title: Ionomycin can elevate intraplatelet Ca2+ and activate phospholipase A without activating phospholipase C.
abstract: Human platelets exposed to ionomycin, a Ca2+ ionophore, exhibit activation of both phospholipases A2 and C. Such platelets manifest a rise in cytoplasmic Ca2+ (monitored by quin 2), a loss in phosphoinositides, formation of lysophosphatidylinositol, thromboxane B2, phosphatidic acid, and phosphorylated 47 kilodalton protein, and secretion. In the absence of thromboxane formation and secreted ADP, phospholipase C is not activated and the 47 kilodalton protein is not phosphorylated. The elevation in Ca2+ is unaffected by inhibition of cyclooxygenase and ADP. Thus, an increase in cytoplasmic Ca2+ is not sufficient to stimulate phospholipase C. Further, secretion can occur in the absence of phospholipase C activation and 47 kilodalton protein phosphorylation.
mesh_terms: D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D004789:Enzyme Activation; D004987:Ethers / Q000494:pharmacology; D006801:Humans; D015759:Ionomycin; D007700:Kinetics; D010716:Phosphatidylinositols / Q000097:blood; D010740:Phospholipases / Q000097:blood*; D010741:Phospholipases A / Q000097:blood*; D010738:Type C Phospholipases / Q000097:blood*
chemical_list: D004987:Ethers; D010716:Phosphatidylinositols; D015759:Ionomycin; D010740:Phospholipases; D010741:Phospholipases A; D010738:Type C Phospholipases; D002118:Calcium