Differences in caveolae dynamics in vascular smooth muscle cells of different phenotypes

Vascular smooth muscle cells shift between two major differentiated states with distinct morphological and functional properties, a contractile and a synthetic phenotype. Here, primary cultures were used to study caveolae exp ression and dynamics in these cells. The results demonstrate that caveolae are more numerous and more actively interact with intracellular organelles in contractile than in synthetic cells. Immunohistochemistry showed that ca veolin-1 was mainly localized to caveolae in contractile cells and partly s hifted to Golgi-associated Vesicles in synthetic cells, whereas caveolin-2 chiefly appeared in cytoplasmic Vesicles in both cases. Cholera toxin B sub unit, a ligand of G(M1) ganglioside, was internalized via caveolae and carr ied to endosomes and Golgi-associated vesicles. In contractile cells, it la ter moved into Golgi and endoplasmic reticulum (ER) cisternae and thus had access to the entire endocytic and exocytic pathways. In contrast, in synth etic cells, the tracer was restricted to the endocytic pathway. Filipin sta ining similarly disclosed that cholesterol was more widely distributed in c ontractile than in synthetic cells, with strong labeling of both caveolae a nd adjacent ER portions. Although no direct continuity between caveolae and ER was detected, it is suggested that cholesterol and other molecules may be translocated between these compartments. The observed differences in cav eolae expression and dynamics are likely to be significant for the differen ces in proliferative capacity and cholesterol transport between contractile and synthetic smooth muscle cells.