Fig. 1. Exposure to EFs increases directional migration of 3T3 fibroblasts. (A) Measurement of migration speed and directed velocity of sparse cells. EF chambers were oriented with the cathode down (=270°); cells traveled distance, d, at migration angle, , relative to the horizontal. Speed was calculated as d/t, where t is elapsed time. Directional velocity was calculated as speedxsin(), as shown. For these measurements, N20 cells each; three experiments per voltage. (B) Voltage dependence of migration speed. Sparse 3T3 cells placed in EFs for 1.5 hours were significantly increased in average motility speed (P<0.05) only at EFs >2 V cm^-1. (C) Voltage dependence of migration direction. Motility angle was plotted as sin() for each EF strength. Notice that, for sparse cells moving towards the cathode, sin()=-1; towards anode, sin()=+1; randomly, sin()=0. Directionality of motility increased significantly (P<0.05) at EFs 2 V cm^-1. (D) EF increases average migration speed. Histograms document speed of individual, sparse cells in a 1.5-hour run in 0 V cm^-1 and 6 V cm^-1 EF. Although speeds are heterogeneous, the 6 V cm^-1 EF increased average speed (arrows) roughly threefold. (E) EF increases average migration speed and directs motility cathodally. Polar plot shows displacement from the origin of individual sparse 3T3 cells during a 1.5-hour run with no electric field (circles) or 6 V cm^-1 EF (triangles). The EF increased directionality, speed and proportion of cells that translocated significantly and decreased the proportion of cells remaining inside a 10-µm-radius circle.