AUTHOR=Toh C Y., Chew S. F., Ip Alex Y.

TITLE=Gene Cloning and mRNA Expression of Glutamate Dehydrogenase in the Liver, Brain, and Intestine of the Swamp Eel, Monopterus albus (Zuiew), Exposed to Freshwater, Terrestrial Conditions, Environmental Ammonia, or Salinity Stress

JOURNAL=Frontiers in Physiology

VOLUME=2

YEAR=2011

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2011.00100

DOI=10.3389/fphys.2011.00100

ISSN=1664-042X

ABSTRACT=<p>The swamp eel, <italic>Monopterus albus</italic>, is an obligatory air-breathing teleost which can undergo long period of emersion, has high environmental and tissue ammonia tolerance, and can survive in brackish water. We obtained a cDNA sequence of glutamate dehydrogenase (<italic>gdh</italic>), which consisted of a 133-bp 5′ UTR, a complete coding sequence region spanning 1629 bp and a 3′ UTR of approximately 717 bp, from the liver, intestine, and brain of <italic>M. albus</italic>. The translated Gdh amino acid sequence had 542 residues, and it formed a monophyletic clade with <italic>Bostrychus sinensis</italic> Gdh1a, <italic>Tetraodon nigroviridis</italic> Gdh1a, <italic>Chaenocephalus aceratus</italic> Gdh1a, <italic>Salmo salar</italic> Gdh1a1 and Gdh1a2, and <italic>O. mykiss</italic> Gdh1a. One day of exposure to terrestrial conditions or 75 mmol l<sup>−1</sup> NH<sub>4</sub>Cl, but not to water at salinity 20, resulted in a significant increase in mRNA expression of <italic>gdh1a</italic> and Gdh amination activity in the liver of <italic>M. albus</italic>. However, exposure to brackish water, but not to terrestrial conditions or 75 mmol l<sup>−1</sup> NH<sub>4</sub>Cl, led to a significant increase in the mRNA expression of <italic>gdh1a</italic> and Gdh amination activity in the intestine. By contrast, all the three experimental conditions had no significant effects on the mRNA expression of <italic>gdh1a</italic> in the brain of <italic>M. albus</italic>, despite a significant decrease in the Gdh amination activity in the brain of fish exposed to 75 mmol l<sup>−1</sup> NH<sub>4</sub>Cl for 6 days. Our results indicate for the first time that the mRNA expression of <italic>gdh1a</italic> was differentially up-regulated in the liver and intestine of <italic>M. albus</italic> in response to ammonia toxicity and salinity stress, respectively. The increases in mRNA expression of <italic>gdh1a</italic> and Gdh amination activity would probably lead to an increase in glutamate production in support of increased glutamine synthesis for the purpose of ammonia detoxification or cell volume regulation under these two different environmental conditions.</p>