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 2s, 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+].