Morphological and functional heterogeniety of sinoatrial node pacemaker cells

虽然窦房结起搏器细胞的电生理特性已被很好地表征，但关于其独特电特性的分子机制的信息有限。本研究利用免疫荧光技术研究了间隙连接蛋白和K+通道的表达和分布。连接蛋白在窦房结的表达。兔窦房结用亚型特异性抗连接蛋白抗体染色，并用共聚焦显微镜分析。结果如下：1)SA结细胞不表达connexin43，但表达connexin45.2) SA结细胞也表达Connexin40。3)在组织制备的某些区域，特别是心内膜侧，细胞同时表达连接蛋白45和连接蛋白43。窦房结内不同类型连接蛋白的表达以及小间隙连接的缺乏可能与窦房结细胞间偶联电导的降低有关。窦房结中Kv1.5通道的表达和定位。我们之前报道过4-AP对窦房结的电活动有明显的影响。本研究研究了4-AP敏感克隆K+通道之一的Kv1.5通道在豚鼠SA结内及周围的分布。Kv1.5在窦房结和房肌中大量表达，但两者的亚细胞分布不同。在心房肌中，Kv1.5通道主要定位于与connexin43密切相关的插盘区，而在窦房结中，Kv1.5通道更分散于整个细胞膜。Kv1.5通道在窦房结中的作用尚未完全确定，但它可能部分解释了4-AP对窦房结的显著影响。

Although the electrophysiological properties of sinoatrial (SA) node pacemaker cells have been well characterized, only limited information is available about the molecular mechanisms underlying the distinct electrical properties. In the present study, the expression and distribution of gap junctional proteins and K+ channels have been studied by immunofluorescence techniques.1.Expression of connexins in the SA node.The rabbit SA node was stained with subtype-specific anti-connexin antibodies and was analyzed by confocal microscopy. The following results were obtained : 1)The SA node cells did not express connexin43 but did express connexin45.2)Connexin40 also appeared to be expressed by the SA node cells. 3)There were regions of tissue preparation, in particular, the endocardial side, in which the cells expressed both connexin45 and 43. The expression of different types of connexins in the SA node in addition to scarce formation of small gap junctions might be involved in the reduced intercellular coupling conductance between SA node cells.2.Expression and localization of the Kv1.5 channel in the SA node.We have previously reported that 4-AP has marked effects on the electrical activity of the SA node. In this study, the distribution of Kv1.5 channel, one of the 4-AP sensitive cloned K+ channels, has been studied in and around the guinea pig SA node. Kv1.5 was abundantly expressed in the SA node as well as the atrial muscle, although the subcellular distribution was different in the two tissues. In the atrial muscle, Kv1.5 channel was localized predominantly at the intercalated disk regions in close apposition with connexin43, whereas in the SA node Kv1.5 was more dispersed throughout the cell membrane. The role of the Kv1.5 channel in the SA node has not well established, but it may partly underlie the marked effects of 4-AP on the SA node.