Apoptosis in vascular smooth muscle cells: role of cell shrinkage.

Cell volume decrease is known to be one of the earliest steps of apoptosis in immune system cells. In this study, we compared the kinetics of apoptosis and cell volume adjustment in cultured vascular smooth muscle cells (VSMC) from the aorta of normotensive Brown-Norway (BN.1x) as well as spontaneously hypertensive (SHR) rats and in Mardin-Darby canine kidney (MDCK) cells. The transfer of VSMC to serum-deprived medium led to a transient cell volume decrease and to increased apoptosis. Both the cell volume decrease and apoptosis displayed faster kinetics in SHR than in BN.1x VSMC. Increased tonicity of serum-deprived medium by the addition of 200 mM mannitol augmented apoptosis in VSMC by 2.5- to 3-fold. In contrast to VSMC, neither apoptosis nor the cell volume of MDCK cells was affected by serum deprivation. Apoptosis in MDCK cells was also insensitive to tonicity of serum-deprived medium. There results demonstrate an initial volume decrease in VSMC undergoing apoptosis and suggest that this phenomenon is involved in triggering the apoptotic process.