超极化激活环核苷酸门控通道(HCN)在Fontan术后房性心动过速中的作用及其机制

Fontan type operation is the first-line treatment for tricuspidal atresia and single ventricle. Post-operation atrial tachycardia (AT) is a very common complication. The recurrency after catheter ablation of intraatrial reeentry tachycardia is high, suggesting that reentry is not the only mechanism of post-Fontan AT and other mechanism may also be important. In the previous studies of our research group, we did find that the incidence of focal AT is about 30%, which own to triggers activity. Trigger activity is known to relate closely to hyperpolarization and cyclic nucleotide (HCN)-gated channels and its the main inward ionic current (If) of diastolic depolarization. To further examine the relationship between HCN and post-Fontan AT , we plan to establish a canine model post Fontan operation followed with induction of AT by fast atrial pacing, then perform the electrophysiological study and rebuild right atrium using 3D-mapping system (Carto) to decide sites with abnormal electrograms. The expression level of HCN in these different sites will be tested and compared; using the whole-cell patch clamp the activation status HCN channel and If the current level will be examined. By giving HCN / If antagonists and in vivo gene transfer technology to interference myocardial HCN gene expression, we will explore the impact of HCN / If on AT post-Fontan operation and its intrinsic molecular mechanisms. Accordingly, in order to improve the efficacy of the AT post Fontan operation,our study is going to provide a theoretical basis for establishing new therapeutic strategies and new drug targets.

房性心动过速（房速）是Fontan术后最常见的并发症。既往针对折返机制的射频消融方法的复发率高，提示折返并不是Fontan术后房速的唯一机制，其他机制可能也很重要。课题组通过前期的研究发现，Fontan术后局灶性房速的发生率约占30%，而局灶性房速的发生与触发机制密切相关。因此，本项目拟通过建立犬Fontan术后房速动物模型，运用三维标测系统标测出与触发机制有关的右房内电生理异常部位，并通过检测这些部位的超极化激活环核苷酸（HCN）门控通道的表达水平，以及运用全细胞膜片钳技术研究其HCN通道蛋白的活化状况以及If电流水平，并最终通过使用HCN/If拮抗剂和体内基因转染技术干扰心肌局部HCN基因表达，以探讨HCN/If对Fontan术后继发房速的影响及其内在分子机制。据此，为提高Fontan术后房速的疗效，确立新的治疗策略和新的药物靶点提供理论依据。

房性心动过速（房速）是Fontan术后最常见的并发症。临床研究提示折返可能并不是Fontan术后房速的唯一机制，很可能有其他机制参与。本项目研究内容主要包括了以下几个部分。1.对犬Fontan术后模型的右房进行了组织学检查，心房电生理检查及心房细胞电生理检查。2.对犬Fontan术后模型的右房心房肌细胞的几个重要的膜通道进行了研究。3. 检测右心房肌细胞中HCN2和HCN4的核酸和蛋白表达和If通道电流。4. 研究Fontan术后犬模型右心房细胞中钙运作机制。本项目重要的研究结果包括以下几个方面：1.犬Fontan术后模型的右房增大且纤维化程度增加（解剖重构）；犬Fontan术后模型的心房率增快，右房心房不应期缩短，更易诱发出房性心动过速，更易出现自发除极。2.Fontan术后的KCND3/Kv4.3 and CACNA1C/Cav1.2表达降低而KCNJ2/Kir2.1表达增高；Ito和ICaL电流密度下降，Ik1电流密度增加。3. Fontan术后模型犬右心房心肌细胞HCN2和HCN4 表达增加，HCN通道电流较正常对照组增大。4. Fontan术后犬右心房肌细胞自发性钙释放事件（SCaEs）结果显示， Fontan术后的右心房心肌细胞更易发生自发电活动.钙瞬变的记录显示Fontan术后犬的心房肌细胞的舒张期细胞内钙离子水平较对照组升高，而钙瞬变幅度较对照组减小。Fontan术后犬右心房心肌细胞NCX1通道在核酸及蛋白表达水平及INCX电流均较对照组增高。本项目第一次系统地描述了Fontan术后右房的电重构，离子通道重构；显示了Fontan术后HCN/If上调，提示其可能参与了房速发生；本项目首次显示了Fontan术后右房心房肌内存在钙离子运作障碍。