Potassium-selective amphotericin B channels are predominant in vesicles regardless of sidedness

Abstract

Amphotericin B (AmB) is a membrane-active antibiotic which has been shown to increase ion and small molecule permeability in a variety of model and biological membrane systems. A major mechanistic model, based on BLM systems, proposes that amphotericin forms barrellike pores with cholesterol which are cation selective when added to one side of the membrane and anion selective when added to both sides. We have tested this hypothesis on small and reverse-phase large unilamellar vesicles (SUV and REV) with and without cholesterol. The method used to measure K+, Cl-, and net ion currents is based on ion/H+ exchange detected by the entrapped pH probe pyranine. We find that AmB forms channels which have net selectivity for K+ over Cl- regardless of sidedness or sterol content in SUV. REV with 10% cholesterol also show net K+ selectivity with double-sided addition. Differences are noted between cholesterol- and non-sterol-containing vesicles consistent with at least two separate modes of action: (1) cholesterol-containing SUV form some larger diameter pores which allow the passage of larger ions especially when added to both sides; (2) SUV without sterol form pores which are still K+ over Cl- selective, but larger ions do not pass. The latter mode of action precludes a sterol/pore type of model but not necessarily a barrellike model consisting only of amphotericin molecules.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibody Array-Generated Profiles of Cytokine Release from THP-1 Leukemic Monocytes Exposed to Different Amphotericin B Formulations

“…Stimulation of Ca 2ϩ influx is a possible mechanism and has been observed in human monocytes (18). However, it is unclear whether Ca 2ϩ is directly transported since the AMB-induced channels in cholesterol-containing model membranes are not appreciably Ca 2ϩ permeant (10,16). Alternatively, monovalent cation permeation could lead to membrane polarization or depolarization, leading to a secondary release of Ca 2ϩ from internal stores or from stimulated outer membrane Ca 2ϩ channels.…”

Interaction of Amphotericin B with Cholesterol in Monolayers, Aqueous Solutions, and Phospholipid Bilayers

“…This suggests that AmB weakly interacts with DPPC molecules. Hartsel et al (5) proposed that the insertion of AmB toward the lipid bilayer brings the polar polyol region in direct contact with the lipid hydrocarbon, and thereby induces some of the local lipid head groups to "fold around" so as to interact with the polyol. Such an unfavorable juxtaposition between AmB and phospholipid appears to occur in monolayers, resulting in the occurrence of a defect in the monolayers.…”

“…It has been accepted that AmB forms barrel-like pores with cholesterol, thus inducing permeability changes in the membranes (3). However, there is evidence that AmB itself interacts with cholesterol-free lipid vesicles to promote and increase the permeability (4)(5)(6). In this manner, while many studies have been performed to characterize the pore formation by AmB, it has been difficult to obtain a definite answer because of the complicated interaction of the drug with itself, with sterol, and with lipid and aqueous environments.…”

Amphotericin B-induced ion flux is markedly attenuated in phosphatidylglycerol membrane as evidenced by a newly devised fluorometric method

“…AmB exerts its selective toxicity by forming ion channel assemblies that permeabilize plasma membranes in a sterol-specific manner. [4][5][6][7][8][9][10][11][12][13] Besides sterols, interaction with phospholipids has recently been reported to be important for the bioactivity of AmB; [14][15][16][17][18] we have previously reported that phosphatidylcholine (PC) with short acyl chains markedly enhanced the membrane-permeabilizing activity of AmB even when added as a minor constituent, while the PC with long acyl chains reduced the potency. 19 These observations can be accounted for by the hydrophobic matching between AmB and the acyl chains.…”