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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY
Department of Biology, Centre of Excellence in Evolutionary Genetics and Physiology, University of Turku, Turku, Finland
Submitted 11 January 2006 ; accepted in final form 9 June 2006
We studied the metabolic rate, cellular energetic state, hypoxia-inducible factor-1 (HIF-1) activation, and expression of enzymes involved in energy metabolism using rainbow trout (Oncorhynchus mykiss) hepatocytes over the oxygen range from 21 to 1 kPa. Oxygen dependence of these factors was assessed by gradually reducing oxygen supply to cells from 21 kPa to 10, 5, 2, and 1 kPa. Moreover, time course experiments for up to 20 h at oxygen tensions of 1 and 2 kPa were carried out. Reduction of oxygen from 21 kPa to 10, 5, 2, and 1 kPa decreased metabolic rate of the cells by 14, 24, 37, and 46%, respectively. This response was instantaneous and fully reversible upon reoxygenation. Cellular ATP content and the expression of all mRNAs studied decreased when oxygen was reduced from 21 to 5 and 2 kPa. The lowest ATP levels,
43% of the initial value, were measured at 5 kPa of oxygen, whereas the reduction in mRNA amounts was most pronounced at 2 kPa. At 1 kPa oxygen tension, both ATP content and mRNA amounts returned to normoxic (21 kPa) levels with a concomitant activation of HIF-1, indicating reorganization of energy metabolism in adaptation of cells to low oxygen supply. These results show that oxygen has a direct regulatory effect on metabolism of trout hepatocyte cultures, supporting the view that oxygen has a profound role in metabolic regulation in cells.
metabolic regulation; energy metabolism; hypoxia-inducible factor-1; hypoxia; teleost
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