Effect of actin filament distribution on tensile properties of smooth muscle cells obtained from rat thoracic aortas

Tensile properties and actin filament distribution of rat aortic smooth muscle cells (SMCs) were measured in the same cells to correlate the mechanical properties of cells with their cytoskeleton. The cells freshly isolated from rat thoracic aorta with enzymatic dispersion (FSMCs), cultured cells (CSMCs), and CSMCs treated with cytochalasin D to disrupt their actin filaments (CSMCs-CYD) were stretched in a Ca²⁺-Mg²⁺-free Hank's balanced salt solution at 37°C with an originally designed micro tensile tester. Some of CSMCs and CSMCs-CYD were fixed and stained with rhodamine phalloidin for actin filament after the tensile test while they remained attached to the tester. The force-elongation curves were almost linear for all of the three groups. Normalized stiffness E_all obtained from the slope of the curves was significantly different among groups and was 11.0±1.9 kPa (mean±SEM, n=8), 2.6±0.5 kPa (n=21), 1.5±0.2 kPa (n=13), for FSMCs, CSMCs, and CSMCs-CYD, respectively. Relative concentration of the actin filament in the central region of the cell F has significant positive correlation with E_all both for CSMCs and CSMCs-CYD. The slope of the regression line ΔE_all/ΔF was much higher in the CSMCs than in the CSMCs-CYD. These results indicate that elastic properties of smooth muscle cells may be affected not only by the amount of their actin filaments, but also by their organization and distribution in cells.