The conducting tissue in the adult chicken atria. A histological and immunohistochemical analysis.

A three-dimensional reconstruction from serial sections of adult chicken heart was made to verify whether Purkinje cells, that can be recognized by a number of well-known histological criteria, form specialized tracts in the adult chicken atria. This reconstruction revealed a loosely arranged network of Purkinje cells connecting the two atria. This network has not been described before. No tracts could be detected between the sinoatrial and the atrioventricular nodes. These atrial Purkinje cells express the atrial and ventricular myosin isoform, as determined by the use of monoclonal antibodies that were prepared against atrial and ventricular myosin isoform, respectively. Some atrial myocytes that are topographically closely related to the Purkinje cells and that cannot be distinguished from the surrounding myocytes with conventional histological criteria, express, apart from the atrial myosin isoform, also the ventricular myosin isoform. The similar expression pattern of these two cell types and their close topographical relationship suggest the presence of a more elaborate system specialized in conduction than the well-known conductive system found with conventional histological techniques.