Local anesthetics facilitate ion transport across lipid planar bilayer membranes under an electric field: dependence on type of lipid bilayer

In order to elucidate the role of structural change of lipid membrane bilayer in the mode of action of local anesthetic, we studied the effects of local anesthetics, charged tetracaine and uncharged benzocaine, on ion permeability across various lipid planar bilayers (PC, mixed PC/PS (4/1, mol/mol); mixed PC/PE (1/1, mol/mol); mixed PC/SM (4/1, mol/mol)) under a constant applied voltage. The membrane conductances increased in the order of PC  PC/PS ≤ PC/SM  PC/PE. When the constant voltage of ?100 or ?70 mV was applied through the lipid bilayer membranes in the presence of positively charged tetracaine, the fluctuating current pulses with the large amplitude generated, but not appeared in the absence of tetracaine. The addition of uncharged benzocaine generated the fluctuating currents with the small amplitude. Both charged tetracaine and uncharged benzocaine facilitated electrophoretically the transport of small ions such as KCl in the buffer solution through the fluctuating pores in the lipid bilayer membranes formed by interaction with the local anesthetic under the negative applied membrane potential. The current pulses also contained actual transport of charged tetracaine together with the transport of the small ions. The amplitude and the duration time of the electrical current generated by adding the local anesthetics were dependent on the type of the lipid, the applied voltage and its voltage polarity.