Summary
Platelets deprived of calcium and incubated at 37° C for 10 min lose their ability
to bind fibrinogen or aggregate with ADP when adequate concentrations of calcium are
restored. Since the calcium complex of glycoproteins (GP) IIb and IIIa is the presumed
receptor for fibrinogen, it seemed appropriate to examine the behavior of these glycoproteins
in incubated non-aggregable platelets. No differences were noted in the electrophoretic
pattern of nonaggregable EDTA-treated and aggregable control CaEDTA-treated platelets
when SDS gels of Triton X- 114 fractions were stained with silver. GP IIb and IIIa
were extracted from either nonaggregable EDTA-treated platelets or aggregable control
platelets with calcium-Tris-Triton buffer and subjected to sucrose density gradient
centrifugation or crossed immunoelectrophoresis. With both types of platelets, these
glycoproteins formed a complex in the presence of calcium. If the glycoproteins were
extracted with EDTA-Tris-Triton buffer, or if Triton-solubilized platelet membranes
were incubated with EGTA at 37° C for 30 min, GP IIb and IIIa were unable to form
a complex in the presence of calcium. We conclude that inability of extracted GP IIb
and IIIa to combine in the presence of calcium is not responsible for the irreversible
loss of aggregability that occurs when whole platelets are incubated with EDTA at
37° C.
Keywords
Platelet aggregation - Glycoproteins IIb and IIIa - EDTA
