Membrane electroporation and electromechanical deformation of vesicles andcells

Analysis of the reduced turbidity (Delta T-/T-0) and absorbance (Delta A(-) /A(0)) relaxations of unilamellar lipid vesicles, doped with the diphenylhe xatrienyl - phosphatidylcholine (beta-DPH pPC) lipids in high-voltage recta ngular electrical field pulses, demonstrates that the major part of the tur bidity and absorbance dichroism is caused by vesicle elongation under elect ric Maxwell stress. The kinetics of this electrochemomechanical shape defor mation (time constants 0.1 less than or equal to tau/mu s less than or equa l to 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 m embrane stretching and smoothing of thermal undulations. Moreover, the abso rbance dichroism indicates local displacements of the chromophore relative to the membrane normal in the held. The slightly slower relaxations of the chemical turbidity (Delta T+/T-0) and absorbance (Delta A(+)/A(0)) modes ar e both associated with the entrance of solvent into the interface membrane/ medium, caused by the alignment of the dipolar lipid head groups in one of the leaflets at the pole caps of the vesicle bilayer. In addition, (Delta T +/T-0) indicates changes in vesicle shape and volume. The results for lipid vesicles provide guidelines for the analysis of electroporative deformatio ns of biological cells.