Lipid membrane deformation in response to a local pH modification: theory and experiments

Abstract

We study the deformation of a lipid membrane in response to a local pH modification. Experimentally, a basic solution is microinjected close to a giant unilamellar vesicle. A local deformation appears in the zone of the membrane that is closest to the micropipette, and relaxes when the injection is stopped. A theoretical description of this phenomenon is provided. It fully takes into account the spatiotemporal evolution of the concentration of hydroxide ions during and after the microinjection, as well as the linear dynamics of the membrane. This description applies to a local injection of any substance that reacts reversibly with the membrane lipids. We compare experimental data obtained in the domain of small deformations to the results of our linear description, and we obtain a good agreement between theory and experiments. In addition, we present direct experimental observations of the pH profile on the membrane during and after the microinjection, using pHsensitive fluorescent lipids.

Electrohydrodynamic instability of a capacitive elastic membrane

“…For example, the pH values of the solvents are known to affect the lipid membrane stability. 24 We are now investigating how the electrohydrodynamic instability reported in this work might be affected by the pH values of solvents.…”

Chemotactic Amoeboid-Like Shape Change of a Vesicle under a pH Gradient

“…This is responsible for the pseudopod-like extrusion toward the higher-pH side. 20 To confirm the effect of the pH gradient, we used HCl as the diffusing species. The pseudopod-like structures were extruded toward the side of the vesicle surrounded by the higher pH in this experiment as well (see SI Figure S4-1).…”

On the hydrodynamics of bilayer membranes

“…Standard parameter values are eC 1 nm, k C 0:1 J/m 2 , κ C 10 À 19 J, bC10 9 J s/m 4 , η s C10 À 9 J s/m 2 and η C 10 À 3 J s/m 3 [17][18][19][20]11]. It follows that the relaxation time τ ¼ 2ðη=q þ η s Þ=k in (60) is extremely short, e.g., of order τ C 10 ns for π=q C 1 μ m. This is because the average density ρ relaxes without causing any intermonolayer friction.…”

“…In the early studies of membrane hydrodynamics the bilayer structure of the membrane was neglected [5,6]. While this is a good approximations for tensionless membranes at length-scales much larger than microns, experiments and theoretical studies have shown that taking into account the bilayer structure is essential at lower length-scales [7][8][9][10][11]. This is chiefly due to the importance of the dissipation caused by intermonolayer friction.…”