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First published online September 19, 2006
Journal of Experimental Biology 209, 3851-3861 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02437

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Effects of long-term hypoxia on enzymes of carbohydrate metabolism in the Gulf killifish, Fundulus grandis

Mery L. Martínez^1,*, Christie Landry^2,, Ryan Boehm¹, Steve Manning³, Ann Oliver Cheek^2, and Bernard B. Rees^1,¶

¹ Department of Biological Sciences, University of New Orleans, New Orleans, LA 70148, USA
² Department of Biological Sciences, Southeastern Louisiana University, Hammond, LA 70402, USA
³ Gulf Coast Research Laboratory, University of Southern Mississippi, Ocean Springs, MS, 39566, USA

^¶ Author for correspondence (e-mail: brees{at}uno.edu)

Accepted 11 July 2006

The goal of the current study was to generate a comprehensive, multi-tissue perspective of the effects of chronic hypoxic exposure on carbohydrate metabolism in the Gulf killifish Fundulus grandis. Fish were held at approximately 1.3 mg l^-1 dissolved oxygen (3.6 kPa) for 4 weeks, after which maximal activities were measured for all glycolytic enzymes in four tissues (white skeletal muscle, liver, heart and brain), as well as for enzymes of glycogen metabolism (in muscle and liver) and gluconeogenesis (in liver). The specific activities of enzymes of glycolysis and glycogen metabolism were strongly suppressed by hypoxia in white skeletal muscle, which may reflect decreased energy demand in this tissue during chronic hypoxia. In contrast, several enzyme specific activities were higher in liver tissue after hypoxic exposure, suggesting increased capacity for carbohydrate metabolism. Hypoxic exposure affected fewer enzymes in heart and brain than in skeletal muscle and liver, and the changes were smaller in magnitude, perhaps due to preferential perfusion of heart and brain during hypoxia. The specific activities of some gluconeogenic enzymes increased in liver during long-term hypoxic exposure, which may be coupled to increased protein catabolism in skeletal muscle. These results demonstrate that when intact fish are subjected to prolonged hypoxia, enzyme activities respond in a tissue-specific fashion reflecting the balance of energetic demands, metabolic role and oxygen supply of particular tissues. Furthermore, within glycolysis, the effects of hypoxia varied among enzymes, rather than being uniformly distributed among pathway enzymes.

Key words: anaerobic metabolism, gluconeogenesis, glycolysis, gene regulation, low oxygen