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First published online May 5, 2005
Journal of Experimental Biology 208, 1793-1801 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01572

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Hypoxic responses of Na⁺/K⁺ ATPase in trout hepatocytes

A. Bogdanova^1,*, B. Grenacher¹, M. Nikinmaa² and M. Gassmann¹

¹ Institute of Veterinary Physiology, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
² Laboratory of Animal Physiology, Department of Biology, University of Turku, Turku, Finland

^* Author for correspondence (e-mail: annab{at}access.unizh.ch)

Accepted 7 March 2005

Reduction in oxygenation induces inhibition of Na⁺/K⁺ ATPase in a number of cells and tissues, including hepatocytes. When not reversed, decrease in Na⁺/K⁺ pump activity leads to a gradual Na⁺ accumulation, cell swelling and death. However, when accompanied by suppression of dissipative cation pathways, it has also been shown to be a beneficial adaptive strategy used by some hypoxia-tolerant species to reduce ATP consumption during prolonged periods of anoxia. This study aims to investigate acute hypoxic responses of the Na⁺/K⁺ ATPase in primary cultures of trout hepatocytes. Gradual decrease in oxygenation was followed by an instantaneous transient dose-dependent downregulation of the Na⁺/K⁺ ATPase transport activity, but was without an effect on hydrolytic function of the enzyme. Hypoxia-induced inhibition of active K⁺ influx was reversed spontaneously when hypoxic incubation time exceeded 20 min. The stimulating effect of prolonged hypoxic exposure on the Na⁺/K⁺ pump is most probably secondary to hypoxia-induced activation of the Na⁺/H⁺ exchanger with the following Na⁺ accumulation leading to Na⁺/K⁺ ATPase activation. Hypoxia-induced inhibition of the Na⁺/K⁺ pump was not caused by ATP depletion or global oxidative stress. However, local controlled production of reactive oxygen species seems to play an important role in hypoxia-induced regulation of the Na⁺/K⁺ ATPase. Treatment of cells with mercaptopropionyl glycine (MPG), a scavenger of , abolished hypoxia-induced inhibition of the Na⁺/K⁺ ATPase. Earlier on we have shown that activation of Na⁺/H⁺ exchanger under hypoxic conditions can be opposed by MPG treatment as well. Taken together our results suggest that regulation of both oxygen-sensitive transporters may be accomplished by local changes in free radical production.

Key words: Na⁺-K⁺ ATPase, hypoxia, redox state, hepatocytes

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