Atomic force pulling: probing the local elasticity of the cell membrane

We present a novel approach, based on atomic force microscopy, for exploring the local elastic properties of the membrane-skeleton complex in living cells. Three major elements constitute the basis for the proposed method: (1) pulling the cell membrane by increasing the adhesion of the tip to the cell surface provided via appropriate tip modification; (2) measuring force-distance curves with emphasis on selecting the appropriate withdrawal regions for analysis; (3) fitting of the theoretical model for axisymmetric bending of an annular thick plate to the experimental curve in the withdrawal region, prior to the detachment point of the tip from the cell membrane. This approach, applied to human erythrocytes, suggests a complimentary technique to the commonly used methods. The local use of this methodology for determining the bending modulus of the cell membrane of the human erythrocyte yields a value of (2.07 +/- 0.32) x 10(-19) J.