Please use this identifier to cite or link to this item: https://doi.org/10.1242/jeb.034074
Title: The freshwater Amazonian stingray, Potamotrygon motoro, up-regulates glutamine synthetase activity and protein abundance, and accumulates glutamine when exposed to brackish (15‰) water
Authors: Ip, Y.K. 
Loong, A.M.
Ching, B.
Tham, G.H.Y.
Wong, W.P.
Chew, S.F.
Keywords: Amino acids
Freshwater stingray
Glutamate
Glutamate dehydrogenase
Glutamine
Glutamine synthetase
Nitrogen metabolism
Potamotrygon motoro
Urea
Issue Date: 1-Dec-2009
Citation: Ip, Y.K., Loong, A.M., Ching, B., Tham, G.H.Y., Wong, W.P., Chew, S.F. (2009-12-01). The freshwater Amazonian stingray, Potamotrygon motoro, up-regulates glutamine synthetase activity and protein abundance, and accumulates glutamine when exposed to brackish (15‰) water. Journal of Experimental Biology 212 (23) : 3828-3836. ScholarBank@NUS Repository. https://doi.org/10.1242/jeb.034074
Abstract: This study aimed to examine whether the stenohaline freshwater stingray, Potamotrygon motoro, which lacks a functional ornithine-urea cycle, would up-regulate glutamine synthetase (GS) activity and protein abundance, and accumulate glutamine during a progressive transfer from freshwater to brackish (15‰) water with daily feeding. Our results revealed that, similar to other freshwater teleoste, P. motoro performed hyperosmotic regulation, with very low urea concentrations in plasma and tissues, in freshwater. In 15‰ water, it was non-ureotelic and non-ureoosmotic, acting mainly as an osmoconformer with its plasma osmolality, [Na+] and [Cl-] comparable to those of the external medium. There were significant increases in the content of several free amino acids (FAAs), including glutamate, glutamine and glycine, in muscle and liver, but not in plasma, indicating that FAAs could contribute in part to cell volume regulation. Furthermore, exposure of P. motoro to 15‰ water led to up-regulation of GS activity and protein abundance in both liver and muscle. Thus, our results indicate for the first time that, despite the inability to synthesize urea and the lack of functional carbamoyl phosphate synthetase III (CPS III) which uses glutamine as a substrate, P. motoro retained the capacity to up-regulate the activity and protein expression of GS in response to salinity stress. Potamotrygon motoro was not nitrogen (N) limited when exposed to 15‰ water with feeding, and there were no significant changes in the animation and deamination activities of hepatic glutamate dehydrogenase. In contrast, P. motoro became N limited when exposed to 10‰ water with fasting and could not survive well in 15‰ water without food.
Source Title: Journal of Experimental Biology
URI: http://scholarbank.nus.edu.sg/handle/10635/101915
ISSN: 00220949
DOI: 10.1242/jeb.034074
Appears in Collections:Staff Publications

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