Cooperativity between platelet-activating factor and collagen in aggregation of bovine platelets, II

When subthreshold amounts of platelet-activating factor (PAF) and collagen were added simultaneously, strong aggregation of platelets was induced. However, each agonist alone at these concentrations could not induce aggregation at all (S. Kojima et al, (1987) Biochem. Biophys. Res. Commun. 145, 915-920). This cooperativity was observed not only in aggregation but also in changes of intracellular Ca2+ concentration, 47 kDa protein phosphorylation, and formation of thromboxane. These findings suggest that various steps of signal transduction pathways are enhanced during their cooperativity.