Revisiting the effects of crowding and feeding in the gulf toadfish, Opsanus beta: The role of Rhesus glycoproteins in nitrogen metabolism and excretion

Tamara M. Rodela, Andrew J. Esbaugh, Dirk Weihrauch, Clémence M. Veauvy, M. Danielle McDonald, Kathleen M. Gilmour, Patrick J. Walsh

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

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 NH 3 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, Rhcgl 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 Rhcgl and Rhcg2 in the stomach and high mRNA abundance of Rhbg, Rhcgl 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 Rhcgl mRNA, gastric Rhcgl 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.

Original languageEnglish (US)
Pages (from-to)301-313
Number of pages13
JournalJournal of Experimental Biology
Volume215
Issue number2
DOIs
StatePublished - Jan 2012

Keywords

  • Ammonia
  • Feeding
  • Gastrointestinal tract
  • Gill
  • Glutamine synthetase
  • Gulf toadfish
  • Nitrogen excretion
  • Opsanus beta
  • Plasma
  • Rhesus proteins
  • Urea

ASJC Scopus subject areas

  • Animal Science and Zoology
  • Ecology, Evolution, Behavior and Systematics
  • Molecular Biology
  • Physiology
  • Insect Science
  • Aquatic Science

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