Document Detail

Intestinal bicarbonate secretion in marine teleost fish-source of bicarbonate, pH sensitivity, and consequences for whole animal acid-base and calcium homeostasis.
MedLine Citation:
PMID:  14729153     Owner:  NLM     Status:  MEDLINE    
Whole animal studies using seawater European flounder (Platichthys flesus) revealed that increasing intestinal [Ca(2+)] to 20 mM stimulated net HCO(3)(-) base secretion by 57%, but this was effectively balanced by an increase in net acid secretion, likely from the gills, to maintain whole animal acid-base status. Higher Ca(2+) concentrations (40 and 70 mM) in ambient seawater resulted in reduced plasma total CO(2). This indicates (1) imperfect acid-base compensation, and (2) that endogenous metabolic CO(2) is insufficient to fuel intestinal HCO(3)(-) secretion, under hyper-stimulated conditions. Bicarbonate secretion plays an important role in preventing calcium absorption by precipitating a large fraction of the imbibed calcium as CaCO(3). Indeed, under high Ca(2+) conditions (20 mM), up to 75% of the intestinal Ca(2+) is precipitated as CaCO(3) and then excreted. This is undoubtedly important in protecting the marine teleost kidney from the need for excessive calcium excretion and risk of renal stone formation. Using an in vitro pH-stat technique with the isolated intestinal epithelium, the replacement of serosal CO(2) with a HEPES buffered saline had no effect on HCO(3)(-) secretion, indicating that the endogenous supply of HCO(3)(-) from CO(2) hydration within epithelial cells is adequate for driving baseline secretion rates. Further, in vitro data demonstrated a stimulatory effect of low pH on intestinal HCO(3)(-) secretion. Thus, both luminal Ca(2+) and H(+) can regulate HCO(3)(-) secretion but the precise mechanisms and their potential interaction are currently unresolved.
Rod W Wilson; Martin Grosell
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Biochimica et biophysica acta     Volume:  1618     ISSN:  0006-3002     ISO Abbreviation:  Biochim. Biophys. Acta     Publication Date:  2003 Dec 
Date Detail:
Created Date:  2004-01-19     Completed Date:  2004-03-23     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0217513     Medline TA:  Biochim Biophys Acta     Country:  Netherlands    
Other Details:
Languages:  eng     Pagination:  163-74     Citation Subset:  IM    
Department of Biological Sciences, Hatherly Laboratories, University of Exeter, Exeter EX4 4PS, UK.
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MeSH Terms
Acid-Base Equilibrium
Bicarbonates / metabolism*
Calcium / metabolism*
Calcium Carbonate / metabolism
Calcium Chloride
Calcium Radioisotopes
Carbon Dioxide / blood,  metabolism
Epithelium / metabolism
Flounder / blood,  metabolism*
Hydrogen-Ion Concentration
Intestines / metabolism*
Reg. No./Substance:
0/Bicarbonates; 0/Calcium Radioisotopes; 10043-52-4/Calcium Chloride; 124-38-9/Carbon Dioxide; 471-34-1/Calcium Carbonate; 7440-70-2/Calcium

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