The effects of 1-oleoyl-2-acetylglycerol on platelet protein phosphorylation and platelet ultrastructure.

1-oleoyl-2-acetylglycerol (OAG), an activator of protein kinase C and a synthetic diglyceride, was used in an investigation of the role of diglycerides in platelet stimulus-activation coupling. OAG (20-100 micrograms/ml) added to platelets resulted in rapid phosphorylation of the 47,000-dalton protein as well as a gradual dose dependent disappearance of alpha granules and dense bodies and the appearance of vacuolar structures containing remnants of granule matrix material. These morphologic changes occurred more slowly than the phosphorylation of 47K, which suggests that if these are related the phosphorylated 47K serves to activate some other mechanism, which is ultimately responsible for the changes observed. These results are most consistent with the role for the phosphorylation of 47K to promote granule labilization. Myosin light chain (MLC) phosphorylation also occurred. An absence of granule centralization suggests that MLC phosphorylation by protein kinase C may not trigger effective actin-myosin contraction.