Abstract
Migration of smooth muscle cells from the media into the intima of the artery to proliferate has been regarded as a primary key event in the morphogenesis of atherosclerosis. Metabolism and functions of vascular smooth muscle cells seem to be deeply influenced by their phenotypes, contractile or synthetic type. Intimal smooth muscle cells obtained from atherosclerotic plaques of animals placed on atherogenic diets exhibited more frequently synthetic phenotype, which is characterized by not only abundant rough surfaced endoplasmic reticuli, free ribosomes and mitochondria but scanty myofilaments, than normal medial smooth muscle cells in vivo and vitro. The former cells showed higher rates of DNA-, collagen- or prostacycline-synthesis and higher activity of various lysosomal enzymes than the latter cells.
In order to disclose the time of the phenotype change at migration, we investigated fine structures of the smooth muscle cells regarded as migrating from the media into the intima, based upon a morphological finding in which cells stretched into the intima through fenestrae of the internal elastic lamella. Out of fourteen migrating cells, 12 cells showed the contractile type in the part of their cytoplasms still remaining in the media, and simultaneously synthetic type in their cytoplasms reached in the intima. There were also few basement-membrane like substances accompanied with the migrating cells, particularly around the medial part. Thick and intermediate filaments were observed more frequently in the intimal part than in the medial part of cytoplasm of the migrating cell.
Finally we could draw the conclusion that change of phenotype of arterial smooth muscle cells migrating occurred within a short period after reach in the intima.
