Document Detail

The African lungfish (Protopterus dolloi): ionoregulation and osmoregulation in a fish out of water.
MedLine Citation:
PMID:  17160883     Owner:  NLM     Status:  MEDLINE    
Although urea production and metabolism in lungfish have been thoroughly studied, we have little knowledge of how internal osmotic and electrolyte balance are controlled during estivation or in water. We tested the hypothesis that, compared with the body surface of teleosts, the slender African lungfish (Protopterus dolloi) body surface was relatively impermeable to water, Na(+), and Cl(-) due to its greatly reduced gills. Accordingly, we measured the tritiated water ((3)H-H(2)O) flux in P. dolloi in water and during air exposure. In water, (3)H-H(2)O efflux was comparable with the lowest measurements reported in freshwater teleosts, with a rate constant (K) of 17.6% body water h(-1). Unidirectional ion fluxes, measured using (22)Na(+) and (36)Cl(-), indicated that Na(+) and Cl(-) influx was more than 90% lower than values reported in most freshwater teleosts. During air exposure, a cocoon formed within 1 wk that completely covered the dorsolateral body surface. However, there were no disturbances to blood osmotic or ion (Na(+), Cl(-)) balance, despite seven- to eightfold increases in plasma urea after 20 wk. Up to 13-fold increases in muscle urea (on a dry-weight basis) were the likely explanation for the 56% increase in muscle water content observed after 20 wk of air exposure. The possibility that muscle acted as a "water reservoir" during air exposure was supported by the 20% decline in body mass observed during subsequent reimmersion in water. This decline in body mass was equivalent to 28 mL water in a 100-g animal and was very close to the calculated net water gain (approximately 32 mL) observed during the 20-wk period of air exposure. Tritiated water and unidirectional ion fluxes on air-exposed lungfish revealed that the majority of water and ion exchange was via the ventral body surface at rates that were initially similar to aquatic rates. The (3)H-H(2)O flux declined over time but increased upon reimmersion. We conclude that the slender lungfish body surface, including the gills, has relatively low permeability to water and ions but that the ventral surface is an important site of osmoregulation and ionoregulation. We further propose that an amphibian-like combination of ventral skin water and ion permeability, plus internal urea accumulation during air exposure, allows P. dolloi to extract water from its surroundings and to store water in the muscle when the water supply becomes limited.
Michael P Wilkie; Tammie P Morgan; Fernando Galvez; Richard W Smith; Makiko Kajimura; Yuen K Ip; Chris M Wood
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't     Date:  2006-11-15
Journal Detail:
Title:  Physiological and biochemical zoology : PBZ     Volume:  80     ISSN:  1522-2152     ISO Abbreviation:  Physiol. Biochem. Zool.     Publication Date:    2007 Jan-Feb
Date Detail:
Created Date:  2006-12-12     Completed Date:  2007-02-16     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  100883369     Medline TA:  Physiol Biochem Zool     Country:  United States    
Other Details:
Languages:  eng     Pagination:  99-112     Citation Subset:  IM    
Department of Biology, McMaster University, Hamilton, Ontario, Canada.
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MeSH Terms
Body Weight
Chlorides / metabolism
Estivation / physiology
Fishes / anatomy & histology,  physiology*
Ions / metabolism
Osmolar Concentration
Sodium / metabolism
Urea / metabolism
Water / metabolism
Water-Electrolyte Balance*
Reg. No./Substance:
0/Chlorides; 0/Ions; 57-13-6/Urea; 7440-23-5/Sodium; 7732-18-5/Water

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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