Interactive Effects of Acute Changes in Temperature and pH on Metabolism in Hepatocytes from the Sea Raven Hemitripterus americanus

Abstract

Sea raven (Hemitripterus americanus) liver metabolism is similar to liver metabolism in other teleost fishes, with the following two notable exceptions: (1) lactate dehydrogenase levels and lactate utilization rates are extremely low, and (2) fatty-acid oxidation rates are much lower than those in other fish. The interaction of variations in temperature and extracellular pH on sea raven hepatocyte metabolism and intracellular pH were examined by measuring their effects on (1) both the rates of release of 14CO2 and production of 14C-glucose from labeled precursors (glucose, alanine, lactate, and oleate) and (2) the distribution ratios of 14C-5,5 dimethyloxazolidine-2,4dione (DMO). Temperature increases (from 10 to 18.5 C) resulted in increased metabolic rates (Q10 ≅ from 2 to 4). However, temperature decreases (from 10 to 2 C) led to marked deactivation of most pathways examined (Q10 ≅ from 5 to 20). Hexose monophosphate shunt activity was less temperature sensitive than glycolysis (as indicated by ratios of CO₂ release rates from C₁- vs. C₆-labeled glucose) and thus exhibited a relative increase in activity at 2 C. Temperature shifts produced small, transient changes in pHi (<0.15 units), which returned to control values by 1–2 h posttransfer. Decreases in pHe (0.4 units) had no significant effect on rates of CO₂ release and glucose production, and this appears to be due to the ability of the hepatocytes to rapidly return pHi to control values. These patterns of adjustment of pHi following temperature and extracellular pH changes observed in sea raven hepatocytes are different than those observed in other fish species (American eel and rainbow trout).