Effect of dipole modifiers on the kinetics of sensitized photoinactivationof gramicidin channels in bilayer lipid membranes

Photodynamic inactivation of gramicidin channels in bilayer lipid membranes induced by single flashes of visible light in the presence of phthalocyani ne has been studied. The kinetic curves of the flash-induced decrease in th e gramicidin-mediated electric current are used for determination of the ra te constants of formation and termination of gramicidin channels in terms o f the channel dimer model. It is revealed that the kinetics of the sensitiz ed photoinactivation of gramicidin in the membrane is altered by agents tha t modify the dipole potential drop at the membrane-wafer interface. The add ition of phloretin. is known to decrease the dipole potential drop, deceler ates the kinetics, whereas the addition of RH421 or 6-ketocholestanol, whic h increases the dipole potential drop, accelerates the kinetics. It is show n that the photoinactivation kinetics is also slowed upon the addition of t he thyroid hormone L-thyronine, which reduces the dipole potential drop sim ilarly to phloretin, as it was found out earlier (Tsybulskaya M.V, Antonenk o Yu.N., Tropsha A.E., Yagnzhinsky L.S, // Biofizika. 1984, V, 29, P, 801-8 05), It is demonstrated that the chanties in the dissociation rate constant of gramicidin dimers under the action of different dipole modifiers correl ate with the changes in the dipole potential drop, it is concluded that the process of the gramicidin channel termination corresponding to the dimer d issociation is sensitive to the dipole potential drop. This conclusion is s upported by the data on the effect of dipole modifiers on the lifetime of s ingle gramicidin channels.