Department of Biochemistry Gifu University School of Medicine Tsukasamachi-40, Gifu 500, Japan.
Abstract:
The time-sequential relationship between Ca2+ flux, phospholipid metabolism and platelet activation have been examined. Thrombin-activation caused a marked enhancement in 45Ca2+ influx and a decrease in extracellular Ca2+ concentration measured by murexide dye, which occurred in parallel with the conversion of 1,2-diacylglycerol (DG) to phosphatidic acid (PA). The incorporated 45Ca2+ was located mainly in cytosolic fraction. The influx of Ca2+ was observed to commence prior to the onset of lysophospholipids formation and subsequent liberation of arachidonic acid. These data provide evidence which indicates a coupling between the rapid PI-turnover and the active Ca2+ influx, in which phosphatidic acid (PA) may serve as a Ca2+ ionophore.