Calcium and Diacylglycerol

Platelet responses to many agonists involve rapid stimulation of calcium fluxes and turnover of phosphoinositides. A rise in cytoplasmic free calcium, [Ca2+]i, has been regarded as the final common pathway for shape change, secretion, and aggregation; phosphoinositide turnover has been viewed mainly as a means of mobilizing calcium [and as one route for releasing arachidonate for formation of thromboxane A2 (TxA2)]. However, much of the evidence is indirect and interpretation necessarily speculative. Two recent developments have allowed a more informed analysis of second messenger pathways.