source] Scn3b knockout mice exhibit abnormal sino-atrial and cardiac conduction propertiesACTA PHYSIOLOGICA, Issue 1 2010P. Hakim Abstract Aim:, In contrast to extensive reports on the roles of Nav1.5 , -subunits, there have been few studies associating the , -subunits with cardiac arrhythmogenesis. We investigated the sino-atrial and conduction properties in the hearts of Scn3b,/, mice. Methods:, The following properties were compared in the hearts of wild-type (WT) and Scn3b,/, mice: (1) mRNA expression levels of Scn3b, Scn1b and Scn5a in atrial tissue. (2) Expression of the ,3 protein in isolated cardiac myocytes. (3) Electrocardiographic recordings in intact anaesthetized preparations. (4) Bipolar electrogram recordings from the atria of spontaneously beating and electrically stimulated Langendorff-perfused hearts. Results:,Scn3b mRNA was expressed in the atria of WT but not Scn3b,/, hearts. This was in contrast to similar expression levels of Scn1b and Scn5a mRNA. Immunofluorescence experiments confirmed that the ,3 protein was expressed in WT and absent in Scn3b,/, cardiac myocytes. Lead I electrocardiograms from Scn3b,/, mice showed slower heart rates, longer P wave durations and prolonged PR intervals than WT hearts. Spontaneously beating Langendorff-perfused Scn3b,/, hearts demonstrated both abnormal atrial electrophysiological properties and evidence of partial or complete dissociation of atrial and ventricular activity. Atrial burst pacing protocols induced atrial tachycardia and fibrillation in all Scn3b,/, but hardly any WT hearts. Scn3b,/, hearts also demonstrated significantly longer sinus node recovery times than WT hearts. Conclusion:, These findings demonstrate, for the first time, that a deficiency in Scn3b results in significant atrial electrophysiological and intracardiac conduction abnormalities, complementing the changes in ventricular electrophysiology reported on an earlier occasion. [source] Calmodulin kinase II initiates arrhythmogenicity during metabolic acidification in murine heartsACTA PHYSIOLOGICA, Issue 1 2009T. H. Pedersen Abstract Aim:, The multifunctional signal molecule calmodulin kinase II (CaMKII) has been associated with cardiac arrhythmogenesis under conditions where its activity is chronically elevated. Recent studies report that its activity is also acutely elevated during acidosis. We test a hypothesis implicating CaMKII in the arrhythmogenesis accompanying metabolic acidification. Methods:, We obtained monophasic action potential recordings from Langendorff-perfused whole heart preparations and single cell action potentials (AP) using whole-cell patch-clamped ventricular myocytes. Spontaneous sarcoplasmic reticular (SR) Ca2+release events during metabolic acidification were investigated using confocal microscope imaging of Fluo-4-loaded ventricular myocytes. Results:, In Langendorff-perfused murine hearts, introduction of lactic acid into the Krebs-Henseleit perfusate resulted in abnormal electrical activity and ventricular tachycardia. The CaMKII inhibitor, KN-93 (2 ,m), reversibly suppressed this spontaneous arrhythmogenesis during intrinsic rhythm and regular 8 Hz pacing. However, it failed to suppress arrhythmia evoked by programmed electrical stimulation. These findings paralleled a CaMKII-independent reduction in the transmural repolarization gradients during acidosis, which previously has been associated with the re-entrant substrate under other conditions. Similar acidification produced spontaneous AP firing and membrane potential oscillations in patch-clamped isolated ventricular myocytes when pipette solutions permitted cytosolic Ca2+ to increase following acidification. However, these were abolished by both KN-93 and use of pipette solutions that held cytosolic Ca2+ constant during acidosis. Acidosis also induced spontaneous Ca2+ waves in isolated intact Fluo-4-loaded myocytes studied using confocal microscopy that were abolished by KN-93. Conclusion:, These findings together implicate CaMKII-dependent SR Ca2+ waves in spontaneous arrhythmic events during metabolic acidification. [source] Impaired