Transport of large organic ions through syringomycin channels in membranes containing dipole modifiers

The effect of the membrane dipole potential (φ _d ) on conductance and the steady-state number of functioning channels formed by cyclic lipodepsipeptide syringomycin E (SRE) in bilayer lipid membranes made from phosphocholine and bathed in 0.4 M solution of sodium salts of aspartate, gluconate, and chloride was shown. The φ _d value varied with the introduction of phloretin to membrane bathing solutions, which reduces φ _d and RH 421, which increases φ _d . It was established that, in all studied systems, an increase in the membrane dipole potential caused a decrease in the steady-state number of open channels. In systems containing sodium salts of aspartate (Asp) or gluconate (Glc), changes in the number of functioning channels are one order lower than those of systems that contain sodium chloride. At the same time, the conductance (g) of single SRE channels in the membranes bathed in NaCl solution increases with increase in φ _d and in the systems containing NaAsp or NaGlc the conductance of single channels does not depend on the φ _d . The latter is due to the lack of cation/anion selectivity of the SRE channels in these systems. The different channel-forming activity of SRE in the experimental systems is determined by the gating charge of the channel and the partition coefficient of the dipole modifiers between the lipid and aqueous phases.