Modulation of smooth muscle cell behaviour by platelet‐derived factors and the extracellular matrix

We have studied the combined effects of platelet‐derived soluble factors and three types of macromolecular substrata on the proliferation and migration of smooth muscle cells in vitro. Bovine aortic smooth muscle cells were plated onto three‐dimensional gels of type I collagen or onto cell‐free extracellular matrices deposited on such gels by either bovine aortic endothelial cells or smooth muscle cells. The cells were cultured in the presence of whole‐blood serum (WBS) or platelet‐poor plasma (PPP). Smooth muscle cell proliferation on type I collagen gels was dependent on the presence of platelet‐derived factors, i.e. the cells proliferated in the presence of WBS but not in PPP. In contrast, cell proliferation on the extracellular matrices occurred at the same rate in PPP and WBS. Smooth muscle cells plated onto collagen gels rapidly migrated down into the gel matrix; the percentage of cells migrating was inversely proportional to cell density. The presence of extracellular matrices did not alter the rate of cell migration into the underlying gel matrix. Irrespective of the substratum used, smooth muscle cell migration was independent of platelet‐derived or plasma factors and occurred in the absence of proliferation. These results indicate that possible chemotactic, chemokinetic, and/or mitogenic factors produced by the vascular cells and deposited within the extracellular matrix may play an important role in modulating smooth muscle cell behaviour in the vascular wall.