Membrane electroporation and electromechanical deformation of vesicles and cells

Analysis of the reduced turbidity (delta T-/T0) and absorbance (delta A-/A0) relaxations of unilamellar lipid vesicles, doped with the diphenylhexatrienyl-phosphatidylcholine (beta-DPH pPC) lipids in high-voltage rectangular electrical field pulses, demonstrates that the major part of the turbidity and absorbance dichroism is caused by vesicle elongation under electric Maxwell stress. The kinetics of this electrochemomechanical shape deformation (time constants 0.1 < or = tau/microsecond < or = 3) is determined both by the entrance of water and ions into the bulk membrane phase to form local electropores, and by the faster processes of membrane stretching and smoothing of thermal undulations. Moreover, the absorbance dichroism indicates local displacements of the chromophore relative to the membrane normal in the field. The slightly slower relaxations of the chemical turbidity (delta T+/T0) and absorbance (delta A+/A0) modes are both associated with the entrance of solvent into the interface membrane/medium, caused by the alignment of the bipolar lipid head groups in one of the leaflets at the pole caps of the vesicle bilayer. In addition, (delta T+/T0) indicates changes in vesicle shape and volume. The results for lipid vesicles provide guidelines for the analysis of electroporative deformations of biological cells.