Lack of evidence for a role for the lipoxygenase pathway in increases in cytosolic calcium evoked by ADP and arachidonic acid in human platelets

We have investigated the possibility that metabolism of arachidonic acid by the lipoxygenase pathway contributes to ADP-evoked rises in [Ca 2+], in human platelets. 30μM BW A4C did not affect ADP-evoked Ca 2+ signals, but inhibited 12-lipoxygenase activity in platelet homogenates. Another lipoxygenase inhibitor, MK 866 was similary without effect on ADP-evoked Ca 2+ signals. ADP was found to liberate little arachidonic acid, and formation of the lipoxygenase product 12-HETE was not detectable. The rise in [Ca 2+] i evoked by arachidonic acid was completely inhibited by the cyclooxygenase inhibitors aspirin or indomethacin. These results indicate that lipoxy genase products do not play an essential role in mediating rises in [Ca 2+] i evoked by ADP, or by arachidonic acid.