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The freeze-avoidance response of smelt Osmerus mordax : initiation and subsequent suppression of glycerol, trimethylamine oxide and urea accumulation

Jason R. Treberg¹, Connie E. Wilson¹, Robert C. Richards², K. Vanya Ewart² and William R. Driedzic^1,*

¹ Ocean Sciences Centre, Memorial University of Newfoundland, St John's Newfoundland, Canada A1C 5S7
² NRC Institute for Marine Biosciences, 1411 Oxford Street, Halifax, Nova Scotia, Canada B3H 3Z1

View larger version (23K): [in a new window]   Fig. 1. Thermal profiles of warm and ambient temperature smelt groups; arrows indicate sampling dates relative to the first day of the month.

View larger version (13K): [in a new window]   Fig. 2. Plasma osmolality, in warm and ambient smelt. Values are means ± S.E.M. (N=2-5); asignificant difference from initial value, *significant difference between warm and ambient fish (P<0.05).

View larger version (13K): [in a new window]   Fig. 3. Glycerol levels in warm and ambient smelt. (A) Plasma; (B) muscle; (C) liver. Values are means ± S.E.M. (N=6 initially; N=5 for all other points). aSignificant difference from initial value; *significant difference between warm and ambient fish (P<0.05).

View larger version (12K): [in a new window]   Fig. 4. TMAO levels in warm and ambient smelt. (A) Plasma; (B) muscle; (C) liver. Values are means ± S.E.M. (N=6 initially; N=5 for all other points). aSignificant difference from initial value; *significant difference between warm and ambient fish (P<0.05).

View larger version (11K): [in a new window]   Fig. 5. Urea levels, in warm and ambient smelt. (A) Plasma; (B) muscle; (C) liver. Values are means ± S.E.M. (N=6 initially; N=5 for all other points). aSignificant difference from initial value; *significant difference between warm and ambient fish (P<0.05).

View larger version (13K): [in a new window]   Fig. 6. Liver activities of aspartate aminotransferase (AspAT), alanine aminotransferase (AlaAT) and glycerol-3-phosphate dehydrogenase (GPDH) from warm and ambient smelt. Values are means ± S.E.M. (N=6 initially; N=5 for all other points). aSignificant difference from initial value.

View larger version (20K): [in a new window]   Fig. 7. Liver glycerol-3-phosphate dehydrogenase (GPDH) mRNA expression in smelt. The blot was probed as described in the Materials and methods. (A) Densitometric analysis of the blots showing mean values ± S.E.M. (B) Blot images for three males sampled on January 11.

View larger version (15K): [in a new window]   Fig. 8. Liver glycogen levels in warm and ambient smelt. Values are means ± S.E.M. (N=6 initially; N=5 for all other points). aSignificant difference from initial value; *significant difference between warm and ambient fish (P<0.05).

View larger version (12K): [in a new window]   Fig. 9. Plasma thermal hysteresis in warm- and ambient-held smelt. Values are means ± S.D. (N=2-5). aSignificantly different (P<0.05) from initial value; *significantly different (P<0.05) between warm and ambient fish.

View larger version (27K): [in a new window]   Fig. 10. Liver AFP mRNA expression in smelt. The blot was probed as described in Materials and methods. (A) Densitometric analysis of the blots; values are means ± S.E.M. (N=3). (B) Blot images for three males sampled on January 11. *Significant difference (P<0.05).

View larger version (17K): [in a new window]   Fig. 11. Proposed pathways for the production of glycerol in smelt. FBP, fructose- 1,6-bisphosphate; GAP, glyceraldehyde-3-phosphate; DHAP, dihydroxyacetone phosphate; G3P, glycerol-3-phosphate; PEP, phosphoenolpyruvate; OAA, oxaloacetate; KG, alpha-ketoglutarate. Enzymes are (1) aspartate aminotransferase; (2) alanine aminotransferase; (3) glutamate dehydrogenase; (4) pyruvate carboxylase; (5) phophoenolpyruvate carboxykinase; (6) aldolase; (7) triose isomerase; (8) glycerol-3-phosphate dehydrogenase; (9) glycerol-3-phosphatase. Dotted arrows indicate multiple conversion steps.