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).