Potential dependent rigidity changes in lipid membrane vesicles

Steady-state fluorescence depolarization measurements of the hydrophobic probe, 1,6-diphenyl-1,3,5-hexatriene (DPH), embedded into lipid membrane vesicles, reveal an increase in the membrane rigidity in the presence of transmembrane potential gradients. The effect depends on the lipid head-group structure and its charge. Additionally, the curvature of the vesicle membrane leads to an asymmetry in the observed phenomena. In consistence with several theories and experiments, it is concluded that besides a possible electrostriction of the membrane the electric field causes alterations in the orientation of the surface dipoles of the lipid molecules. The biological significance of these observations is briefly discussed.