Membrane tubulation from giant lipid vesicles in alternating electric fields

We report on the formation of tubular membrane protrusions from giant unilamellar vesicles in alternating electric fields. The construction of the experimental chamber permitted the application of external AC fields with strength of dozens of V/mm and kHz frequency during relatively long time periods (several minutes). Besides the vesicle electrodeformation from quasispherical to prolate ellipsoidal shape, the formation of long tubular membrane protrusions with length of up to several vesicle diameters, arising from the vesicular surface in the field direction, was registered and analyzed. The threshold electric field at which the electro-induced protrusions appeared was lower than the field strengths inducing membrane electroporation.

Figure 1

Schematic presentation of the experimental setup for electrodeformation of GUVs consisting of a flat optical capillary $(200\mu \mathrm{m}$-thick walls at a distance $d=200\mu \mathrm{m})$ and a pair of aluminum electrodes, placed directly on the outside of the capillary glass wall; the distance between the electrodes is $l=2$ mm.

Figure 2

Vesicle morphology under AC voltage of different amplitude $U$ at $f=2$ kHz: (a) $U=0$ V; (b) $U=300$ V; (c) $U=350$ V; (d) $U=500$ V. The bar corresponds to $50\mu \mathrm{m}$.

Figure 3

Dependence of the tether length on the electric field strength for three vesicle radii.

Figure 4

Experimental data for the tube radius $r$ and the corresponding vesicle radius $R$. The error bars are determined from the optical resolution of the system $(0.52\mu \mathrm{m}$/pixel)

Figure 5

Pulling tubular protrusions from a vesicle in alternating electric field. Dotted line denotes the initial quasispherical shape of the vesicle (at $E=0)$. The inset shows the cap's neck with its zero total curvature.

Figure 6

(a) Vesicle morphology under AC voltage of amplitude $U=1200$ V and $f=1$ kHz. Relaxation after switching off the field $(U=0$ V): (b) 1 s; (c) 5 s; (d) 10 s; (e) 20 s. The bar corresponds to $50\mu \mathrm{m}$.