| Reduction in the rates of protein and amino acid catabolism to slow down the accumulation of endogenous ammonia: a strategy potentially adopted by mudskippers (Periophthalmodon schlosseri snd Boleophthalmus boddaerti) during aerial exposure in constant darkness. | |
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MedLine Citation:
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PMID: 11398749 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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This study was designed to elucidate the strategies adopted by mudskippers to handle endogenous ammonia during aerial exposure in constant darkness. Under these conditions, specimens exhibited minimal locomotory activity, and the ammonia and urea excretion rates in both Periophthalmodon schlosseri and Boleophthalmus boddaerti decreased significantly. As a consequence, ammonia accumulation occurred in the tissues of both species of mudskipper. A significant increase in urea levels was found in the liver of P. schlosseri after 24h of aerial exposure, but no similar increase was seen in the tissues of B. boddaerti. It is unlikely that these two species of mudskipper detoxified ammonia to urea during aerial exposure since B. boddaerti does not possess a complete ornithine-urea cycle (OUC) and, although all the OUC enzymes were present in P. schlosseri, the activity of carbamoyl phosphate synthetase present in the liver mitochondria was too low to render the OUC functional for ammonia detoxification. Peritoneal injection of 15NH4Cl into P. schlosseri showed that this mudskipper was capable of incorporating some of the labelled ammonia into urea in its liver. However, aerial exposure did not affect this capability and did not induce detoxification of the accumulated ammonia to urea. Mudskippers exposed to terrestrial conditions and constant darkness did, however, show significant decreases in the total free amino acid content in the liver and blood, in the case of P. schlosseri and in the muscle of B. boddaerti. No changes in the alanine or glutamine content of the muscle were found in either species. Analyses of the balance between the reduction in nitrogenous excretion and the increase in nitrogenous accumulation further revealed that these two species of mudskipper were capable of reducing their protein and amino acid catabolic rates. Such adaptations constitute the most efficient way to avoid the build-up of internal ammonia, and would render unnecessary the detoxification of ammonia through energetically expensive pathways. This finding may be the first report of a teleost fish showing a reduction in proteolysis and amino acid catabolism in response to aerial exposure. |
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Authors:
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C B Lim; S F Chew; P M Anderson; Y K Ip |
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Publication Detail:
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Type: Journal Article |
Journal Detail:
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Title: The Journal of experimental biology Volume: 204 ISSN: 0022-0949 ISO Abbreviation: J. Exp. Biol. Publication Date: 2001 May |
Date Detail:
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Created Date: 2001-06-08 Completed Date: 2001-07-19 Revised Date: 2003-11-14 |
Medline Journal Info:
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Nlm Unique ID: 0243705 Medline TA: J Exp Biol Country: England |
Other Details:
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Languages: eng Pagination: 1605-14 Citation Subset: IM |
Affiliation:
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Department of Biological Science, National University of Singapore, Kent Ridge, Singapore 117543, Republic of Singapore. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Air* Alanine / metabolism Amino Acids / blood, metabolism* Ammonia / metabolism* Ammonium Chloride / administration & dosage, metabolism Animals Carbamoyl-Phosphate Synthase (Ammonia) / metabolism Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / metabolism Darkness* Glutamine / metabolism Kinetics Liver / metabolism Metabolic Detoxication, Drug Mitochondria, Liver / enzymology Motor Activity Muscles / metabolism Perciformes / metabolism* Proteins / metabolism* Urea / metabolism |
| Chemical | |
Reg. No./Substance:
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0/Amino Acids; 0/Proteins; 12125-02-9/Ammonium Chloride; 56-41-7/Alanine; 56-85-9/Glutamine; 57-13-6/Urea; 7664-41-7/Ammonia; EC 6.3.4.16/Carbamoyl-Phosphate Synthase (Ammonia); EC 6.3.5.5/Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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