Combined effects exerted by amphotericin B and lucensomycin on cation permeability in a unilamellar vesicle system.

The permeability of artificial unilamellar vesicles and of plasma membrane vesicles from homogenized yeast in aqueous solutions of polyene antibiotics (amphotericin B and lucensomycin) was studied by measuring proton leakage by a pH-stat method. Micromolar concentrations of amphotericin B induced a remarkable proton efflux from the vesicles. Lucensomycin exerted similar effects only at 100 times higher concentrations. The latter antibiotic, at concentrations one order of magnitude lower than those necessary to induce a detectable proton efflux, seemed to protect the vesicles from the subsequent permeabilizing action of amphotericin B.