Use of a Laser Interference Microscope for Estimating Fluctuations and the Equivalent Elastic Constant of Cell Membranes

— An automated interference microscope has been used to determine the rms amplitude of fluctuations of living cells in vitro . The geometric thickness of cells has been calculated based on the measured optical path differences of light waves and the equivalent elastic constants of these cells have been estimated. The determined rms amplitude of fluctuations of the optical path difference is 0.3–2.7 nm, which corresponds to 4–40 nm rms amplitude of membrane-thickness fluctuations. The amplitudes of fluctuations of spread cells (endothelial cells and macrophages) are smaller relative to unattached cells ( in vitro red blood cells and lymphocytes). At the same time, the amplitude of fluctuations observed in HeLa tumor cells spread on a substrate exceeds the amplitude of fluctuations of other spread cells (endothelial cells and macrophages). The obtained experimental data are in agreement with the earlier results obtained using other optical methods.