Continuous Photobleaching to Study the Growth Modes of Focal Adhesions

We combine total internal reflection fluorescence microscopy with continuous photobleaching to study the growth mode of focal adhesions in rat embryonic fibroblasts (REF-52). We measured GFP-labelled beta 3 integrin, which exhibits a diffusion rate of 10(-14)-10(-13) m(2)/s when it is not bound to a focal adhesion. We show that exchange of beta 3 integrin between focal adhesions and the surrounding membrane occurs only at the edges of the focal adhesion. We, therefore, conclude that focal adhesions show an edge-on/edge-off growth, in contrast to the bulk-on/bulk-off growth mode that is assumed in many theoretical treatments. (C) Koninklijke Brill NV, Leiden, 2010