Effect of monovalent anions on water transmembrane transport.

Biological structures consist of lipid bilayers immersed in the aqueous phase. They can be considered as a two-phase system where the two phases are separated (connected) by the transition regions (interphases), which properties are affected by both lipid and aqueous phases. Interphase structure and dynamics might influence properties and/or functioning of the lipid bilayer core, including osmotically induced water flow. It has been shown previously that the osmotically induced water flow depends on the membrane lipid composition, which determines the packing of the membrane core, but the role of the aqueous phase composition has not been studied previously. Ionic composition of an aqueous phase may affect behavior of biological structures. Chaotropic ions interact strongly with a lipid bilayer affecting its molecular packing whereas kosmotropic ions have only limited effect. In the paper result of studies on the dependence of the osmotically induced water flow on the ionic composition of the aqueous phase are presented. The stopped flow technique, with the light scattering as the detection quantity, was adopted, and a new experimental design was developed for the monitoring of the intravesicle salt concentration. Obtained results show that the strength of selected anions interactions with the lipid bilayer does not correlate with their capacity to affect the osmotically induced water flow. Specifically, the measured water permeability coefficient does not depend on the quantity and type of ions present in the aqueous phase.