A lipid vesicle system for probing voltage‐dependent peptide–lipid interactions: Application to alamethicin channel formation

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Abstract
A membrance potential is shown to be established in phosphatidylcholine/cholesterol unilamellar vesicles using valinomycin in conjunction with a potassium ion gradient; this potential is monitored using the externally added fluorescent dye Safranine O. In the same system, transmembrance calcium fluxes are then detected using the (internally trapped) fluorescent dye Quin-2. The calcium-transport behavior of the channel-forming peptide alamethicin is shown to be potential dependent in this system, in contrast to calcium transport by the ionophore Br-A23187, which is unaffected by the potential. The observation of this potential-dependent behavior for alamethicin suggests that this vesicle system may be suitable for direct spectroscopic observation of the voitage-gating process.