Effective gating charge of ion channels induced by toxin syringomycin E in lipid bilayers.

To elucidate the voltage gating of syringomycin E (SRE) ion channels in lipid bilayers, the effective gating charge q was measured under different conditions. It was shown that q and its sign are dependent on membrane surface charge, dipole potential, and the outer potential (Delta phi). The q values were positive for charged bilayers and negative for uncharged bilayers bathed in the same 0.1 M NaCl solutions. Effects of dipole modifying agents on the gating properties of SRE channels were measured. In uncharged bilayers, addition of phloretin resulted in an increase of q values. For charged bilayers, the presence of RH-421 or 6-ketocholestanol leads to the reverse in the sign of q from positive to negative. The q values were potential-dependent at higher negative voltages with charged membranes bathed in solutions with high salt concentrations. It is concluded that lipid molecules participating in the SRE channel structure contribute to channel formation work due to Coulomb and dipolar interactions with the electric field applied to a membrane. The potential dependence of q is explained by interactions of charged and uncharged lipids with SRE molecules in the channels.