[Caveolae membrane domains, specialized transmembrane exchange zones implicated in cell signalling]

Caveolae are small pockets or invaginations localized at the plasma membrane. They are enriched in glycosphingolipids, cholesterol, sphingomyelin and lipid-enchored membrane proteins, and they are characterized by a light buoyant density and resistance to solubilization by Triton X-100 at 4 C. Caveolins are the principal protein components of caveolae and play an important structural role in the formation of caveolae membranes. Numerous molecules involved in cell signalling have been identified in caveolae, suggesting that these structures may serve to compartimentalize, modulate and integrate signalling events at the cell surface. Depletion of membrane cholesterol disrupts the formation and function of caveolae, suggesting that these membrane microdomains are involved in a range of biological processes. Moreover, exposure of endothelial cells to high levels of cholesterol upregulates the caveolin abundance in caveolae, and decreases nitric oxide synthesis, suggesting that this may be an early event in atherogenesis. Alteration in the expression of caveolin genes has also been implicated in human diseases such as cancers, diabetes, Alzheimer's disease and muscular distrophy.