Measurement of IP3 mass as a monitor of phospholipase C activation in stimulated human platelets.

The activation of phospholipase C and consequent formation of myoinositol trisphosphate (IP3) from phosphatidylinositol 4,5-bisphosphate has been shown to be an important signaling event in numerous tissues. We have undertaken studies, using column and gas chromatographic techniques, to quantitate the mass of IP3 which accumulates in human platelets under various stimulatory conditions. We have found that the platelet is capable of forming microM quantities of IP3 within a few seconds of addition of the platelet agonists thrombin or U46619. The amounts of IP3 formed transiently in stimulated platelets are thus similar to those which have been reported to cause Ca2+ mobilization in other systems. In contrast, the passive movement of Ca2+ induced by ionophore A23187, in the absence of prostaglandin formation, does not result in measurable increases in IP3.