Rac and Cdc42 are activated during platelet spreading on surfaces coated with collagen or TS2/16.

Washed platelets were added to collagen- (A) or TS2/16-coated (B) dishes and incubated at 30°C for the indicated time frame. Reactions were terminated with lysis buffer B, and a small aliquot of each supernatant was used to check the equal loading of samples (see total Rac in A, inset). The rest of the lysate was used to precipitate active forms of Rac (see active Rac in A, inset) or Cdc42 with PBD-bound glutathione Sepharose 4B. The sample was then Western blotted with anti-Rac or Cdc42 antibody. Levels of the active Rac (open circles) and Cdc42 (open squares) were quantified and adjusted by the total Rac and Cdc42, respectively. The data are expressed as the fold increases relative to those on BSA-coated surfaces (the mean ± SD of the total points).