title: Primary role of calcium ions in arachidonic acid release from rat platelet membranes. Comparison with human platelet membranes.
abstract: The liberation of arachidonic acid (AA) was investigated in platelet membranes prelabelled with [3H]AA. In rat platelet membranes, Ca2+ at concentrations over several hundred nanomolar induced [3H]AA release, with a concurrent decrease in 3H radioactivity of phosphatidylethanolamine and phosphatidylcholine. Some 4-6% of total radioactivity incorporated into platelet membrane lipids was released at 1-10 microM-Ca2+, which is nearly equivalent to that attained in agonist-stimulated platelets. Formation of lysophospholipids in [3H]glycerol-labelled membranes and decrease in [3H]AA liberated by the phospholipase A2 inhibitors mepacrine and ONO-RS-082 suggest that [3H]AA release is mainly catalysed by phospholipase A2. In intact platelets agonist-stimulated [3H]AA release was markedly decreased in the absence of extracellular Ca2+ or in the presence of the intracellular Ca2+ chelator quin 2. These results indicate that in rat platelets the rise of intracellular Ca2+ plays a primary role in the activation of phospholipase A2. In contrast, Ca2+ even at high millimolar concentrations did not effectively stimulate [3H]AA release in human platelet membranes. Thus factor(s) additional to or independent of Ca2+ is required for the liberation of AA in human platelets.
authors.affiliation: Department of Biochemistry, Gifu University School of Medicine, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Nakashima
authors.forename: A
authors.initials: A
authors.lastname: Suganuma
authors.forename: A
authors.initials: A
authors.lastname: Matsui
authors.forename: H
authors.initials: H
authors.lastname: Hattori
authors.forename: M
authors.initials: M
authors.lastname: Sato
authors.forename: A
authors.initials: A
authors.lastname: Takenaka
authors.forename: Y
authors.initials: Y
authors.lastname: Nozawa
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000097:blood*; D001792:Blood Platelets / Q000378:metabolism* / Q000648:ultrastructure; D002118:Calcium / Q000097:blood*; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D010741:Phospholipases A / Q000097:blood; D054467:Phospholipases A2; D051381:Rats
chemical_list: D001095:Arachidonic Acids; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium