APPLICATION OF A FAST CHARGE-PULSE TECHNIQUE TO STUDY THE EFFECT OF THE DIPOLAR SUBSTANCE 2,4-DICHLOROPHENOXYACETIC ACID ON THE KINETICS OF VALINOMYCIN MEDIATED K+-TRANSPORT ACROSS MONOOLEIN MEMBRANES

We report on a modified charge-pulse relaxation technique applied at planar lipid membranes. The method has an improved time resolution of 20-30 ns, It is based on the capacitive coupling of a voltage-jump to the membrane. The method was used to study the fast relaxation processes induced by valinomycin/K+ in the presence of 2,4-dichlorophenoxyacetic acid (2,4-D). The change of the rate constants of the ion carrier valinomycin was analysed as a consequence of the adsorption of the dipolar substance 2,4-D to the membrane/water interface of monoolein membranes. The effect of 2,4-D can be explained solely via the influence of the introduced dipole potential, V-D. The latter was found to act (primarily) on the inner membrane barrier experienced by the positively charged carrier-ion complex and on the interfacial barriers responsible for complex formation and dissociation. No evidence for a change of the microviscosity of the membrane interior was obtained.