Cytochalasin D does not produce net depolymerization of actin filaments in HEp-2 cells

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Abstract
The altered morphology and disappearance or disruption of actin filaments (microfilaments) in cells treated with cytochalasin has sometimes been attributed to depolymerization of filamentous actin (F-actin) to its globular subunit (G-actin). Treatment of purified actin filaments with cytochalasin B (CB) decreased their viscosity, consistent with depolymerization, which was not revealed by EM, although the filaments appeared abnormal. CB increased the ATP-ase activity of F-actin, suggesting that it had been destabilized while actin filaments in the acrosomal process were not depolymerized. CB or cytochalasin D (CD) dissolved actin gels without depolymerizing their filaments. The disrupted actin structures in CD-treated cells bound heavy meromysin, implying that at least some of the cellular acting was filamentous. Using a rapid assay for G- and F-actin in cell extracts based on the inhibition of DNase I, short- and long-term exposure of HEp-2 cells to CD produced no net depolymerization of actin filaments.