Summary
Cytochalasin D was used to investigate the role of intracellular cyto-skeleton in
the stabilization of platelet aggregation induced by strong platelet agonists. Incubation
of gel-filtered platelets with increasing concentrations of cytochalasin D resulted
in a dose-dependent inhibition of actin polymerization and association of actin-binding
proteins with the Triton X-100-insoluble material induced by the thromboxane analogue,
U46619, and the thrombin receptor activating peptide, TRAP. The same concentrations
of cytochalasin D did not significantly inhibit platelet aggregation promoted by the
two agonists. The addition of the chelating agent EDTA to fully aggregated platelets,
that had been treated with cytochalasin D, resulted in the rapid and almost complete
disaggregation. EDTA did not cause disaggregation of control, solvent-treated, aggregated
platelets. The degree of platelet disaggregation induced by EDTA was dependent on
the dose of cytochalasin D used, and was correlated with the inhibition of the cytoskeletal
reorganization. Aggregation of cytochalasin D-treated platelets stimulated with U46619
or TRAP was also reverted by the addition of the tetrapeptide RGDS or the fibrinogen
y-chain dodecapeptide, which competitively interfere with fibrinogen binding to the
glycoprotein Ilb-IIIa complex. These results indicate that the intracellular cytoskeleton
plays an essential role in the stabilization of the fibrinogen-platelet interaction,
and is necessary for the irreversibility of platelet aggregation induced by strong
agonists.
