Fig. 7. Some FN fibrils remain fixed and others contract following cytochalasin B treatment. (a,b) show the cell two hours before and immediately before adding 4 µM cytochalasin B. (c,d) panels are 30 minutes after adding cytochalasin. The upper panels (a-c) show actin in red and FN in green; (d) shows staining for ß1 integrin. The elongated fibril (upper arrowhead) contracted before cytochalasin treatment. Another fibril (lower arrowhead) extended during the two hour period, then contracted after the addition of cytochalasin. The fibril indicated by the upper arrow elongated considerably in the two hour period and then remained unchanged, presumably bound to the substrate. This fibril maintained a streak of colocalized ß1 integrin. The lower panels show superimposition of the FN label at two time points: (a,b) shows minus 120 minutes in red and 0 minutes in green; (b,c) shows 0 minutes in green and plus 30 minutes in red. The arrows indicate the elongated fibrils in (a,b) and the contracted fibrils in (b,c). Most FN fibrils appeared to be attached to the substrate, as they did not move before or after the addition of cytochalasin. However, some fibrils showed substantial contraction: the most conspicuous examples are shown at higher magnification (x2) in b' and c' (showing only the FN fluorescence). Bar, 20 µm.

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