The Role Of Gap Junction Alteration In Ventricular Arrhythmogenasis Induced By Drugs

PartⅠ. The role of gap junction in electrophysiological instability in rabbit wedge ventricular model of LQT2Objective The present study was to test the hypothesis that the functional change of gap junction contributes the electrophysiological instability in rabbit wedge ventricular model of LQT2.Materials and Methods Thirty female New Zealand White rabbits weighing 1.8-2.2kg were studied. An arterially-perfused rabbit left ventricular wedge preparation and an Ikr blocker, E-4031, was used to establish a model of LQT2. Preparations were randomly assigned to normal control group, LQT2 model group and AAP10 group. Transmural ECG as well as action potential from both endocardium and epicardium was simultaneously recorded in the whole process of all experiments. Changes of Cx43 and dephosphorylated Cx43 were measured by Western blot, the distribution of Cx43 and dephosphorylated Cx43 was examined by confocal laser scanning microscopy.Results①In LQT2 model, the QT interval prolonged(P<0.05), TDR decreased(P<0.05 or 0.01) and dephosphorylated Cx43 contents in LQT2 group increased significantly comparing to the normal control group (p<0.01);②the QT interval shortened(P<0.05), TDR decreased (P<0.05 or 0.01) and dephosphorylated Cx43 contents decreased significantly in AAP10 group comparing to the LQT2 group (P<0.01).③No significant change of total Cx43 contents was observed among normal control group, LQT2 group and AAP10 Group(P>0.05).Conclusion The presence of 500nmol/L AAP10 reduces TDR and enhances the couple of gap junction which was partially uncoupled in rabbit ventricular model of LQT2. This study provides a direct evidence of the functional change of gap junction contributes the electrophysiological instability in rabbit ventricular model of LQT2. PartⅡ. The mechanism of cardiac arrhythmogenesis induced by protein kinase C activationObjective To observe the effect of protein kinase C agonist, phorbol ester (PMA) on rabbit ventricular arrhythmia and to investigate its mechanism.Materials and Methods An arterially-perfused rabbit left ventricular preparation were randomly assigned to control and PMA500 nmol/L groups. Transmural ECG as well as action potential from both endocardium and epicardium were simultaneously recorded in the whole process of all experiments. Changes of Cx43 and dephosphorylated Cx43 on S368 was measured by Western blot.Results Compared with the control group, the QT interval (260±25 ms vs.302±21ms, P <0.01) was shortened significantly in the PMA group as well as a significant increase of Tp-e(61±13ms vs.51±7ms, P<0.01) and Tp-e/QT (0.24±0.05 vs.0.17±0.02, P<0.01); PMA led a significant decrese of connexin43(P<0.05) and nonphosphorylated connexin43 at S368(P<0.01); Nonsustained ventricular tachycardia (VT) could be induced in six out of ten animals in the PMA group (70% vs.0, P<0.01).Conclusion Down-regulation of cardiac gap junction by protein kinase C activation contributes to arrhythmogenesis in Rabbit Left Ventricular Wedge. PartⅢ. Effects of antiarrhythmic peptide on cardiac arrhythmogenesis induced by protein kinase C activationObjective To observe the effects of antiarrhythmic peptide on cardiac arrhythmogenesis induced by protein kinase C activation and to investigate its mechanism.Materials and Methods An arterially-perfused rabbit left ventricular preparation were randomly assigned to control, PMA 0.5um/L and PMA 0.5um/L+AAP10 0.5um/L groups. Transmural ECG as well as action potential from both endocardium and epicardium were simultaneously recorded in the whole process of all experiments. Changes of Cx43 and dephosphorylated Cx43 on S368 was measured by Western blot.Results Compared with the control group, the QT interval(260±25 ms vs.302±21ms, P <0.01) was shortened significantly in the PMA group, Tp-e(61±13ms vs.51±7ms, P <0.01) and Tp-e/QT (0.24±0.05 vs.0.17±0.02, P<0.01) increased, the amount of connexin43(P<0.05) and nonphosphorylated connexin43 on S368(P<0.01) decreased, Nonsustained ventricular tachycardia (VT) could be induced in seven out of ten animals (70% vs.0%, P<0.05) in the PMA group. Compared with the PMA group, no significant differences of the QT interval (241±22ms vs.256±24 ms, P>0.05) and the amount of nonphosphorylated connexin43 on S368 (P>0.05) in the AAP10 group, Tp-e(41±6ms vs. 61±13ms, P<0.01) and Tp-e/QT (0.17±0.03 vs.0.24±0.05, P<0.01) increased, the amount of connexin43 (P<0.05) decreased, VT could be induced in two out of ten animals (20% vs.70%, P<0.05) in the AAP10 group.Conclusion AAP10 can prevent PMA-induced rabbit ventricular arrhythmias by attenuating the down-regulation of cardiac gap junction.