Phase-state dependent current fluctuations in pure lipid membranes.

Current fluctuations in pure lipid membranes have been shown to occur under the influence of transmembrane electric fields (electroporation) as well as a result from structural rearrangements of the lipid bilayer during phase transition (soft perforation). We demonstrate that the ion permeability during lipid phase transition exhibits the same qualitative temperature dependence as the macroscopic heat capacity of a D15PC/DOPC vesicle suspension. Microscopic current fluctuations show distinct characteristics for each individual phase state. Although current fluctuations in the fluid phase show spikelike behavior of short timescales (approximately 2 ms) with a narrow amplitude distribution, the current fluctuations during lipid phase transition appear in distinct steps with timescales of approximately 20 ms. We propose a theoretical explanation for the origin of timescales and permeability based on a linear relationship between lipid membrane susceptibilities and relaxation times near the phase transition.

Phase transition induced fission in lipid vesicles.

In this work we demonstrate how the first order phase transition in giant unilamellar vesicles (GUVs) can function as a trigger for membrane fission. When driven through their gel-fluid phase transition GUVs exhibit budding or pearl formation. These buds remain connected to the mother vesicle presumably by a small neck. Cooling these vesicles from the fluid phase (T>T(m)) through the phase transition into the gel state (T

Thermodynamic relaxation drives expulsion in giant unilamellar vesicles.

We investigated the thermodynamic relaxation of giant unilamellar vesicles (GUVs) which contained small vesicles within their interior. Quenching these vesicles from their fluid phase (T > T(m)) through the phase transition in the gel state (T < T(m)) drives the inner vesicles to be expelled from the larger mother vesicle via the accompanying decrease in the vesicle area by approximately 25% which forces a pore to open in the mother vesicle. We demonstrate that the proceeding time evolution of the resulting efflux follows the relaxation of the membrane area and describes the entire relaxation process using an Onsager-like non-equilibrium thermodynamics ansatz. As a consequence of the volume efflux, internal vesicles are expelled from the mother vesicle. Although complete sealing of the pore may occur during the expulsion, the global relaxation dynamics is conserved. Finally, comparison of these results to morphological relaxation phenomena found in earlier studies reveals a universal relaxation behaviour in GUVs. When quenched from the fluid to gel phase the typical time scale of relaxation shows little variation and ranges between 4 and 5 s.