模拟缺血时兔心室肌细胞快钠通道跨壁异质性的变化

Alteration of the heterogeneity of Na^+ channel in rabbit ventricular myocytes under simulated Ischemia

目的探讨缺血时心肌细胞钠通道的异质性变化。方法以酶解法分离兔心室肌三层细胞,先后用正常和缺血液灌流模拟正常和缺血状态,并采用膜片钳全细胞记录法观察三层心室肌细胞快钠通道的活性和异质性变化。结果缺血后三层细胞失活曲线均左移,失活加速,三层细胞间INa失活半电压差异发生变化;缺血30 m in时INa灭活后恢复曲线与原来的三层细胞间由差异无统计学意义(P>0.05)变为差异有统计学意义(P<0.05)。各层细胞自身INa灭活后恢复随着缺血时间延长而减慢,但无统计学意义;缺血后三层细胞的钠电流(INa)电压依赖性、I-V曲线的形态轨迹未变,INa峰电流密度减小,三层细胞间峰电流密度差异发生变化。结论缺血时心肌钠通道的活性发生变化,从而影响心室肌三层细胞间INa的异质性及与通道电流平衡,与缺血性心律失常的发生有关,并可部分解释抗心律失常药物在正常和缺血心肌的不同作用。

Objective To study the heterogeneity alteration of Na^＋ channel in rabbit myocytes under ischemia condition. Methods Single myocytes were enzymatieally isolated from the epicardium, midmyocardium and endocardium of the free left ventricle wall of rabbit, then INa of the three cellular subtypes （superfused with normal and then simulated ischemia solution） were recorded using whole-cell patchclamp techniques. Result （1）After simulated isehemia, INa steady-state inactivation curves were all shifted significantly in the hyperpolarizing direction in three cellular subtypes and the inactivation rates were accelerated. The differences of the half maximal inactivation voltages （ V0.5 ） among the three cellular subtypes were also changed. （2）After simulated isehemia, INa recoveries from inactivation states of three cellular subtypes were all slower than those in normal condition, but without statistical significance. There were significant differences among the recovery from inactivation curves of three cellular subtypes after 30minutes of simulated ischemia. （3）After simulated ischemia, there were no changes in the configuration of INa Ⅰ-Ⅴ curves and the dependence of voltage, but the peak INa densities （ at -20mV ） were significantly reduced in three cellular subtypes. Meanwhile, the differences of INa peak current densities among the three cellular subtypes were changed. Conclusion The alteration of the Na^＋ channel activity under ischemia condition can affect the heterogeneity of INa and the balance of ion channel currents among three cellular subtypes. These could be responsible for ischemic arrhythmias and could be the reason for different pharmacology reactions under normal and ischemie conditions.