FIGURE 1.

(A) Model for the control of platelet function by cAMP signaling in platelets. Segregated pools of cAMP are formed by the individual isoforms of AC. The cAMP generated may target individual PKA isoforms. AKAPs act to focus isoform specific PKA activity to individual substrates that are linked to distinct platelet functions. The AKAPs may also act to localize PDE isoforms in manner that controls specific signaling events. (B) PKA substrates are differentially distributed and targeted by PKA in an AKAP-dependent manner. Washed platelets (5 × 10⁸/mL) were left untreated or pre-treated for 60 min with RIAD-Arg₁₁ (2 μM) or stHt31 (2 μM), which target PKA-I and PKA-II specific AKAPs respectively, followed by PGI₂ (50 nM) for 1 min. Platelets were lysed then subjected into subcellular fractionation (20,000 × g, 90 min at 4°C) to separate platelet membranes. Membrane and cytosol fractions (20 μg) were analyzed by SDS-PAGE and immunoblotting using phosphoPKA substrate antibody and integrin β as a membrane marker. Blots are representative of three independent experiments. Membranes were visualized using enhanced chemiluminescence. Red and blue arrows represent AKAP sensitive bands in membrane and cytosolic bands respectively.