Platelet-released ADP stabilizes PAF-induced rabbit platelet aggregation by stabilizing intracellular calcium.
OBJECTIVE
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 Ca2+ was measured using Ca(2+)-sensitive fluorescent indicator Fura 2-AM.


RESULTS
PAF > or = 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 ([Ca2+]i) which peaked at approximately 15 s. Then the [Ca2+]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 [Ca2+]i to a lower level (171 +/- 29 nmol.L-1).


CONCLUSIONS
Platelet-released ADP stabilizes PAF-induced rabbit platelet aggregation by stabilizing [Ca2+]i at elevated level.
Yi
F X
FX
Laboratory of Molecular Pharmacology, Hu-nan Medical University, Changsha, China.
Guo
Z G
ZG
D000244:Adenosine Diphosphate / Q000097:blood*; D000818:Animals; D001081:Apyrase / Q000494:pharmacology*; D001792:Blood Platelets / Q000378:metabolism; D002118:Calcium / Q000097:blood*; D010972:Platelet Activating Factor / Q000494:pharmacology*; D010974:Platelet Aggregation / Q000187:drug effects*; D011817:Rabbits
D010972:Platelet Activating Factor; D000244:Adenosine Diphosphate; D001081:Apyrase; D002118:Calcium