Spatiotemporal differences in V
between the leading edge and the rear end in cathode (Calvaria)- or anode (SaOS-2)-directed cells. Fluorescence images showing the uptake of Vmem reporter dye DiBAC4(3) at different time points after addition to the cells. White arrows in the second row point to the depolarized cell membrane, wherein the anionic dye first enters from sites that have a decreased number of negative charges (depolarized) at the rear end in both anode (left)- and cathode (right)-directed cells (A). pH bubbles (white arrows), especially recognizable in cathode-directed cells (right column), can be observed at the termini of membrane protrusions along the cell periphery in randomly migrating, nonpolarized cells and at the leading-edge of directed, polarized cells. False colored (LUT) images generated from ratiometric images showing cells loaded with BCECF-AM, a pH reporter, ratiometric dye (B). In both (A) and (B), the first row shows DIC images of the cells during random (no EF) and directed (0.5 V/mm) migration. Black arrows in the DIC images indicate the direction of migration.