银杏叶提取物对家兔心室肌细胞瞬时外向钾电流和动作电位的影响

Effects of Ginkgo Biloba Extract on Transient Outward Potassium Current and Action Potential of Cardiomyocytes in Rabbits

目的:探讨银杏叶提取物(Egb761)对家兔心室肌细胞瞬时外向钾电流(Ito)和动作电位的作用,揭示其抗心肌缺血及缺血引起的心律失常的离子机制。方法:酶解法分离家兔的心室肌细胞。全细胞膜片钳技术记录心肌细胞的Ito和动作电位及其被Egb761作用后的变化。结果:①在电压钳制方式下,60μg/L Egb761作用心室肌细胞5 min后,各个钳制电位下的Ito均明显增大,在钳制电位为+50 mV时,Egb761使Ito的电流密度由对照组的(7.59±0.19)pA/pF增加到(11.18±0.89)pA/pF(P<0.01,n=8),Egb761还使Ito的I-V曲线比对照组Ito的I-V明显抬高,但I-V曲线方向没有发生改变,表明Egb761引起了心肌细胞Ito的明显外流。②在电流钳制下,对照组心室肌细胞动作电位都具有从0期到4期的动作电位形态,60μg/L Egb761使心肌细胞动作电位形态呈三角形尖锥锋形,动作电位时程(APD)明显缩短,其复极化50%时程(APD50)和复极化90%时程(APD90)分别由(83.6±4.3)ms缩短为(51.3±3.2)ms和由(168.7±4.1)ms缩短为(93.8±4.4)ms(分别与对照组相比,P<0.01,n=8),尽管Egb761使动作电位幅度(APA)和静息电位(RP)降低,但与对照组相比,没有显著性差异(P>0.05)。结论:Egb761可使心室肌细胞Ito显著增加和APD明显缩短,从而减轻心肌缺血时细胞内阳离子超载对心肌造成的损伤和心肌缺血引起的心律失常的发生,以及增加心脏泵血功能。

Objective： To investigate the effects of ginkgo biloba extract （Egb761） on transient outward potassium current （Ito） and action potential of cardiomyocytes in rabbits, and to explore its ion channel mechanism in antagonizing ischemia-induced myocardial injury and arrhythmia. Methods： Cardiomyocytes from rabbit ventricle were obtained by enzymatic dissociation. The whole-cell patch-clamp technique was used to assess the effect of Egb761 on Ito and action potential. Results： （1） With voltage clamp and administration of Egb761 （60μg/L）, the current densities of Ito in car- diomyocytes significantly ascended in every commanding potential. When holding potential was --50 mV and commanding potential was -50 mV, the current densities of Ito were markedly in- creased from （7.59±0.19） pA/pF to （11.18±0.89） pA/pF with Egb761 （60 μg/L） perfusion in 5 min （versus control, P〈0.01, n=8）. Egb761 still maybe completely changed the I-V curve upward without changing the I-V curve direction.（2）According to current clamp protocol, action potentials recorded in control groups in rabbit cardiomyoytes consisted of five phases from up- stroke to phase four. With administration of Egb761 （60μg/L）, action potentials were shaped an acute triangle with rather shorter action potential durations （APD50and APD900）, which were ob- viously shortened from （83.6＋4.3） ms to （51.3＋3.2） ms and from （168.7±4.1） ms to （93.8 ＋4.4） ms, respectively （versus control, P〈0.01, n=8, respectively）. Conclusion： It suggests that Egb761 might increase Ito and shorten the action potential duration in cardiomyoytes. It might contribute to the protection of heart with ischemia and antiarrhythmia and increase heart function during the ischemic injury.