Signal transducing mechanisms in human platelets stimulated by cotton bract tannin.
Cotton bract tannin is a potent stimulus for platelet aggregation and secretion. Tannin has been shown to stimulate the phosphorylation of two 19-kD and 47-kD cytosolic proteins in platelets, but earlier steps in signal transducing mechanisms of platelet activation are unknown. In this study, measurements of 32P-labeled phospholipids, 14C-labeled arachidonic acid, and levels of intracellular free calcium (Ca2+) were performed before and after the addition of thrombin (1 U/ml) or various concentrations of tannin to human platelets. The results showed that tannin induced a dose-dependent synthesis of phosphatidic acid, an early and transient hydrolysis of phosphatidylinositol monophosphate and bisphosphate, a transient synthesis of diacylglycerol, and a release of arachidonic acid metabolites. The kinetics of phosphatidic acid, diacylglycerol, and arachidonic acid metabolite synthesis were similar after platelet stimulation by tannin (75 micrograms/ml) or thrombin. Tannin also induced a reversible rise of intracellular Ca2+ due to a mobilization of the internal stores and an influx of extracellular Ca2+. These results suggest that cotton bract tannin, as thrombin, activates human platelets by phospholipase C and A2 activations, release of diacylglycerol, and mobilization of intracellular free Ca2+.
Lauque
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Department of Internal Medicine, Unité U 326, Centre Hospitalo-Universitaire Purpan, Toulouse, France.
Prevost
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MC
Carles
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Chap
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D001095:Arachidonic Acids / Q000378:metabolism; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism; D003368:Gossypium; D006801:Humans; D007700:Kinetics; D010712:Phosphatidic Acids / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D010766:Phosphorylation; D015539:Platelet Activation; D012701:Serotonin / Q000378:metabolism; D015398:Signal Transduction; D013634:Tannins / Q000494:pharmacology*; D013917:Thrombin / Q000494:pharmacology
D001095:Arachidonic Acids; D004075:Diglycerides; D010712:Phosphatidic Acids; D010716:Phosphatidylinositols; D010743:Phospholipids; D013634:Tannins; D012701:Serotonin; D013917:Thrombin; D002118:Calcium