普罗帕酮对兔心室肌细胞动作电位的影响及对快钠电流的使用依赖性阻滞作用

Effects of Propafenone on Action Potential of Rabbit Ventricular Myocytes and the Use-dependent Block of Transient Sodium Current

目的:探讨普罗帕酮对兔心室肌细胞动作电位(AP)的影响及对快钠电流的张力性阻滞和使用依赖性阻滞作用。方法:选取10只成年新西兰大白兔,急性分离兔心脏,应用消化酶消化分离获得单个心室肌细胞(n=10),采用微电极技术记录AP的最大舒张期电位、0相最大上升速率(Vmax)、AP振幅,以及复极化20%、50%和90%时的动作电位时程(依次简写为APD20、APD50和APD90)。应用全细胞膜片钳技术检测兔心室肌细胞快钠电流的I-V曲线及不同频率下的峰值电流,并用10μmol/L普罗帕酮溶液灌流干预,最后进行统计分析。结果:与普罗帕酮灌流前相比,普罗帕酮灌流后,兔心室肌细胞最大舒张电位无明显变化[(-80±6)mV vs(-82±5)mV,P>0.05],AP振幅显著降低[(95±12)m V vs(125±10)m V,P<0.05],Vmax明显减慢[(330±43)V/s vs(420±54)V/s,P<0.05)],APD20[(8±2)ms vs(6±2)ms,P>0.05]、APD50[(16±3)ms vs(12±3)ms,P>0.05]和APD90[(86±14)ms vs(85±12)ms,P>0.05]无显著变化。普罗帕酮干预后,快钠电流的I-V曲线较干预前明显上移,峰值电流下降[(3 001±383)pA vs(4 193±378)pA,P<0.05]。分别予0.06、1、2、5、10 Hz频率刺激,普罗帕酮干预前快钠电流均未显示出使用依赖性阻滞作用,第10个刺激与第1个刺激诱发的快钠电流之间的差异无统计学意义(P>0.05)。普罗帕酮干预后,在2、5、10 Hz频率刺激下,阻滞率分别为(22±11)%、(38±14)%和(52±17)%,与普罗帕酮灌流前及普罗帕酮在0.06 Hz和1 Hz刺激时的阻滞率间的差异有显著统计学意义(P<0.05),三组间两两比较差异亦有统计学意义(P<0.05)。结论:普罗帕酮减慢AP的Vmax,降低AP振幅,对APD无显著影响。普罗帕酮对快钠电流不但有张力性阻滞作用,更有显著的使用依赖性阻滞作用,这样不但减轻了对QT间期的影响,也可减少心动过缓的发生。

Objective： To study the effects of propafenone on action potential（AP） of rabbit ventricular myocytes with the tonic block and use-dependent block of transient sodium current（INa-T）. Methods： A total of 10 adult New Zealand white rabbits were sacrificed and 10 individual ventricular myocytes were isolated by enzyme digestion method. Microelectrode technologies were used to record AP-related parameters： maximum diastolic potential（MDP）, maximum rate of rise of the action potential upstroke（Vmax）, action potential amplitude（APA） and action potential duration at 20%, 50% and 90%（APD20, APD50 and APD90）. INa-T was measured, I-V curves and peak currents at different frequencies were detected by whole cell patch clamp before and after propafenone perfusion at 10 μmol/L. Results： There was no statistical difference in MDP at before and after propafenone perfusion as（-80 ± 6） mV vs（-82 ± 5） mV, P〈0.05. After perfusion, APA was significantly decreased as（95 ± 12） mV vs（ 125 ± 10） mV, P〈0.05, the Vmax slowed down as（330 ± 43） V/s vs（420 ± 54） V/s, P〈0.05, while APD20, APD50 and APD90 were unchanged as（8 ± 2） ms vs（6 ± 2） ms, P〈0.05,（16 ± 3） ms vs（12 ± 3） ms, P〉0.05 and（86 ± 14） ms vs（85 ± 12） ms, P〉0.05. After propafenone perfusion, I-V curve of INa-T was shifted upward and the peak current was decreased as（3001 ± 383） pA vs（4193 ± 378） pA, P〈0.05. Before perfusion, when stimulated at 0.06 Hz, 1 Hz, 2 Hz, 5 Hz and 10 Hz, there were no significant use-dependent block in INa-T, and no real difference in ItNa-T between the 10 h and 1st pulse, P〈0.05. After perfusion, no significant usedependent block was observed when stimulated at 0.06 Hz and 1 Hz, P〈0.05, while at 2 Hz, 5 Hz and 10 Hz, propafenone perfusion demonstrated significant use-dependent block upon INa-T with the inhibition fractions of（22 ± 11）%,（38 ± 14）% and（52 ± 17）% respectively, those were significantly different from the inhibition fractions at either 0.06 Hz or 1Hz, P〉0.05. When the inhibition fractions were compared by each 2 conditions, all P〈0.05.Conclusion： Propafenone may slow down the Vmax of AP, reduce APA and without the impact on APD; the effects on INa-T is not only in tonic block, but also more obviously in use-dependent block in isolated ventricular myocytes of New Zealand rabbit. Such influences minimized the impact on QT interval and meanwhile, decreased the incidence of brad arrhythmia.