Fine structure of arterial smooth muscle cells cultured in the presence of whole blood serum or plasma-derived serum.

Normal diploid cells require serum to proliferate in culture. Platelet-derived growth factor has been identified as the main serum component responsible for this effect. Here, smooth muscle cells were isolated enzymatically from the aorta of 5-day-old rats and cultured in the presence of 10% whole blood serum (WBS) or plasma-derived serum (PDS), i.e. with or without platelet factor, and studied by transmission electron microscopy. The cells proliferated actively in WBS-medium but remained quiescent in PDS-medium. Fine structurally, cells from WBS-cultures demonstrated numerous mitochondria, an extensive rough endoplasmic reticulum (RER), a large Golgi complex, a few lysosomes, and microfilaments arranged in parallel bundles. After transfer to PDS-medium, the RER- and Golgi cisternae were markedly dilated and the number of membrane-associated ribosomes decreased. Segregation of fragments of cytoplasm within autophagosomes was frequently observed and the number of lysosomes increased. Lipid droplets were more abundant and often gathered in the Golgi area. Moreover, the cells had become more irregular in shape and showed many bleb-like processes at their surface. Microfilament bundles had also become more prominent and crossed each other in different directions. These observations show that the removal of platelet factor from the medium clearly modifies the fine structure of cultured smooth muscle cells. The findings are in good agreement with the concept that platelet factor not only supports the proliferation of cultured cells but also stimulates their secretory activity.