Density-related expression of caldesmon and vinculin in cultured rabbit aortic smooth muscle cells

Quantitative immunoblotting techniques were used to study the effects of seeding density on the expression of caldesmon and vinculin variants, which are sensitive markers of vascular smooth muscle cell (SMC) phenotypic modulation in culture. Rabbit aortic SMC were seeded at different densities: 13 x 10(4) cells/cm2 (high density), 3 x 10(4) cells/cm2 (medium density), and 0.2 x 10(4) cells/cm2 (low density) and cultured in the presence of 5% fetal calf serum. Irrespective of cell density and growth phase, caldesmon150 was gradually and irreversibly substituted by caldesmon77, but at high seeding density this substitution proceeded at a slower rate. The fraction of meta-vinculin (smooth muscle variant of vinculin) was reduced after seeding SMC in culture, but was reestablished when the cells reached confluency. Thus, high SMC seeding density is essential but not sufficient to keep vascular SMC cultured in the presence of serum in the contractile phenotype.