oxygen kinetics in beta-thalassaemia major patientsACTA PHYSIOLOGICA, Issue 3 2009I. Vasileiadis Abstract Aim:, Beta-thalassaemia major (TM) affects oxygen flow and utilization and reduces patients' exercise capacity. The aim of this study was to assess phase I and phase II oxygen kinetics during submaximal exercise test in thalassaemics and make possible considerations about the pathophysiology of the energy-producing mechanisms and their expected exercise limitation. Methods:, Twelve TM patients with no clinical evidence of cardiac or respiratory disease and 10 healthy subjects performed incremental, symptom-limited cardiopulmonary exercise testing (CPET) and submaximal, constant workload CPET. Oxygen uptake (Vo2), carbon dioxide output and ventilation were measured breath-by-breath. Results:, Peak Vo2 was reduced in TM patients (22.3 ± 7.4 vs. 28.8 ± 4.8 mL kg,1 min,1, P < 0.05) as was anaerobic threshold (13.1 ± 2.7 vs. 17.4 ± 2.6 mL kg,1 min,1, P = 0.002). There was no difference in oxygen cost of work at peak exercise (11.7 ± 1.9 vs. 12.6 ± 1.9 mL min,1 W,1 for patients and controls respectively, P = ns). Phase I duration was similar in TM patients and controls (24.6 ± 7.3 vs. 23.3 ± 6.6 s respectively, P = ns) whereas phase II time constant in patients was significantly prolonged (42.8 ± 12.0 vs. 32.0 ± 9.8 s, P < 0.05). Conclusion:, TM patients present prolonged phase II on-transient oxygen kinetics during submaximal, constant workload exercise, compared with healthy controls, possibly suggesting a slower rate of high energy phosphate production and utilization and reduced oxidative capacity of myocytes; the latter could also account for their significantly limited exercise tolerance. [source] Purinergic activation of a leak potassium current in freshly dissociated myocytes from mouse thoracic aortaACTA PHYSIOLOGICA, Issue 2 2009S. Hayoz Abstract Aim:, Exogenous ATP elicits a delayed calcium-independent K+ current on freshly isolated mouse thoracic aorta myocytes. We investigated the receptor, the intracellular pathway and the nature of this current. Methods:, The patch-clamp technique was used to record ATP-elicited delayed K+ current in freshly dissociated myocytes. Results:, ATP-elicited delayed K+ current was not inhibited by a ,cocktail' of K+ channel blockers (4-AP, TEA, apamin, charybdotoxin, glibenclamide). The amplitude of the delayed K+ current decreased after the reduction of extracellular pH from 7.4 to 6.5. These two characteristics suggest that this current could be carried by the TASK subfamily of ,twin-pore potassium channels' (K2P). Purinergic agonists including dATP, but not ADP, activated the delayed K+ current, indicating that P2Y11 is the likely receptor involved in its activation. The PKC activator phorbol ester 12,13-didecanoate stimulated this current. In addition, the PKC inhibitor Gö 6850 partially inhibited it. Real-time quantitative PCR showed that the genes encoding TASK-1 and TASK-2 are expressed. Conclusion:, Our results indicate that blocker cocktail-insensitive delayed K+ current in freshly dissociated aortic myocytes is probably carried by the TASK subfamily of twin-pore channels. [source] Dystrophin upregulation in pressure-overloaded cardiac hypertrophy in ratsCYTOSKELETON, Issue 1 2003Masato Maeda Abstract Dystrophin is a cytoskeletal protein localized to the sarcolemma of skeletal and cardiac muscle, and neurons. We have recently demonstrated that a significant cardiac damage including myocytes injury, inflammation, and fibrosis, was found in dystrophin-deficient myocardium during pressure overload [Kamogawa et al., 2001: Cardiovasc Res 50:509,515]. However, little is known about how the cardiac sarcolemmal cytoskeleton produces qualitative and quantitative changes in response to pressure overload. Accordingly, we investigated dystrophin gene expression and protein accumulation during cardiac hypertrophy. Cardiac hypertrophy was produced by banding of the abdominal aorta of rats. Total RNA from the left ventricle of the heart was used for a quantitative reverse transcription-polymerase