Effect of cytochalasin D on the mechanical properties and morphology of passive human neutrophils

The actin-rich cortex plays a major role in neutrophil chemotaxis and phagocytosis. In passive neutrophils, 30-50% of the actin molecules are in the F (filamentous) form, and it is the shifting of equilibrium with its monomeric G (globular) form that controls cell motility and phagocytosis. Cytochalasins have been shown to inhibit cell phagocytosis and ruffling. In purified actin, cytochalasins have been shown to decrease the amount of F-actin by capping the fast-growth end of actin filaments. Recent studies with intact cells, however, reveal that the most potent cytochalasin, cytochalasin D (CD), actually increases F-actin content suggesting that CD disrupts the actin network so as to increase the number of actin-filament ends for further actin polymerization. In this paper, we report the effects of CD on the passive mechanical behavior and morphology of human neutrophils with 1, 2, 10, and 20 microM CD. At 1 and 2 microM CD, the cells remain spherical. However, in the presence of 10 and 20 microM CD, cells are severely deformed and "blebby" as shown by light and scanning electron microscopy. After 1 and 2 microM CD treatment, the cells show a decrease of 43 and 66%, respectively, in cortical tension when measured by static micropipet aspiration experiments. Similarly, the cytoplasmic viscosities of 1 and 2 microM CD-treated cells are decreased, but only by 17 and 24%, respectively. A proportionally greater effect on the cortical tension suggests that CD acts mainly on the actin-rich cortex by disrupting the filament network.