title: Inositol lipids, phosphatidate and diacylglycerol share stearoylarachidonoylglycerol as a common backbone in thrombin-stimulated human platelets.
abstract: Gel-filtered human platelets were stimulated with 5i.u. of thrombin/ml for times up to 1 min. The fatty acid composition of inositol-containing phospholipids, phosphatidic acid and diacylglycerol was determined by g.l.c. in control and thrombin-stimulated platelet suspensions. Inositol phospholipids were found to have similar proportions of stearic and arachidonic acids, the sum of these representing 86.6% of the total fatty acids in phosphatidylinositol (PtdIns), 76.9% in phosphatidylinositol 4-phosphate (PtdIns4P) and 85.4% in phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. However, arachidonic and stearic acids were less abundant in phosphatidic acid (PtdA) and diacylglycerols in non-stimulated platelets. A transient decrease in the mass of PtdIns(4,5)P2 was observed after 5-10s of thrombin stimulation, followed by an increase after 30s. The amounts of PtdIns4P and PtdIns decreased throughout the experiment. A transient accumulation of stearoylarachidonoylglycerol was observed at 5s, whereas stearoylarachidonoylglycerol 3-phosphate (PtdA) was produced in increasing amounts throughout the experiment. The decrease in inositol-containing phospholipids was not fully compensated for by the production of diacylglycerol or PtdA [or PtdIns(4,5)P2] at 1 min. All the changes in inositol phospholipids, as well as those observed in diacylglycerols and PtdA, were due to a parallel reduction or increase in the contents of stearic and arachidonic acids, with a stoichiometry equal to 1. Taken together, this suggests an interconversion of all these lipids with the utilization of a common backbone, stearoylarachidonoylglycerol. The deacylation of this diacylglycerol could account for up to 4-5nmol of arachidonate/10(9) platelets after 1 min stimulation by thrombin.
mesh_terms: D001792:Blood Platelets / Q000378:metabolism*; D004075:Diglycerides / Q000097:blood*; D005227:Fatty Acids / Q000032:analysis; D005989:Glycerides / Q000097:blood*; D006801:Humans; D066298:In Vitro Techniques; D008956:Models, Chemical; D010712:Phosphatidic Acids / Q000097:blood*; D010716:Phosphatidylinositols / Q000097:blood*; D013917:Thrombin / Q000494:pharmacology
chemical_list: D004075:Diglycerides; D005227:Fatty Acids; D005989:Glycerides; D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; C037149:stearoylarachidonylglycerol; D013917:Thrombin