Platelet adherence and detachment--in what ways is surface-bound albumin different from surface-bound fibrinogen?

The adhesion and detachment of platelets on surface-bound albumin and surface-bound fibrinogen were studied. Fluorescent video-microscopy of platelets labelled with mepacrine was used to provide continuous information. Glass tubes (I.D. 1.3 mm) were precoated with either human albumin or human fibrinogen before exposure to a suspension of washed platelets and red cells. Observations were made 0.5 cm from the tube's entrance over a 1370 micron 2 portion of lumen. The rate at which cells leave the measurement area and the percent of initially attaching cells which leave are independent of protein coating but increase with flow rate. The percent of initially attaching platelets which permanently adhere is equal for both protein coatings but the pathways leading to this result can be different. For the lower shear rate studied, 80 s-1, the percent of cells which permanently adhere on first contact is less for albumin than for fibrinogen; the percent of initially attaching cells which adhere and then move before permanent adhesion is greater for albumin. The mechanism of detachment and reattachment leads to the equality of the overall adhesion efficiencies for the two protein coatings at 80 s-1. For the higher shear rate studied, 456 s-1, the adhesion pathways for both coatings were the same.