Fig. 4. Host calcium response during parasite invasion. (A) Fluo-4 calcium flux in untreated host cells. Fluo-4 AM loaded fibroblasts were observed by time-lapse fluorescent video microscopy with frames captured every 0.5 seconds. The bright object in the center is the nucleus of the cell. Shown are selected frames with the time elapsed between frames in seconds indicated. Bar, 10 µm. (B) Phase images of T. gondii parasites invading fluo-4 AM loaded fibroblasts and recorded by time-lapse video. Phase and fluorescent images were acquired with 0.5 seconds between each pair. Bar, 5 µm. (C) Fluorescent images corresponding to the panels in (B) are shown, with the elapsed time between frames indicated. Also see Movie 2 at jcs.biologists.org/supplemental.