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Mechanics of lipid bilayer junctions affecting the size of a connecting lipid nanotube.

Karlsson R, Kurczy M, Grzhibovskis R, Adams KL, Ewing AG, Cans AS, Voinova MV - Nanoscale Res Lett (2011)

Bottom Line: 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.In particular, this model allows us to estimate the surface tension coefficients from R(L) measurements.

View Article: PubMed Central - HTML - PubMed

Affiliation: BioNano Systems Laboratory, Institute for Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg, Sweden. marina.voinova@chalmers.se.

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.

No MeSH data available.


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Experimental configurations. Sketches of the geometries of the large unilamellar vesicles interconnected with a common LNT; (A) the "two-vesicle" configuration, where the LNT is connected between the mother vesicle and a small daughter vesicle inside of the mother vesicle, (B) the "tube-only" configuration where the LNT is connected between the tip of a glass pipette and the giant unilamellar vesicle.
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Figure 1: Experimental configurations. Sketches of the geometries of the large unilamellar vesicles interconnected with a common LNT; (A) the "two-vesicle" configuration, where the LNT is connected between the mother vesicle and a small daughter vesicle inside of the mother vesicle, (B) the "tube-only" configuration where the LNT is connected between the tip of a glass pipette and the giant unilamellar vesicle.

Mentions: Following their initial discovery, the lipid membrane nanotubes (LNTs) have been created artificially in several model membrane systems. By attaching a bead or a micropipette to a point on the membrane and applying a localized mechanical force to the bilayer surface it has been shown that a lipid tether can be pulled from the vesicle membrane [3-5,11]. The size of the structure is a result of the interplay between the curvature elasticity effects maintaining the original geometry and the membrane tension [12]. Tether pulling experiments can be used for estimations of tube diameters. By measuring the forces required for pulling a tube, the diameter of the LNTs were estimated to be 50-200 nm [13]. From a tube coalescence method [14] and video pixel analysis of accumulated fluorescence images as well as from micrographs obtained with differential interference contrast optics [5], the LNT diameters were determined to be in the range of 100-300 nm [13]. To complement these methods, we developed an electrochemical method to monitor the diffusion of electroactive molecules through the LNT, thus allowing the LNT diameter to be measured as a function of nanotube length [11]. The method relies on the formation of a vesicle-LNT network by using a micropipette technique [5,15]. The micropipette-assisted vesicle-LNT network formation allows us to create complex systems of vesicles interconnected by LNTs, including a so-called inward configuration where a small daughter vesicle is created inside a larger mother vesicle, the two vesicles being connected by a LNT [6] (see Figure 1A). During network formation, the LNT is pulled with a micropipette to the interior of the vesicle and thus the opening of the tube faces outward to the exterior of the vesicle. This makes it possible to monitor the diffusion of a marker molecule from the micropipette, through the tube, and out of the nanotube opening. The concentration of the molecules measured at the opening of the LNT is directly related to the inner diameter of a LNT of determined length [11]. In this article we use the electrochemical method for monitoring the size of a nanotube attached directly to the micropipette in the configuration we refer to as the tube-only configuration (TOC) (see Figure 1B).


Mechanics of lipid bilayer junctions affecting the size of a connecting lipid nanotube.

Karlsson R, Kurczy M, Grzhibovskis R, Adams KL, Ewing AG, Cans AS, Voinova MV - Nanoscale Res Lett (2011)

Experimental configurations. Sketches of the geometries of the large unilamellar vesicles interconnected with a common LNT; (A) the "two-vesicle" configuration, where the LNT is connected between the mother vesicle and a small daughter vesicle inside of the mother vesicle, (B) the "tube-only" configuration where the LNT is connected between the tip of a glass pipette and the giant unilamellar vesicle.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211838&req=5

Figure 1: Experimental configurations. Sketches of the geometries of the large unilamellar vesicles interconnected with a common LNT; (A) the "two-vesicle" configuration, where the LNT is connected between the mother vesicle and a small daughter vesicle inside of the mother vesicle, (B) the "tube-only" configuration where the LNT is connected between the tip of a glass pipette and the giant unilamellar vesicle.
Mentions: Following their initial discovery, the lipid membrane nanotubes (LNTs) have been created artificially in several model membrane systems. By attaching a bead or a micropipette to a point on the membrane and applying a localized mechanical force to the bilayer surface it has been shown that a lipid tether can be pulled from the vesicle membrane [3-5,11]. The size of the structure is a result of the interplay between the curvature elasticity effects maintaining the original geometry and the membrane tension [12]. Tether pulling experiments can be used for estimations of tube diameters. By measuring the forces required for pulling a tube, the diameter of the LNTs were estimated to be 50-200 nm [13]. From a tube coalescence method [14] and video pixel analysis of accumulated fluorescence images as well as from micrographs obtained with differential interference contrast optics [5], the LNT diameters were determined to be in the range of 100-300 nm [13]. To complement these methods, we developed an electrochemical method to monitor the diffusion of electroactive molecules through the LNT, thus allowing the LNT diameter to be measured as a function of nanotube length [11]. The method relies on the formation of a vesicle-LNT network by using a micropipette technique [5,15]. The micropipette-assisted vesicle-LNT network formation allows us to create complex systems of vesicles interconnected by LNTs, including a so-called inward configuration where a small daughter vesicle is created inside a larger mother vesicle, the two vesicles being connected by a LNT [6] (see Figure 1A). During network formation, the LNT is pulled with a micropipette to the interior of the vesicle and thus the opening of the tube faces outward to the exterior of the vesicle. This makes it possible to monitor the diffusion of a marker molecule from the micropipette, through the tube, and out of the nanotube opening. The concentration of the molecules measured at the opening of the LNT is directly related to the inner diameter of a LNT of determined length [11]. In this article we use the electrochemical method for monitoring the size of a nanotube attached directly to the micropipette in the configuration we refer to as the tube-only configuration (TOC) (see Figure 1B).

Bottom Line: 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.In particular, this model allows us to estimate the surface tension coefficients from R(L) measurements.

View Article: PubMed Central - HTML - PubMed

Affiliation: BioNano Systems Laboratory, Institute for Microtechnology and Nanoscience, Chalmers University of Technology, 41296 Gothenburg, Sweden. marina.voinova@chalmers.se.

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.

No MeSH data available.


Related in: MedlinePlus