Permeability of phospholipid membrane for small polar molecules determined from osmotic swelling of giant phospholipid vesicles

TL;DR

This paper introduces a new optical method to measure phospholipid membrane permeability for small polar molecules by analyzing osmotic swelling of giant vesicles, offering an alternative to existing techniques.

Contribution

The authors present a novel microscopy-based approach to determine membrane permeability using osmotic swelling of GUVs, providing a simpler and potentially more accurate method.

Findings

Both methods yield consistent permeability estimates.

The technique allows real-time monitoring of vesicle swelling.

It offers an alternative to traditional electrical and light scattering methods.

Abstract

A method for determining permeability of phospholipid bilayer based on the osmotic swelling of micrometer-sized giant unilamellar vesicles (GUVs) is presented as an alternative to the two established techniques, dynamic light scattering on liposome suspension, and electrical measurements on planar lipid bilayers. In the described technique, an individual GUV is transferred using a micropipette from a sucrose/glucose solution into an isomolar solution containing the solute under investigation. Throughout the experiment, vesicle cross-section is monitored and recorded using a digital camera mounted on a phase-contrast microscope. Using a least-squares procedure for circle fitting, vesicle radius R is computed from the recorded images of vesicle cross-section. Two methods for determining membrane permeability from the obtained R(t) dependence are described: the first one uses the slope of R(t) for a spherical GUV, and the second one the R(t) dependence around the transition point at which a flaccid vesicle transforms into a spherical one. We demonstrate that both methods give consistent estimates for membrane permeability.