Platelet-released ADP stabilizes PAF-induced rabbit platelet aggregation by stabilizing intracellular calcium

Platelet released ADP stabilizes PAF induced rabbit platelet aggregation by stabilizing intracellular calcium 1

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AIM: To examine whether platelet released adenosine diphosphate (ADP) would contribute to the stabilization of rabbit platelet aggregation induced by platelet activating factor (PAF). METHODS: Rabbit platelet aggregation induced by PAF was measured turbimetrically. ADP release from rabbit platelets stimulated by PAF was determined by HPLC. Intracellular Ca 2+ was measured using Ca 2+ sensitive fluorescent indicator Fura 2 AM. RESULTS: PAF≥1 nmol·L -1 induced full platelet aggregation, which did not deaggregate over 5 min after aggregation reached peak. Platelet aggregation was deaggregated in a concentration dependent manner by subsequent addition of ADP scavenger ATP diphosphohydrolase (apyrase) at 5-100 mg·L -1 . PAF 3 nmol ·L -1 stimulated release of ADP (29 % vs 6 % of control), and elicited a rapid rise in intracellular calcium ([Ca 2+ ] i) which peaked at approximately 15 s. Then the [Ca 2+ ] i gradually decayed from 585±80 nmol ·L -1 within 100 s to a low level (364±82 nmol ·L -1 ). Apyrase 100 mg·L -1 , added 2 min after PAF, reduced [Ca 2+ ] i to a lower level (171±29 nmol·L -1 ). CONCLUSION: Platelet released ADP stabilizes PAF induced rabbit platelet aggregation by stabilizing [Ca 2+ ] i at elevated level.