Analysis of the changes in internalshvctures and mechanical propertiesofvasctilazsmooth naivete cells after tensile strain application

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A system for the analysis of the changes in internal structures and mechanical properties of cultured cells after the application of tensile strain has been designed. Using this system, the stiffness of vascular smooth muscle cells before and after application of static tensile strain have been determined and compared.1. The system consists of an inverted microscope equipped with a confocal laser scanner unit, an atomic force microscope (AFM) unit, and a specially designed cell stretching apparatus. Cells are cultured on a thin silicone membrane that is mounted to the cell stretching apparatus and stretched from its both side at the same time. The bottom of the apparatus is made of cover glass so as to observe the cells from the bottom. The cells adhered to the central portion of the membrane do not move after stretching the membrane. Mechanical properties of the cells can be measured by micro indentation test using the AFM. If intracellular structures were fluorescently stained, the structure can be observed by means of confocal laser scanning microscopy after AFM measurement.2. The strain distribution in single smooth muscle cells was determined from the images of cells and small polystyrene particles attached on the surface of cells recorded before and after the application of 10% static tensile strain. The strain distribution was not uniform even in the cytoplasmic regions; the strain was much larger in the cytoplasmic regions than in the nuclear regions.3. The stiffness of vascular smooth muscle cells was measured with the system before and after stretching their substrate by 10%. A tendency that the stiffness of the cells was increased by the application of strain was observed. The increased stiffness of cells by stretching their substrate might be attributable to the increase in the tension in actin filaments.