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First published online October 10, 2003

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Energy budget of hepatocytes from Antarctic fish (Pachycara brachycephalum and Lepidonotothen kempi) as a function of ambient CO₂: pH-dependent limitations of cellular protein biosynthesis?

M. Langenbuch and H. O. Pörtner

Alfred-Wegener-Institut für Polar- und Meeresforschung, Ökophysiologie und Ökotoxikologie, Postfach 120161, D-27515 Bremerhaven, Germany

View larger version (14K): [in a new window]   Fig. 1. Steady state intracellular pH values (pHi) of isolated hepatocytes from P. brachycephalum under conditions of normoand hypercapnia, measured after 50 min of exposure to media of different pH. *pHi significantly different from the control value at pHe 7.90. Values are means ± S.D., N=5-6.

View larger version (20K): [in a new window]   Fig. 4. Correlated changes in rates of oxygen consumption and intracellular (A) and extracellular (B) bicarbonate concentrations determined in hepatocytes isolated from P. brachycephalum. Intracellular values were measured after 50 min of exposure to normocapnic and hypercapnic media of different pH. *Oxygen consumption rate significantly different from the respective control value at pHe 7.90. Values are means ± S.D., N=4.

View larger version (14K): [in a new window]   Fig. 2. Rates of oxygen consumption by isolated hepatocytes from L. kempi (A) and P. brachycephalum (B) at different extracellular pH values during normocapnic or hypercapnic incubation. *Oxygen consumption rate significantly different from the respective control value at pHe 7.90. Values are means ± S.D., N=6-7 for L. kempi and N=4 for P. brachycephalum.

View larger version (16K): [in a new window]   Fig. 3. Relationship between rates of oxygen consumption by isolated hepatocytes from P. brachycephalum and intracellular pH, measured at different values of extracellular pH during normocapnic or hypercapnic incubation. *Oxygen consumption rate significantly different from the respective control value at pHe 7.90. Values are means ± S.D., N=4.

View larger version (35K): [in a new window]   Fig. 5. Rates of oxygen consumption by isolated hepatocytes from L. kempi (A) and P. brachycephalum (B), measured after exposure to media of different pH and PCO2. Control values at the respective pHe were determined after incubation of cells without cycloheximide. To measure the decrease of oxygen consumption rate induced by inhibition of protein biosynthesis, cells were incubated for 60 min with 35.5 µmol l-1 cycloheximide prior to analysis of metabolic rate. aOxygen consumption rates significantly different from the respective control value at pHe 7.90 or pHe 6.50; boxygen consumption rates significantly different from the respective cycloheximide-inhibited value at pHe 7.90 (significant differences within normalized data were identified using the Mann-Whitney rank sum test; all results were confirmed by an additional analysis of original data with the Student's t-test for paired samples). Values are means ± S.D., N=6 for both species.