KINETICS OF THE ELECTROPORATIVE DEFORMATION OF LIPID VESICLES AND BIOLOGICAL CELLS IN AN ELECTRIC-FIELD

The electric conductivity of a suspension of unilamellar lipid vesicle s of phosphatidylcholine and phosphatidylglycerol. filled with electro lyte, increases after exposure to external field pulses. The electroly te efflux through the electropores is described in terms of volume dec rease under Maxwell stress at constant membrane surface area. Applying the Hagen-Poiseuille Ansatz, the exact analytical solution for the ki netics of the electromechanical vesicle deformation is obtained in ter ms of a LambertW function. The initial and final phases of the volume decrease can be approximated by exponential functions with the time co nstants tau and 2 tau, respectively. It is found that tau is proportio nal to E-2.a(9), describing the extreme sensitivity of the deformation to the vesicle radius a in electric field of strength E. The kinetic analysis yields the membrane bending rigidity kappa=3.0+/-0.3.10(-20) J, At the field strength E=1.0 MV m(-1) and in the range of pulse dura tion 5 less than or equal to t(E)/ms less than or equal to 60, the num ber of water-permeable electropores is found to be N=35+/-5 per vesicl e of radius a=50 nm with mean parr radius r(p)=0.9+/-0.1 nm. The kinet ic analysis developed here for vesicles is readily applied to cell mem branes, aiming at physical-chemical guidelines to optimize the membran e electroporation techniques for the direct transfer of drugs and gene s into tissue cells.