Tension-induced pore formation and leakage in adhering vesicles

– The influence of inclusion-induced tension on pore formation is studied theoretically and experimentally. It is shown that fluorescently labeled lipids can enhance pore formation and induce leakage of adhering vesicles. These effects are more pronounced for smaller vesicles. The theoretical predictions are confirmed by experimental two-color fluorescent data. Finally, the influence of the pore formation dynamics on rupture processes of vesicles is analyzed yielding a new picture of the transition to bilayer disks. Supported lipid bilayers provide an ideal system for the investigation of cellular membrane interactions [1] such as formation of the immunological synapse [2] and SNARE driven vesicle fusion in simplified environments [3]. They are also the basis for a variety of bio-sensors [4–6]. There are several methods of forming supported bilayers, including deposition by LangmuirBlodgett techniques [7], spreading over a surface from a bulk lipid source [8], or simply by vesicle fusion to a substrate [9]. The fundamental mechanisms leading to bilayer formation via vesicle fusion are only partially understood. It is generally believed that it proceeds via the following steps: i) vesicle adhesion, ii) vesicle fusion, and iii) vesicle rupture. This picture relies strongly on the theory developed by Lipowsky and Seifert [10,11]. In [11] it has been predicted that with increasing volume (driven by vesicle-vesicle fusion events) the adsorbed vesicles become flatter and flatter until at a critical rupture radius R∗ bd they undergo a transition to a bilayer disk. This has been confirmed in recent experimental studies [12–14]; however, in [15] R∗ bd was found to be higher than theoretically expected. There are experimental indications [16] that the strength of the adhesion potential W is a critical parameter in these processes which would explain why supported bilayers only form on very few substrates, namely those with large enough W . Fusion and rupture transitions lead to a change in the vesicle’s topology and thus require (as an essential step) the formation of holes, i.e. pores. In this paper, we analyze the influence of inclusion-induced tension on pore formation. This work focuses on adhering vesicles with a c © EDP Sciences Article published by EDP Sciences and available at http://www.edpsciences.org/epl or http://dx.doi.org/10.1209/epl/i2006-10150-5 660 EUROPHYSICS LETTERS