Actin microfilaments transmit traction and contraction forces generated within a cell to the extracellular matrix during embryonic development, wound healing and cell motility, and to maintain tissue structure and tone. Therefore, the state of the actin cytoskeleton strongly influences the mechanical properties of cells and tissues. Cytochalasin D and Latrunculin are commonly used reagents that, by different mechanisms, alter the state of actin polymerization or the organization of actin filaments. We have investigated the effect of a wide range of Cytochalasin D and Latrunculin B concentrations (from 40 pM to 10 microM) on the mechanical properties of the cells within fibroblast populated collagen matrices. Contractile force and dynamic stiffness were measured by uniaxial stress-strain testing. The range of effective concentrations of Cytochalasin D (200 pM-2 microM) was broader than that of Latrunculin B (20 nM-200 nM). Activating the cells by serum did not change the effective range of Cytochalasin D concentrations but shifted that of Latrunculin B upward by tenfold. Simple mathematical binding models based on the presumed mechanisms of action of Cytochalasin D and Latrunculin B simulated the concentration-dependent mechanical changes reasonably well. This study shows a strong dependence of the mechanical properties of cells and tissues on the organization and degree of polymerization of actin filaments.

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