R. Beernink

The binding of human blood platelets to fibrinogen-fibronectin-, and Arg-Gly-Asp-derivatized Sephadex G-10

The adhesive proteins fibrinogen (FG) and fibronectin (FN) were immobilized to glycine-Sephadex G-10. The derivatized Sephadex G-10 gels were used to bind human blood platelets. For comparison, Gly-Arg-Gly-Asp-Ser-Pro(GRGDSP)-derivatized Gly-Sephadex G-10 was used. FG-, FN-, and GRGDSP-Gly-Sephadex G-10 each bound a substantial number of activated blood platelets (> or = 5 x 10(8) ml-1 gel) while non-activated platelets were not bound. Binding of ADP-treated blood platelets to the affinity adsorbents was dependent on the ADP-concentration which was used, reaching a near-maximal value at about 10 microM ADP. Platelet binding to the three types of affinity gels could be completely inhibited by dissolved GRGDSP as well as monoclonal anti-platelet glycoprotein IIb/IIIa (GPIIb/IIIa) antibody CLB-C17, which demonstrates that platelet binding specifically involves the fibrinogen binding site on GPIIb/IIIa. Platelet binding to all three affinity gels required free Ca2+ and Mg2+ ions: platelets binding in the absence of these divalent cations was considerably lower than platelet binding in buffer containing 2 mM Ca2+ and 1 mM Mg2+. Moreover, activated ethylenediamine-tetraacetate (EDTA)-treated platelets did not bind at all to the affinity gels. The finding that non-activated platelets did not bind to the affinity gels is thought to be related to both the high hydrophilicity of the Sephadex basic material and to the native state of the gel-bound fibrinogen and fibronectin.