Thrombin proteolysis of GP V from the surfaces of L2H/V cells. (A) Residual binding of the anti-GP V monoclonal antibody SW16 to L2H/V cells incubated with either buffer alone (none) or 1 nmol/L α-thrombin or PPACK-thrombin for 20 minutes. Untreated parental L cells represent background binding. After the incubation period, hirudin was added to inactivate thrombin. *Significantly different v pretreatment of cells with native thrombin (Student's t test: n = 4, t = 12.415, P < .001). (B) Analysis of GP V released into the supernatant of thrombin-treated cells. Cells were incubated with thrombin for the designated times before addition of hirudin. Aliquots of the supernatant were vacuumed onto nitrocellulose paper using a dot-blot apparatus, and the retained GP V was detected using SW16 and a chemiluminescence detection system. Five similar experiments were performed; the mean ± SD of the values obtained by densitometry of the x-ray film are shown.