Movement of fibrinogen receptors on the ventral membrane of spreading platelets

We have used fibrinogen-gold conjugates and fluorescein-labelled fibrinogen to examine the presence of fibrinogen receptors on the ventral membrane of spreading platelets and to visualize the redistribution of the receptors during platelet spreading. The movement of fibrinogen-gold conjugates was observed in real time using video-enhanced interference reflection microscopy (VEIRM) and the redistribution of fluorescein-labelled fibrinogen was examined using video-intensified epifluorescence microscopy (VIFM). Fibrinogen was picked up by spreading platelets and moved towards the centre of the platelets. The velocity of the movement of fibrinogen-gold conjugates under the ventral membrane ranged from less than 0.1 μm min−1 to more than 10 μm min−1. The average velocity in the peripheral web region was more than 6 μm min−1, and was reduced to around 1 μm min−1 in the outer and inner filamentous zones. The centralized fibrinogen molecules were internalized and eventually removed from the platelets. Video microscopy in conjunction with colloidal gold particles provides a simple method for real-time observation of the movement of fibrinogen receptors on the ventral membrane of spreading platelets.