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.

Development of intestinal ion‐transporting mechanisms during smoltification and seawater acclimation in Atlantic salmon Salmo salar

“…The further increase in both NKA α1c transcript and protein levels 4 days after SW transfer indicate an increased capacity of the enterocytes to drive the ion‐coupled fluid transport necessary for a hypo‐osmoregulation in SW (Grosell, ; Sundell & Sundh, ). The increased NKA α1c transcript and protein expression in this study is consistent with several previous studies where higher α‐subunit mRNA levels and increased NKA activity are shown in pyloric caeca and intestine of SW‐acclimated euryhaline teleosts compared with FW‐acclimated animals (Colin et al , ; Fuentes et al , ; Seidelin et al , ; Sundell et al , ; Veillette et al , ; Chew et al , ; Tipsmark et al , ).…”

Occurrence of ghrelin-producing cells, the ghrelin receptor and Na+,K+-ATPase in tissues of Atlantic halibut (Hippoglossus hippoglossus) during early development

“…Atlantic halibut larvae have rudimentary non-functional gills at hatching (Pittman et al 1990) and the presence of Na + ,K + -ATPase-immunoreactive cells in the gills at stages 3 to 4 probably signals the start of their osmoregulatory function. Na + ,K + -ATPase immunoreactivity has also been detected on the basolateral side of the epithelial cells in the intestine, the kidneys, and urinary bladder as previously reported in other seawateradapted teleosts (Masini et al 2001;Chew et al 2010). The occurrence of ghrelin-positive cells in the osmoregulatory organs of Atlantic halibut larvae is intriguing and indicates direct action in the regulation of hydromineral balance.…”

Ammonia production, excretion, toxicity, and defense in fish: a review

“…Increased production of glutamate after feeding can be an important adaptation to avoid or reduce postprandial ammonia toxicity (Tng et al, 2008). Subsequently, Chew et al (2010) reported that exposure to seawater for 14 days also led to a significant increase in GDH activities, in the amination directions, and in GDH protein abundance from the intestine of juvenile O. marmorata . Their results (Chew et al, 2010) suggest that excess glutamate formed in the intestine could be transported to the liver and muscle to facilitate increased amino acid synthesis for the purpose of cell volume regulation (Chew et al, 2009).…”

“…Subsequently, Chew et al (2010) reported that exposure to seawater for 14 days also led to a significant increase in GDH activities, in the amination directions, and in GDH protein abundance from the intestine of juvenile O. marmorata . Their results (Chew et al, 2010) suggest that excess glutamate formed in the intestine could be transported to the liver and muscle to facilitate increased amino acid synthesis for the purpose of cell volume regulation (Chew et al, 2009). Furthermore, Peh et al (2009) reported recently that the intestinal GDH was involved in ammonia detoxification in B. sinensis exposed to environmental ammonia in seawater.…”