Fig. 3. Regulation of Rac1 activity by cell adhesion to fibronectin. 0.5% serum-starved CHO, ß1, ß3 and ß1-3-1 cells were detached and kept in suspension in DMEM for 1 hour and then either plated on fibronectin-coated dishes for 4 hours (A) or used as suspension controls (B). Rac1 activity was determined by a PBD assay followed by immunoblotting with an anti-Rac1 antibody. The bottom immunoblot shows Rac1 in whole cell lysates. The amount of activated Rac1 was normalized by the amount of Rac1 in whole cell lysates. The bar graphs are densitometric analyses of mean±s.d. from three separate experiments. The asterisk indicates significant differences (P<0.05) compared with CHO cells.