Fig. 3.

P2X1-mediated Ca ²⁺ responses to FcγRIIa receptor activation are resistant to NO and elevated apyrase levels, but are abolished by PGI ₂ . Representative [Ca ²⁺ ] _i responses ( A, B, D ) induced by FcγRIIa receptor activation by cross-linking of mAb IV.3 in the presence of elevated apyrase levels (3.2 U/mL), spermine NONOate (sNO; 100 μM), and prostacyclin (PGI ₂ ; 500 nM). Control traces are representative of the vehicle-treated platelet samples in each panel (saline, 0.01 M NaOH and dH ₂ O, respectively). P2X1 receptor desensitization was achieved by pretreatment with 600 nM α,β-meATP. ( C ) Effect of a submaximal concentration of PGI ₂ (500 nM) on [Ca ²⁺ ] _i induced by 0.03 U/mL thrombin. ( E, F ) PGI ₂ (500 nM) substantially inhibited FcγRIIa-mediated ATP secretion. ( G ) Average peak [Ca ²⁺ ] _i responses obtained in the presence of inhibitors used, compared with the average of control responses (first column).