The Brain Lactate Dehydrogenase of Little Ground Squirrels (Spermophilus pygmaeus Pall.) during Hibernation and Arousal

Hibernation is a form of adaptation of some mammals, which is characterized by a significant decrease in the metabolic rate and body temperature, suppression of a number of physiological functions. It lasts for several months and is accompanied by periodic awakenings, during which the animals warm up, and the biochemical and physiological parameters return to the euthermic level. Periodic switching between two different modes of functioning of the body (hibernation–arousal) is accompanied by significant restructuring in metabolic pathways and requires flexible mechanisms for changing the catalytic properties of their key enzymes. In this paper, the activity and kinetic parameters of LDH in the brain of ground squirrels in the hibernation–arousal cycle were studied. The study showed that hibernation is accompanied by a significant decrease in the catalytic efficiency of LDH, a change in the nature of the concentration dependence, an increase in Km and Ki, and a shift in the position of the optimum point towards higher concentrations. A decrease in LDH activity in the brain during hibernation can prevent excessive lactate accumulation, reduce the glycolytic flow rate and glucose consumption in the brain, which will suppress the electrical activity of neurons, as well as implement a carbohydrate-saving strategy. In the dynamics of arousal, already at its early stages (25°C), when active thermogenesis begins to connect, a sharp increase in the efficiency of enzyme catalysis occurs, which can be contributed by both an increase in Vmax and a decrease in Km of the enzyme. At complete normalization of the body temperature of arousal animals, the rate of catalysis becomes significantly higher than the control values. This indicates a close relationship between the enzyme and high electrical activity of the brain and demonstrates the important role of lactate in neuronal energetics, synaptic plasticity of the brain and synaptogenesis.