Cytochalasin B-induced depolymerization of F-actin in chick embryo fibroblasts is dependent on cell density and anchorage to substratum.

The effect of cytochalasin B on F-actin amount and organization was measured in chick embryo fibroblasts (CEF) grown on solid substratum at low density, at high density, and suspended in a fluid medium. It was found that: 1) Cytochalasin B induced decrease in F-actin content only in cells growing at low density, in density-inhibited or suspended cells cytochalasin B had no effect on F-actin amount. 2) In cells grown at low density F-actin filaments organized in stress fibers are more resistant to cytochalasin B than F-actin which is not organized in fibrils. In cell density-inhibited or suspended in a fluid medium F-actin filaments are insensitive to the action of cytochalasin B, although they are not organized in stress fibers. These results are interpreted to reflect the influence of contact reactions on treadmilling in F-actin filaments.