title: Diacylglycerol elevations in control platelets are unaccompanied by pleckstrin phosphorylation. Implications for the role of diacylglycerol in platelet activation.
abstract: Several laboratories have reported that diacylglycerol levels in human platelets (approximately 100 pmol/10(9) platelets) increased severalfold in response to 0.5-1 U/ml thrombin. We report here fluctuations in diacylglycerol mass in control platelets, the magnitude of which were 60-90% of that measured in platelets treated with 0.2-0.5 U/ml of thrombin. These control platelets were not activated by such criteria as absence of aggregation, secretion, phosphatidic acid production and phosphorylation of the protein kinase C substrate, pleckstrin. Thrombin treatment evoked all of the above responses. Analysis of the diacylglycerol molecular species by reverse-phase HPLC of the dimethylated, phosphorylated derivatives showed that all of the molecular species that were present in control platelets were also present in thrombin-treated platelets. Most of the species appeared to fluctuate at random in control platelets with the exception of 1-stearoyl-2-arachidonoyl-sn-glycerol which was more or less stable and increased severalfold over control values only upon thrombin treatment. Furthermore, only this species accumulated as [32P]phosphorylated PtdOH in thrombin-treated platelets prelabelled with [32P]Pi. Our findings show that, in platelets, elevation of diacylglycerol molecular species other than the 1-stearoyl-2-arachidonoyl species occurs, but these changes are not necessarily linked to activation of protein kinase C as measured by pleckstrin phosphorylation which was observed only upon elevation of 1-stearoyl-2-arachidonoyl-sn-glycerol.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Bergen, Norway.
authors.forename: M H
authors.initials: MH
authors.lastname: Fukami
authors.forename: H
authors.initials: H
authors.lastname: Holmsen
mesh_terms: D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D001798:Blood Proteins / Q000378:metabolism*; D004075:Diglycerides / Q000097:blood*; D006358:Hot Temperature; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010750:Phosphoproteins; D010766:Phosphorylation; D015539:Platelet Activation; D013917:Thrombin / Q000494:pharmacology
chemical_list: D001798:Blood Proteins; D004075:Diglycerides; D010750:Phosphoproteins; C039077:platelet protein P47; D013917:Thrombin