membranemembrane_tenisonphase_separation
question: does increasing membrane tension promote or inhibit membrane phase separation
from FliptR paper
The last possibility to explain the coupled changes in lifetime and tension was that tension changes induce phase separation (Fig. 4d). Recent studies have shown that changes in tension can cause a lipid phase separation to accommodate the area change46,47,48,49,50,51. In such a case, while the membrane is initially homogeneous, domains appear on increasing the membrane tension. The newly formed Ld phase supports most of the stretch, while Lo domains cluster the lipids that cannot be stretched easily.
46 Mixing Water, Transducing Energy, and Shaping Membranes: Autonomously Self-Regulating Giant Vesicles link in 3.1.2 When subject to hypotonic conditions as described above, the optically homogeneous vesicles break up into surface patterns consisting of large microscopic rounded liquid-disordered domains bounded by a spatially continuous liquid-ordered region.
hypotonic shock allow more water flow in to balance osmolarity thus increase volume as well as surface area which increases membrane tension. tension ↑ → phase separation ↑
the author in 46 didn’t do the experiment, it is from Sarah’s paper in 2005 (need further invesitgation) no it is not from sarah’s paper, it is actually the original 47. sarah’s paper didn’t cover any tension mediated change but only different composition
47 Oscillatory phase separation in giant lipid vesicles induced by transmembrane osmotic differentials link this is also cited in 46
cholesterol (Ch), sphingomyelin (SM), and the unsaturated phospholipid, POPC (1-palmitoyl-2-oleoyl-sn-1-glycero-3-phosphocholine) are the GUV(1:1:1) used in 47, 0.5 mol% of Rho-DPPE was used to fluorescently label phase. after dilution of extra-vesicular medium, the initially homogenous GUV changed into a phase separated one.
48 Shape Deformation of Ternary Vesicles Coupled with Phase Separation a little bit technical
for sphere condition, lowering temperature from 60C to 24C + add salt, spherical GVs(DPPC/DOPC/Chol = 4/4/2.) began to show small domains pointing outwards.
49 Osmotic Gradients Induce Bio-Reminiscent Morphological Transformations in Giant Unilamellar Vesicles
this one is super weird seems like both hypo- hyper- osmotic shock could result in separation (as put in this paper, negative→ hypo, positive → hyper)
50 Three dimensional (temperature–tension–composition) phase map of mixed DOPC–DPPC vesicles: Two solid phases and a fluid phase coexist on three intersecting planes
51 Lateral phase separation in tense membranes
also osmotic pressure
from paper Osmotic-Tension-Induced Membrane Lateral Organization | Langmuir (acs.org)
They measured phase diagram under different temperature with different tension in GPMVs (using 180mM hypotonic shock). there is an increase in the miscibility temperature upon hypotonic shock, which is contradictory to Sarah kellar’s pipette aspiration result
also this effect is reduced with less cholesterol in the GPMV.