P. Savi et al., EFFECT OF CLOPIDOGREL TREATMENT ON ADP-INDUCED PHOSPHORYLATIONS IN RAT PLATELETS, British Journal of Haematology, 97(1), 1997, pp. 185-191
Phosphorylations induced by 2-MeS-ADP, a potent agonist of platelet AD
P receptors, have been studied in rat platelets, and the effect of clo
pidogrel, a compound which inhibits platelet aggregation by selectivel
y reducing the binding of ADP to its low affinity receptors on platele
ts, has been determined, 2-MeS-ADP induced platelet activation (shape
change and aggregation) simultaneously with the phosphorylation of myo
sin light chain (P-20) and plekstrin (P-47). Phosphorylation of P-20 a
nd P-47 was transient, a maximum being observed 10s after addition of
the agonist when shape change reached its maximum. P-20 and P-47 phosp
horylations were not strongly affected by clopidogrel treatment. Follo
wing stimulation of platelets with 2-MeS-ADP, several proteins were ph
osphorylated at tyrosine residues. Clopidogrel treatment inhibited the
increase in phosphorylation of P-140, P-100, P-80/85, P-66 and P-55 c
oncomitantly with the inhibition of platelet aggregation. However, clo
pidogrel did not interfere with the early phosphorylation of the P-80/
85 kD doublet which occurs at the time of the shape change. P-80/85, i
dentified by immunodetection as cortactin, could be involved in the re
organization of the cytoskeleton necessary for morphological changes.
Thus, by using clopidogrel-treated rat platelets, we were able to dete
rmine some of the phosphorylations coupled either to clopidogrel-resis
tant high-affinity ADP receptors leading to shape change or to clopido
grel sensitive low-affinity ADP receptors coupled to the aggregation p
rocess.