Protein turnover in the smooth muscle cell of the aortic tunica media as visualized by radioautography.

The turnover of newly formed proteins in the aortic myocyte was studied by means of quantitative light and electron microscopic radioautography. Adult and young mice were sacrificed at long intervals between 4 h and 108 days after one injection of tritiated leucine. The results showed that secretory activity, important in the post-natal myocyte, persists noticeably in the mature myocyte. The similarity in sedentary protein turnover, noted in both the thoracic and abdominal aortic segments of the adult and young animals, seems to be expressed by the same labelling patterns of the myoplasma. Turnover of exportable protein, which varies with age and anatomical level, appears to be related to the higher rate of elastin synthesis in the thoracic aorta of the young animal.