An in vitro investigation of gastrointestinal Na+ uptake mechanisms in freshwater rainbow trout

Sunita R. Nadella, Dhanisha Patel, Allen Ng, Chris M. Wood

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

In vitro gut-sac preparations of all four sections (stomach, anterior, mid, and posterior intestine) of the gastrointestinal tract (GIT) of freshwater rainbow trout, together with radiotracer (22Na) techniques, were used to study unidirectional Na+ uptake rates (UR, mucosal → blood space) and net absorptive fluid transport rates (FTR) under isosmotic conditions (mucosal = serosal osmolality). On an area-specific basis, unidirectional Na+ UR was highest in the mid-intestine, but when total gut area was taken into account, the three intestinal sections contributed equally, with very low rates in the stomach. The theoretical capacity for Na+ uptake across the whole GIT is sufficient to supply all of the animal’s nutritive requirements for Na+. Transport occurs by low affinity systems with apparent Km values 2–3 orders of magnitude higher than those in the gills, in accord with comparably higher Na+ concentrations in chyme versus fresh water. Fluid transport appeared to be Na+-dependent, such that treatments which altered unidirectional Na+ UR generally altered FTR in a comparable fashion. Pharmacological trials (amiloride, EIPA, phenamil, bafilomycin, furosemide, hydrochlorothiazide) conducted at a mucosal Na+ concentration of 50 mmol L−1 indicated that GIT Na+ uptake occurs by a variety of apical mechanisms (NHE, Na+ channel/H+ ATPase, NCC, NKCC) with relative contributions varying among sections. However, at a mucosal Na+ concentration of 10 mmol L−1, EIPA, phenamil, bafilomycin, and hydrochlorothiazide were no longer effective in inhibiting unidirectional Na+ UR or FTR, suggesting the contribution of unidentified mechanisms under low Na+ conditions. A preliminary model is presented.

Original languageEnglish
Pages (from-to)1003-1019
Number of pages17
JournalJournal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology
Volume184
Issue number8
DOIs
StatePublished - Jan 1 2014

Fingerprint

Oncorhynchus mykiss
Fresh Water
rainbow
Gastrointestinal Tract
Hydrochlorothiazide
hydrochlorothiazide
gastrointestinal system
uptake mechanisms
Intestines
Fluids
Stomach
fluid
stomach
intestines
Proton-Translocating ATPases
digestive system
Amiloride
Furosemide
furosemide
Osmolar Concentration

Keywords

  • Diet
  • Gut sacs
  • Low-affinity transport
  • Mucus
  • Na
  • Pharmacological agents
  • Transport kinetics

ASJC Scopus subject areas

  • Physiology
  • Ecology, Evolution, Behavior and Systematics
  • Animal Science and Zoology
  • Biochemistry
  • Endocrinology

Cite this

An in vitro investigation of gastrointestinal Na+ uptake mechanisms in freshwater rainbow trout. / Nadella, Sunita R.; Patel, Dhanisha; Ng, Allen; Wood, Chris M.

In: Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology, Vol. 184, No. 8, 01.01.2014, p. 1003-1019.

Research output: Contribution to journalArticle

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