<title>Big softer hole on living cells: elasticity imaging with AFM</title>

We have focused on effects of local mechanical properties of the cell on cell motion. By using atomic force microscopy, we measured spatial distribution of local elastic modulus on mouse fibroblasts, which is living in a physiological condition. In order to examine validity of AFM elastic measurements, we measured local elastic modulus of gels as elastic reference materials. The results obtained with AFM were compared with values obtained by tensile creep method. It is verified that these values are proportional each other. The AFM experiments on living cells revealed that center area of cell surface is about 10 times softer than the surroundings and looks like a big softer hole in the elasticity image. We fixed the cell just after the AFM measurements and carried out immunofluorescence observation for cytoskeletal filaments of actin filaments, microtubules and intermediate filaments. A comparison between distribution of local elasticity and cytoskeletones indicates that harder area on the cell results mainly from concentration of actin filaments. However, we found that some areas like the big softer hole do not correspond to distribution of actin filaments.