Protein synthesis in hypometabolic fishes

Lewis, Johanne M. (2007) Protein synthesis in hypometabolic fishes. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The objective of this doctoral thesis was to investigate protein synthesis in two species of hypomctabolic telcosts: the north temperate labrid, Tautogolabrus adspersus (cunner) and the Amazonian cichlid, Astronotus ocellatus (oscar). The Hooding dose methodology, which measures in vivo rates of tissue protein synthesis following the injection of a large dose of radiolabeled phenylalanine, was used to measure rates of amino acid incorporation at three key time points with respect to metabolic depression: 1) the entrance into metabolic depression; 2) while in a metabolically depressed state; and 3) during the return to regular activity levels. Additionally, rates of phenylalanine incorporation in the subcellular protein pool were determined in cunner in response to acute hypothermia and hypoxia. In general, an active decrease in protein synthesis (55-65%), in both the whole tissue and subcellular protein pools, accompanied the metabolic depression observed at the whole animal level. However, tissue specific responses in protein synthesis were evident in both species and appeared to play an adaptive role in extending survival time while in an energetically compromised state. Only a modest decrease in brain protein synthesis was observed in hypoxic oscar (30%), which may be linked to the maintenance low levels of activity for predator avoidance. Protein synthesis was defended in the mitochondrial protein pool of the cunner gills during both acute hypoxia and hypothermia challenges, suggesting its importance to the maintenance of ion and gas exchange in this tissue. In addition, a significant hypcractivation of liver protein synthesis occurs in metabolically depressed cunner, which may be associated with the production of antifreeze proteins at extreme low temperatures. During the post-dormancy recovery period a significant hypcractivation of protein synthesis occurred in white muscle, heart and liver in cunner. In contrast, post-hypoxic oscars do not experience a hypcractivation in protein synthesis despite a significant increase in oxygen consumption during recovery. This latter result suggesting that the accumulation of a protein debt is either stress specific or an artifact of the length of time spent in a hypometabolic state.

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