THE ELECTROSTRICTION, SURFACE-POTENTIAL AND CAPACITANCE RELAXATION OFBILAYER-LIPID MEMBRANES INDUCED BY TETRACAINE

The interaction of local anesthetic tetracaine (TCC) with planar bilay er lipid membranes (BLM) of egg PC and cholesterol was studied by the measurement of elasticity modulus perpendicular to the plane of the me mbrane, surface potential difference, electrical capacitance and capac itance relaxation following the voltage jump (yielding relaxation time s for molecular dipoles or dipolar domains). Addition of TTC to one si de of the BLM in the concentration range 0.3-33 mu M leads to a more p ositive membrane surface potential, to slight increase of membrane cap acitance, while elasticity modulus minimally changes. The surface pote ntial increased with increasing concentration of TTC and was higher fo r 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 cha nge of surface potential comes from the dipole potential of membrane s urface. The 33 mu M ITC concentration induced changes of dipole potent ial about 5.3 +/- 2.0 mV and 29.8 +/- 3.0 mV at pH 6 and pH 9, respect ively, which corresponds to the change of surface dipole moment of 8.1 +/- 3.0 and 34.0 +/- 3.5 Debye, respectively. Unmodified BLMs were ch aracterized by a singe relaxation time of about 5 mu s corresponding t o reorientation of molecular dipoles. Addition of TTC (final concentra tion 0.1 mM) resulted in appearance of additional slower relaxation co mponent of 50 mu s at electrolyte pH 9, while at pH 6 no changes of re laxation 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 pe rturbation of the bilayer dynamic. (C) 1998 Elsevier Science S.A. All rights reserved.