Nitrogen metabolism, acid–base regulation, and molecular responses to ammonia and acid infusions in the spiny dogfish shark (Squalus acanthias)

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Biochemical, systemic, and environmental physiology, 2015-07, Vol.185 (5), p.511-525
• Main Authors: Nawata, C. Michele, Walsh, Patrick J., Wood, Chris M.
• Format: Article
• Language: English
• Subjects: Acid-Base Equilibrium - drug effects; Acid-Base Equilibrium - physiology; Acidosis; Ammonia; Ammonia - blood; Ammonium Chloride - administration & dosage; Ammonium Chloride - adverse effects; Analysis of Variance; Animal Physiology; Animals; Bicarbonates - administration & dosage; Bicarbonates - adverse effects; Biochemistry; Biomedical and Life Sciences; Biomedicine; DNA Primers - genetics; Elasmobranchii; Gene Expression Regulation - drug effects; Glycoproteins; Human Physiology; Hydrochloric Acid; Life Sciences; Marine; Membrane Glycoproteins - metabolism; Metabolism; Nitrogen; Nitrogen - metabolism; Original Paper; Plasma; Polymerase Chain Reaction; Sodium Chloride; Spectrophotometry, Atomic; Squalus acanthias; Squalus acanthias - metabolism; Squalus acanthias - physiology; Urea; Urea - metabolism; Zoology
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s00360-015-0898-4

Although they are ureotelic, marine elasmobranchs express Rh glycoproteins, putative ammonia channels. To address questions raised by a recent study on high environmental ammonia (HEA) exposure, dogfish were intravascularly infused for 24 h at 3 ml kg −1 h −1 with isosmotic NaCl (500 mmol l −1 , control), NH 4 HCO 3 (500 mmol l −1 ), NH 4 Cl (500 mmol l −1 ), or HCl (as 125 mmol l −1 HCl + 375 mmol l −1 NaCl). While NaCl had no effect on arterial acid–base status, NH 4 HCO 3 caused mild alkalosis, NH 4 Cl caused strong acidosis, and HCl caused lesser acidosis, all predominantly metabolic in nature. Total plasma ammonia (T Amm ) and excretion rates of ammonia ( J Amm ) and urea-N ( J Urea-N ) were unaffected by NaCl or HCl. However, despite equal loading rates, plasma T Amm increased to a greater extent with NH 4 Cl, while J Amm increased to a greater extent with NH 4 HCO 3 due to much greater increases in blood-to-water PNH 3 gradients. As with HEA, both treatments caused large (90 %) elevations of J Urea-N , indicating that urea-N synthesis by the ornithine-urea cycle (OUC) is driven primarily by ammonia rather than HCO 3 − . Branchial mRNA expressions of Rhbg and Rhp2 were unaffected by NH 4 HCO 3 or NH 4 Cl, but v - type H + - ATPase was down-regulated by both treatments, and Rhbg and Na + /H + exchanger NHE2 were up-regulated by HCl. In the kidney, Rhbg was unresponsive to all treatments, but Rhp2 was up-regulated by HCl, and the urea transporter UT was up-regulated by HCl and NH 4 Cl. These responses are discussed in the context of current ideas about branchial, renal, and OUC function in this nitrogen-limited predator.