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The roles of ADP and TXA 2 in botrocetin/VWF‐induced aggregation of washed platelets
Author(s) -
Liu J.,
Pestina T. I.,
Berndt M. C.,
Steward S. A.,
Jackson C. W.,
Gartner T. K.
Publication year - 2004
Publication title -
journal of thrombosis and haemostasis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.947
H-Index - 178
eISSN - 1538-7836
pISSN - 1538-7933
DOI - 10.1111/j.1538-7836.2004.01023.x
Subject(s) - thromboxane a2 , microbiology and biotechnology , glycoprotein ib , platelet activation , platelet , chemistry , secretion , dense granule , von willebrand factor , signal transduction , platelet glycoprotein gpib ix complex , biochemistry , receptor , biology , immunology
Summary. Background: Binding of von Willebrand factor (VWF) to the platelet membrane glycoprotein (GP) Ib‐IX‐V complex initiates a cascade of events leading to α IIb β 3 activation and platelet aggregation. The roles of ADP and thromboxane A 2 (TXA 2 ) in agglutination‐induced GPIbα‐mediated platelet activation have not been fully described. Methods: Botrocetin and human VWF were used to stimulate washed mouse platelets. Platelets deficient in TXA 2 receptors, Gαq, or α IIb β 3 , and inhibitors and chelating agents were used to investigate the roles of TXA 2 , ADP, α IIb β 3 and Ca 2+ in botrocetin/VWF‐induced signaling. Results: Our data demonstrate that botrocetin/VWF/GPIbα‐mediated agglutination results in calcium‐independent protein kinase C (PKC) and phospholipase A2 (PLA2) activities required for GPIbα‐elicited TXA 2 production that in turn causes dense granule secretion. Aggregation of washed platelets requires TXA 2 ‐induced α IIb β 3 activation and ADP signaling. TXA 2 or ADP can activate α IIb β 3 , but both are required for α‐granule secretion and aggregation. Botrocetin/VWF‐induced dense granule secretion is Gαq‐dependent. α‐Granule secretion requires initial ADP signaling through P2Y1 and subsequent signaling through P2Y12. Signaling initiated by agglutination is propagated and amplified in an α IIb β 3 ‐dependent manner. Conclusions: In contrast to adhesion or shear stress‐induced GPIb‐elicited signaling, agglutination‐elicited GPIb signaling that activates α IIb β 3 requires TXA 2 . Agglutination‐elicited TXA 2 production is independent of Ca 2+ influx and mobilization of internal Ca 2+ stores. Therefore, our results demonstrate that agglutination‐elicited GPIb signaling causes α IIb β 3 activation by a mechanism that is distinct from those used by adhesion, or shear stress‐induced GPIb signaling.