Polyphosphoinositide synthesis in platelets stimulated with low concentrations of thrombin is enhanced before the activation of phospholipase C.
When platelets, prelabelled with [32P]orthophosphate, were stimulated with thrombin (0.5 U.ml-1) there was an immediate increase in the radioactivity associated with the pools of polyphosphoinositides. Only subsequent to this increase, did the radioactivity of these phospholipid pools decrease as expected from a receptor-mediated activation of phospholipase C (phosphoinositidase). Phosphorylation of diacylglycerol (one of the second messengers formed in the hydrolysis of phosphatidylinositol-bisphosphate) to phosphatidic acid took place with a lag phase of about 3-5 s. Together these experiments suggest that stimulation of kinases phosphorylating phosphatidylinositol and phosphatidylinositol-phosphate may precede or occur in parallel with activation of receptor-linked phosphoinositidase.
Lassing
I
I
Department of Zoological Cell Biology, Arrhenius Laboratory, Stockholm University, Sweden.
Lindberg
U
U
D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D004075:Diglycerides / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000096:biosynthesis*; D010766:Phosphorylation; D013917:Thrombin / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000378:metabolism*
D004075:Diglycerides; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010738:Type C Phospholipases; D013917:Thrombin