In mammals, treatment with low doses of nitrite has a cytoprotective effect in ischemia/reperfusion events, as a result of nitric oxide formation and S-nitrosation of proteins. Interestingly, anoxia-tolerant lower vertebrates possess an intrinsic ability to increase intracellular nitrite concentration during anoxia in tissues with high myoglobin and mitochondria content, such as the heart. Here, we tested the hypothesis that red and white skeletal muscles develop different nitrite levels in crucian carp exposed to deep hypoxia and assessed whether this correlates with myoglobin concentration. We also tested whether liver, muscle and heart tissue possess nitrate reductase activity that supplies nitrite to the tissues during severe hypoxia. Crucian carp exposed to deep hypoxia (1<PO2<3 mmHg) for 1 day increased nitrite in red musculature to more than double the value in normoxic fish, while nitrite was unchanged in white musculature. There was a highly significant positive correlation between tissue concentrations of nitrite and nitros(yl)ated compounds. Myoglobin levels were 7 times higher in red than in white musculature, but there was no clear correlation between nitrite and myoglobin levels. Finally, we found a low but significant nitrate reductase activity in liver and white muscle, but not in cardiomyocytes. Nitrate reduction was inhibited by allopurinol, showing that it was partly catalyzed by xanthine oxidoreductase.
The authors declare no competing or financial interests.
M.N.H., F.B.J. and J.O.L. conceived and designed the experiments; M.N.H., F.B.J., M.F., A.F. and N.M.G.C. performed the experiments; M.N.H., F.B.J., M.F., A.F. and N.M.G.C. analyzed the data; M.N.H. and F.B.J. wrote the paper; M.N.H., F.B.J., J.O.L., M.F., A.F. and N.M.G.C. revised the manuscript.
The study was supported by Natur og Univers, Det Frie Forskningsråd (10-084565 and 4181-00094).
- Received September 2, 2016.
- Accepted September 27, 2016.
- © 2016. Published by The Company of Biologists Ltd