large unilamellar vesicles
Springer Online Journal Archives 1860-2000
Abstract 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). In the presence of the channel-forming compounds, gramicidin D or amphotericin B, permeability developed in a few minutes whatever the concentration used. The percentage of total titratable proton released depends upon the antibiotic concentration. 31P-NMR spectra shows two signals from internal phosphate: one signal corresponding to the initial pH and a second signal corresponding to the pH at equilibrium indicating an all-or-none mode of action; just after addition of the antibiotic, two populations of vesicles coexist in proportions that depend on ionophore concentration; after longer incubation times all vesicles are permeabilized. The results obtained primarily reflect the differences in the mode of interaction with the membrane, of valinomycin as compared to the channel-forming reagents, gramicidin D or amphotericin B.
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