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Concentration and time dependence of amphotericin B-induced permeability changes across plasma membrane vesicles from
1Department of Cell Biology, Faculty of Sciences, Central University of Venezuela, Caracas.
Abstract:
The main purpose of this paper is to show that the polyene antibiotic amphotericin B may form two types of channels in plasma membrane vesicles from Leishmania sp.: ionic and aqueous. The experimental design was to follow the light scattering changes of a suspension of membrane vesicles under an osmotic shock. The results show that a low concentration of amphotericin B(0.2 to 0.8 microM) led to an enhancement of urea and salt permeability without affecting the total osmotic response of Leishmania vesicles. Such an increment of solute permeability induced by low concentrations of amphotericin B was 100% blocked by tetraethylammonium. Low concentrations of amphotericin B were also able to induce an enhancement of glucose permeability but only after Leishmania membrane vesicles were incubated for 15 min with the antibiotic, previous to mixing. On the other hand, high amphotericin B concentrations (greater than 0.8 microM) induced a decrease in the total extent of shrinkage of membrane vesicles immediately after its mixing with urea solutions. At this high concentration of amphotericin B the blocking of tetraethylammonium was reduced by 50%. These results support the authors' previous conclusion (1) that in ergosterol-containing membranes, amphotericin B may form two different types of channels differing in internal diameter.
Insights
Amphotericin B forms two distinct channels in Leishmania membranes: ionic and aqueous. These channels differ in size, affecting solute permeability and osmotic response, as demonstrated by light scattering experiments.
Area of Science:
- Biochemistry
- Membrane Biology
- Pharmacology
Background:
- Amphotericin B is a polyene antibiotic known to interact with cell membranes.
- Ergosterol-containing membranes are susceptible to Amphotericin B's effects.
- Understanding channel formation is crucial for its therapeutic and toxicological profiles.
Purpose of the Study:
- To investigate the channel-forming properties of amphotericin B in Leishmania plasma membrane vesicles.
- To differentiate between ionic and aqueous channel formation by amphotericin B.
- To elucidate the concentration-dependent effects of amphotericin B on membrane permeability.
Main Methods:
- Utilized light scattering changes in membrane vesicle suspensions.
- Applied osmotic shock to assess vesicle response.
- Measured permeability changes for urea, salts, and glucose.
- Investigated the effect of tetraethylammonium as a blocking agent.
Main Results:
- Low concentrations (0.2-0.8 microM) of amphotericin B enhanced urea, salt, and glucose permeability, forming aqueous channels.
- Tetraethylammonium completely blocked the solute permeability enhancement at low amphotericin B concentrations.
- High concentrations (>0.8 microM) of amphotericin B decreased vesicle shrinkage, suggesting the formation of larger, ionic channels.
- Tetraethylammonium partially blocked the effect at high amphotericin B concentrations.
Conclusions:
- Amphotericin B forms at least two types of channels (ionic and aqueous) in Leishmania plasma membranes.
- Channel type and function are dependent on amphotericin B concentration.
- The distinct internal diameters of these channels explain the differential effects on membrane permeability.