Related Experiment Videos
ADP causes partial degranulation of platelets in the absence of aggregation
S L Janes1, D J Wilson, A D Cox
1Academic Department of Haematology, Royal Free Hospital and School of Medicine, London.
Abstract:
Whole blood flow cytometry has revealed that platelets undergo partial degranulation in response to ADP, in the absence of aggregation, as evidenced by the expression of the P-selectin and CD63 antigens of the alpha-granule and lysosomal membranes respectively. With maximum ADP (10(-5) M) fibrinogen bound to 76.1 +/- 7.2% of platelets but P-selectin and CD63 antigen were expressed on 26.9 +/- 9.8% and 8.6 +/- 3.5% of platelets respectively. Maximum fibrinogen binding, P-selectin and CD63 expression induced by alpha-thrombin were 96.1 +/- 1.4%, 92.8 +/- 2.3% and 77.6 +/- 9.7% respectively. beta-thromboglobulin release from the ADP-stimulated platelets correlated closely with the expression of P-selectin and CD63 (r = 0.98 +/- 0.02 for both antigens). No platelet aggregates were seen by flow cytometry and the absence of aggregation was confirmed by single cell counting. Addition of the GPIIb-IIIa antagonist echistatin, at concentrations that totally blocked fibrinogen binding to ADP-stimulated platelets, had no effect on the expression of the granule membrane antigens. The partial degranulation of normal platelets was independent of thrombin generation since it was not inhibited by hirudin (5 units/ml). In conclusion, ADP is capable of causing partial degranulation of platelets independently of aggregation, fibrinogen binding or thrombin generation. Thus release of potent procoagulant, vasoactive and mitogenic substances from the platelets could continue in the presence of thrombin inhibitors and GPIIb-IIIa antagonists.
Insights
Adenosine diphosphate (ADP) triggers partial platelet degranulation, marked by P-selectin and CD63 expression, without causing aggregation or fibrinogen binding. This degranulation is independent of thrombin generation, highlighting ADP
Area of Science:
- Hematology
- Platelet Biology
- Cellular Signaling
Background:
- Platelet activation is crucial for hemostasis and thrombosis.
- Adenosine diphosphate (ADP) is a key platelet agonist.
- Platelet degranulation releases bioactive substances, but its mechanisms independent of aggregation are not fully understood.
Purpose of the Study:
- To investigate whether ADP induces platelet degranulation independently of platelet aggregation.
- To determine if ADP-mediated degranulation is linked to fibrinogen binding or thrombin generation.
- To assess the role of GPIIb-IIIa receptors in ADP-induced degranulation.
Main Methods:
- Whole blood flow cytometry was used to analyze platelet activation markers.
- P-selectin and CD63 expression were measured as indicators of alpha-granule and lysosomal release.
- Fibrinogen binding, beta-thromboglobulin release, and platelet aggregation were assessed.
- Experiments included the use of ADP, alpha-thrombin, echistatin (GPIIb-IIIa antagonist), and hirudin (thrombin inhibitor).
Main Results:
- ADP induced partial degranulation, evidenced by P-selectin and CD63 expression, without causing platelet aggregation.
- Fibrinogen binding and P-selectin/CD63 expression were significantly lower with ADP compared to alpha-thrombin.
- Echistatin blocked fibrinogen binding but did not affect ADP-induced degranulation.
- Hirudin did not inhibit ADP-induced degranulation, indicating independence from thrombin generation.
- Beta-thromboglobulin release correlated with P-selectin and CD63 expression.
Conclusions:
- ADP can induce partial platelet degranulation independently of platelet aggregation, fibrinogen binding, and thrombin generation.
- This ADP-mediated degranulation pathway allows the release of procoagulant, vasoactive, and mitogenic substances.
- The findings suggest that platelet degranulation can occur even when aggregation is inhibited, with implications for therapies involving thrombin inhibitors or GPIIb-IIIa antagonists.