Caveolae: an alternative membrane transport compartment.

Caveolae are omega-shaped invaginations of the plasma membrane with a diameter of 50-100 nm. Caveolae invaginations can detach from the plasma membrane to form discrete functional caveolae vesicles within the cell cytoplasm. Caveolae are most prominent in adipocytes, fibroblasts, muscle cells (skeletal, smooth and cardiac), capillary endothelium and type I pneumocytes, although other cell types also display these structures but at a lower numerical density. The key structural and functional protein for caveolae is caveolin. At the plasma membrane caveolae serve to compartmentalize and integrate a wide range of signal transduction processes. Caveolae also serve transport functions including that of the vesicular internalisation of small molecules by the process of potocytosis, and the endocytic and transcytotic movements of macromolecules. Opportunities exist for basic and applied investigators working within the pharmaceutical sciences to exploit caveolae membrane interactions with the aim to develop novel cellular or transcellular drug delivery strategies.