| Summary: | The stress relaxation test was performed for cultured rat aortic smooth muscle cells (SMCs) to investigate the effect of actin filaments (AFs) on viscoelastic properties of the cells. Untreated cells and cells treated with cytochalasin D to disrupt their AFs were stretched by 70-85%, and their length was kept constant with a laboratory-made micro tensile tester with feed-back control to obtain their stress relaxation curve. Viscoelastic analysis with 4-parameter Maxwell model showed that the stress relaxation process of the cells could be divided into two phases with different time constants: a fast phase with a time constant in the order of minutes, and a slow phase with a time constant in the order of hours. Elastic parameters in the two phases decreased similarly by about a half with AF disruption. Viscous parameters also decreased by ∼1/3 and ∼1/4 in the fast and the slow phase, respectively, with AF disruption. No difference was observed for the relaxation time constant in the fast phase in response to AF disruption, while the time constant in the slow phase decreased significantly by about a half. Fluctuation in tension was observed in the stress relaxation curve of the untreated cells. Such fluctuation disappeared in cells treated with cytochalasin D. These results indicates that AFs have significant effects on viscosity of SMCs in the slow phase and on the fluctuation in tension, both of which may be caused by the dynamic change of AFs.
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