Effects of Temperature on the (Na++ K+)-ATPase and Oxygen Consumption in Hepatocytes of Two Species of Freshwater Fish, Roach (Rutilus rutilus) and Brook Trout (Salvelinus fontinalis)

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Abstract
Effects of temperature on the (Na⁺ + K⁺)-ATPase were studied in isolated hepatocytes of two species of freshwater fish acclimated to different temperatures. Binding of ³H⁺-ouabain to hepatocytes was used to determine the density of (Na⁺ + K⁺)-ATPase, and oxygen consumption was measured to estimate the cost of cation pumping. Intracellular sodium concentration was manipulated by incubating hepatocytes at 20°C or 0°-4°C before the measurement of oxygen consumption. In hepatocytes of Rutilus rutilus, the maximal number of ouabain binding sites per 10⁶ cells ( ) was 1.86 times higher in the 5° C- acclimated than in the 20° C-acclimated group. The equilibrium dissociation constants ( ) in both acclimation groups were not statistically different. In Salvelinus fontinalis, and values did not change with temperature acclimation. Ouabain-sensitive oxygen consumption (OS) in hepatocytes of R. rutilus was 1.60-1. 73 times higher in the cold- than in the warm-acclimated group. In S. fontinalis, acclimation temperature did not affect OS. On the other hand, cold preincubation of hepatocytes significantly increased OS in both acclimation groups and species. Results are discussed with regard to species-specific differences in the adaptation to temperature change at the cellular level, the main point being that in response to cold-acclimation R. rutilus adjusts the activity of the (Na⁺ + K⁺)-ATPase in a compensatory fashion, whereas S. fontinalis modulates passive ion leakage.

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