CHARACTERISTICS OF PROTEIN-KINASE C-INDEPENDENT EXOCYTOSIS IN HUMAN PLATELETS

We evaluated the characteristics of the protein kinase C (PKC)-indepen dent mechanism for ATP release in platelet-rich plasma. When ADP (10 m u M) and U46619 (1 mu M) were both added as agonists, a significant re lease was observed immediately after stimulation. The PKC inhibitor, R o-31-7549 (10 mu M), or a cyclooxygenase inhibitor, aspirin (400 mu M) or indomethacin (20 mu M), partially inhibited ATP release with littl e effect on platelet aggregation. The ATP release observed in the pres ence of Ro-31-7549 was abolished by a cyclooxygenase inhibitor or by p reventing aggregation without stirring. In the nonstirred condition, t hromboxane B2 formation was reduced by 93%. When sodium arachidonate ( 1 mM) rather than U46619 was used with ADP, ATP release in the presenc e of Ro-31-7549, was abolished by stopping the stirring with no effect on thromboxane B2 formation. In contrast, ADP/U46619-induced ATP rele ase observed in the presence of aspirin was only partially inhibited w hen the stirring was stopped. This release was also inhibited dose-dep endently by Ro-31-7549 at concentrations between 1 and 10 mu M These r esults suggest that PKC-independent ATP-release in this system require s aggregation and is inhibited by a cyclooxygenase inhibitor, while PK C-dependent exocytosis is insensitive to aggregation and a cyclooxygen ase inhibitor. (C) 1997 Elsevier Science Ltd.