Some factors affecting the valinomycin-induced leak from liposomes

Abstract

Experiments dealing with the valinomycin-induced K + leak from egg lecithin liposomes have demonstrated the importance of the enclosed anion. Except when lipophilic anions are enclosed, the addition of both valinomycin and a uncoupler, e.g. carbonylcyanide p-trifluoromethoxyphenylhydrazone, is necessary to induce a significant increase of the K + leak. In the presence of uncouplers the leak of K + is accompanied by an inward transport of H + generating a pH gradient over the membrane. Within the liposomes a considerable acidification takes place, resulting in the formation of undissociated acid molecules which rapidly permeate the membrane and produce, as a net result, the translocation of a pottassium ion and an anion. This hypothesis was tested by measuring fluxes of K +, H + and the enclosed anion. Furthermore, it is shown that when valinomycin is preincubated in alcohol : water mixtures, the effect of the ionophore on the initial increase of the K + leak from liposomes containing potassium thiocyanate decreases at ratios less than 50 : 50. This phenomenon is primarily caused by a reversible inactivation of the ionophore, possibly due to a conformational change, which is followed by partial absorption to the wall of the reaction vessel.