Electrodeformation of DMPC vesicle membranes near the main phase transition

The physical properties of lipid membranes are essential to cellular function, with membrane fluidity playing a key role in the mobility of embedded biomolecules. Fluidity is governed by the membrane's phase state, which is known to depend on composition and temperature. However, in living cells, the transmembrane electric potential may also influence membrane fluidity. In this study, we use giant unilamellar vesicles composed of dimyristoylphosphatidylcholine to examine the membrane's response to electric fields near its main phase transition temperature. Below the transition temperature, the vesicle remains undeformed, indicating a bilayer in the gel phase. However, near the transition, the vesicle elongates into an ellipsoid, and the evolution of the aspect ratio exhibits a two-step response: an initial rapid increase followed by a slower elongation. Electrodeformation experiments at various temperatures relative to the transition temperature T_m reveal that the duration of the fast step increases as the temperature approaches T_m, and the slow step vanishes for a bilayer the fluid phase. We attribute the initial rapid response to the fluid phase and the subsequent slow response to a thermal expansion induced by Joule heating from the electric field.