Figure 3.

The activation of G protein–coupled receptor-mediated proximal signaling in platelets is independent of filamin A (FLNA). (A) Washed platelets from control (red line) and Flna knockout (platelet-specific KO, blue line) mice were loaded with the calcium indicator dye Fluo-4/AM prior to activation with collagen-related peptide (CRP) in the presence of 1 mM CaCl₂. Representative tracing illustrating the changes in [Ca²⁺]_i is shown. (B) The bar graph depicts the maximal CRP–induced increase in [Ca²⁺]_i relative to that at baseline in control (red bar) and FLNA-null (platelet-specific KO, blue bar) platelets. Data are presented as mean ± SEM (∗∗P < .01, based on the Student’s t-test) and represent a minimum of 4 independent experiments. (C) The bar graph depicts the maximal thrombin (aka F2)-induced increase in [Ca²⁺]_i relative to that at baseline in control (red bar) and FLNA-null (platelet-specific KO, blue bar) platelets at the indicated doses and in the presence of 1 mM CaCl₂. Data are presented as mean ± SEM (not significant, based on analysis of variance and Bonferroni multiple comparison tests) and represent a minimum of 4 independent experiments. (D) Representative tracings of U46619-induced [Ca²⁺]_i flux in control (red line) and FLNA-null (platelet-specific KO, blue line) platelets. (E) The bar graph depicts the maximal U46619-induced increase in [Ca²⁺]_i relative to that at baseline in control (red bar) and FLNA-null (platelet-specific KO, blue bar) platelets. Data are presented as mean ± SEM (not significant, based on the Student’s t-test) and represent a minimum of 4 independent experiments. CRP, collagen-related peptide; ns, not significant.