[Characteristics of the heterogeneity of the physical properties of the lipid phase of synaptic membranes from the rat brain using the fluorescent probe pyrene]. / Kharakteristika geterogennosti fizicheskikh svoistv lipidnoi fazy sinapticheskikh membran iz mozga krys s pomoshch'iu fluorestsentnogo zonda pirena.

A theoretical analysis of the dependence of pyrene excimerization on its concentration in biological membranes was carried out. It was shown that in synaptic membranes the concentration dependencies of pyrene excimerization parameter upon direct stimulation appear as nonlinear, thus being reflective of the heterogeneity of physical properties of the lipid phase. Upon pyrene excitation at the expense of the energy transfer from tryptophanyl residues the dependence is linear, which points to the homogeneity of the anular lipid pool. It was assumed that a comparison of microviscosity of the anular and bilayer lipids requires independent measurements of the coefficient of the probe distribution between the lipids or of the anular lipid content in the membrane.

Inactivation of muscarinic acetylcholine receptors in brain synaptic membranes by free fatty acids. Evaluation of the role of lipid phase.

Arachidonic, linolenic and linoleic acids decreased the binding of the m-cholinergic antagonist [3H] QNB and did not affect the ratio of high to low affinity binding sites to the agonist carbamoylcholine in rat brain synaptic membranes. In the presence of arachidonic acid, SH-reagent N-ethylmaleimide acquired the ability to block QNB binding to receptor. Lipids in the bilayer and annular regions were probed by fluorescence of 1,6-diphenyl-1, 3, 5-hexatriene and pyrene. A microviscosity drop induced by increasing temperature from 10 to 37 degrees C did not affect the level of QNB equilibrium binding, whereas arachidonic acid strongly inhibited the binding at concentrations inducing the same drop in microviscosity as that induced by heating. For various unsaturated fatty acids an equal extent of receptor blocking was reached at quite different degrees of bilayer fluidization, the state of annular lipid being not changed under these conditions. It is suggested that the effect of unsaturated acids is reached through their direct interaction with the receptor, which undergoes a conformational change, rather than by an alteration of the physical state of the lipid phase of the membrane.

[Effect of arachidonic acid on the physical properties of bilayer and annular lipids of synaptic membranes]. / Vliianie arakhidonovoi kisloty na fizicheskie svoistva bisloinykh i pribelkovykh lipidov sinapticheskikh membran.

It has been found by fluorescence analysis of pyrene excimerization that arachidonic acid while decreasing microviscosity of lipid bilayer increases it in the annular lipid zone. After incorporation of fatty acid into the membrane the annular lipid acquires the properties of a cooperative system manifested in the appearance of thermal transition near 25 degrees C.