Abstract
The time-sequential relationships between Ca2+ fluxes and phospholipid metabolism have been examined in activated human platelets. Thrombin-activation caused a marked acceleration of 45Ca2+ influx and a decrease in extracellular Ca2+ concentration measured by murexide dye, which occurred in pallalel with the accumulation of phosphatidic acid (PA). The incorporated 45Ca2+ was found mainly in cytosolic fraction. The influx of Ca2+ was observed to precede to the onset of lysophospholipids formation and subsequent liberation of arachidonic acid. These data provide evidence that PA. generated upon platelet activation, may serve as a calcium ionophore.
