IMAGING OF THE SURFACE OF LIVING CELLS BY LOW-FORCE CONTACT-MODE ATOMIC-FORCE MICROSCOPY

The membrane surface of living CV-1 kidney cells in culture was imaged by contact-mode atomic force microscopy using scanning forces in the piconewton range. A simple procedure was developed for imaging of the cell surface with forces as low as 20-50 pN, i.e., two orders of magni tude below those commonly used for cell imaging. Under these condition s, the indentation of the cells by the tip could be reduced to less th an 10 nm, even at the cell center, which gave access to the topographi c image of the cell surface. This surface appeared heterogeneous with very few villosities and revealed, only in distinct areas, the submemb rane cytoskeleton. At intermediate magnifications, corresponding to 20 -5 mu m scan sizes, the surface topography likely reflected the organi zation of submembrane and intracellular structures on which the plasma membrane lay. By decreasing the scan size, a lateral resolution bette r than 20 nm was routinely obtained for the cell surface, and a latera l resolution better than 10 nm was obtained occasionally. The cell sur face appeared granular, with packed particles, likely corresponding to proteins or protein-lipid complexes, between similar to 5 and 30 nm x y size.