Gastrointestinal processing of Na+, Cl-, and K + during digestion: Implications for homeostatic balance in freshwater rainbow trout

Carol Bucking, Chris M. Wood

Research output: Contribution to journalArticle

59 Citations (Scopus)

Abstract

The role of the gastrointestinal tract in maintaining ionic homeostasis during digestion, as well as the relative contribution of the diet for providing electrolytes, has been generally overlooked in many aquatic species. An experimental diet that contained an inert reference marker (lead-glass beads) was used to quantify the net transport of Na+, K+, and Cl- during the digestion and absorption of a single meal (3% ration) by freshwater rainbow trout (Oncorhynchus mykiss). Secretion of Cl- into the stomach peaked at 8 and 12 h following feeding at a rate of 1.1 mmol·kg-1·h-1, corresponding to a theoretical pH of 0.6 in the secreted fluid (i.e., 240 mmol/l HCl). The majority (∼90%) of dietary Na+ and K+ was absorbed in the stomach, whereas subsequent large fluxes of Na+ and Cl- into the anterior intestine corresponded to a large flux of water previously observed. The estimated concentration of Na+ in fluids secreted into the anterior intestine was ∼155 mmol/l, equivalent to reported hepatic bile values, whereas the estimated concentration of Cl- (∼285 mmol/l) suggested seepage of HCl acid from the stomach in advance of the chyme front. Net absorption of K+ in the stomach occurred following the cessation of Cl- secretion, providing indirect evidence of K+ involvement with HCl acid production. Overall, 80-90% of the K+ and Cl- contents of the meal were absorbed on a net basis, whereas net Na+ absorption was negligible. Chyme-to-plasma ion concentration gradients were often opposed to the direction of ion transport, especially for Na+ and Cl-.

Original languageEnglish
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume291
Issue number6
DOIs
StatePublished - Dec 18 2006

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Oncorhynchus mykiss
Fresh Water
Digestion
Stomach
Intestines
Meals
Diet
Acids
Ion Transport
Bile
Electrolytes
Glass
Gastrointestinal Tract
Homeostasis
Ions
Water
Liver

Keywords

  • Ballotini beads
  • Inert markers
  • Ionoregulation
  • Oncorhynchus mykiss

ASJC Scopus subject areas

  • Physiology

Cite this

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title = "Gastrointestinal processing of Na+, Cl-, and K + during digestion: Implications for homeostatic balance in freshwater rainbow trout",
abstract = "The role of the gastrointestinal tract in maintaining ionic homeostasis during digestion, as well as the relative contribution of the diet for providing electrolytes, has been generally overlooked in many aquatic species. An experimental diet that contained an inert reference marker (lead-glass beads) was used to quantify the net transport of Na+, K+, and Cl- during the digestion and absorption of a single meal (3{\%} ration) by freshwater rainbow trout (Oncorhynchus mykiss). Secretion of Cl- into the stomach peaked at 8 and 12 h following feeding at a rate of 1.1 mmol·kg-1·h-1, corresponding to a theoretical pH of 0.6 in the secreted fluid (i.e., 240 mmol/l HCl). The majority (∼90{\%}) of dietary Na+ and K+ was absorbed in the stomach, whereas subsequent large fluxes of Na+ and Cl- into the anterior intestine corresponded to a large flux of water previously observed. The estimated concentration of Na+ in fluids secreted into the anterior intestine was ∼155 mmol/l, equivalent to reported hepatic bile values, whereas the estimated concentration of Cl- (∼285 mmol/l) suggested seepage of HCl acid from the stomach in advance of the chyme front. Net absorption of K+ in the stomach occurred following the cessation of Cl- secretion, providing indirect evidence of K+ involvement with HCl acid production. Overall, 80-90{\%} of the K+ and Cl- contents of the meal were absorbed on a net basis, whereas net Na+ absorption was negligible. Chyme-to-plasma ion concentration gradients were often opposed to the direction of ion transport, especially for Na+ and Cl-.",
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AU - Bucking, Carol

AU - Wood, Chris M.

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