Deformation on normal and fused haematopoietic blasts in ac electric fields

Abstract

Changes in the physical properties of a cell plasma membrane following electrically induced cell fusion have been studied alongside changes in the mechanical properties of the system. This allows direct comparison of the experimental results with the theory of the electromechanical stresses produced in the plasma membrane by electric fields. The geometrical deformation of K-562 cells (Ph + haematopoietic blasts) and their fusates (produced by electric fusion of 2 or 3 K-562 cells) in ac electric fields has been investigated. For electric fields in the range 0–270000 V/m (at a frequency of 370 kHz) the eccentricity of both cells and fusates increased with field strength asymptotically. The effect of field strength on eccentricity was similar for cells and fusates. There was an almost linear relationship between the ratio of the major to the minor semi-axes of cells and fusates and the field strength. Smaller cells underwent larger deformations in an electric field. An increase in electric field intensity caused an increase in the surface area of cells and fusates while the volume of cells and fusates was independent of the field. For a given field strength, cell and fusate deformation increased with excitation frequency over the range 100–450 kHz, with a broad peak in the region 350–450 kHz, and was almost constant at higher frequencies. A time constant of approximately 15 s was obtained for deformation of K-562 cells and two- and three-nuclei fusates. The dynamics of cell and fusate deformation indicates that 50 s after exposure to an electric field no additional changes in geometrical deformation occurred. For small deformations the restoring stress is probably dominated by the mechanical stress set up in the membrane. Employing Maxwell's tensor for the distorting force ensures consistency between theory and the experimental results.