Looks like somebody's salty: neutrons reveal how ions influence model cell membranes

A team of researchers at the ILL investigated how salt alters the shape of lipid vesicles.

All life forms, from bacteria to animals, contain cells and organelles, which are surrounded by membranes. The main constituents of these membranes are lipids—molecules made of hydrophilic (water loving) "heads" and hydrophobic (water fearing) "tails". In the presence of water, these molecules form closed, hollow spherical structures called vesicles. These vesicles can also be used as carriers for drugs and vaccines.

In biological systems, natural or artificial, substances such as salts are usually present. Normally, these do not cross lipid membranes. If the concentration of such components (also known as “osmolytes”) inside and outside the vesicle differs, a so-called osmotic pressure builds up and water will permeate the membrane to even out osmolyte concentrations – if the concentration inside the closed structure is higher, water will come inside the vesicle, thereby making it swell; if, however, the concentration outside the vesicle is higher, water will leave the vesicle, deflating it.

Vesicles are often produced in pure water and therefore the influence of osmolytes is rarely investigated. However, the biological relevance of osmolytes implies that their influence is important to understand. This topic was studied by Alice Piccinini's as part of her PhD thesis, jointly co-supervised by Anja Winter at the University of Keele, UK, and Sylvain Prévost at the ILL. "We wanted to understand how adding different osmolytes, in particular salts, but also electrically neutral molecules such as glucose and a simple oligomer, alter vesicles consisting of model lipids," says Piccinini, who is the first author of a recently published article based on this work.