Fig. 5 Quantitation of actin filament polarity in keratocyte lamellipodia. Polarity of filament orientation was determined with respect to the leading edge as being in one of three categories (see Materials and Methods): barbed end forward, pointed end forward, or parallel to the edge. Determinations were made in cells of similar size and morphology, covering the whole width of the lamellipodia, within 2 µm zones parallel to the leading edge, and for a depth of 12 µm behind the leading edge. A total of 3761 filaments were scored in 5 cells, converted to % per cell and the mean percentages plotted against distance from the leading edge. The percentage of filaments in each category remained constant throughout the lamellipodia (0 - 8 µm) until the transitional zone was reached (8 -12 µm).