The W3:4-1 and W4:4-1 loops of αIIb determine the responsiveness of αIIbβ3 to RGDS. (A) Effect of increasing concentration of RGDS on FITC-labeled fibrinogen binding to CHO cells expressing recombinant αIIbβ3 containing WT HαIIb, HαIIb containing a RαIIb W3:4-1 loop (HαIIb + RW3:4-1), HαIIb containing a RαIIb W4:4-1 loop (HαIIb + RW4:4-1), or RαIIb. (B) Percent inhibition of FITC-fibrinogen binding to CHO cells expressing recombinant αIIbβ3 containing WT human or rat αIIb or the designated human/rat αIIb chimeras by 1 mM RGDS. The data shown are the mean plus or minus 1 SE of 5 or more separate experiments, each performed in triplicate. ■ represent WT HαIIb and HαIIb containing the designated RαIIb loops; 
represent RαIIb and RαIIb containing the designated HαIIb loops. *P < 10−14 compared with WT HαIIb.
