The electrostriction, surface potential and capacitance relaxation of bilayer lipid membranes induced by tetracaine

Abstract

The interaction of local anesthetic tetracaine (TTC) with planar bilayer lipid membranes (BLM) of egg PC and cholesterol was studied by the measurement of elasticity modulus perpendicular to the plane of the membrane, surface potential difference, electrical capacitance and capacitance relaxation following the voltage jump (yielding relaxation times for molecular dipoles or dipolar domains). Addition of TTC to one side of the BLM in the concentration range 0.3–33 μM leads to a more positive membrane surface potential, to slight increase of membrane capacitance, while elasticity modulus minimally changes. The surface potential increased with increasing concentration of TTC and was higher for less charged form of local anaesthetics (at pH 9) than that for more charged one (pH 6). This proves that the main contribution to the change of surface potential comes from the dipole potential of membrane surface. The 33 μM TTC concentration induced changes of dipole potential about 5.3±2.0 mV and 29.8±3.0 mV at pH 6 and pH 9, respectively, which corresponds to the change of surface dipole moment of 8.1±3.0 and 34.0±3.5 Debye, respectively. Unmodified BLMs were characterized by a singe relaxation time of about 5 μs corresponding to reorientation of molecular dipoles. Addition of TTC (final concentration 0.1 mM) resulted in appearance of additional slower relaxation component of 50 μs at electrolyte pH 9, while at pH 6 no changes of relaxation time occurred. We assume that due to more neutral form (at pH 9), TTC penetrates deeper into the lipid bilayer. Interaction of TTC with BLM probably induces phase separation of phospholipids and the perturbation of the bilayer dynamic.