Abstract
In this study we report a physical analysis of the membrane mechanics affecting the size of the highly curved region of a lipid nanotube (LNT) that is either connected between a lipid bilayer vesicle and the tip of a glass microinjection pipette (tube-only) or between a lipid bilayer vesicle and a vesicle that is attached to the tip of a glass microinjection pipette (two-vesicle). For the tube-only configuration (TOC), a micropipette is used to pull a LNT into the interior of a surface-immobilized vesicle, where the length of the tube L is determined by the distance of the micropipette to the vesicle wall. For the two-vesicle configuration (TVC), a small vesicle is inflated at the tip of the micropipette tip and the length of the tube L is in this case determined by the distance between the two interconnected vesicles. An electrochemical method monitoring diffusion of electroactive molecules through the nanotube has been used to determine the radius of the nanotube R as a function of nanotube length L for the two configurations. The data show that the LNT connected in the TVC constricts to a smaller radius in comparison to the tube-only mode and that tube radius shrinks at shorter tube lengths. To explain these electrochemical data, we developed a theoretical model taking into account the free energy of the membrane regions of the vesicles, the LNT and the high curvature junctions. In particular, this model allows us to estimate the surface tension coefficients from R(L) measurements.
Highlights
Membrane tethers have been studied extensively over the past 40 years [1,2,3,4,5,6,7,8,9,10,11]
We developed an electrochemical method to monitor the diffusion of electroactive molecules through the lipid nanotube (LNT), allowing the LNT diameter to be measured as a function of nanotube length [11]
The experimental observations show that the nanotube diameter is reduced at shorter lengths and that the diameter is consistently smaller for the two-vesicle configuration (TVC) as compared to the tube-only configuration (TOC) for a given length
Summary
Membrane tethers have been studied extensively over the past 40 years [1,2,3,4,5,6,7,8,9,10,11]. These structures, called membrane nanotubes, were observed during fluid shear deformation of live cells attached to a substrate. It has been reported that cells have the ability to use membrane nanotubes for the exchange of organelles [7], and this
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