chain reaction (RT-PCR). Dystrophin mRNA expression significantly increased by 33 ± 18% at 1 day (P < 0.05) and 45 ± 19% at 2 days (P < 0.01) after banding, while G3PDH mRNA showed no significant change. RT-PCR for dystrophin tissue-specific exon 1 revealed that only muscle type promoter, but not non-muscle type promoter (brain and Purkinje-cell type), was activated immediately after banding. Immunohistochemistry for dystrophin showed intense cellular membrane staining with an increase in the perimeter of the myocytes by 14% at 3 days (46.3 ,m, P < 0.01) and 19% at 7 days (51.2 ,m, P < 0.01) after banding. Western blotting also showed dystrophin protein increased by 14 ± 6% at 2 days (P < 0.05) and by 32 ± 10% at 3 days (P < 0.01) after aortic banding. In conclusion, upregulation of dystrophin mRNA expression and protein accumulation occurs in response to cardiac hypertrophy. These data and the vulnerability of dystrophin-deficient myocardium to pressure overload suggest that dystrophin could play an important role in maintaining the integrity of the sarcolemma. Cell Motil. Cytoskeleton 55:26,35, 2003. © 2003 Wiley-Liss, Inc. [source] Acute effects of desmin mutations on cytoskeletal and cellular integrity in cardiac myocytesCYTOSKELETON, Issue 2 2003Kurt Haubold Mutations in desmin have been associated with a subset of human myopathies. Symptoms typically appear in the second to third decades of life, but in the most severe cases can manifest themselves earlier. How desmin mutations lead to aberrant muscle function, however, remains poorly defined. We created a series of four mutations in rat desmin and tested their in vitro filament assembly properties. RDM-G, a chimera between desmin and green fluorescent protein, formed protofilament-like structures in vitro. RDM-1 and RDM-2 blocked in vitro assembly at the unit-length filament stage, while RDM-3 had more subtle effects on assembly. When expressed in cultured rat neonatal cardiac myocytes via adenovirus infection, these mutant proteins disrupted the endogenous desmin filament to an extent that correlated with their defects in in vitro assembly properties. Disruption of the desmin network by RDM-1 was also associated with disruption of plectin, myosin, and ,-actinin organization in a significant percentage of infected cells. In contrast, expression of RDM-2, which is similar to previously characterized human mutant desmins, took longer to disrupt desmin and plectin organization and had no significant effect on myosin or ,-actinin organization over the 5-day time course of our studies. RDM-3 had the mildest effect on in vitro assembly and no discernable effect on either desmin, plectin, myosin, or ,-actinin organization in vivo. These results indicate that mutations in desmin have both direct and indirect effects on the cytoarchitecture of cardiac myocytes. Cell Motil. Cytoskeleton 54:105,121, 2003. © 2003 Wiley-Liss, Inc. [source] Periostin promotes a fibroblastic lineage pathway in atrioventricular valve progenitor cellsDEVELOPMENTAL DYNAMICS, Issue 5 2009Russell A. Norris Abstract Differentiation of prevalvular mesenchyme into valve fibroblasts is an integral step towards the development of functionally mature cardiac valves. Although clinically relevant, little is known regarding the molecular and cellular mechanisms by which this process proceeds. Genes that are regulated in a spatio-temporal pattern during valve remodeling are candidates for affecting this differentiation process. Based on its expression pattern, we have focused our studies on the role of the matricellular gene, periostin, in regulating the differentiation of cushion mesenchymal cells into valve fibroblasts. Herein, we demonstrate that periostin expression is coincident with and regulates type I collagen protein production, a major component of mature valve tissue. Adenoviral-mediated knock-down of periostin in atrioventricular mesenchyme resulted in a decrease in collagen I protein expression and aberrant induction of myocyte markers indicating an alteration in AV mesenchyme differentiation. In vitro