Freshwater Fish Gill Ion Transport: August Krogh to morpholinos and microprobes.

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  • Author(s): Evans, D. H.
  • Source:
    Acta Physiologica. Jul2011, Vol. 202 Issue 3, p349-359. 11p. 2 Diagrams.
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    • Abstract:
      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 and Cl/HCO 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 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 diffusing through the paracellular junctions or NH 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. [ABSTRACT FROM AUTHOR]
    • Abstract:
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