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Freshwater Fish Gill Ion Transport: August Krogh to morpholinos and microprobes.
MedLine Citation:
PMID:  20874801     Owner:  NLM     Status:  In-Data-Review    
August Krogh proposed that freshwater fishes (and other freshwater animals) maintain body NaCl homoeostasis by extracting these ions from the environment via separate Na(+) /NH(4) (+) and Cl(-) /HCO(3) (-) exchangers in the gill epithelium. Subsequent data from other laboratories suggested that Na(+) uptake was more probably coupled to H(+) secretion via a vesicular proton pump (V-ATPase) electrically coupled to a Na(+) channel. However, despite uncertainty about electrochemical gradients, evidence has accrued that epithelial Na(+) /H(+) exchange indeed may be an alternative pathway for Na(+) uptake. The specific pathways for Na(+) uptake may be species and environment specific. An apical Cl(-) /HCO(3) (-) exchanger is generally accepted for most species (some species do not extract Cl(-) from freshwater), but the relative roles of anion exchanger-like (SLC4A1) vs. pendrin-like (SLC26Z4) exchangers are unknown, and also may be species specific. Most recently, data have supported the presence of an apical Na(+)  + Cl(-) cotransporter (NCC-type), despite thermodynamic uncertainty. Ammonia extrusion may be via NH(3) diffusing through the paracellular junctions or NH(4) (+) substitution on both basolateral and apical ionic exchangers (Na(+)  + K(+) -ATPase; Na(+)  + K(+)  + Cl(-) - cotransporter; and Na(+) /H(+) exchanger), but recent evidence suggests that Rhesus-glycoproteins mediate both basolateral and apical movement of ammonia.
D H Evans
Publication Detail:
Type:  Journal Article     Date:  2010-11-09
Journal Detail:
Title:  Acta physiologica (Oxford, England)     Volume:  202     ISSN:  1748-1716     ISO Abbreviation:  Acta Physiol (Oxf)     Publication Date:  2011 Jul 
Date Detail:
Created Date:  2011-06-14     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101262545     Medline TA:  Acta Physiol (Oxf)     Country:  England    
Other Details:
Languages:  eng     Pagination:  349-59     Citation Subset:  IM    
Copyright Information:
© 2010 The Author. Acta Physiologica © 2010 Scandinavian Physiological Society.
Department of Biology, University of Florida, Gainesville, FL; and Mt Desert Island Biological Laboratory, Salisbury Cove, ME, USA.
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