analyses using a novel "cardiotube" assay further demonstrated that expression of periostin regulates lineage commitment of valve precursor cells. In these cells, expression of periostin and collagen I are regulated, in part, by TGF,-3. We further demonstrate that TGF,-3, through a periostin/collagen pathway, enhances the viscoelastic properties of AV cushion tissue surface tension and plays a crucial role in regulating valve remodeling. Thus, data presented here demonstrate that periostin, a TGF,-3 responsive gene, functions as a crucial mediator of chick AV valve maturation via promoting mesenchymal-to-fibroblast differentiation while blocking differentiation of alternative cell types (myocytes). Developmental Dynamics 238:1052,1063, 2009. © 2009 Wiley-Liss, Inc. [source] Cardiac expression patterns of endothelin-converting enzyme (ECE): Implications for conduction system developmentDEVELOPMENTAL DYNAMICS, Issue 6 2008David Sedmera Abstract The spatiotemporal distribution of the endothelin-converting enzyme (ECE) protein in the embryonic chick heart and the association of this polypeptide with the developing cardiac conduction system is described here for the first time. Further, we show how cardiac hemodynamic load directly affects ECE level and distribution. Endothelin (ET) is a cytokine involved in the inductive recruitment of Purkinje fibers. ET is produced by proteolytic cleavage of Big-ET by ECE. We generated an antibody against chick ECE recognizing a single band at ,70 kD to correlate the cardiac expression of this protein with that reported previously for its mRNA. ECE protein expression was more widespread compared to its mRNA, being present in endothelial cells, mesenchymal cells, and myocytes, and particularly enriched in the trabeculae and nascent ventricular conduction system. The myocardial expression was significantly modified under experimentally altered hemodynamic loading. In vivo, ET receptor blockade with bosentan delayed activation sequence maturation. These data support a role for ECE in avian cardiac conduction system differentiation and maturation. Developmental Dynamics 237:1746,1753, 2008. © 2008 Wiley-Liss, Inc. [source] Characterization of Bves expression during mouse development using newly generated immunoreagentsDEVELOPMENTAL DYNAMICS, Issue 6 2006Travis K. Smith Abstract Bves (blood vessel/epicardial substance) is a transmembrane protein postulated to play a role in cell,cell interaction/adhesion. It was independently isolated by two groups as a gene product highly enriched in the developing heart. Disagreement exists about its expression during development. Most notably, the expression of Bves in non-muscle cells is disputed. Determining the expression profile of Bves is a critical initial step preceding the characterization of protein function in development and in the adult. We have generated new monoclonal antibodies against mouse Bves and used these immunoreagents to elucidate Bves expression in development. As expected, we detect Bves in myocytes of the developing heart throughout development. In addition, skeletal and smooth muscle cells including those of the coronary system express Bves. Finally, specific, but not all, epithelial derivatives of the three germ layers are stained positively with these monoclonal antibodies. Protein expression in cultured epithelial and muscle cell lines corroborate our in vivo findings. Taken together, these results demonstrate the expression of Bves in a wide range of epithelial and muscle cells during mouse embryogenesis and indicate a broad function for this protein in development, and show that these newly generated reagents will be invaluable in further investigation of Bves. Developmental Dynamics 235:1701,1708, 2006. © 2006 Wiley-Liss, Inc. [source] Zebrafish IRX1b in the embryonic cardiac ventricle,DEVELOPMENTAL DYNAMICS, Issue 4 2004Elaine M. Joseph Abstract The synchronous contraction of the vertebrate heart requires a conduction system. While coordinated contraction of the cardiac chambers is observed in zebrafish larvae, no histological evidence yet has