The interaction of cells expressing GP Ibα mutants with immobilized VWF under flow. Cells expressing either wild-type (A) or charge mutants of (B) GP Ibα were introduced into a parallel-platelet flow chamber and allowed to settle on the surface of immobilized VWF for 1 minute before the chamber was perfused with TBS at flow rates that generated wall shear stresses of 2.5, 10, or 20 dynes/cm². The rolling velocities of the mutant-expressing cells were measured and compared with the rolling velocity of cells expressing wild-type GP Ibα.