Effects Of Tumor Necrosis Factor-α On Ventricular Arrhythmias During Early Acute Myocardial Infarction

Part one Effects of tumor necrosis factor-a on ventricular arrhythmias during early acute myocardial infarction in vivoObjective:To study the relationship between expression of tumor necrosis factor-a (TNF-a) in rats with acute myocardial infarction (AMI) and electrophysiological heterogeneity/ventricular arrhythmias (VAs) in vivo.Methods:A rat model of AMI was created by ligation of the left anterior descending (LAD) coronary artery. ECG and spontaneous VAs were observed during the whole experiment. Monophasic action potentials (MAP) among ischemic zone, border zone and non-ischemia zone was observed and Monophasic action potential repolarization dispersion (MAPDd) were calculated. TNF-a protein expression were measured using Western blot and laser scanning confocal fluorescence microscopy. Linear correlation analysis was used to assess the relationship between TNF-a protein expression and MAPDd of the border zone.Results:The incidence of VAs in AMI group was markedly increased at each time interval after ligation compared with Etanercept group (p<0.05). The MAPDd from the border zone of the ischemic myocardium was significantly increased at each time point after ligation compared with the ischemic zone and non-ischemic zone of the epicardium (p<0.05). Moreover, the MAPDd from the border zone of ischemic myocardium was significantly increased in the AMI group compared with the Etanercept group (p<0.05). The temporal changes of the MAPDd in the border zone coincided with the incidence of VAs in vivo during early AMI. The levels of TNF-a protein expression in the AMI group began to increase at10min and reached a peak at20min after ligation; then, they decreased. The correlation coefficient of TNF-a protein expression and MAPDd of the border zone was0.96(p<0.01) and showed a positive linear correlation.Conclusion:The expression of TNF-a increased after ligation. TNF-a could increase the MAPDd in the border zone, and promote the onset of VAs, while Etanercept could decrease the MAPDd in the border zone and lessen the incidence of VAs in rats with AMI. Part two Effects of tumor necrosis factor-a on ventricular arrhythmias during early acute myocardial infarction in vitroObjective:To explore the relationship between expression of tumor necrosis factor-a (TNF-a) and electrophysiological heterogeneity/ventricular arrhythmias (VAs) in isolated perfused rat heart with acute myocardial infarction (AMI). A single dose of TNF-a whether would result in a difference of MAPD between the endocardium and epicardium in isolated heart tissues was further examined.Methods:Langendorff perfused isolated rat heart models were used to verify the arrhythmogenic effects of TNF-a. Electrophysiological experiments, Western blot and laser scanning confocal fluorescence microscopy were performed to study the relationship between expression of TNF-a and electrophysiological heterogeneity/VAs. Linear correlation analysis was used to assess the relationship between TNF-a protein expression and MAPDd of the border zone in rats with AMI in vitro. The MAPs of the endocardium and epicardium from the isolated heart tissues were recorded by electrophysiological experiments.Results:The levels of TNF-a in the LAD ligation group, determined by Western blot and LSCFM, began to increase at10min, peaked at20min after ligation and then decreased. The incidence of VAs in LAD ligation group was markedly increased at each time interval after ligation compared with LAD ligation+etanercept group (p<0.05). The MAPDd from the border zone of ischemic myocardium in the LAD ligation group was significantly increased at each time point after ligation compared with the LAD ligation+etanercept group (p<0.05). The temporal changes of the MAPDd in the border zone coincided with the incidence of VAs in vitro during early AMI. The incidences of VAs dose-dependently increased at each time period with increasing doses of TNF-a in vitro. The MAPDd in the border zone adjacent to ischemic myocardium of in vitro hearts dose-dependently increased with increasing TNF-a perfusion. The correlation coefficient of TNF-a protein expression and MAPDd in the border zone in vitro was0.97(p<0.01) and showed a positive linear correlation. TNF-a could cause MAP duration (MAPD) prolongation, and a single dose of TNF-a differentially affected the MAPs of endocardium and epicardium of isolated heart tissues.Conclusion:The levels of TNF-a protein expression underwent a time-dependent increase during early AMI in vitro. TNF-a in vitro can lead to VAs. TNF-a could cause not only the MAPDd in different regions of epicardium but also a difference in MAPD between the endocardium and epicardium, and this heterogeneity is important for arrhythmogenesis. Part three Effects of tumor necrosis factor-a on intracellular calcium concentration and electrophysiological characteristics in isolated rat ventricular myocytesObjective:To investigate the effects of tumor necrosis factor-a (TNF-a) on intracellular calcium concentration and electrophysiological characteristics in isolated rat ventricular myocytes. The arrhythmogenic mechanisms of TNF-a were further studied.Methods:The isolated rat ventricular myocytes were obtained by enzymatic dissociation. Laser scanning confocal fluorescence microscopy were performed to confirm the effects of TNF-a on intracellular calcium concentration. Action potentials (APs) and K+currents (Ito, Ik1) were recorded by using whole cell patch clamp technique.Results:Intracellular calcium concentrations dose-dependently increases with TNF-a in isolated rat ventricular myocytes. TNF-a can dose-dependently prolong APD by lengthening the plateau of the action potential and changing the action potential configuration in isolated rat ventricular myocytes. The K+currents (Ito, Ik1) were dose-dependently decreased in the presence of TNF-a in rat ventricular myocytes.Conclusion:TNF-a was arrhythmogenic and could induce ventricular arrhythmias by prolongation of APD and contribute to re-entrant VAs which resulted from enhancement of intracellular calcium concentration and decreased K+currents (Ito)...