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First published online September 19, 2008
Journal of Experimental Biology 211, 3111-3122 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.019117

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

Lindsay A. Jibb and Jeffrey G. Richards^*

Department of Zoology, The University of British Columbia, 6270 University Boulevard, Vancouver, BC, Canada V6T 1Z4

^* Author for correspondence (e-mail: jrichard{at}zoology.ubc.ca)

Accepted 23 July 2008

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 12 h exposure to severe hypoxia (0.3 mg O₂ l^–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 0.5 h hypoxia exposure and this increase in activity was temporally associated with an 11-fold increase in [AMP_free]/[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 -subunit isoforms and caused an 50% decrease in the mRNA levels of AMPK β-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 12 h hypoxia exposure suggesting a tissue-specific regulation of AMPK possibly related to a lack of change in cellular [AMP_free]/[ATP] as observed in muscle.

Key words: energy charge, fish, phosphorylation potential, protein synthesis

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