Cyclooxygenase--independent pathway of phospholipase activation in carrageenan--induced platelet aggregation

Carrageenan induced aggregation and ATP release of washed rabbit platelets. The aggregation was resistant to indomethacin or creatine phosphate/creatine phosphokinase system but sensitive to mepacrine or p-bromophenacyl bromide. Chlorpromazine, verapamil or tetracaine inhibited carrageenan-induced aggregation, ATP release reaction and membrane-bound calcium redistribution in washed platelets. Agents elevating cyclic nucleotides selectively inhibited the release reaction without affecting the aggregation. The mechanism of carrageenan-mediated platelet responses may be due to both activation of phospholipases A2 and C. Platelet activating factor, protein kinase C and inositol triphosphate or phosphatidic acid could be mediated by carrageenan to accomplish the cyclooxygenase-independent events.