PROPERTIES OF ION CHANNELS FORMED BY THE ANTIBIOTIC SYRINGOMYCIN-E INLIPID BILAYERS - DEPENDENCE ON THE ELECTROLYTE CONCENTRATION IN THE BATHING SOLUTION

Using the planar lipid bilayer technique, organization of ion channels formed by the lipodepsipeptide antibiotic syringomycin E applied to o ne (cis) side of a lipid bilayer was studied. At low concentrations of NaCl (0.01-0.1 M), an opening and closing of two types of channels, t he ''small'' and the ''large'' ones, were observed. The large channels showed single channel conductances that were approximately 6 times gr eater than those of the small ones. An increase in the NaCl concentrat ion (0.6-1.0 M) decreased almost completely the chance to reveal the l arge channels. Although the syringomycin channels exhibited the anion selectivity within the whole range of the NaCl concentrations in the b athing solutions (from 0.001 to 1.0 M) whereas the concentration gradi ents across the bilayers were 2 and 4, the transfer numbers for Cl- de creased with an increase in the mean NaCl concentration (from 0.83 for 0.005 M to 0.70 for 0,5 M). Moreover, at each mean value of NaCl conc entration, all conductance levels had the same ion selectivity (identi cal reversal potential). These results suggest that at low NaCl concen trations, the large channels are clusters of the small ones that synch ronously open and close, while at high electrolyte concentrations, the screening of the charged groups that are responsible for the channel interactions prevents the cluster formation. A new theoretical approac h for the estimation of the channel radius and the number of elementar y charges located at its inner surface (based on the experimental curv e of dependence of transfer number on the NaCl concentration) was deve loped. Based on this theoretical approach, the channel radius equal to 1 nm and one elementary charge located at its inner surface were obta ined.