The Time Profile of the Effects of Moderate Hypothermia on Synaptic Acetylcholinesterase in Rat Brain.

Hypothermia in homeotherms significantly affects the neurotransmitter systems of the brain, including the cholinergic system. The function of the brain cholinergic system during prolonged moderate hypothermia is not known yet. We studied the effects of moderate hypothermia of various durations on the activity and kinetic parameters of synaptic acetylcholinesterase in rat brain. Immediately after body temperature decrease to 30°C, the efficiency of synaptic acetylcholinesterase catalysis significantly increases due to changes in both the maximum rate of reaction (Vmax; the rate of reaction when the enzyme is saturated with substrate) and Michaelis constant (Km). However, in the dynamics of prolonged hypothermia (1-3 h), it decreases to a level of intact animals, which was associated with normalization of the kinetic parameters of the enzyme. The detected changes in the kinetic parameters of the enzyme are compensatory and can be associated with both its reversible post-translational modifications and changes in the annular lipids.

A New Tellurium- and Selenoorganic Compound as an Inhibitor of Acetylcholinesterase in Brain.

We studied the effect of a new cyanine dye containing selenium and tellurium on acetylcholinesterase activity in synaptic membrane in rat brain. The cyanine dye dose-dependently inhibits activity of this enzyme, and the concentration of half-maximal inhibition of acetylcholinesterase activity was 20.46 µM. The cyanine dye instantly inhibits the enzyme; the degree of inhibition depends on acetylthiocholine concentration: the lower is acetylthiocholine concentration, the higher is the degree of inhibition. On the Lineweaver-Burk plot, the concentration dependence curves of acetylcholinesterase with and without cyanine dye intersect in one point on the abscissa axis. In this case, the cyanine dye reduces the maximum inhibition rate (Vmax) and does not affect Michaelis constant (Km). The calculated inhibition constant Ki for the cyanine dye is 7.74 µM. Thus, the cyanine dye is a non-competitive inhibitor of acetylcholinesterase.

[Effect of total hypothermia on the fatty acid composition of blood phospholipids of rats and sousliks and light irradiation on chemical processes in lipid extract].

Effect of hypothermia on the fatty acid composition of rat and souslik blood phospholipids is studied. Different reaction of these animals to cooling is revealed: in rats no changes were observed in the fatty acid composition of blood phospholipids, whereas in the hibernating there were significant changes in the content of individual fatty acids (FA). The content of monoenic acids in sousliks decreased almost by 50%, while the content of saturated acid (C18) and of polyenic acids C18 : 2omega6 and C20 : 4omega6 rose significantly. Such changes seem to be the mechanism that promotes maintenance of the organism viability under conditions of a decreased level of metabolism, heart rhythm, and body temperature and is evolutionarily acquired. At the same time, the observed changes in the content of individual FA do not lead to sharp changes in such integrative parameters as the total non-saturation of phospholipids, which determines liquid properties of chylomicrons and other lipolipoprotein transport particles of the souslik blood. There are studied absorption spectra of blood lipid extracts of rats and sousliks under effect of light as well as effect of light upon the FA composition of lipid extracts of these animals. The FA composition of lipid extracts has been established to remain practically constant, whereas the character of changes of spectra under action of light indicates the presence in the extracts of oxidation-reduction reactions. The obtained data allow suggesting that in the lipid extract there occurs cooperation both of the phospholipid molecules themselves and of them with other organic molecules, which makes it possible for fatty acids to participate in processes of transport both of electrons and of protons. This novel role of FA as a participant of the electron transfer might probably be extrapolated to chemical reactions (processes) occurring inside the membrane.

Effects of dalargin on free radical processes in the blood of rats exposed to moderate hypothermia.

Moderate hypothermia stimulates LPO processes in rat plasma and erythrocytes and simultaneously increases antioxidant activity in the plasma and SOD activity erythrocyte. Dalargin prevents stimulation of LPO in the blood in hypothermia by reducing the generation of active oxygen species and maintaining the level of low-molecular antioxidants.

[Oxidative modification of proteins and antioxidative blood activity of ground squirrels during induced awakening from winter sleep].

The intensity of oxidative modification of plasma proteins and activity of the antioxidative system of the blood of the ground squirrels during awakening from winter sleep is studied. During waking of animals, processes of oxidative modification of proteins in the blood plasma intensify. While the body temperature rises, the antioxidative activity of hydrophylic components of the blood plasma grows essentially, and erythrocyte superoxide dismutase too. Activity of erythrocyte catalase at all stages of waking is definitely higher than in the control. The received results evidence that the high activity of various links of antioxidative blood protection provides stability to oxidative stress during waking of animals from deep sleep.

