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Characterization of the thrombin-induced desensitization of platelet activation by thrombin
Insights
Brief exposure to thrombin desensitizes platelets to further activation. This desensitization depends on thrombin concentration and exposure time, suggesting a catalytic receptor modification. Further research is needed.
Area of Science:
- Biochemistry
- Hematology
- Cell Biology
Background:
- Platelets play a crucial role in hemostasis and thrombosis.
- Thrombin is a key enzyme in the coagulation cascade, activating platelets.
- Platelet activation is a complex process involving various signaling pathways.
Purpose of the Study:
- To further define the conditions and mechanisms of thrombin-induced platelet desensitization.
- To investigate the role of prostacyclin in modulating thrombin-induced platelet activation.
- To explore the relationship between thrombin concentration, exposure time, and platelet desensitization.
Main Methods:
- Incubation of platelets with thrombin under varying conditions (prostacyclin inhibition, thrombin concentration, temperature, platelet concentration).
- Washing and subsequent testing of platelets for thrombin-induced adenosine triphosphate (ATP) secretion.
- Utilizing hirudin to inhibit thrombin activity post-pretreatment.
Main Results:
- Platelet desensitization to thrombin was observed following brief exposure.
- Prostacyclin inhibition of thrombin-induced activation was temporary and dependent on various factors.
- Desensitization was concentration and time-dependent, suggesting catalytic receptor modification.
- Sub-threshold thrombin exposure also induced a less extensive desensitization.
Conclusions:
- Platelet desensitization to thrombin is a defined phenomenon influenced by pretreatment conditions.
- The findings support a model involving catalytic modification of platelet receptors.
- Understanding these desensitization mechanisms can provide insights into platelet function regulation.
Abstract:
Brief exposure of platelets to thrombin makes them less sensitive to subsequent activation by thrombin, a phenomenon demonstrated by Shuman, Botney, and Fenton [J. Clin. Invest., 63, 1211-1218, 1979] by incubating prostacyclin-inhibited platelets with thrombin; after removal of thrombin and prostacyclin, the platelets were selectively desensitized to subsequent activation by thrombin. The conditions for this desensitization have been further defined. Inhibition of thrombin-induced platelet activation by prostacyclin was not absolute, it was only temporary, it could be overcome with higher thrombin concentrations, and it varied with platelet concentration and temperature. With low enough thrombin concentrations, high enough prostacyclin concentrations and short enough times of exposure, platelets could be pretreated with thrombin with no evidence of activation. After addition of hirudin to inhibit thrombin, the platelets were washed and tested for thrombin-induced secretion of ATP. Desensitization to thrombin depended on the concentration of thrombin during pretreatment and on the length of pretreatment, consistent with a catalytic modification of a receptor. A less extensive desensitization was observed when platelets without inhibitor were incubated with a sub-threshold level of thrombin before addition of an activating concentration of thrombin. This desensitization also varied with the time of pretreatment and the concentration of sub-threshold thrombin.