RESUMO
The integral conductance of planar lipid bilayer membranes in the presence of two Poloxamers (Pluronics) L61 and F68 with the same lengths of hydrophobic poly(propylene oxide) blocks and the different lengths of hydrophilic poly(ethylene oxide) blocks increases with an increase in the concentration of both Pluronics; however, the shape of the conductance-concentration curves is super linear for L61 and sublinear for F68. In the presence of both Pluronics, rare discrete current jumps are observed against the background of continuous current. At high concentrations, the I-V curves of membranes with both L61 and F68 became nonlinear at sufficiently low voltages but differed significantly. At voltages greater than 50 mV, the conductance of membranes with L61 increased sharply and quantized jumps were observed toward higher conductance, which could be interpreted as the appearance of additional pores. On the contrary, the conductance of membranes with F68 decreased and quantized jumps to lower conductance were observed, which could be interpreted as blocking of already existing pores. We attributed the differences in the conductance-concentration and I-V curves of these two Pluronics to their different effects on the dynamics of membrane hydration and, accordingly, on the probability of formation of conducting pores.
RESUMO
Eu3+-tetracycline complex (EuT) increased the chemiluminescence (CL) intensity of linolenic acid micells (UFA-somes) oxidized with lipoxygenase and CL of the lecithin liposomes peroxidized with Fe2+ ions by 3 orders of magnitude. In the systems producing oxygen radicals (xanthine + xanthine oxidase and Fenton's reagent) EuT was ineffective. Luminol increased CL intensity up to 4 orders of magnitude in Fenton's reagent and by 2 orders of magnitude in xanthine oxidase reaction. The sensitization of CL in Fe2+-induced lipid peroxidation (LPO) of liposomes was by a factor 40, while in lipoxygenase reaction very low sensitization was observed. By means of cut-off light filter OS-12 (Soviet) having short wave-length transmittance limit at 560 nm it was possible to measure separately in the same sample the luminol-sensitized CL (maximal emission near 480 nm) and EuT-sensitized CL (maximum at 620 nm); these two CL components reflect, correspondingly, the production rate of oxygen- and lipid-free radicals. Mannitol, the OH radical scavenger, inhibited luminol-dependent component of CL in peroxidized liposomes and did not inhibited EuT sensitized CL in the same system. Apparently, hydroxyl radicals are produced in LPO reactions and responsible for the effect of CL sensitization by luminol, but are not involved in the chain LPO process.
