Dynamics of Secondary Metabolites and Free Amino Acids in the Heart of the Fish Amur Sleeper Perccottus glenii (Odontobutidae) during Winter Hypobiosis

The freshwater fish Perccottus glenii is of interest owing to its tolerance to a wide range of environmental temperatures; however, the details of the mechanisms of its low-temperature adaptation have been insufficiently studied. Our previous work has shown the involvement of secondary metabolites and amino acids in the compensatory responses to near-zero temperatures of skeletal muscles, brain, blood plasma, and liver of P. glenii. In the current study we report their compensatory responses in the heart. It has been shown that, at the beginning of hypobiosis (December), at a water temperature of 1°C, the level of taurine almost halves in comparison with summer concentration (9.70 ± 0.55 μmol/g wet weight), and it decreases further to 3.80 ± 0.25 μmol/g by the end of winter hypobiosis (beginning of April). Phosphoethanolamine was not detected in summer, but it appears in December (0.81 ± 0.07 μmol/g) and increases until the end of hibernation. Cysteic acid was also found only in December but its concentration decreased before the end of hypobiosis. The ratio of glutamate and alanine pools, the indicator of the metabolic contribution of aerobic and anaerobic energy, showed a slight decrease of glutamate during hypobiosis and increase of alanine. Amino acid responses suggest that oxidative phosphorylation and the tricarboxylic acid cycle are actively involved in the energy supply of the heart of P. glenii even at the end of hypobiosis.