Model of Arf6-mediated fibrinogen endocytosis. Arf6 is a key intracellular trafficking molecule and, in platelets, enhances fibrinogen engulfment into intracellular vesicles. Arf6 also influences platelet spreading and clot retraction through mechanisms that remain incompletely understood. GDP, guanosine diphosphate; GTP, guanosine triphosphate.