FIGURE 3. Role of ADP receptors in PAR-induced platelet activation.

A, to determine the importance of PAR-mediated purinergic regulation of platelet activation, washed platelets were treated with or without 100 μm MRS-2179, 50 μm 2-MeSAMP, or both. After pretreatment, platelet aggregation was measured following ADP stimulation. Inhibition of the P2Y₁ receptor was unable to inhibit ADP-induced platelet aggregation. Inhibiting the P2Y₁₂ receptor resulted in a 90% inhibition of platelet aggregation, and inhibiting both receptors resulted in a complete block of platelet aggregation in response to ADP (n = 3). B, washed platelets were treated with or without MRS-2179, 20 μm BAPTA-AM, or both followed by stimulation with 20 μm PAR1-AP. Aggregation was then measured for each of the conditions up to 10 min post-stimulation (n = 3). C, washed platelets were treated with or without MRS-2179, 20 μm BAPTA-AM, or both followed by stimulation with 200 μm PAR4-AP. Aggregation was then measured for each of the conditions up to 10 min post-stimulation (n = 3).