ELECTROPORATIVE DEFORMATION OF SALT FILLED LIPID VESICLES

Membrane electroporation, vesicle shape deformation and aggregation of small, NaCl-filled lipid vesicles (of radius a = 50 nm) in DC electri c fields was characterized using conductometric and turbidimetrical da ta, At pulse durations t(E) less than or equal to 55 +/- 5 ms the incr ease in the conductivity of the vesicle suspension is due to the field -induced efflux of electrolyte through membrane electropores. Membrane electroporation and Maxwell stress on the vesicle membrane lead to ve sicle elongation concomitant with small volume reduction (up to 0.6% i n an electric field of E = 1 MV m(-1)). At t(E) > 55 +/- 5 ms, further increases in the conductivity and the optical density suggest electro aggregation and electrofusion of vesicles. The conductivity changes af ter the electric pulse termination reflect salt ion efflux through slo wly resealing electropores, The analysis of the volume reduction kinet ics yields the bending rigidity kappa = (4.1 +/- 0.3) . 10(-20) J of t he vesicle membrane, If the flow of Na+ and Cl(-)ions from the vesicle interior is treated in terms of Hagen-Poiseuille's equation, the numb er of permeable electropores is N = 39 per vesicle with mean pore radi us r(p) = 0.85 +/- 0.05 nm at E = 1 MV m(-1) and t(E) less than or equ al to 55 +/- 5 ms. The turbidimetric and conductometric data suggest t hat small lipid vesicles (a less than or equal to 50 nm) are not assoc iated with extensive membrane thermal undulations or superstructures, In particular with respect to membrane curvature, the vesicle results are suggestive for the design and optimization of electroporative deli very of drugs and genes to cell tissue at small field strengths (less than or equal to 1 MV m(-1)) and large pulse durations (less than or e qual to 100 ms).