Atrioventricular node and purkinje fibers of the guinea pig heart

Abstract The ultrastructure of the atrioventricular node and Purkinje fibers of the guinea pig heart was studied. The atrioventricular node consists of slender, irregularly shaped muscle cells which are arranged in a complex network with frequent interdigitation. Nodal cells contact with each other by means of many desmosomes (maculae adherentes) and rare intercalated discs that contain short nexal regions (gap junctions). The Purkinje fibers are much larger and show less cellular interdigitation than the fibers of the atrioventricular node. Desmosomes are infrequent but there are many intercalated discs with rather a long nexus between the Purkinje fibers. The T‐system is not present in the atrioventricular node or in the Purkinje fibers. The most pronounced morphological differences between the atrioventricular node and Purkinje fibers are the size of the cells and the mode of intercellular connection, which may be related to different conduction velocities in these two regions.