家兔房室结三层细胞超微结构的观察

Observation on ultrastructural differences between three cellular layers of atrioventricular node in rabbits

目的探讨房室结不同层面与细胞传导有关的细胞超微形态及连接方式有无差异。方法用家兔含房室结组织块半薄及超薄切片，光镜及透射电镜观察。结果光镜下家兔房室结由三层细胞组成，上层细胞细长，排列不整齐；中层细胞短小，排列紊乱；下层细胞粗长，排列整齐。透射电镜下，下层细胞线粒体和肌丝丰富，可见不完整的肌节，相邻细胞间有片状润盘样结构及缝隙连接，靠近心室肌的下层细胞甚至可见较完整的肌节；中层细胞线粒体和肌丝均较少，无肌节，细胞间特化的连接复合体及润盘样结构罕见，其中可见圆形细胞，其核较大，胞桨肌丝极少，胞内空泡样结构较多；上层细胞的线粒体和肌丝较下层细胞少，肌丝排列紊乱，肌节少见，细胞间特化连接复合体较少，偶见润盘样结构。结论家兔房室结不同层面细胞超微形态及其连接方式有明显差异。下层细胞束可能传导较快，上层细胞可能传导较慢，中层细胞可能传导最慢。

The ultrastructures and the connection patterns of the conduction relevant cells in different layers of the rabbit atrioventricular node were investigated. Methods The structures of rabbit atrioventricular node tissue were observed by semithin and ultrathin sections under light microscope.The cells forming the superficial layer were slender and longer and irregularly arranged.The cells froming the middle layer were oval and shorter,assuming intricately interwoven arrangement.The cells forming the deep layer were broader and longer and arraned in parallel.Observed under electron microscope,the cells at the deep layer contained abundant mitochondria,myofibrils and incomplete myomeres.Intercalated discs and gap junctions could be seen between neighboring cells.Even more integrated myomeres could be seen in the cells of the deep layer closing to ventricular myocardium.These structures were rarely found in the middle layer.where round cells with larger nuclei,less cytoplasm,scarce myofibrils,but with more intracellular vacuoles could be seen.The contents of mitochondria and myofibrils in the cells of the superficial layer were less than those in the deep layer.In the superficial layer,myofibrils were irregularly arranged,and less sarcomeres,intercellular specialized connections and intercalated discs could beseen. Conclusion There were marked differences in cellular ultrastuctures and connection patterns between diferent layers of rabbit atrioventricular node tissue.The conduction velocity might be quicker in the deep layer,slower in the superficial layer,and the slowest in the middle layer.