Triplet-free platelets are more aggregative and remarkably so on
adding ADP
Aggregation of platelets in suspension was monitored in terms of
reduction in the absorbance of the suspension at 405 nm. Native
(non-denuded) platelets were little aggregated upon addition of ADP
regardless of their pre-treatment with jacalin. Triplet-free (denuded)
platelets that were more prone to aggregation than their native
counterparts even before ADP addition, aggregated substantially more
upon addition of ADP (Fig.6). However, pre-treatment of denuded triplets
with jacalin offered near complete protection from ADP-mediated
aggregation. The primary event in ADP-mediated platelet aggregation is
binding to the two G-protein-coupled receptors P2Y1 and P2Y12 on
platelet surface [24]. Though no data on O-glycan dependence of this
binding was available, involvement of GPIIb/IIIa in subsequent events in
ADP-mediated aggregation has been reported [20]. Besides explaining
the jacalin-mediated inhibition of ADP-induced aggregation of denuded
platelets, results in Fig.6 also suggested the possibility that
GPIIb/IIIa that gets exposed following denudation was a triplet reeptor.