An improved method for studying the elastic properties of erythrocyte membranes.

An improved variation of a technique recently published by Brailsford et al.6 to determine the elastic properties of erythrocytes is presented. The method involves the use of Nuclepore filters (pore diameter, 0.7 im or 1.0 tm and pore density, 2 x 1 0 pores/sq cm), erythrocytes being partially aspirated by the action of positive hydrostatic pressure. The dimensions of the aspirated “tongue,” as observed by SEM after glutaraldehyde fixation, were determined and related to the applied pressure. Selected erythrocytes with a single tongue protruding at or near the center dimpled region of a discoid erythrocyte were measured. The hydrostatic pressure ranged from 200 to 800 dyne/sq cm, and the plot of a dimensionless deformation (D /R ) against a dimensionless tension parameter (P x R / t) was linear with the elastic shear modulus. i = 10.4 x i0 dyne/cm. These results are in agreement with those obtained using the micropipette aspiration technique and differ from the results obtained by Brailsford et al. It is argued that the nonlinear elastic behavior of the erythrocyte membrane that Brailsford et al.6 found using the filter technique may have depended on their experimental conditions, in which, because of the formation of multiple tongues, the whole cell membrane is under tension and the onedimensional extension theory is not applicable.