Intestinal bicarbonate secretion by marine teleost fish - Why and how?

Rod W. Wilson, Jonathan M. Wilson, Martin Grosell

Research output: Contribution to journalArticlepeer-review

171 Scopus citations

Abstract

Intestinal fluids of most marine teleosts are alkaline (pH 8.4-9.0) and contain high levels of HCO3- equivalents (40-130 mM) which are excreted at a significant rate (>100 μEq kg-1 h-1). Recent research reveals the following about this substantial HCO3- secretion: (1) It is not involved in acid-base regulation or neutralisation of stomach acid, but increases in parallel with drinking rate at elevated ambient salinities suggesting a role in osmoregulation; (2) In species examined so far, all sections of the intestine can secrete bicarbonate; (3) The secretion is dependent on mucosal Cl-, sensitive to mucosal DIDS, and immuno-histochemistry indicates involvement of an apical Cl-/HCO3- exchanger. In addition, hydration of CO2 via carbonic anhydrase in combination with proton extrusion appears to be essential for bicarbonate secretion. The mode of proton extrusion is currently unknown but potential mechanisms are discussed. One consequence of the luminal alkalinity and high bicarbonate concentrations is precipitation of calcium and magnesium as carbonate complexes. This precipitation is hypothesised to reduce the osmolality of intestinal fluids and thus play a potential role in water absorption and osmoregulation. The present studies on European flounder reveal that elevated luminal calcium (but not magnesium) concentrations stimulate intestinal bicarbonate secretion both acutely and chronically, in vitro and in vivo. At the whole animal level, the result of this elevated bicarbonate secretion was increased calcium precipitation with an associated reduction in the osmolality of rectal fluids and plasma. These observations suggest direct functional links between intestinal bicarbonate secretion, divalent cation precipitation and osmoregulation in marine teleost fish.

Original languageEnglish (US)
Pages (from-to)182-193
Number of pages12
JournalBiochimica et Biophysica Acta - Biomembranes
Volume1566
Issue number1-2
DOIs
StatePublished - Nov 13 2002
Externally publishedYes

Keywords

  • Calcium
  • Chloride-bicarbonate exchange
  • Osmoregulation
  • pH-stat titration
  • Precipitation
  • Water absorption

ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Biophysics

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