大鼠窦房结电压门控钠通道不同亚型的表达及其对心率的影响

目的 检测大鼠窦房结中电压门控钠通道不同亚型的表达情况并探讨其功能.方法 采用免疫荧光技术检测钠通道亚型Nav1.1、Nav1.2、Nav1.3、Nav1.5、Nav1.6、Nav1.7在大鼠窦房结中的表达,用激光共聚焦显微镜进行观察和图像分析.建立大鼠离体灌流心脏模型,观察钠通道特异性阻断剂河豚毒素对离体灌流心脏自发性节律即固有心率的影响.结果 河豚毒素敏感的神经型钠通道亚型Nav1.1、Nav1.6、Nav1.7以及河豚毒素不敏感的心脏型Nav1.5均存在于大鼠窦房结组织中,但是神经型钠通道的蛋白表达更为丰富(P＜0.05).100 nmol/L河豚毒素灌流可以选择性阻断神经型钠通道亚型(推测为Nav1.1、Nav1.6、Nav1.7),同时不阻断河豚毒素不敏感的钠通道亚型(推测为Nav1.5),大鼠固有心率不受影响[(0.5±2.9)%,P＞0.05];2 μmol/L河豚毒素同时阻断河豚毒素敏感的钠通道亚型以及对河豚毒素不敏感的钠通道亚型后,大鼠固有心率显著下降[(22.1±2.1)%,P＜0.001].结论 Nav1.1、Nav1.5、Nav1.6和Nav1.7在大鼠窦房结组织中均有表达.虽然神经型钠通道亚型的蛋白含量更为丰富,心脏型Nav1.5对于维持正常的窦房结活动可能更为重要.

Expression and function of voltage-gated Na+ channel isoforms in rat sinoatrial node

OBJECTIVE: To detect the expression of voltage-gated Na(+) channel (NaCh) isoforms in rat sinoatrial node and explore their functions. METHODS: Expressions of NaCh isoforms Nav1.1, Nav1.2, Nav1.3, Nav1.5, Nav1.6 and Nav1.7 in the rat sinoatrial node were detected by immunohistochemistry. The functional roles of the NaChs were tested by observing the effect of tetrodotoxin, a specific blocker of NaChs, on the intrinsic heart rate of isolated rat working heart. RESULTS: The tetrodotoxin- sensitive neuronal isoforms Nav1.1, Nav1.6 and Nav1.7 as well as the tetrodotoxin-resistant cardiac isoform Nav1.5 were present in the rat sinoatrial node, and the neuronal isoforms were more abundant than Nav1.5 (P<0.05). The selective blockade of tetrodotoxin-sensitive isoforms (presumably Nav1.1, Nav1.6 and Nav1.7) by 100 nmol/L tetrodotoxin scarcely affected the intrinsic heart rate (0.5-/+2.9%, P>0.05) while blockade of tetrodotoxin-resistant isoform (presumably Nav1.5) by 2 micromol/L tetrodotoxin resulted in an obvious decline in the intrinsic heart rate (22.1-/+2.1%, P<0.001). CONCLUSIONS: Nav1.1, Nav1.5, Nav1.6 and Nav1.7 are all present in rat sinoatrial node. Although neuronal isoforms are more abundant, Nav1.5 seems to contribute more to activity of the sinoatrial node.