Ion-diffusion potentials and electrical rectification across lipid membranes activated by excitation-induced material

Membranes synthesized from sphingomyelin-tocopherol mixtures and treated with the protein, "excitation-inducing material," to increase their electrical conductance were tested for applicability of the Nernst equation and changes in electrical rectifying behavior with temperature. Above pH 7, and in the temperature range 303-323 degrees K, ion-diffusion potentials created by salts of monovalent cations showed that areas of the membrane activated by excitation-inducing material were only permeable to cations. Results also indicated that a parallel current with an activation energy of 1.00 eV per molecule passed through unactivated areas of the membrane. Below pH 7, the ratio of measured diffusion potentials to predicted values decreased steadily. Electrical rectification was exhibited by membranes activated by excitation-inducing material with positive current consistently passing preferentially from the side rich in excitation-inducing material to the opposite side. For a given membrane, the current-voltage curves did not change from 312 to 323 degrees K; but below 312 degrees K, the membrane suddenly increased its conductance and became ohmic. This phenomenon was independent of salt concentration and pH, and resembled a phase transition.