Qd. Liu et al., ATP does not affect fibrinogen binding to platelet GPIIbIIIa in systems free of signal transduction, PLATELETS, 10(6), 1999, pp. 407-416
Recent studies have suggested that the platelet fibrinogen (Fg) receptor, p
latelet membrane glycoprotein IIbIIIa (GPIIbIIIa, or integrin alpha(IIb)bet
a(3)) is also an adenosine triphosphate (ATP) binding site, and that the bi
nding of ATP can directly inhibit the Fg-binding function of GPIIbIIIa, How
ever, any direct effect of ATP on GPIIbIIIa function in intact fresh platel
ets is difficult to distinguish from indirect inhibitory effects via compet
ition with ADP or elevation of platelet cyclic AMP levels. We therefore stu
died effects of ATP on Fg binding to activated GPIIbIIIa on the following m
odel particles: externally activated and fixed platelets, as well as latex
particles and liposomes containing functionally competent activated GPIIbII
Ia receptors for Fg, These particles have 'normal', activated GPIIbIIIa in
terms of: (1) binding affinity, (2) specificity to Fg, and (3) conformation
al change(s) after Fg binding. These particles neither require nor respond
to further activation in order to bind Fg, With these model particles, we s
howed that ATP does not have any direct effect on the binding of Fg to plat
elet GPIIbIIIa and platelet aggregation. These simplified model particles a
re useful tools in the mechanistic study of platelet GPIIbIIIa function and
the interaction between platelet GPIIbIIIa and its ligands.