Reversible metabolic depression in hepatocytes of lamprey (Lampetra fluviatilis) during pre-spawning: regulation by substrate availability.

The regulation of oxidative metabolism in hepatocytes of lampreys (Lampetra fluviatilis) during the freshwater pre-spawning period of their life cycle was studied. The energy metabolism in these cells is characterized by a simplified scheme, where glycolytic ATP production is insignificant and fatty acids are the major respiratory substrates. Seasonal changes in aerobic cell metabolism include a considerable reversible depression of metabolic rate in lamprey hepatocytes during the winter months of the pre-spawning period. The depression is characterized by a more than twofold decrease in hepatocyte endogenous respiration rate, a reduction of oxidative phosphorylation and drop in cellular ATP content. The addition of fatty acids to the hepatocyte incubation medium prevents the decrease in the metabolic rate. In spring, before spawning, a marked activation of energy metabolism in lamprey hepatocytes is found. These observations support the conclusion that the regulation of lamprey hepatocyte energy metabolism is realized through the availability of fatty acids for oxidation.