Ion transport mechanism in gramicidin A channels formed in floating bilayer lipid membranes supported on gold electrodes
The ion channel properties of gramicidin A (gA) in a model floating bilayer lipid membrane were studied by electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). To determine if the transport of Na+ across the membrane is coupled with the transport of the counterion, fluoride and perchlorate anions were explored due to their large differences in hydration energy. The combined EIS and IR experiments demonstrated that in contrast to valinomycin, the mechanism of Na+ transfer through the gA channel is independent of the accompanying anion present in the supporting electrolyte. These studies also demonstrated that the conductivity of the gA sodium channel depends on the transmembrane potential and the IR measurements indicated that more gA molecules insert into the bilayer with the decrease of the transmembrane potential. The results of this present study demonstrate that the fBLM system is a suitable model bilayer for the in situ investigations of membrane-active peptides.