Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
9001893 | Biochemical Pharmacology | 2005 | 8 Pages |
Abstract
A pH sensitive fluorescence probe piranine trisulfonate, entrapped inside small unilamellar liposomes formed with egg yolk phosphatidylcholine, was applied to investigate effect of polyene antibiotic amphotericin B (AmB) on proton transport across lipid membranes. Time dependencies of fluorescence-monitored pH changes inside lipid vesicles, upon sudden acidification of the liposome suspension, were analyzed in terms of two-exponential kinetics. It appears that addition of AmB at 3Â mol%, with respect to lipid, considerably increases the rate constant of the fast component of proton transport (a change from (60 to 149)Â ÃÂ 10â3Â sâ1) and decreases the rate constant of the slow component (a change from (11 to 5)Â ÃÂ 10â3Â sâ1). Incorporation of 0.1Â mol% AmB results in the decrease of both parameters (to (33 and 2)Â ÃÂ 10â3Â sâ1, respectively). The increase in the rate of proton transfer across the lipid membrane is interpreted as related to the formation of membrane channels by AmB, at higher concentration of the drug or nonspecific destabilization of the membrane structure. At low concentrations, at which formation of molecular structures of AmB is not possible, the antibiotic molecules are oriented horizontally with respect to the plane of the membrane and act in making the membrane more compact and less permeable to ions. The presence of sterols (cholesterol, ergosterol and cholesterol dimer) in the lipid phase, in the concentration 3Â mol% and lower, decreased the rate constants of proton transfer across the membranes but did not influence significantly the effect of AmB on the ion transport. The presence of AmB in the bathing solutions of tonoplast membranes isolated from Conocephalum conicum at the concentrations range 1Â ÃÂ 10â7 to 3.6Â ÃÂ 10â5 does not influence considerably the ion current, as monitored by means of the patch-clamp technique.
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Authors
Monika HereÄ, Halina DziubiÅska, Kazimierz TrÄbacz, Jacek W. Morzycki, WiesÅaw I. Gruszecki,