Background The rapidly activating delayed rectifier potassium current （/Kr）, whose pore-forming alpha subunit is encoded by the human ether-a-go-go-related gene （hERG）, is a key contributor to the third phase of action potential repolarization. The aim of this study was to investigate the effect and mechanism of arecoline hydrobromide induced inhibition of hERG K^＋ current （/hERG）. Methods Transient transfection of hERG channel cDNA plasmid pcDNA3.1 into the cultured HEK293 cells was performed using Lipofectamine. A standard whole-cell patch-clamp technique was used to record the /hI=RG before and after the exposure to arecoline. Results Arecoline decreased the amplitude and the density of the /bERG in a concentration-dependent manner （IC5o=9.55 μmol/L）. At test potential of ＋60 mV, the magnitude of lhERG tail at test pulse of -40 mV was reduced from （151.7±6.2） pA/pF to （84.4±7.6） pA/pF （P 〈0.01, n=20） and the magnitude of IhERG tail at test pulse of -110 mV was reduced from （-187.5±9.8） pA/pF to （-97.6±12.6） pA/pF （P 〈0.01, n=20）. The blockade of arecoline in the open and inactivated state was significant in a state-dependent manner. The maximal blockade was achieved in the inactivated state. Studies of gating mechanism showed that the steady-state activation curve of IhERG was significantly negatively shifted by arecoline. Time constants of activation were shortened. Steady-state inactivation curve and time constants of fast inactivation were not significantly affected by arecoline. Furthermore, the inhibition of IhERG by arecoline was characterized markedly by a frequency-dependent manner from 0.03 to 1.00 Hz pulse. Conclusion Arecoline could potently block IhERG in both frequency and state-dependent manner.
ZHAO Xu-yanLIU Yu-qiFU Yi-chengXU BinGAO Jin-liaoZHENG Xiao-qinLIN MinCHEN Mei-yanLI Yang
The noninfarcted myocardium underwent significant electrophysiological remodelling as part of the healed myocardial infarction remodelling. This study aimed at investigating the effects of nervous growth factor （NGF） on delayed afterdepolarizations （DADs） and triggered activity （TA） of the noninfarcted myocardium in the myocardial infarcted rabbit model. Rabbits with the left anterior descending coronary artery occlusion were prepared and recovered for 8 weeks （HMI group, n=9）. Other rabbits with myocardial infarction were infused NGF to the left stellate ganglion （HMI＋NGF group, 400 U/day for 8 weeks, n=8）. Myocytes were isolated from regions of the noninfarcted left ventricular free wall. Action potentials and ion currents were recorded with whole-cell patch clamp. The results showed that more DADs and TA events of HMI＋NGF myocytes than that of HMI and Ctrl group. Iti and ICa-L of NGF＋HMI myocytes were increased significantly compared with HMI and Ctrl cells, which contributed to DADs-related triggered arrhythmia. Comparing with HM1 and Ctrl myocytes, significant prolongations of APD50 and APD90 in HMI＋NGF myocytes were found. The results indicated the electrophysiological change of HMI myocytes with NGF infusion. It suggested that more events of DADs and TA in HMI myocytes with NGF treatment. The underlying mechanism may be involved in the increase of Iti and ICa-L.
Gao Yuling Liu Yuqi Lan Yunfeng Wen Yi Fang Zhou Gao Jinliao Wang Xueping Wang Hongjuan Li Yang
Objectives This study aimed at investigating the cellular mechanism of isoproterenol （ISO） on delayed afterdepolarizations （DADs） and triggered activity （TA） of the noninfarcted myocardium in the myocardial infarcted rabbit model.Methods Rabbits with the left anterior descending coronary artery occlusion were prepared and recovered for 8 wk （healed myocardial infarction, HMI）. Myocytes were isolated from regions of the noninfarcted left ventricular free wall. ISO was added to cellular surface by perfusion way. Action potentials and ion currents were recorded with whole-cell patch clamp. Results The results showed that treatment with ISO induced more DADs and TA events in HMI myocytes. Iti and IC,_L of myocytes treated with ISO were increased significantly compared with HMI cells, which contributed to DADs-related triggered arrhythmia. Conclusions The results suggested that more arrhythmia events of DADs and TA developed in myocytes with ISO treatment. The underlying mechanism was associated with the augment of I6 and calcium influxing
Jin-Liao Gao Hong-Juan Wang Yun-Feng Lan Zhou Fang Yan Liu Min Lin Yi-Cheng Fu Yang Li