been found for the existence of a cardiac conduction system in this tractable teleost. The homeodomain transcription factor gene IRX1 has been shown in the mouse embryo to be a marker of cells that give rise to the distinctive cardiac ventricular conduction system. Here, I demonstrate that zebrafish IRX1b is expressed in a restricted subset of ventricular myocytes within the embryonic zebrafish heart. IRX1b expression occurs as the electrical maturation of the heart is taking place, in a location analogous to the initial expression domain of mouse IRX1. The gene expression pattern of IRX1b is altered in silent heart genetic mutant embryos and in embryos treated with the endothelin receptor antagonist bosentan. Furthermore, injection of a morpholino oligonucleotide targeted to block IRX1b translation slows the heart rate. Developmental Dynamics 231:720,726, 2004. © 2004 Wiley-Liss, Inc. [source] Wnt11 and Wnt7a are up-regulated in association with differentiation of cardiac conduction cells in vitro and in vivoDEVELOPMENTAL DYNAMICS, Issue 4 2003Jacqueline Bond Abstract The heart beat is coordinated by a precisely timed sequence of action potentials propagated through cells of the conduction system. Previously, we have shown that conduction cells in the chick embryo are derived from multipotent, cardiomyogenic progenitors present in the looped, tubular heart. Moreover, analyses of heterogeneity within myocyte clones and cell birth dating have indicated that elaboration of the conduction system occurs by ongoing, localized recruitment from within this multipotent pool. In this study, we have focused on a potential role for Wnt signaling in development of the cardiac conduction system. Treatment of embryonic myocytes from chick with endothelin-1 (ET-1) has been shown to promote expression of markers of Purkinje fiber cells. By using this in vitro model, we find that Wnt11 are Wnt7a are up-regulated in association with ET-1 treatment. Moreover, in situ hybridization reveals expression, although not temporal coincidence of, Wnt11 and Wnt7a in specialized tissues in the developing heart in vivo. Specifically, whereas Wnt11 shows transient and prominent expression in central elements of the developing conduction system (e.g., the His bundle), relative increases in Wnt7a expression emerge at sites consistent with the location of peripheral conduction cells (e.g., subendocardial Purkinje fibers). The patterns of Wnt11 and Wnt7a expression observed in vitro and in the embryonic chick heart appear to be consistent with roles for these two Wnts in differentiation of cardiac conduction tissues. Development Dynamics 227:536,543, 2003. © 2003 Wiley-Liss, Inc. [source] Reactive species and early manifestation of insulin resistance in type 2 diabetesDIABETES OBESITY & METABOLISM, Issue 2 2006L. E. Fridlyand The early stages of type 2 diabetes mellitus are characterized by the development of insulin resistance (IRe) in muscle cells and adipocytes with the concomitant loss of ,-cell compensation. We have extensively reviewed the literature related to metabolic and signalling pathways of reactive oxygen species (ROS) in regard to the coordinated development of oxidative stress and IRe. We considered the hypothesis that oxidative stress leads to IRe in muscle cells and adipocytes, but found that the data are more consistent with the hypothesis that the cellular mechanisms that protect against oxidative stress per se are capable of creating an ROS-dependent insulin-resistant state. Furthermore, ROS-induced mitochondrial dysfunction can lead to disruptions of lipid metabolism, increasing the intracellular lipid content, and, in addition, contribute to lipid-dependent IRe in myocytes. Together, these two ROS-activated pathways to IRe can contribute to a global state of profound resistance to insulin action. Therapeutic strategies should, therefore, be directed towards reducing insulin resistance without an increase in ROS production or concentration. Pharmacological or other approaches to IRe that result in the activation of mitochondrial biogenesis in particular