Cytochalasin
 
 Cytochalasins are a group of fungal metabolites that can permeate cell membranes and exert very strong effects on the cytoskeleton: ruffling and translocation are stopped, and cells round up (1, 2).  In addition, cytochalasins A and B also inhibit glucose transport across the plasma membrane. Although it was originally believed that the main action of the cytochalsins on the cytoskeleton was binding with high affinity to the barbed, or fast-growing end of the actin filament, and inhibiting subunit addition and loss, it has become clear that the effects are more complex. The concentrations of cytochalasins used in cell biological experiments will have strong effects on actin monomers and may convert much of a cell's monomeric G-ATP actin to G-ADP actin (3). In addition, even at saturating concentrations cytochalasins do not completely block the fast-growing ends with respect to subunit addition or loss (3). Thus, the action of cytochalsin on a living cell is likely to be complicated and may affect the interactions of actin with many actin-binding proteins. Nevertheless, as a result of the large effect cytochalsins have on actin, they have been widely used to study the role of the actin cytoskeleton in cellular processes.
References
1. I. Yahara, F. Harada, S. Sekita, K. Yoshihira, and S. Natori (1982) J. Cell Biol. 92, 69–78.
2. M. Schliwa (1982) J. Cell Biol. 92, 79–91. 
3. P. Sampath and T. D. Pollard (1991) Biochemistry 30, 1973–1980