Annual cycle in glycerol production and clearance in the rainbow smelt (Osmerus mordax) is partially regulated by cytosolic and mitochondrial glycerol 3-phosphate dehydrogenase

Robinson, Jason Lorne (2010) Annual cycle in glycerol production and clearance in the rainbow smelt (Osmerus mordax) is partially regulated by cytosolic and mitochondrial glycerol 3-phosphate dehydrogenase. Masters thesis, Memorial University of Newfoundland.

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Abstract

In winter, rainbow smelt (Osmerus mordax) increase plasma glycerol concentrations to ≥400 mM to prevent freezing. Glycerol levels then decrease in the late winter/early spring. To enhance understanding of the biochemical mechanisms controlling changes in glycerol levels in rainbow smelt I: 1) examined the tissue distribution of cytosolic glycerol 3-phosphate dehydrogenase (cytGPDH) in the rainbow smelt, and two species that do not accumulate glycerol in the plasma for colligative freeze avoidance (the Atlantic salmon and capelin) when held at warm (10°C) and cold (~1 °C) temperatures; 2) established which cytGPDH isoforms are present in rainbow smelt liver and white muscle; and 3) examined the potential role of mitochondrial glycerol 3-phosphate dehydrogenase (mGPDH) in the late winter/early spring decrease in plasma glycerol levels. The tissue distribution study of cytGPDH confirmed the liver as the primary source of glycerol in the rainbow smelt, and cytGPDH does not respond to cold exposure in the Atlantic salmon and capelin. However, it also raised the possibility that muscle cytGPDH may contribute to glycerol accumulation in the smelt. Zymograms revealed differential cytGPDH regulation, with 4 isozymes in the liver and only 2 in the muscle of rainbow smelt. However, this distribution pattern was not affected by temperature (ie. glycerol production status). Higher activity levels of hepatic mGPDH were measured just before plasma glycerol levels returned to basal levels, and mGPDH mRNA expression was generally higher during the glycerol decrease than during the accumulation phase. Collectively, the results suggest that both cytosolic and mitochondrial GPDH enzymes play important roles in glycerol regulation.

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