Chemotactic amoeboid-like shape change of a vesicle under a pH gradient

Abstract

A vesicle that exhibited the extrusion and contraction of a pseudopod-like structure under a pH gradient was studied. The vesicle is composed of oleate and oleic acid, and transforms from a double-spherical shape to a disk-like shape after numerous cyclic shape changes, including the reversal and rotation of the double-spherical vesicle. A pseudopod-like structure is extruded from the vesicle toward a pH gradient, created by NaOH diffusion, and is then contracted. This reversible motion is repeated many times. Notably, NaCl diffusion produces a monotonic and irreversible extrusion. The difference between the two systems could be explained by the cation permeability across the membrane. A mathematical model that accounted for this characteristic reproduced the experimental results semi-quantitatively. Vesicles exhibiting amoeboid-like behaviors, which may be useful in the design of amphiphilic molecular assemblies with biomimetic characteristics, have rarely been reported and are poorly understood. The present study may provide significant insight into the design of such biomimetic vesicles.