PAC1 binding to the _IIbβ₃-mutant receptors. The binding of the activation-dependent ligand mimetic antibody PAC1 to CHO cells transfected with the indicated _IIb mutant and the β₃ subunit was examined by flow cytometry. To determine PAC1 binding, transfected cells were incubated (activated) with 4 μmol/L anti-LIBS6, followed by the addition of PAC1. The binding of PAC1 was analyzed in the presence (open histogram) and absence (shaded histogram) of the competitve inhibitor Ro43-5054. Untransfected CHO cells stained with PAC1 in the presence of anti-LIBS6 are depicted by the dotted histogram.