TRANSPORT OF LARGE ORGANIC IONS THROUGH SYRINGOMYCIN CHANNELS
IN THE MEMBRANES CONTAINING DIPOLE MODIFIERS
S. S. Efimova,1, * O. S. Ostroumova,1 V. V. Malev,1, 2 L. V. Schagina 1
1 Institute of Cytology RAS, St. Petersburg, and 2 St. Petersburg State University;
* e-mail: ssefimova@mail.ru
The effect of the membrane dipole potential (φd) on a conductance and a 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
magnitude of φd was varied with the introduction to membrane bathing solutions of phloretin, which reduces the
φd , and RH 421, increasing the φd . It was established that in all studied systems the increase in the membrane dipole
potential cause a decrease in the steady-state number of open channels. In the systems containing sodium
salts of aspartate (Asp) or gluconate (Glc), changes in the number of functioning channels are in an order of
magnitude smaller than in systems containing sodium chloride. At the same time, the conductance (g) of single
SRE-channels on the membranes bathed in NaCl solution increases with the increase in φd , and in the systems
containing NaAsp or NaGlc the conductance of single channels does not depend on the φd . The latter is due to
the lack of cation/anion selectivity of the SRE-ñhannels in these systems. The different channel-forming activity
of SRE in the experimental systems is defined by the gating charge of the channel and the partition coefficient of
the dipole modifiers between the lipid and aqueous phases.
Key words: bilayer lipid membranes, single ion channels, membrane dipole potential, channel-forming
toxins, large organic anions
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