Morphological and functional heterogeniety of sinoatrial node pacemaker cells

虽然电生理特性的窦房结（SA）起搏细胞已得到很好的表征，只有有限的信息是可用的不同的电特性的分子机制。本研究应用免疫荧光技术研究了SA结中缝隙连接蛋白和K+通道的表达和分布。1.连接蛋白在SA结中的表达：用亚型特异的抗连接蛋白抗体对兔SA结进行染色，并通过共聚焦显微镜进行分析。结果表明：（1）SA结细胞不表达Cx43，但表达Cx45;（2）SA结细胞也表达Cx40。3)有组织制备区域，特别是内皮细胞侧，其中细胞表达连接蛋白45和43。SA结中不同类型的连接蛋白的表达以及小缝隙连接的缺乏可能与SA结细胞间耦合电导的降低有关。2. SA结中Kv1.5通道的表达和定位我们以前报道过4-AP对SA结的电活动有显著的影响。本研究对豚鼠窦房结内及周围的4-AP敏感性克隆钾通道之一Kv1.5通道的分布进行了研究。Kv1.5在SA结和心房肌中大量表达，尽管两种组织中的亚细胞分布不同。在心房肌中，Kv1.5通道主要位于闰盘区域，与连接蛋白43紧密并列，而在SA结中，Kv1.5更分散于整个细胞膜。Kv1.5通道在SA结中的作用尚未完全确定，但它可能是4-AP对SA结的显著影响的部分基础。

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.