Atrial specific granules of the human auricle in embryogenesis, tissue culture, and hypertrophy.

The ultrastructure of atrial specific granules of the human auricle has been studied in myoblasts of 8-12 week embryos, in myoblasts cultured for 15 days, and in cells of the hypertrophied juvenile and adult atrium. The granules of young myoblasts and those of cultured cells are fairly evenly distributed throughout the sarcoplasm. Myocytes of the hypertrophied juvenile auricle show structural characteristics indicative of granule formation. Structural evidence of exocytosis has not been observed in either of the tissues studied. In the cultured and the hypertrophied tissue the granules are structurally well preserved even in areas with extensive intracellular lysis.