AMP-activated protein kinase activity during metabolic rate depression in the hypoxic goldfish, Carassius auratus.

Cell survival during hypoxia exposure requires a metabolic reorganization to decrease ATP demands to match the reduced capacity for ATP production. We investigated whether AMP-activated protein kinase (AMPK) activity responds to 12h exposure to severe hypoxia (-0.3mgO2l-1) in the anoxia-tolerant goldfish (Carassius auratus). Hypoxia exposure in goldfish was characterized by a strong activation of creatine phosphate hydrolysis and glycolysis in liver and muscle. AMPK activity increased by ~5.5-fold in goldfish liver within 0.5h hypoxia exposure and this increase in activity was temporally associated with an 11-fold increase in [AMPfree]/[ATP]. No changes in total AMPK protein amount were observed, suggesting that the changes in AMPK activity are due to post-translational phosphorylation of the protein. Hypoxia exposure had no effect on the expression of two identified AMPK α- subunit isoforms and caused an ~50% decrease in the mRNA levels of AMPK p-subunit isoform. Changes in AMPK activity in the liver were associated with an increase in percentage phosphorylation of a well-characterized target of AMPK, eukaryotic elongation factor-2 (eEF2), and decreases in protein synthesis rates measured in liver cell-free extracts. No activation of AMPK was observed in muscle, brain, heart or gill during the 12h hypoxia exposure suggesting a tissue-specific regulation of AMPK possibly related to a lack of change in cellular [AMPfree]/[ATP] as observed in muscle. [ABSTRACT FROM AUTHOR]