SUB-SECOND OSCILLATIONS OF INOSITOL 1,4,5-TRISPHOSPHATE AND INOSITOL 1,3,4,5-TETRAKISPHOSPHATE DURING PLATELET ACTIVATION BY ADP AND THROMBIN - LACK OF CORRELATION WITH CALCIUM KINETICS

The hypothesis that ADP and thrombin liberate Ins(1,4,5)P3 in blood platelets, with kinetics consistent for releasing Ca2+ within 2 s, was tested by quenched-flow techniques. Both agonists stimulated transient and equal synthesis of Ins(1,4,5)P3 and Ins(1,3,4,5)P4 near 200 ms and later short-lived peaks, which were not correlated with the slower steady increase in intracellular [Ca2+] between 0.5 to 2 s detected by Indo-1. Shear forces alone caused transient liberation of these inositol phosphates within 0.5 s and up to 4 s, yet failed to increase intracellular [Ca2+].