Ion transport mediated by inverted micellar aggregates across a phosphatidylcholine-octanol liquid membrane

Abstract The ionophoretic activity of dipalmitoyl-DL-α-phosphatidylcholine (DPPC) was investigated on the system in which two aqueous NaCl solutions are separated by a porous support membrane impregnated with a 1-octanol solution of DPPC. Transmembrane potential and conductance measurements were carried out with changing temperature to estimate the membrane permeability to ions. To clarify the mechanism of ion transport through an immobilized DPPC-1-ctanol membrane, differential scanning calorimetry and photon correlation spectroscopy were employed to investigate the molecular properties of DPPC in a water-saturated 1-octanol system. An endothermic peak was detected at around 18°C in the water-saturated 1-octanol system, but not in the pure 1-ctanol system. Laser light scattering study indicated that DPPC molecules form aggregates, ca. 0.1 μm in diameter, in water-saturated 1-octanol, but not in pure 1-octanol. Temperature dependences of the relaxation time estimated by the light scattering study changed above and below 18°C. The critical temperature, 18°C, correlates well with that at which modes of the temperature dependences of membrane permeability are altered. Results obtained by these three types of experiments indicate that inverted micellar aggregates of DPPC function as an ionophore.