Localization of rac in resting and activated platelets.

Immunogold localization of rac at the edge of cytoskeletal preparations from activated platelets. Rac was localized using a combination of mouse anti-rac IgG and 8 nm gold particles coated with goat antimouse IgG. Bar, 100 nm. (A) Representative cortical region from a mechanically unroofed platelet showing anti-rac gold, which locates near the margin of the cell in small clusters. Gold clusters are also found near the ends of actin filaments, where they appear to intersect residual plasma membrane. The apical plasma membrane is labeled. The line delineates the edge of the cytoskeleton. (B) Representative Triton X-100 detergent cytoskeleton showing the localization of rac. Anti-rac gold is localized along the edge of the actin cytoskeleton. (C) Distribution of rac in resting (D) and activated platelets (C,E) determined by immunofluorescence microscopy. Rac is visualized with mouse anti-rac IgG and TRITC-labeled donkey antimouse IgG. In resting platelets, rac is uniformly distributed. After activation, rac concentrates near the cell margins and in densities near the cell center. The movement of rac to the cell cortex is not affected by treatment of the platelets with wortmannin (E).