Inhibition of myosin IIA and F-actin stabilization arrests retrograde flow. (A) A kymograph was generated along the diameter of a cell pretreated with 25 µM Y-27632 and spreading on OKT3-coated coverglasses. The arrowhead along the time axis indicates the addition of 1 µM JAS to the well. The kymograph was sharpened in Photoshop to accentuate F-actin features. (B) Time-lapse series of cells pretreated with 25 µM Y-27632 and allowed to interact with the stimulatory surface for 5 min before addition of either DMSO or 1 µM JAS. 30 s after the treatment, a portion of F-actin, marked with an asterisk, was photobleached, and fluorescence recovery was recorded. Bars, 5 µm.