Experimental Estimation of Membrane Tension Induced by Osmotic Pressure

Abstract

Osmotic pressure (P) 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 P. 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 P on the rate constant, k p , of constant-tension (s ex )-induced rupture of dioleoylphosphatidylcholine (DOPC)-GUVs using the method developed by us recently. We obtained the s ex dependence of k p in GUVs under P and by comparing this result with that in the absence of P, we estimated the tension of the membrane due to P at the swelling equilibrium, s eq osm . Next, we measured the volume change of DOPC-GUVs under small P. The experimentally obtained values of s eq osm and the volume change agreed with their theoretical values within the limits of the experimental errors. Finally, we investigated the characteristics of the P-induced pore formation in GUVs. The s eq osm corresponding to the threshold P at which pore formation is induced is similar to the threshold tension of the s ex -induced rupture. The time course of the radius change of GUVs in the P-induced pore formation depends on the total membrane tension, s t ; for small s t , the radius increased with time to an equilibrium one, which remained constant for a long time until pore formation, but for large s t , the radius increased with time and pore formation occurred before the swelling equilibrium was reached. Based on these results, we discussed the s eq osm and the P-induced pore formation in lipid membranes.

Differential interactions of bacterial lipopolysaccharides with lipid membranes: implications for TRPA1-mediated chemosensation

“…Therefore, changes in membrane physical properties such as order, tension, thickness and curvature resulting from the insertion of LPS in the close vicinity of the channel might in principle alter the TRPA1-bilayer interaction that may induce channel opening 46 . However, if considering that bilayer stretching is associated with membrane fluidization 47 , our results indicate that LPS produces lateral compression. This indicates, in turn, that the mechanism underlying TRPA1 activation by LPS is different from that operating in “classical” mechanosensitive channels activated by membrane stretch 48 – 50 .…”

Pore formation in lipid membrane II: Energy landscape under external stress

“…In the work ref. 47 , GUVs were initially held to the micropipette by a small hydrostatic pressure generating the lateral tension of ∼0.5 mN/m, which is a widely used procedure allowing to release the so-called hidden area of the membrane 48 . After 2 minutes, the tension was rapidly increased to the desired value (7–8 mN/m) and maintained constant until GUV rupture.…”

Effect of membrane tension on transbilayer movement of lipids

“…Several external factors such as forces, 1,2 electric fields, 3 and osmotic pressure 4 produce lateral membrane tension in the plasma membranes of cells and the lipid bilayers of vesicles, inducing stretching and compression of these membranes. It is well known that this stretching affects the physical properties of the membranes as well as the functions of membrane proteins.…”

“…The tension-induced pore formation and rupture of vesicles have been investigated using giant unilamellar vesicles (GUVs). [1][2][3][4][6][7][8][9] Theorizing about tension-induced pore formation has led to the development of the following well-recognized model. [10][11][12] Thermal fluctuations of lipid bilayers are believed to induce various transient rarefactions (i.e., areas of the lower lipid density).…”