title: Effect of physiologic shear stresses and calcium on agonist-induced platelet aggregation, secretion, and thromboxane A2 formation.
abstract: BACKGROUND
  Platelets in vivo react under low-shear venous-flow as well as high-shear arterial-flow conditions. Because most studies were carried out at low shear stresses, platelet granule secretion at high shear has not been examined thoroughly. We investigated the secretion of all three types of platelet granules and thromboxane A(2) formation at high shear after stimulation with ADP or thrombin.
  
  
  METHODS
  Washed human platelets were reacted rapidly (<5 s) in a quenched-flow system simulating high-shear arterial-flow conditions (30 dyn/cm(2)). For comparison, we employed a low-shear stirring system (1-5 dyn/cm(2)). Serotonin release and membrane exposure of P-selectin (alpha), CD63 (dense), and CD107a (lysosomes) were used to assess granule secretion. Aggregation was evaluated by resistive-particle counting of the remaining platelet singlets.
  
  
  CONCLUSIONS
  ADP and thrombin induced similar strong levels of aggregation ( approximately 70%) at high shear by 5 s. Thrombin also caused release of about 40% of all alpha and dense granules within 5 s. However, by 5 s at high shear, ADP failed to induce significant granule secretion or thromboxane A(2) formation (<5%, p>0.05). By 10 min at low shear, ADP caused secretion and thromboxane A(2) formation only at non-physiological, micromolar extracellular Ca(2+) concentrations. These results emphasize the ability of thrombin to initiate multiple aspects of platelet function within seconds, while ADP was only able to induce rapid aggregation.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA. dv9x@virginia.edu
authors.forename: Delia
authors.initials: D
authors.lastname: Viisoreanu
authors.forename: Adrian
authors.initials: A
authors.lastname: Gear
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D000925:Anticoagulants / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000494:pharmacology*; D019343:Citric Acid / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006490:Hemostatics / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D010974:Platelet Aggregation / Q000187:drug effects*; D053657:Platelet-Rich Plasma; D051745:Protein Kinase C-delta / Q000378:metabolism; D022142:Secretory Vesicles / Q000187:drug effects / Q000502:physiology; D012701:Serotonin / Q000378:metabolism; D013314:Stress, Mechanical; D013917:Thrombin / Q000494:pharmacology; D013928:Thromboxane A2 / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D000925:Anticoagulants; D006490:Hemostatics; D019343:Citric Acid; D012701:Serotonin; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D051745:Protein Kinase C-delta; D013917:Thrombin; D002118:Calcium