Latrunculin treatment reduces the filament elongation rate in a dose-dependent manner. (A) Representative cell treated with 1 µM LatB has numerous, short filaments or fragments as well as several large cables. Actin filaments or fragments grow rather slowly, if at all. Time points indicate elapsed time from start of video sequence. Bar, 2 µm. See Video 9 for full time-lapse series (available). (B) Kymograph of the single filament marked in A. This short filament undergoes slow elongation and rapid shrinkage events. (C) Plot of average rate (±SD) of filament elongation in control and LatB-treated cells. Treatments with 100 nM and 1 µM LatB for 1–10 min significantly reduce the rate of filament elongation (P < 0.0001).