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Title: | Functional characterization of renal ammonia transport and acid-base regulation in teleost and elasmobranch fishes |
Authors: | Lawrence, Michael J. |
Advisor: | Wood, Chris M. Wright, Patricia A. |
Department: | Biology |
Keywords: | Ammonia;Renal ammonia transport;Kidney;Sodium;Rhesus glycoproteins;Acid-base regulation;Teleost fish;Elasmobranch fish;Comparative and Evolutionary Physiology;Systems and Integrative Physiology;Biology;Cellular and Molecular Physiology;Metabolic Acidosis;Gills;Amino acid metabolism;H+ ATPase |
Publication Date: | 2014 |
Abstract: | Teleost fishes incorporate renal ammonia excretion as part of a greater acid-base regulatory system. However, the transport mechanisms employed by the renal epithelium to excrete ammonia are relatively unknown. I hypothesized that, under metabolic acidosis, increased renal ammonia excretion would be the product of tubular secretion and involve a Na+/NH4+ exchange metabolon mediated through Rhesus (Rh) glycoproteins. To induce metabolic acidosis, goldfish (Carassius auratus) were exposed to a low pH environment (pH 4.0; 48-h). There was a clear signal of metabolic acidosis: a reduction in both plasma [HCO3-] and blood pH with no influence on plasma PCO2. Goldfish demonstrated an elevation in total plasma [ammonia] with a reduction in PNH3 under acidosis. Metabolic acidosis induced higher rates of urinary excretion of acidic equivalents in the form of both NH4+ and titratable acidity-HCO3- (TA-HCO3-) excretion. Urinary Na+ excretion was not affected by acidosis and urine [Na+] did not correlate with urinary [ammonia]. Alanine aminotransferase activity in the kidney was higher in acidotic goldfish. Glomerular filtration rate and urine flow rate were not affected by acidosis. Increased renal NH4+ excretion was due to increased secretion, and not increased filtration, of ammonia. There was a corresponding elevation in Rhcg1b mRNA expression but no change in renal Na+ reabsorption. My data support a secretion-based mechanism of teleost renal ammonia transport. This system is Na+ independent and is likely mediated by Rh glycoproteins and H+ ATPase, involving a parallel H+/NH3 secretion mechanism. To investigate effects of metabolic acidosis on elasmobranch fish, Pacific spiny dogfish (Squalus acanthias suckleyi) were infused with an acidic saline (125 mM HCl/375 mM NaCl; 3 ml/kg/h; 24-h). The results are preliminary, with no marked effects of HCl infusion on plasma acid-base or N-status, but increased branchial NHE2 and lower renal NHE3 protein expressions. These data are summarized in an Appendix. |
URI: | http://hdl.handle.net/11375/16316 |
Appears in Collections: | Open Access Dissertations and Theses |
Files in This Item:
File | Description | Size | Format | |
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Functional Characterization of renal ammonia transport and acid base regulation in teleost and elasmobranch fish Michael J Lawrence.pdf | Compiled Thesis | 1.03 MB | Adobe PDF | View/Open |
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