1,721,010 research outputs found
Interazione degli antibiotici polienici con membrane naturali e modello : studi di legame e di permeabilità
No full textInteraction of the polyene antibiotic etruscomycin with large unilamellar lipid vesicles: binding and proton permeability inducement
No full textThe effect of the polyene antibiotic etruscomycin on the permeability of large unilamellar lipid vesicles was investigated. Proton leakage was induced in egg-yolk phosphatidylcholine (EPC) vesicles only when sterol was present in the membrane; the extent of leakage was limited. High etruscomycin/lipid ratios (R) were necessary (R greater than 0.1). Higher percentages of sterol increased the permeability, slightly more strongly for ergosterol than for cholesterol. Dipalmitoylphosphatidylcholine (DPPC) vesicles were more sensitive to permeability inducement, even in the absence of sterol in the bilayer (inducement for R greater than 0.06). The interactions of etruscomycin with the vesicles were examined by circular dichroism, fluorescence and 31P-NMR. In the range of antibiotic concentration where permeability was induced, R greater than 0.1 for EPC vesicles, R greater than 0.06 for DPPC vesicles, etruscomycin exhibited characteristic circular dichroism spectra independent of the presence of sterol. Under the same conditions, 31P-NMR and fluorescence studies indicated a destruction or a fusion of the vesicle bilayer. At lower etruscomycin concentrations (R less than 0.03), the etruscomycin circular dichroism spectra were different, indicating that the interaction with membranes containing ergosterol differed from that with membranes containing cholesterol. From correlating the increase in fluorescence intensity with this interaction, as well as from exchange experiments, it was inferred that etruscomycin at a low antibiotic/lipid ratio is more strongly bound to ergosterol-containing vesicles than to cholesterol-containing vesicles. These results and their comparison with the results obtained with other polyene antibiotics indicate that at low R etruscomycin resembles amphotericin rather than filipin in its preferential binding to ergosterol-containing vesicles. At higher R, that is in conditions where permeability is induced, the selectivity is different. The corresponding mechanism seems not to involve the formation of an etruscomycin-sterol channel, since the hydrophobic chain of the complex would be too short to form a channel
Effects of the semisynthetic bis-indole derivative KAR-2 on store-operated calcium entry in human neutrophils
No full textWe studied the effect of KAR-2 on cytosolic Ca2+ level in human neutrophils by using a fluorescent dye (Fura-2) trapped in the cells. KAR-2 is a semisynthetic bis-indole derivative that shares vinblastine anti-microtubular properties, but does not share the vinblastine antagonistic effect on calmodulin. Therefore KAR-2 offers a convenient mean of studying the effect of microtubule destabilization, without concomitant calmodulin alterations. We found that KAR-2 induces Ca2+ release from intracellular stores, whereby the stores are depleted. In addition KAR-2 reduces store-operated entry of extracellular Ca2+ induced by agonists such as thapsigargin or ATP. On the other hand, in Ca2+ refilled cells, KAR-2 promotes limited entry of extracellular Ca2+ in the absence of agonist, but still interferes prominently with Ca2+ entry triggered by ATP and with Ca2+ uptake by intracellular stores. We suggest that Ca2+ traffic through the plasma membrane is operated by two diverse pathways: the prominent pathway is interfered with by microtubule destabilization, while an alternate and minor pathway is actually favored (or uncovered) following microtubule destabilization
Unilamellar-vesicle systems as model for studying membrane permeabilization by polyene antibiotics
No full textPermeabilization of phospholipid/sterol unilamellar vesicles by polyene antibiotics (amphotericin B and lucensomycin) was studied by measuring proton leakage with a pH-stat method. The percentage of proton release was directly related to the antibiotic concentration. Using ergosterol-containing vesicles, a relevant proton efflux was induced by micromolar concentrations of amphotericin B, whereas lucensomycin caused membrane permeabilization at higher concentrations (0.1 mM). Cholesterol-containing vesicles were less sensible to the lytic action of polyenes. When amphotericin B was carried in cholesterol-containing liposomes, the selectivity towards ergosterol-containing vesicles was enhanced. An increase in drug selectivity was also observed by dissolving amphotericin B in fresh human plasma. At concentrations one order of magnitude lower than those necessary to induce a detectable proton efflux, lucensomycin seemed to protect the vesicles from the subsequent permeabilizing action of amphotericin B
Regulation of polymorphonuclear leukocyte function by nitroenkephalin, a nitrated biomolecule formed by activated human neutrophils.
No full textMembrane systems as model for studying permeabilization exemplified by polyene antibiotics.
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KINETICS OF BINDING OF LUCENSOMYCIN TO NATURAL AND ARTIFICIAL MEMBRANES
No full textThe binding of the polyenic antibiotic lucensomycin to native or modified human erythrocyte ghosts and to model membranes has been studied by monitoring the absorbance variations of the polyene at 320 nm. The non-steroidal components of the membranes (such as proteins and phospholipids) seem to affect the rate of the individual reaction steps leading to the formation of cholesterol-lucensomycin complexes rather than the ratio among these heterologous aggregates at equilibrium
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