EFFECT OF THE DIPOLE POTENTIAL OF A BILAYER-LIPID MEMBRANE ON GRAMICIDIN CHANNEL DISSOCIATION KINETICS

A technique of measuring of the light-induced transients of the gramic idin-mediated electric current across a membrane in the presence of a photosensitizer has been applied for the study of the effect of agents modifying the dipole potential of a bilayer lipid membrane (phloretin , 6-ketocholestanol, and RH421) on the processes of the gramicidin cha nnel dissociation and formation, It is shown that phloretin, known to lower the dipole potential, decelerates the flash-induced decrease in the current, whereas 6-ketocholestanol and RH421, known to raise the d ipole potential, accelerate the current decrease, It is revealed that the addition of phloretin leads to a decrease in the dissociation rate constant, whereas addition of either 6-ketocholestanol or RH421 cause s an increase in this constant, Single-channel data show that phloreti n brings about an increase in the lifetime of the gramicidin channels, whereas RH421 produces a more complicated effect. It is concluded tha t the dipole potential affects the process of channel dissociation, pr esumably via the influence on the movement of the dipoles of gramicidi n molecules through the layer of the dipole potential drop near the me mbrane-water interface.