Kinetic Characteristics of Erythrocyte Membrane Acetylcholinesterase in Ground Squirrels During Hibernation and Arousal

Hibernation of small mammals is unique in that it consists of bouts—alternating periods of deep hibernation and inter-bout arousals, during which the animals warm up and many body parameters return to the euthermic level. Significant fluctuations in body temperature during the transition of an animal from a torpid state to a euthermic one can affect membrane-bound enzymes. In this work, the activity and kinetic parameters of acetylcholinesterase (AChE) in erythrocyte membranes of small ground squirrels (Spermophilus pygmaeus Pall.) during deep torpor and in the dynamics of exit from it was studied. The activity of AChE in the membranes of ground squirrel erythrocytes was determined by Ellman’s method. The kinetic characteristics of AChE (maximum velocity (Vm), Michaelis constant (Km) and substrate inhibition constant (Ki)) were found by the least squares method in accordance with the Haldane model. The study showed that in the torpid state, the activity and Vm of AChE do not change significantly. At the same time, Km decreases and Ki increases, which contributes to a significant change in the character of the concentration dependence of AChE and a decrease in the degree of substrate inhibition. During arousal of ground squirrels from hibernation at Tb 25°C, Vm increases significantly, which sharply increases the efficiency of AChE catalysis, despite the fact that the Km value also increases. After the final warming of the ground squirrels from hibernation (Tb 37°C), the values of Vm and Km of AChE and, accordingly, the efficiency of catalysis do not normalize but remain at the level achieved at Tb 25°C. In this case, Ki values decrease relative to hibernation, which increases the degree of substrate inhibition and narrows the range of effective acetylcholine concentrations. The detected sharp changes in the activity of AChE of ground squirrel erythrocytes AChE during awakening can play an important role in the rapid decrease in the level of circulating acetylcholine and the improvement of peripheral microcirculation.