The Antiarrhythmic Effects Of Mallotoxin Against LQT2 Induced By Dofetilide And Plus Low K~+ In Isolated Guinea Pig Hearts

Objective:To investigate the effect of MTX on action potential in isolated guinea pig ventricular myocytes and myocardial electrobiology on guinea pig isolated heart. To study the effects of MTX anti-LQT1 and anti-LQT2.Method:1. Langendorff perfusion is used to produce guinea pig isolated heart. Record the ECG of guinea pig hearts. The effect of MTX and MTX plus dofetilide of ECG were observed and recorded with MP150. To observe the effect of MTX in the presence of dofetilide and measure the QT interval and other index of myocardial electrobiology.The effect of MTX and MTX plus dofetilide or low K+ plus dofetilide of ECG were observed and recorded with MP150. To observe the effect of MTX in the presence of dofetilide and low K+ and measure the QT interval and other index.2. Single guinea pig ventricular myocyte was rapidly isolated from guinea pig heart by enzymatic dissociation. Action potential is recorded under the current clamp method. Effects of MTX on action potential were observed and recorded with whole-cell patch clamp. The effect of three concentration groups of MTX to action potential is observed, and we can also observe the effect of MTX to dofetilide induced prolonged action potential.3. Langendorff perfusion is used to produce guinea pig isolated heart. The effect of MTX and MTX in the presence of Chromanol 293 B of ECG were observed and recorded with MP150. To observe the effect of MTX in the presence of Chromanol293 B and measure the QT interval and other index in the presence of Chromanol293 B or not.4. HEK-293 cells were divided into normal group and experimental groups. The expressions of h ERG were evaluated by western blotting.Results:1. Compared with the normal group, MTX shorted the period of QTc, from189.42±3.28 ms to159.32±3.92 ms(n=6, p<0.01)and reduced r Tp-e by 23.17%(n=6,p<0.01). Compared with the normal group, 0.4 ?mol·L-1MTX significantly shorted the ERP and JT interval(n=6, p<0.01)on ECG, but had no significant effects on RR interval and HR.2. Compared with the normal group, dofetilide prolonged the QT interval and QTc(n=6, p<0.01); compared with the dofetilide group, 0.4 ?mol·L-1? 0.6 ?mol·L-1MTX shorted QTc(n=6, p<0.01) and reduced r Tp-e(n=6, p<0.01) of ECG in the presence of dofetilide significantly, but have no effect by 0.2 ?mol·L-1 MTX.3. Compared with the normal group, low K+ had no effect on the QT interval and QTc, but increaced r Tp-e(n=6, p<0.01); compared with the low K+group, 0.4?mol·L-1MTX shorted QTc(n=6, p<0.01) and reduced r Tp-e(n=6, p<0.01) of ECG in the presence of low K+ significantly.4. Compared with the normal group, low K+ combined dofetilide prolonged the QT c and increased r Tp-e(n=6, p<0.01); compared with the low K+combined dofetilide group, 0.4 ?mol·L-1MTX shorted QTc(n=6, p<0.01) and reduced r Tp-e(n=6, p<0.01) of ECG in the presence of dofetilide significantly, but have no effect by 0.2 ?mol·L-1MTX. MTX reduced the QT interval variability in the presence of low K+ combined dofetilide(n=6, p<0.01).5. MTX of each concentration shorted 90% of the action potential duration(n=8,p<0.01), from 220.1±2.03 ms to 205.4±1.97 ms, 189.8±0.79 ms and 152.7±2.80 ms respectively.6. The action potential duration were significantly shortened by different concentration MTX in the presence of dofetilide(n=8, p<0.01), APD90, APD50 and APD20 were shortened as well(n=8, p<0.01).7. The action potential duration were significantly shortened by 0.4 ?mol·L-1MTX in the presence of Chromanol 293B( n=8, p<0.01), and MTX recovered liability of APD with 293 B.8. Compared with the Chromanol 293 B group, 0.4 ?mol·L-1 MTX shorted QTc( n=6, p<0.01) and reduced r Tp-e( n=6, p<0.01) of ECG in the presence of Chromanol 293 B significantly.9. Western blot analysis shows that, Fluoxetine of different concentration reduce the expression of h ERG protein on cell membrane, separately, however MTX of different concentration have no significance to the expression of h ERG protein on cell membrane, separately.Conclution:1. MTX can short the QT interval of ECG of guinea pig isolated heart in the normal condition or in the presence of dofetilid, so that it had the effect to LQT2.2. MTX shorted the QT interval of ECG of guinea pig isolated heart in the low K+ solution or in the presence of dofetilide combining with low K+.3. The action potential duration were significantly shortened by MTX in the normal condition or in the presence of dofetilide.4. MTX invert the 293 B induced-LQT1.5. MTX shows negative effect to h ERG protein.