Cell spreading assay. (A) Differential interference contrast (DIC) images of CHO-K1 stable transfectants after adhering at 37°C to immobilized human fibrinogen (in the presence of 10 μg/mL mAb LM609) or ligand-mimic mAb PAC-1 in the presence or absence of 1 mM DTT. The images are representatives from 1 of 3 independent experiments. Scale bar represents 10 μm. (B) Quantification of the areas of adhering/spreading cells as described in “Cell spreading and microscopy.” Error bars are SD. (C) Reduction of the disulfide bond by DTT. The (35)S-labeled transfectants were allowed to adhere on immobilized fibrinogen at 37°C for 1 hour in the presence or absence of 1 mM DTT, followed by immunoprecipitation with 10E5 (anti- αIIb), and loaded on 7.5% SDS-PAGE under nonreducing condition. The bands corresponding to αIIb (α), β3 (β), or αIIbβ3 (α/β) heterodimer are indicated. Positions of protein molecular size markers (in kDa) are shown on the left.