Water Permeability and Mechanical Strength of Polyunsaturated Lipid Bilayers

Abstract

Micropipette aspiration was used to test mechanical strength and water permeability of giant-fluid bilayer vesicles composed of polyunsaturated phosphatidylcholine PC lipids. Eight synthetic-diacyl PCs were chosen with 18 carbon chains and degrees of unsaturation that ranged from one double bond (C18:0/1, C18:1/0) to six double bonds per PC molecule (diC18:3). Produced by increasing pipette pressurization, membrane tensions for lysis of single vesicles at 21 degrees C ranged from approximately 9 to 10 mN/m for mono- and dimono-unsaturated PCs (18:0/1, 18:1/0, and diC18:1) but dropped abruptly to approximately 5 mN/m when one or both PC chains contained two cis-double bonds (C18:0/2 and diC18:2) and even lower approximately 3 mN/m for diC18:3. Driven by osmotic filtration following transfer of individual vesicles to a hypertonic environment, the apparent coefficient for water permeability at 21 degrees C varied modestly in a range from approximately 30 to 40 microm/s for mono- and dimono-unsaturated PCs. However, with two or more cis-double bonds in a chain, the apparent permeability rose to approximately 50 microm/s for C18:0/2, then strikingly to approximately 90 microm/s for diC18:2 and approximately 150 microm/s for diC18:3. The measurements of water permeability were found to scale exponentially with the reduced temperatures reported for these lipids in the literature. The correlation supports the concept that increase in free volume acquired in thermal expansion above the main gel-liquid crystal transition of a bilayer is a major factor in water transport. Taken together, the prominent changes in lysis tension and water permeability indicate that major changes occur in chain packing and cohesive interactions when two or more cis-double bonds alternate with saturated bonds along a chain.

Confined Bilayers Passively Regulate Shape and Stress

“…4(c), filled circle], whereas in a stronger hyperosmotic shock, the elongation proceeds more rapidly Theoretically, we can fit the tube dynamics by using a permeation coefficient 60 times smaller than the one used in Fig. 4(a) or reported for DOPC vesicles under tension [24]. We rationalize the reduced water permeation by the decreased area per lipid in the tubes under negative tension, consistent with previous experiments on bilayers of different composition [25].…”

“…where P f is the osmotic water permeation coefficient [24,25], V w is the volume of a water molecule, and S m is the surface area of the semipermeable membrane. In hypoosmotic conditions, we observe that the apparent diameter of most buds grows monotonically (vertical paths in Fig.…”

ArfGAP1 promotes COPI vesicle formation by facilitating coatomer polymerization

“…In some work, dioleoyl lipids were used, with the most efficient effects observed with dioleoyl-phosphatidic acid. 58 The high content of unsaturated lipid increases the elasticity of the bilayer 59,60 and, consequently, the membranes are easier to deform. Phosphatidic acid, used in as least two reports 58,61 induces membrane curvature, [62][63][64] which would favor vesicle budding.…”

Electromechanical Limits of Polymersomes

“…Assuming incompressibility, the thickness at rupture is given by d c d͑͞1 1 a c ͒, where a c is the area strain at rupture as measured directly from images of aspirated vesicles. For lipids, a c is very small, typically 0.03 0.05 [18] (Fig. 2).…”