Acute, short term cooling of North Sea eelpout Zoarces viviparus is associated with a reduction of tissue redox state and activation of hypoxia inducible factor (HIF-1) in the liver. The present study explores the response of HIF-1 to seasonal cold in Zoarces viviparus, and to latitudinal cold by comparing the eurythermal North Sea fish to stenothermal Antarctic eelpout (Pachycara brachycephalum). Hypoxic signalling (HIF-1 DNA binding activity) was studied in liver of summer and winter North Sea eelpout as well as of Antarctic eelpout at habitat temperature of 0°C and after long-term warming to 5°C. Biochemical parameters like tissue iron content, glutathione redox ratio, and oxidative stress indicators were analyzed to see whether the cellular redox state or reactive oxygen species formation and HIF activation in the fish correlate. HIF-1 DNA binding activity was significantly higher at cold temperature, both in the interspecific comparison, polar vs. temperate species, and when comparing winter and summer North Sea eelpout. Compared at the low acclimation temperatures (0°C for the polar and 6°C for the temperate eelpout) the polar fish showed lower levels of lipid peroxidation although the liver microsomal fraction turned out to be more susceptible to lipid radical formation. The level of radical scavenger, glutathione, was twofold higher in polar than in North Sea eelpout and also oxidised to over 50%. Under both conditions of cold exposure, latitudinal cold in the Antarctic and seasonal cold in the North Sea eelpout, the glutathione redox ratio was more oxidised when compared to the warmer condition. However, oxidative damage parameters (protein carbonyls and thiobarbituric acid reactive substances (TBARS) were elevated only during seasonal cold exposure in Z. viviparus. Obviously, Antarctic eelpout are keeping oxidative defence mechanisms high enough to avoid accumulation of oxidative damage products at low habitat temperature. The paper discusses how HIF could be instrumental in cold adaptation in fish.

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We studied the seasonal variation on aerobic metabolism and the response of oxidative stress parameters in the digestive glands of the subpolar limpet Nacella (P.) magellanica. Sampling was carried out from July (winter) 2002 to July 2003 in Beagle Channel, Tierra del Fuego, Argentina. Whole animal respiration rates increased in early spring as the animals spawned and remained elevated throughout summer and fall (winter: 0.09 ± 0.02. Oxidative stress was assessed at the hydrophilic level as the ascorbyl radical content / ascorbate content ratio (A U / AH − ). The A U / AH − ratio showed minimum values in winter (3.7 ± 0.2 10 − 5 AU) and increased in summer (18 ± 5 10 − 5 AU). A similar pattern was observed for lipid radical content (122 ± 29 pmol mg − 1 fresh mass [FW] in winter and 314 ± 45 pmol mg − 1 FW in summer), iron content (0.99 ± 0.07 and 2.7 ± 0.6 nmol mg − 1 FW in winter and summer, respectively) and catalase activity (2.9 ± 0.2 and 7 ± 1 U mgFW in winter and summer, respectively). Since nitrogen derived radicals are thought to be critically involved in oxidative metabolism in cells, nitric oxide content was measured and a significant difference in the content of the Fe-MGD-NO adduct in digestive glands from winter and summer animals was observed. Together, the data indicate that both oxygen and nitrogen radical generation rates in N. (P.) magellanica are strongly dependent on season.

The aim of this work was to characterize nitric oxide (NO) generation during the growth of Chlorella sp. cells. The profile of NO production was compared with that observed in Chlorella from temperate climate and Antarctic Chlamydomonas sp. A distinctive electron paramagnetic resonance (EPR) signal for the adduct MGD-Fe-NO was detected in the Antarctic Chlorella sp. cells on days 6 and 7 of growth. An assay based upon the time-dependent detection of NO by EPR was developed to assess both nitrate reductase (NR) and NO synthase (NOS)-like activities. A significant increase in both enzymatic activities was observed on day 6 of growth of Antarctic Chlorella sp. cells. However, NOS-like activity proved undetectable on day 10 of growth, while NR activity was observed until day 22 of growth. When the cultures were supplemented with No-nitro-L-arginine methyl ester (L-NAME) from day 0 to day 13, no growth was observed. After administration of L-NAME from day 5 to day 12, growth rate at log phase was inhibited from 0.18 AE 0.02 (control) to 0.11 AE 0.01 per day. Removal of L-NAME on day 12 increased the growth rate to 0.15 AE 0.02 per day. Supplementation with S-nitroso-N-acetylpenicillamine on day 5, in the presence of L-NAME from day 0, restored the growth rate to control values. The same profile of NO generation was observed during the growth of Antarctic Chlamydomonas sp.; however, Chlorella cells from temperate climate did not show any difference in NO generation over the growth period. The data reported here are the first observations, by employing EPR, of NO and the activity of the enzymes responsible for its generation during the growth of Antarctic photosynthetic alga.Abbreviations -EPR, electron paramagnetic resonance; L-NAME, No-nitro-L-arginine methyl ester; MGD, sodium-N-methyl-D-glucamine dithiocarbamate; NOS, nitric oxide synthase; NR, nitrate reductase; SNAP, S-nitroso-N-acetyl-penicillamine; TEMPO, 2,2,5,5-tetramethyl piperidine 1-oxyl.