[Use of excimerization of pyrene for assessing lipid microviscosity in biological membranes]. / Ispol'zovanie éksimerizatsii pirena dlia otsenko mikroviazkkosti lipidov v biologicheskikh membranakh.

A method for estimating the fluidity of natural membranes from the pyrene excimer/monomer fluorescence ratio (Ie/Im) is proposed. The method makes it possible to exclude artefacts such as fluorescence quenching, aggregation, and redistribution of the probe in lipid mains with different microviscosity. It is shown that, upon variation of intramembrane pyrene concentration [pyr], the occurrence of a common crossover point in pyrene fluorescence spectra normalized to the corresponding probe concentration (isoemission or isobestic point) or, as a consequence, the linear dependence of Ie/[pyr] on Im/[pyr] can serve as a criterion of diffusion (fluidity)-controlled excimerization of pyrene. The isobestic point can be used for determining the range of working concentrations of the probe in membrane suspension. It was found from the intensity of pyrene fluorescence in the isobestic point and quenching with potassium iodide that at t < 30 degrees C, the probe is uniformly distributed throughout the membrane, and its excimerization is mainly controlled by the microviscosity of environment.

[Effect of ischemic damage factors on lipid peroxidation in rat brain synaptosomes]. / Vliianie faktorov ishemicheskogo povrezhdeniia na perekisnoe okislenie lipidov v sinaptosomakh mozga krys.

Accumulation of TBA-reactive substances after a 40 min incubation of rat brain synaptosomes at 37 degrees C was analysed. A lowering of pH to 6.5-5.5 or arachidonic acid (0.1-1.0 mM) increased lipid peroxidation which was blocked by antioxidants. Acidosis (pH 6.0) and arachidonic acid used in combination had a strong synergic effect. Depolarisation of plasma membranes or intrasynaptosomal mitochondria were without influence on lipid peroxidation at neutral or acid pH. The results support a leading role of acidosis and phospholipases in stimulation of peroxidation under ischaemia.

Effect of proteolysis on the state of lipid phase in rat brain synaptosomal membranes.

Enzymatic proteolysis of the proteins of synaptic membranes has been found to be accompanied by the promotion of lipid peroxidation probably mediated by the liberation of membrane-bound iron. As fluorescent probes pyrene and diphenylhexatriene show, the microviscosity and micropolarity of membrane lipid phase rise as a result of lipid peroxidation. Different structural changes induced by proteolysis are displayed under inhibition of lipid peroxidation. Thus, the microviscosity of the bulk lipid phase appears to be lowered and the annular lipid microviscosity raised. Another explanation of the fluorescent data for annular lipids is the exclusion of pyrene molecules from this lipid pool, leading to a reduction of the probe local concentration. The changes observed in membrane lipid phase are considered as primary structural effects of proteolysis, not mediated by a phospholipase activation.

Effect of gamma-irradiated carbohydrates on isolated synaptic membranes.

The effect of gamma-irradiated solutions of carbohydrates, mainly glucose, upon Na+, K(+)-ATPase and lipid peroxidation in rat brain synaptosomal membranes was studied. The membrane damage by irradiated glucose was enhanced in the presence of Fe2+ and was diminished when a free-radical scavenger (BHT) or metal chelators (EDTA, EGTA) were present. It is suggested that a key element in the free-radical membrane damage by irradiated carbohydrates is an Fe(2+)-complex of some species of the radiolysis products. Participation of radiotoxins of carbohydrate origin in radiobiological effects is discussed.

[Effect of temperature on polarity of an annular and bilayer synaptic membrane lipid]. / Vliianie temperatury na poliarnost' anuliarnogo i bisloinogo lipida sinapticheskikh membran.

Using fluorescent probe pyrene a study was carried out of temperature dependence of the annular and lipid bilayer polarity in synaptic membranes. Polarity of microenvironment was evaluated by a ratio of intensities of vibronic bands in pyrene fluorescence spectra at direct excitation of probe or through energy transfer from protein molecules. At the temperature range 10-50 degrees C the polarity of bilayer was shown to increase while that of annular lipid underwent biphasic changes. Above 20 degrees C polarity of the bilayer was higher than of the annular zone. From experiments on pyrene fluorescence quenching with potassium iodide the conclusion has been made that changes in polarity correlate with pyrene accessibility to water.