Digestion of a single meal affects gene expression of ion and ammonia transporters and glutamine synthetase activity in the gastrointestinal tract of freshwater rainbow trout

Abstract

Experiments on freshwater rainbow trout, Oncorhynchus mykiss, demonstrated how digestion affected the transcriptional expression of gastrointestinal transporters following a single satiating meal (~3% body mass ration) after a 1-week fast. Quantitative real-time polymerase chain reaction was employed to measure the relative mRNA expression of three previously cloned and sequenced transporters [H(+)-K(+)-ATPase (HKA), Na(+)/HCO(3)(-) cotransporter (NBC), and the Rhesus glycoprotein (Rhbg1; an ammonia transporter)] over a 24-h time course following feeding. Plasma total ammonia increased about threefold from pre-feeding levels to 288 μmol l(-1), whereas total ammonia levels in chyme supernatant reached a sixfold higher value (1.8 mmol l(-1)) than plasma levels. Feeding did not appear to have a statistically significant effect on the relative mRNA expression of the gastric HKA or Rhbg1. However, the relative mRNA expression of gastric NBC was increased 24 h following the ingestion of a meal. Along the intestinal tract, feeding increased the relative mRNA expression of Rhbg1, but had no effect on the expression of NBC. Expression of the gastric HKA was undetectable in the intestinal tract of freshwater rainbow trout. Digestion increased the activity of glutamine synthetase in the posterior intestine at 12 and 24 h following feeding. This study is among the first to show that there are digestion-associated changes in gene expression and enzyme activity in the gastrointestinal tract of teleost fish illustrating the dynamic plasticity of this organ. These post-prandial changes occur over the relative short-term duration of digesting a single meal.

Rh proteins and NH4+-activated Na+-ATPase in the Magadi tilapia (Alcolapia grahami), a 100% ureotelic teleost fish

“…Therefore, CPSase III is set up to trap metabolic ammonia directly, and funnel it immediately into urea-N production. The presence of Rhag in red blood cells, and of Rhbg and Rhcg2 in OUC tissues such as white muscle and liver, likely facilitates the shuttling of ammonia to sites where it can be trapped by glutamine synthetase and/or detoxified through the OUC by conversion into urea-N. Microbial activity in the faeces also produces ammonia , which may explain the Rh expression in the intestine (Bucking and Wood, 2012). Rh expression levels are relatively high in brain, which suggests that future studies should check the brain for both OUC activity and other detoxification mechanisms such as glutamine synthesis.…”

Nitrogen metabolism of the intestine during digestion in a teleost fish, the plainfin midshipman (Porichthys notatus)

“…Additionally, rainbow trout (N=3, 318-337g) were fed to satiation with 5pt floating pellet food and killed (1gl −1 MS-222) 24h following ingestion of the meal [based on Bucking and Wood (Bucking and Wood, 2012)]. The three intestinal sections (anterior, mid and posterior) were visually identified based on anatomical structures and individually removed, cleaned of chyme, freezeclamped and stored at −80°C as with the midshipman tissues.…”

“…Additionally, we now know that the concentration of ammonia along the GI tract during digestion is very high in species examined to date [~2mmol l −1 Bucking and Wood, 2012)], presenting potentially toxic circumstances on the local scale of the gut. One potential way that the GI tissue could limit the toxicological effects of this extreme ammonia concentration is by blocking uptake of intestinal ammonia through a downregulation or an entire lack of enterocyte ammonia transporter expression.…”

Genistein Induces Increase in Fluid pH, Na+ and HCO3− Concentration, SLC26A6 and SLC4A4 (NBCe1)-B Expression in the Uteri of Ovariectomized Rats

“…NBCe1-A mediates basolateral electrogenic sodium-base transport for example in the kidney proximal tubule and is critically required for transepithelial HCO 3 − absorption [20]. Meanwhile, in the secretory epithelia such as pancreatic duct [21], gastrointestinal tract [22] and parotid-salivary ducts [23], NBCe1-B is abundantly expressed and is responsible for basolateral HCO 3 − uptake for secretion at the apical membrane. In the corneal endothelia, NBCe-1, which was expressed at both the apical [24] and basolateral membranes [25], is responsible for HCO 3 − secretion into the aqueous humor.…”