Induction of patching and its reversal on surface-activated human platelets.

Fibrinogen coupled to colloidal gold (Fgn/Au) has been used to follow GPIIb-IIIa receptors on surface-activated platelets and to evaluate the effects of the anti-actin agent, cytochalasin B (CB), on the movement of receptor-ligand complexes. Fgn/Au binds diffusely to spread platelets, but is translocated rapidly from the peripheral margin to cell centres and to channels of the open canalicular system (OCS). CB added after spreading and incubation with Fgn/Au reverses the centripetal movement of receptor-ligand complexes. Fgn/Au particles move back toward the margins of spread cells and form patches. The patches of receptor-ligand complexes overlie segments of the OCS filled with Fgn/Au. Washing out the CB reverses the process and receptor-ligand complexes are again translocated toward platelet centres.