Aggregation of human platelets stimulates calcium ion movement and release reaction

We studied the effect of inhibition of platelet aggregation (obtained by omitting sample stirring and by the addition of ASA and GRGDS peptide) on ATP secretion and Ca(2+) movements. When collagen was the agonist, platelet aggregation stimulated release reaction and Ca(2+) movements in both the presence and absence of extracellular Ca(2+). When platelets were stimulated by thrombin, ATP release and Ca(2+) movements were largely independent of aggregation. Our data suggest that platelet aggregation stimulates Ca(2+) movement, and that this phenomenon of feedback amplification of platelet activation plays an important role in platelet function when collagen is the agonist, while it has little or no role when thrombin is the stimulus.