Ion transport across bilayer lipid membranes between two aqueous phases in the presence of iodide and triiodide ions

I^- and I₃^- usually coexist in nature, and it is well-known that I₃^- is much more hydrophobic than I^-. Both I^- and I₃^- play a crucial role in human physiological activities and can be applied to various medical applications, such as synthesis of medicine, antibiotics, <i>etc.</i> During the measurement of the ion-transport current of KI aqueous solution, I₃^- is spontaneously generated and causes an increase in ion permeation. However, the mechanism of facilitated ion transport remains unclear. In this study, the influence of I₃^- on the ion transport across bilayer lipid membranes (BLMs) was elucidated. Physically stabilized BLMs were formed using the track-etched membrane (TM), and the ion-transport current was measured by applying a membrane potential across BLMs. Under asymmetric ionic concentration conditions, the permeability of K⁺, I^-, and I₃^- was evaluated. The permeability of I^- across BLMs was about 8 times higher than that of K⁺. In the presence of I₃^-, the permeability of K⁺ across BLMs drastically increased. The permeability of K⁺ became 9 times higher than that of I^- in the presence of 50 µM I₃^-. It is considered that I₃^- facilitated the transport of K⁺ across BLMs by serving as a carrier of K⁺ within BLMs.