[Calcium transport in brain synaptosomes during depolarization. The role of potential-dependent channels and Na+/Ca2+ metabolism]. / Transport kal'tsiia v sinaptosomakh mozga pri depoliarizatsii. Rol' potentsialzavisimykh kanalov i Na+/Ca2+-obmena.

The contribution of Ca2+ channels and Na+/Ca2+ exchange to Ca2+ uptake in rat brain synaptosomes upon long- (t greater than or equal to 30 s) and short-term (t less than 30 s) depolarization by high K+ was studied by measuring the 45Ca content and free Ca2+ concentration (from Quin-2 fluorescence). At 37 degrees C, the system responsible for the K+-stimulated uptake of 45Ca (t greater than or equal to 30 s) and the Na+/Ca+ exchanger are characterized by a similar concentration dependence of external Ca2+ (Ca0(2+] and K0+ as well as by an equal sensitivity to verapamil (Ki = approximately 20-40 microM) and La2+ (Ki = approximately 50 microM). These data and the results from predepolarization suggest that the 45Ca entry into synaptosomes at t greater than or equal to 30 s is due to the activation of Na+/Ca+ exchange caused by its electrogenic component, while the insignificant contribution of Ca2+ channels can be accounted for by their inactivation. At low temperatures (2-4 degrees C) which decelerate the inactivation, the initial phase of 45Ca uptake is fully provided for by Ca2+ channels, showing a lower (as compared to the exchanger) affinity for Ca0(2+) (K0.5 greater than 1 mM)m a greater sensitivity to La3+ (Ki = approximately 0.2-0.3 microM) and verapamil (Ki = approximately 2-3 microM); these channels are fully inactivated by predepolarization with K0+, ouabain and batrachotoxin. The Ca2+ channels can be related to T-type channels, since they are not blocked by nicardipine and niphedipine.

[Effect of microenvironment on the conformation of m-cholinoreceptors in brain synaptic membranes]. / Vliianie mikrookruzheniia na konformatsionnoe sostoianie m-kholinoretseptorov sinapticheskikh membran mozga.

Sensitivity of m-cholinergic receptor of synaptic membranes to SH-reagents (PChMB and NEM) was compared before and after its solubilization with detergents. PChMB blocked specific binding of m-antagonist QNB to both forms of the receptor in equal extent, while NEM was effective only after solubilization. After the membranes modification with butanol or arachidonic acid the membrane-bound receptor became sensitive to NEM. The solubilized receptor lost its ability to allosteric inhibition by acid. It is suggested that the receptor conformation is under the control of the membrane microenvironment.

[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.

[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.

[Membrane potential and transport of neuromediators in synaptosomes of the brain of rats with spontaneous hypertension]. / Membrannyi potentsial i transport neiromediatorov v sinaptosomakh golovnogo mozga krys so spontannoi gipertenziei.

The transport of 3H-GABA, 14C-choline, 14C-noradrenaline and 3H-serotonin in brain synaptosomes of spontaneously-hypertensive rats (SHR) which is controlled by the carrier whose activity is dependent on the sodium gradient and electric potential of the plasma membrane was studied. The initial rate of GABA uptake by SHR synaptosomes was reduced by 25%. The steady state of the content of GABA, noradrenaline and serotonin in SHR synaptosomes was reduced by 15-20%, whereas the steady state of choline content by 35%. The differences are levelled when synaptosomes are depolarized, both due to the elimination of K+-diffusion potential, and the opening of Na channels. An increase in the extracellular calcium concentration up to 1 mmol results in a 20% synaptosomal GABA rise that is unrelated to membrane hyperpolarization. In the presence of the Ca-ionophore A-23187, a similar effect is observed with a 1-2 mmol Ca2+ concentration. The electric potential of SHR synaptosomes which is studied by means of the fluorescent dye dis-C3-(5) was shown to be reduced by 5-10 mV. Partial depolarization of SHR synaptosomes is supposed to be the principal cause of the decrease in both the initial rate of uptake and the steady state of the content of neuromediators.