[Temperature dependence of the acetylcholinesterase activity in synaptic membranes of the rat brain].

The temperature dependence (5-40 degrees C) of the acetylcholinesterase activity in synaptic membranes of the rat brain at different substrate concentrations was studied. At low substrate concentrations, the Arrhenius plot has two linear sections. At high concentration, there is one linear section throughout the temperature range. The addition of glycerol to incubation medium to final concentrations of 1 and 2% (w/v) increases the Michaelis constant, without affecting the maximal rate and the inhibition constant. The role of diffusion in the temperature dependence of the acetylcholinesterase activity is discussed.

[The effect of hypothermia on kinetic characteristics of the rat brain synaptic membrane Na,K-ATPase].

The effect of profound hypothermia (acute or prolonged) on Km for ATP, Vm and strophanthine K affinity to Na,K-ATPase in the rat brain synaptosomal membranes was investigated. The temperature dependence of Na,K-ATPase activity in temperature range 5-40 degrees C was also studied. Hypothermia decreases Km and Vm, and increases affinity of strophanthine K to the enzyme. There are two linear sections in Arrhenius plots ofNa,K-ATPase activity. Hypothermia does not change position of the break point in Arrhenius plots. The mechanisms and biological significance of the changes revealed are discussed.

Effect of hypothermia on kinetic characteristics of acetylcholine esterase in rat erythrocyte membranes.

We studied kinetic and thermodynamic characteristics of acetylcholine esterase in rat erythrocyte membrane after whole-body hypothermia (20 degrees C) of different duration. Hypothermia increased the degree of substrate inhibition for acetylcholine esterase, maximum rate, and Michaelis constant. The temperature dependence of acetylcholine esterase activity remained practically unchanged.

Oxidative modification of plasma proteins during hypothermia and after dalargin administration.

Short-term and prolonged (3 h) moderate (30 degrees C) hypothermia intensified oxidative modification of plasma proteins, while deep hypothermia (20 degrees C) decreased the intensity of this process to a control level. Preliminary intraperitoneal injection of dalargin had practically no effect on oxidative modification of plasma proteins during moderate hypothermia.

[Effect of hypothermia on Na(+)-K(+)-ATPase activity and hemoglobin binding in the rat erythrocyte membranes]. / Vliianie gipotermii na aktivnost' Na(+)-K(+)-ATFazy i sviazyvanie gemoglobina v membranakh éritrotsitov krys.

The activity of Na+/K(+)-ATPase and hemoglobin binding in membranes of rat erythrocytes during hypothermia (20 degrees C) was studied. Hypothermia causes an increase in hemoglobin binding and a decrease in Na+/K(+)-ATPase activity. It was found in in vitro experiments that the addition of hemoglobin to the membranes does not affect the Na+/K(+)-ATPase activity in control animals and decreases the activity of the enzyme in hypothermia.

[Acetylcholinesterase activity in brain slices of rats subjected to cooling]. / Aktivnost' atsetilkholinesterazy v srezakh golovnogo mozga krys pri okhlazhdenii.

The acetylcholinesterase (AChE) activity is studied in rat slices of the cerebral cortex, corpus striatum, hypothalamus and medulla oblongata of rats during hypothermia (20 degrees C) and also 1 and 7 days after the posthypothermal period. Cooling of animals down to 20 degrees C is accompanied by an increase in the AChE activity in the brain both under incubation temperature of 20 degrees and 37 degrees C. Under prolonged hypothermia the AChE activity in the investigated brain regions, except for corpus striatum, returns to the control level. By the 7th day of posthypothermal period the AChE activity in corpus striatum, hypothalamus and medulla oblongata does not restore completely. The most substantial changes in the AChE activity both under hypothermia and posthypothermal period occur in corpus striatum, which obviously reflects its complicated functional role.

[ATPase and acetylcholinesterase activity of the brain in hypothermia]. / ATFaznaia i atsetilkholinésteraznaia aktivnost' mozga pri gipotermii.

Short-term hypothermia, caused by cooling of rats down to 20 degrees, decreased distinctly the Na+, K+-ATPase activity in brain homogenates incubated at 37 degrees and did not affect the enzyme activity in the homogenates incubated at 20 degrees. The longer hypothermia (2 hrs at 20 degrees) did not affect the Na+, K+-ATPase activity at 37 degrees (during incubation) and decreased the enzymatic activity in homogenates of middle brain and diencephalon at 20 degrees during the incubation. Contrary to Na+, K+-ATPase, the activity of acetylcholinesterase was markedly increased in brain tissues of rats with hypothermia (irrespective of the temperature of incubation) as compared with control animals.