Revisiting the effects of crowding and feeding in the gulf toadfish, Opsanus beta: the role of Rhesus glycoproteins in nitrogen metabolism and excretion
- 15 January 2012
- journal article
- Published by The Company of Biologists in Journal of Experimental Biology
- Vol. 215 (2), 301-313
- https://doi.org/10.1242/jeb.061879
Abstract
SUMMARY: Models of branchial transport in teleosts have been reshaped by the recent discovery of Rhesus (Rh) glycoproteins, a family of proteins that facilitate the movement of NH3 across cell membranes. This study examines the effects of crowding and feeding on ammonia excretion in gulf toadfish (Opsanus beta) within the context of Rh glycoproteins and the ammonia-fixing enzyme, glutamine synthetase (GS). Four Rh isoforms (Rhag, Rhbg, Rhcg1 and Rhcg2) were isolated from toadfish. Tissue distributions showed higher levels of mRNA expression in the gills and liver, moderate levels in the intestine and lower levels in the stomach. Crowding significantly lowered branchial Rh expression and ammonia excretion rates in fasted toadfish. A comparison of Rh expression in the digestive tract revealed relatively low levels of Rhcg1 and Rhcg2 in the stomach and high mRNA abundance of Rhbg, Rhcg1 and Rhcg2 in the intestine of fasted, crowded toadfish. We speculate that these trends may reduce secretion and enhance absorption, respectively, to minimize the amount of ammonia that is lost through gastrointestinal routes. By contrast, these patterns of expression were modified in response to an exogenous ammonia load via feeding. Post-prandial ammonia excretion rates were elevated twofold, paralleled by similar increases in branchial Rhcg1 mRNA, gastric Rhcg1 mRNA and mRNA of all intestinal Rh isoforms. These changes were interpreted as an attempt to increase post-prandial ammonia excretion rates into the environment owing to a gradient created by elevated circulating ammonia concentrations and acidification of the digestive tract. Overall, we provide evidence that toadfish modulate both the expression of Rh isoforms and urea synthesis pathways to tightly control and regulate nitrogen excretion.Keywords
This publication has 64 references indexed in Scilit:
- The responses of zebrafish (Danio rerio) to high external ammonia and urea transporter inhibition: nitrogen excretion and expression of rhesus glycoproteins and urea transporter proteinsJournal of Experimental Biology, 2009
- Identification of two glucocorticoid response elements in the promoter region of the ubiquitous isoform of glutamine synthetase in gulf toadfish,Opsanus betaAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2009
- Post-prandial metabolic alkalosis in the seawater-acclimated trout: the alkaline tide comes inJournal of Experimental Biology, 2009
- The alkaline tide and ammonia excretion after voluntary feeding in freshwater rainbow troutJournal of Experimental Biology, 2008
- Amino acid metabolismPublished by Elsevier BV ,2001
- Absorption of glucose, amino acids, and dipeptides by the intestines of Atlantic salmon (Salmo salar L.)Fish Physiology and Biochemistry, 2000
- The interactive effects of feeding and exercise on oxygen consumption, swimming performance and protein usage in juvenile rainbow trout (Oncorhynchus mykiss)Journal of Experimental Biology, 1997
- The Relationship between Specific Dynamic Action (SDA) and Protein Synthesis Rates in the Channel CatfishPhysiological Zoology, 1991
- Modes of Ammonia Transport Across the Gill Epithelium of the Marine Teleost Fish Opsanus BetaJournal of Experimental Biology, 1989
- Daily Pattern of Nitrogen Excretion and Oxygen Consumption of Sockeye Salmon (Oncorhynchus nerka) under Controlled ConditionsJournal of the Fisheries Research Board of Canada, 1975