could be highly beneficial in the prevention or treatment of both insulin resistance and type 2 diabetes. [source] Effects of sulfonylureas on mitochondrial ATP-sensitive K+ channels in cardiac myocytes: implications for sulfonylurea controversyDIABETES/METABOLISM: RESEARCH AND REVIEWS, Issue 5 2006Toshiaki Sato Abstract Background Mitochondrial ATP-sensitive K+ (mitoKATP) channel plays a key role in cardioprotection. Hence, a sulfonylurea that does not block mitoKATP channels would be desirable to avoid damage to the heart. Accordingly, we examined the effects of sulfonylureas on the mitoKATP channel and mitochondrial Ca2+ overload. Methods Flavoprotein fluorescence in rabbit ventricular myocytes was measured to assay mitoKATP channel activity. The mitochondrial Ca2+ concentration was measured by loading cells with rhod-2. Results The mitoKATP channel opener diazoxide (100 µM) reversibly increased flavoprotein oxidation to 31.8 ± 4.3% (n = 5) of the maximum value induced by 2,4-dinitrophenol. Glimepiride (10 µM) alone did not oxidize the flavoprotein, and the oxidative effect of diazoxide was unaffected by glimepiride (35.4 ± 3.2%, n = 5). Similarly, the diazoxide-induced flavoprotein oxidation was unaffected both by gliclazide (10 µM) and by tolbutamide (100 µM). Exposure to ouabain (1 mM) for 30 min produced mitochondrial Ca2+ overload, and the intensity of rhod-2 fluorescence increased to 197.4 ± 7.2% of baseline (n = 11). Treatment with diazoxide significantly reduced the ouabain-induced mitochondrial Ca2+ overload (149.6 ± 5.1%, n = 11, p < 0.05 versus ouabain alone), and the effect was antagonized by the mitoKATP channel blocker 5-hydroxydecanoate (189.8 ± 27.8%, n = 5) and glibenclamide (193.1 ± 7.7%, n = 8). On the contrary, cardioprotective effect of diazoxide was not abolished by glimepiride (141.8 ± 7.8%, n = 6), gliclazide (139.0 ± 9.4%, n = 5), and tolbutamide (141.1 ± 4.5%, n = 7). Conclusions Our results indicate that glimepiride, gliclazide, and tolbutamide have no effect on mitoKATP channel, and do not abolish the cardioprotective effects of diazoxide. Therefore, these sulfonylureas, unlike glibenclamide, do not interfere with the cellular pathways that confer cardioprotection. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effects of labedipinedilol-A, third-generation dihydropyridine-type calcium blocker, on ouabain-induced arrhythmiaDRUG DEVELOPMENT RESEARCH, Issue 1 2008Jhy-Chong Liang Abstract Labedipinedilol-A, a novel dihydropyridine-type calcium antagonist with ,/,-adrenoceptor blocking properties, has been reported to produce a cardioprotective effect against ischemia reperfusion injury in rats. We investigated the protective effects of labedipinedilol-A on ouabain-induced tonotropy and arrhythmias in isolated whole atria, and using patch-clamp techniques to study the underlying mechanism of its antiarrhythmic activity on isolated cardiac myocytes. Labedipinedilol-A (10,µM) suppressed the tonotropic effect of ouabain significantly and prolonged the onset time of extra-systole (arrhythmia) induced by ouabain in isolate atria. In the voltage-clamp study, labedipinedilol-A (1,100,µM) reduced the peak amplitude of sodium inward current (INa) and L-type calcium current (ICa-L), and shifted the current-voltage (I-V) curve upward in a concentration-dependent manner. In contrast, the addition of labedipinedilol-A increased transient outward potassium current (Ito) and inward rectifier potassium current (IK1) significantly. Labedipinedilol-A (10,µM) also effectively depressed the isoproterenol-induced increase in the Ca2+ current. These results show that labedipinedilol-A blocks ICa-L and INa, and increases Ito and IK1. These findings indicate that labedipinedilol-A produces direct cardiac action, probably due to the inhibition of cardiac Na+ and Ca2+ channels. Our results suggest that labedipinedilol-A may reduce the membrane conduction through inhibition of ionic channels which decrease ouabain-induced arrhythmia. Drug Dev Res 69:26,33, 2008 © 2008 Wiley-Liss, Inc. [source] | ||||||||||||||||||||||||||||||||||