Hypoxia-tolerant animals use metabolic suppression as an essential strategy to survive low
oxygen. Ectotherms can alter
membrane lipid composition in response to changes in environmental temperature, but it is currently unknown whether chronic
hypoxia can also elicit membrane restructuring. The goal of this study was to investigate a possible physiological link between membrane remodelling and metabolic suppression in goldfish exposed to prolonged
hypoxia (4 weeks
at 10% air saturation). We have tested the hypothesis that chronic
hypoxia would modulate
membrane lipid composition in ways that are consistent with known mechanisms of
ion pump inhibition. Because homeoviscous membrane restructuring could interfere with the response to
hypoxia, measurements were made at 2 temperatures. Results show that hypoxic goldfish suppress metabolic rate by 74% (at 13 °C) and 63% (at 20 °C). This study is the first to reveal that cold-acclimated animals undergo extensive, tissue-specific restructuring of
membrane lipids as they reach minimal metabolic rates. However,
hypoxia does not affect membrane composition in fish acclimated to 20 °C. The strong membrane response of cold-acclimated fish involves increases in
cholesterol abundance (in white muscle and gills) and in
fatty acid saturation, mainly caused by a reduction in %22:6 (
docosahexaenoic acid in gills and liver). Major
ion pumps like Na+/K+-
ATPase are known to be inhibited by
cholesterol and activated by 22:6. Because ion pumping by membrane-bound
ATPases accounts for a large fraction of basal cellular energy use, we propose that the membrane responses reported here could be a novel mechanism to promote metabolic suppression in cold-acclimated animals.