Protoplast Dielectrophoresis in Axisymmetric Fields

Pea protoplasts dielectrophoretic coefficients were measured in alternating electric fields of frequency 1 MHz and voltage 5 V applied between two concentric cylindrical metal electrodes of outer and inner radii 0.24 mm and 1 mm, respectively. They do not vary significantly with solution osmolarity, but* show a clear expressed maximum in isotonic conditions; the values in 0.4 m , 0.5 m , 0.6 m and 0.7 m manitol solutions are (6.5, 10.2, 8.8 and 5.6) x lO*24 A 2s4/kg, respectively. The average cell radii in those conditions are 14.2 (im, 14.6 [im, 13.8 jim and 13.6 [im. The radii of cell-to-electrode contacts follow the same dependence on the osmolarity as the dielectrophoretic coefficients; they do not depend on the applied voltages up to 18V. The times of cell approach near to the electrode were too short to be explained by the action only of the dielectrophoretic force; consequently an attractive force appeared at very close approach. These results may be of use in future studies of membrane adhesion and fusion.