[Radioautographic study of the incorporation sites and migration pathways of tritiated leucine in aortic myocytes].

The synthesis and fate of newly-formed proteins in the aortic media cell of 21 days old mice were investigated by quantitative radioautography after intravenous injection of tritium-labelled leucine. At 2 mn after injection, radioactivity was detected over the polysomes, the myofilaments and the rough endoplasmic reticulum, indicating that sedentary and exportable proteins were synthesized. It remained high on the sarcoplasm rich in polysomes and the myofilaments until 240 mn. However, the peak of radioactivity occured at 20 mn in the sarcoplasm and at 30 mn in the myoplasm. Therefore, the elaboration of sedentary proteins seems preponderant and they participate noticeably in the formation of the contractile apparatus. At 10 mn, radioactivity appeared in the Golgi apparatus at a high level, while increasing until 30 mn in the rough endoplasmic reticulum. By 20 mn, the labelling intensified along the plasma membrane and over the connective time lamellae. It occured earlier and was more intense on collagen fibrills than elastin, suggesting that the biosynthesis of elastin takes place more slowly. Thus, the pattern of two different metabolic pathways, as defined generally for the two types of proteins--sedentary and exportable--is true for the aortic media cell.