Key Points
- To elucidate the intermediate signaling steps of thrombin-induced human platelet secretion using prostacyclin to temporarily uncouple receptor activation from granule release.
- Washed human platelets pretreated with prostacyclin were briefly exposed (15–30 seconds) to low concentrations of human thrombin (0.01–0.2 U/ml).
- Prostacyclin and thrombin were washed out, and platelets were restimulated with fresh thrombin or alternative agonists including collagen, wheat germ agglutinin, and ionophore A23187.
- Assayed [(3)H]serotonin release, thrombin-binding capacity, and the effects of diisopropyl fluorophosphate-inactivated thrombin.
- Prior exposure to thrombin produced irreversible, concentration-dependent inhibition of subsequent thrombin-induced [(3)H]serotonin secretion despite identical surface thrombin binding.
- Refractoriness was agonist-specific, as platelet secretion triggered by collagen, wheat germ agglutinin, or ionophore A23187 remained minimally affected.
- Inactivated diisopropyl fluorophosphate-thrombin failed to trigger desensitization, demonstrating that initial refractoriness relies on thrombin's secretory signaling pathway rather than esterase or clotting activity.
Structured PICO
PPopulationWashed human platelets
IInterventionBrief exposure (15-30 s) to low concentrations of human thrombin (0.01-0.2 U/ml) after prostacyclin treatment
CComparatorControl platelets not pretreated with thrombin
OOutcomeCapacity to secrete [(3)H]serotonin upon subsequent thrombin exposuresurrogate
Brief exposure of prostacyclin-treated platelets to thrombin induces a concentration-dependent, thrombin-specific refractoriness to subsequent serotonin secretion.