背景:多病灶异位Purkinje相关的早搏(MEPPC)与SCN5A变异体相关。然而,为什么浦肯野纤维,但不是心室心肌,在心律失常发生中起主要作用。
目的:本研究旨在探索MEPPC的潜在机制。
方法:本研究采用全细胞膜片钳和分子生物学技术。
结果:来自一名R814W变异患者的临床数据显示MEPPC综合征,对胺碘酮反应良好。与犬心室肌细胞相比,浦肯野细胞(PC)具有明显较大的钠电流(INa),INa激活和失活曲线向左移动,提示PCs中钠通道的兴奋性较高。实时聚合酶链反应和Westernblot分析表明,犬浦肯野纤维中NaVβ1和NaVβ3的mRNA和蛋白表达高于心室心肌。共表达NaV1.5和NaVβ1/NaVβ3的异源中国仓鼠卵巢细胞表达系统中的INa在PC中表现出类似的INa生物物理特性。R814W变异体在超去极化方向上移位了INa激活,导致更大的窗口电流,并在去极化电压下产生外栅孔电流。NaVβ1/NaVβ3与Nav1.5-R814W的共表达进一步左移INa激活,并引起更大的窗口电流和门控孔电流,表明浦肯野纤维对R814W变体的敏感性更高。胺碘酮抑制INa,将其失活转移到更多的负电压,并显著降低了窗口电流。
结论:β1和β3亚基的较高表达有助于心脏浦肯野纤维中更高的钠通道兴奋性,使他们更容易受到MEPPC的影响。
Multifocal ectopic Purkinje-related premature contractions (MEPPCs) are associated with SCN5A variants. However, it is not well understood why Purkinje fibers, but not ventricular myocardium, play a predominant role in arrhythmogenesis.
This study sought to explore the underlying mechanisms of MEPPC.
Whole-cell patch-clamp and molecular biology techniques were used in the present study.
Clinical data from one patient with R814W variant showed MEPPC syndrome, which is well responsive to amiodarone. Compared with canine ventricular myocytes, Purkinje cells (PCs) had significantly larger sodium current (INa), leftward shift of INa activation and inactivation curves, suggesting higher sodium channel excitability in PCs. Real-time polymerase chain reaction and Western blot analysis showed that the mRNA and protein expression of NaVβ1 and NaVβ3 was higher in canine Purkinje fibers than in ventricular myocardium. INa in heterologous Chinese hamster ovary cell expression system co-expressing NaV1.5 and NaVβ1/NaVβ3 exhibited similar biophysical properties of INa in PCs. R814W variant shifted INa activation in a hyperdepolarized direction, caused a larger window current, and generated an outward-gating pore current at depolarized voltages. Coexpression of NaVβ1/NaVβ3 with Nav1.5-R814W further left-shifted INa activation and caused an even larger window current and gating pore current, suggesting higher susceptibility of Purkinje fibers to R814W variant. Amiodarone inhibited INa, shifted its inactivation to more negative voltages, and significantly decreased the window current.
A higher expression of β1 and β3 subunits contributes to higher sodium channel excitability in cardiac Purkinje fibers, making them more susceptible to MEPPC.