Fig. 2. Upon BMP-2 stimulation, caveolin-1 ß moves into caveolae enriched in caveolin-1 . A431 cells were either cultured normally in DMEM with 10% FBS (N) or were serum-starved (S). After 3 days, starved cells were stimulated (S+B), or not stimulated (S) with BMP-2, fixed and labeled for (B) caveolin-1 [] or (A) caveolin-1 ß [ß] with monoclonal antibodies against the caveolin-1 isoforms and a secondary fluorescently labeled antibody against the caveolin-1 antibodies. Cell membrane expression was visualized by confocal microscopy. From 40 different cells 40 high-magnification images of the membrane were collected and the average intensity of the labeled caveolin-1 was calculated. For each image, the cluster density (CD) of each of the caveolin-1 isoforms was calculated by ICS (see Materials and Methods) and expressed as a ratio relative to the CD observed for the antibodies recognizing caveolin-1 and ß (C).