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Journal of Histochemistry and Cytochemistry, Vol. 50, 185-196, February 2002, Copyright © 2002, The Histochemical Society, Inc.
Caveolae and Cholesterol Distribution in Vascular Smooth Muscle Cells of Different Phenotypes
Johan Thyberga
a Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden
Correspondence to:
Johan Thyberg, Dept. of Cell and Molecular Biology, Karolinska Institutet, Box 285, S-17177 Stockholm, Sweden. E-mail: johan.thyberg@cmb.ki.se
Vascular smooth muscle cells (SMCs) grown in primary culture are converted from a contractile to a synthetic phenotype. This includes a marked morphological reorganization, with loss of myofilaments and formation of a large ERGolgi complex. In addition, the number of cell surface caveolae is distinctly reduced and the handling of lipoprotein-derived cholesterol changed. Here we used filipin as a marker to study the distribution of cholesterol in SMCs by electron microscopy. In contractile cells, filipinsterol complexes were preferentially found in caveolae and adjacent ER cisternae (present in both leaflets of the membranes). After exposure to LDL or cholesterol, labeling with filipin was increased both in membrane organelles and in the cytoplasm. In contrast, treatment with mevinolin (a cholesterol synthesis inhibitor) or ß-cyclodextrin (a molecule that extracts cholesterol from cells) decreased the reaction with filipin but did not affect the close relation between the ER and the cell surface. In synthetic cells, filipinsterol complexes were diffusely spread in the plasma membrane and the strongest cytoplasmic reaction was noted in endosomes/lysosomes, both under normal conditions and after incubation with LDL or cholesterol. On the basis of the present findings, we propose a mechanism for direct exchange of cholesterol between the plasma membrane and the ER and more active in contractile than in synthetic SMCs. (J Histochem Cytochem 50:185195, 2002)
Key Words:
caveolae, cholesterol, smooth muscle cells, differentiation, filipin

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