TPO increases SFLLRN-mediated fibrinogen binding, integrin αIIbβ3 expression levels and delays the disappearance of fibrinogen binding sites. Washed platelets were incubated with 100 ng/mL TPO for 5 minutes before stimulation with the indicated concentrations SFLLRN for 15 minutes in the presence of FITC-fibrinogen (A), PE-anti-P-selectin Ab (B), or PE-anti-integrin αIIb antibody (C). Alternatively, platelets were first stimulated with 10 μM SFLLRN and FITC-fibrinogen was added after the indicated time periods (D) for 15 minutes. Samples were fixed in 1% formaldehyde and analyzed by FACS analysis. Results are expressed as average ± SEM of percentage maximal fibrinogen binding of vehicle treated platelets (A, n = 17), percentage of maximum P-selectin surface expression of vehicle treated platelets (B, n = 9), fold-increase in integrin αIIb integrin expression (C, n = 6), and percentage of maximal fibrinogen binding (D, n = 4).
