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Experimental Estimation of Membrane Tension Induced by Osmotic Pressure.

ABSTRACT: Osmotic pressure (Π) induces the stretching of plasma membranes of cells or lipid membranes of vesicles, which plays various roles in physiological functions. However, there have been no experimental estimations of the membrane tension of vesicles upon exposure to Π. In this report, we estimated experimentally the lateral tension of the membranes of giant unilamellar vesicles (GUVs) when they were transferred into a hypotonic solution. First, we investigated the effect of Π on the rate constant, k_p, of constant-tension (σ_ex)-induced rupture of dioleoylphosphatidylcholine (DOPC)-GUVs using the method developed by us recently. We obtained the σ_ex dependence of k_p in GUVs under Π and by comparing this result with that in the absence of Π, we estimated the tension of the membrane due to Π at the swelling equilibrium, σ_osm^eq. Next, we measured the volume change of DOPC-GUVs under small Π. The experimentally obtained values of σ_osm^eq and the volume change agreed with their theoretical values within the limits of the experimental errors. Finally, we investigated the characteristics of the Π-induced pore formation in GUVs. The σ_osm^eq corresponding to the threshold Π at which pore formation is induced is similar to the threshold tension of the σ_ex-induced rupture. The time course of the radius change of GUVs in the Π-induced pore formation depends on the total membrane tension, σ_t; for small σ_t, the radius increased with time to an equilibrium one, which remained constant for a long time until pore formation, but for large σ_t, the radius increased with time and pore formation occurred before the swelling equilibrium was reached. Based on these results, we discussed the σ_osm^eq and the Π-induced pore formation in lipid membranes.

SUBMITTER: Alam Shibly SU

PROVIDER: S-EPMC5112947 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Many cell division processes have been conserved throughout evolution and are being revealed by studies on model organisms such as bacteria, yeasts, and protozoa. Cellular membrane constriction is one of these processes, observed almost universally during cell division. It happens similarly in all organisms through a mechanical pathway synchronized with the sequence of cytokinetic events in the cell interior. Arguably, such a mechanical process is mastered by the coordinated action of a constriction machinery fueled by biochemical energy in conjunction with the passive mechanics of the cellular membrane. Independently of the details of the constriction engine, the membrane component responds against deformation by minimizing the elastic energy at every constriction state following a pathway still unknown. In this paper, we address a theoretical study of the mechanics of membrane constriction in a simplified model that describes a homogeneous membrane vesicle in the regime where mechanical work due to osmotic pressure, surface tension, and bending energy are comparable. We develop a general method to find approximate analytical expressions for the main descriptors of a symmetrically constricted vesicle. Analytical solutions are obtained by combining a perturbative expansion for small deformations with a variational approach that was previously demonstrated valid at the reference state of an initially spherical vesicle at isotonic conditions. The analytic approximate results are compared with the exact solution obtained from numerical computations, getting a good agreement for all the computed quantities (energy, area, volume, constriction force). We analyze the effects of the spontaneous curvature, the surface tension and the osmotic pressure in these quantities, focusing especially on the constriction force. The more favorable conditions for vesicle constriction are determined, obtaining that smaller constriction forces are required for positive spontaneous curvatures, low or negative membrane tension and hypertonic media. Conditions for spontaneous constriction at a given constriction force are also determined. The implications of these results for biological cell division are discussed. This work contributes to a better quantitative understanding of the mechanical pathway of cellular division, and could assist the design of artificial divisomes in vesicle-based self-actuated microsystems obtained from synthetic biology approaches.

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Experimental Estimation of Membrane Tension Induced by Osmotic Pressure.

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