Heterogeneity in migration of smooth muscle cells from normal and injured rat thoracic aorta in primary culture

Aside from proliferation, migration of smooth muscle cells is an essential component of the arterial sclerotic reaction. The aim of this study was to define a model to study migration. Primary cultures of smooth muscle cells were derived from normal or injured rat thoracic aorta. An image analysis system was used to track cells migrating out of the explants and measure the displacement of their centre of gravity. Migration speeds for smooth muscle cells randomly sampled from the normal whole media were very heterogeneous. The media were therefore separated into three vertical segments. Cells from the middle third migrated faster than those from the upper and lower thirds, regardless of whether they originated from the anterior and posterior parts of the segment (P = 0.001). Heparin (10 micrograms.ml-1) only inhibited smooth muscle cell migration from the middle segment (P < 0.001). Migration of smooth muscle cells from explants of aorta 3 and 14 d after injury was also studied using a balloon catheter. Three days after injury, cell velocity varied widely among the segments of the same media. In contrast, 14 d after injury cells from neointimal explants migrated homogeneously and at a slower rate than those obtained from normal media. These experiments show migratory variations among smooth muscle cells depending upon their position in the normal aorta and their state of activation after arterial injury. This variability must be taken into account when planning experiments to study smooth muscle cell migration.