Cation permeability induced by valinomycin, gramicidin D and amphotericin B in large lipidic unilamellar vesicles studied by 31P-NMR

Permeability induced by mobile carriers and channel-forming compounds in large unilamellar lipidic vesicles (LUV) has been studied by the proteon-cation exchange method. Proton movement has been monitored by pH-stat and 31P-NMR techniques. pH-stat measurements indicate that, in the presence of valinomycin, the proton efflux develops with a rate dependent upon valinomycin concentration, until equilibrium is reached. 31P-NMR spectra, monitoring pH-dependent intravesicular phosphate ionization, show that after addition of valinomycin the initial pH peak (pH 5.5; δ=0.25) shifts progressively to the position corresponding to the pH at equilibrium (pH 7.4; δ=2.20).