title: Phosphoinositides are required for store-mediated calcium entry in human platelets.
abstract: We have recently observed that small GTP-binding proteins are important for mediation of store-mediated Ca(2+) entry in human platelets through the reorganization of the actin cytoskeleton. Because it has been shown in platelets and other cells that small GTP-binding proteins regulate the activity of phosphatidylinositol 3-kinase and phosphatidylinositol 4-kinase, whose products, phosphoinositides, play a key role in the reorganization of the actin cytoskeleton, we have investigated the role of these lipid kinases in store-mediated Ca(2+) entry. Treatment of platelets with LY294002, an inhibitor of phosphatidylinositol 3- and phosphatidylinositol 4-kinases, resulted in a concentration-dependent inhibition of Ca(2+) entry stimulated by thapsigargin or the physiological agonist, thrombin. In addition, wortmannin, another inhibitor of these kinases, which is structurally unrelated to LY294002, significantly reduced store-mediated Ca(2+) entry. The inhibitory effect of LY294002 was not mediated either by blockage of Ca(2+) channels or by modification of membrane potential. LY294002 inhibited actin polymerization stimulated by thrombin or thapsigargin. These results indicate that both phosphatidylinositol 3-kinase and phosphatidylinositol 4-kinase are required for activation of store-mediated Ca(2+) entry in human platelets and that the mechanism could involve the reorganization of the actin cytoskeleton.
authors.affiliation: Department of Physiology, University of Cambridge, Downing St., Cambridge CB2 3EG, United Kingdom.
authors.forename: J A
authors.initials: JA
authors.lastname: Rosado
authors.forename: S O
authors.initials: SO
authors.lastname: Sage
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase / Q000037:antagonists & inhibitors; D000730:Androstadienes / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D017136:Ion Transport; D009025:Morpholines / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000502:physiology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D013917:Thrombin / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D010716:Phosphatidylinositols; D000081082:Phosphoinositide-3 Kinase Inhibitors; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D014443:Tyrosine; D019870:1-Phosphatidylinositol 4-Kinase; D013917:Thrombin; D002118:Calcium; D000077191:Wortmannin