title: Intestinal osmoregulatory acclimation and nitrogen metabolism in juveniles of the freshwater marble goby exposed to seawater.
abstract: The objective of this study was to elucidate the role of the intestine from juveniles of the marble goby, Oxyeleotris marmorata, during seawater (SW) exposure. It has been reported elsewhere that SW-exposed juvenile O. marmorata exhibits hypoosmotic and hypoionic regulation, with the induction of branchial Na(+)/K(+)-ATPase (NKA), Na(+):K(+):2Cl(-) cotransporter (NKCC), and cystic fibrosis transmembrane receptor-like chloride channels. Here, we report that SW exposure also led to significant increases in the activity and protein abundance of NKA in, and probably an increase in Na(+) uptake through, its intestine. Additionally, there was an increase in apical NKCC immunoreactivity in the intestinal epithelium, indicating that there could be increased Cl(-) uptake through the intestine. These results suggest that absorption of ions, and hence water, from the intestinal lumen could be an essential part of the osmoregulatory process in juvenile O. marmorata during exposure to SW. Furthermore, there were significant increases in the glutamate content, and the aminating activity and protein abundance of glutamate dehydrogenase (GDH) in the intestine of fish exposed to SW. Since the intestinal glutamine synthetase activity and protein abundance decreased significantly, and the intestinal glutamine content remained unchanged, in the SW-exposed fish, excess glutamate formed via increased GDH activity in the intestine could be channeled to other organs to facilitate the increased synthesis of amino acids. Taken together, our results indicate for the first time that, besides absorbing ions and water during SW exposure, the intestine of juvenile O. marmorata also participated in altered nitrogen metabolism in response to salinity changes.
authors.affiliation: Natural Sciences and Science Education, National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Republic of Singapore. sfun.chew@nie.edu.sg
authors.forename: Shit F
authors.initials: SF
authors.lastname: Chew
authors.forename: Yvonne Y M
authors.initials: YY
authors.lastname: Tng
authors.forename: Nicklaus L J
authors.initials: NL
authors.lastname: Wee
authors.forename: Chia Y
authors.initials: CY
authors.lastname: Tok
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Wilson
authors.forename: Yuen K
authors.initials: YK
authors.lastname: Ip
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000502:physiology*; D008856:Microscopy, Fluorescence; D009584:Nitrogen / Q000378:metabolism*; D010473:Perciformes / Q000502:physiology*; D054712:Salinity; D012623:Seawater; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology*
chemical_list: D000596:Amino Acids; D028021:Sodium-Potassium-Chloride Symporters; D018698:Glutamic Acid; D005969:Glutamate Dehydrogenase; D000254:Sodium-Potassium-Exchanging ATPase; D009584:Nitrogen