Identification of caveolae and detection of caveolin in normal human osteoblasts

Caveolae, specialised regions of the cell membrane which have been detected in a wide range of mammalian cells, have not been described in bone cells. They are plasmalemmal invaginations, 50 to 100 nm in size, characterised b y the presence of the structural protein, caveolin, which exists as three s ubtypes. Caveolin-1 and caveolin-2 are expressed in a wide range of cell ty pes whereas caveolin-3 is thought to be a muscle-specific subtype, There is little information on the precise function of caveolae, but it has been pr oposed that they play an important role in signal transduction, As the principal bone-producing cell, the osteoblast has been widely studie d in an effort to understand the signalling pathways by which it responds t o extracellular stimuli, Our aim in this study was to identify caveolae and their structural protein caveolin in normal human osteoblasts, and to dete rmine which subtypes of caveolin were present. Confocal microscopy showed s taining which was associated with the plasma membrane. Transmission electro n microscopy revealed the presence of membrane invaginations of 50 to 100 n m, consistent with the appearance of caveolae, Finally, we isolated protein from these osteoblasts, and performed Western blotting using anti-caveolin primary antibodies. This revealed the presence of caveolin-1 and -2, while caveolin-3 was absent, The identification of these structures and their associated protein may pro vide a significant contribution to our further understanding of signal tran sduction pathways in osteoblasts.