Na(+)-independent, H(+)-coupled transepithelial beta-alanine absorption by human intestinal Caco-2 cell monolayers

D T Thwaites, G T McEwan, C D Brown, B H Hirst, N L Simmons

Research output: Contribution to journalArticle

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Abstract

beta-Alanine transport across intact human intestinal epithelial (Caco-2) cell layers has been investigated. In Na(+)-containing solutions, net absorptive flux of beta-alanine from apical-to-basal surfaces is small or absent, despite Na(+)-dependent intracellular beta-alanine accumulation across both apical and basal surfaces. Upon apical acidification (apical pH 6.0, basal pH 7.5), beta-alanine absorptive flux and accumulation across the apical surface are increased. In Na(+)-free conditions, a significant absorptive flux of beta-alanine is observed, which is markedly stimulated upon apical acidification (pH 6.0). Cellular accumulation of beta-alanine across the apical but not basal surface is observed in Na(+)-free conditions, and this is increased by acidic (pH 6.0) solutions. Absorptive beta-alanine flux in Na(+)-free conditions with acidic apical solutions displays saturation kinetics and competitive inhibition by alanine and glycine, but not valine or serine. Addition of 20 mM beta-alanine to the apical solution of epithelial monolayers loaded with the pH indicator 2',7'-bis(2-carboxyethyl-5(6)-carboxyfluorescein) causes a marked decrement in intracellular pH. beta-Alanine transport is also electrogenic, a concentration-dependent increase in an inward short circuit current being observed in voltage-clamped epithelial monolayers. We conclude that a proton-dependent, but Na(+)-independent, amino acid transporter is expressed at the apical membrane of human intestinal Caco-2 cells, and we provide direct evidence for amino acid-stimulated proton influx across the apical membrane in this intact epithelial cell system.
Original languageEnglish
Pages (from-to)18438-41
Number of pages4
JournalThe Journal of Biological Chemistry
Volume268
Issue number25
Publication statusPublished - 5 Sep 1993

Fingerprint

beta-Alanine
Caco-2 Cells
Intestinal Absorption
Monolayers
Fluxes
Acidification
Protons
Membranes
Amino Acid Transport Systems
Saturation (materials composition)
Valine
Alanine
Short circuit currents
Glycine
Serine
Epithelial Cells
Amino Acids
Kinetics

Keywords

  • Biological Transport
  • Cell Line
  • Electric Conductivity
  • Epithelium
  • Fluoresceins
  • Fluorescent Dyes
  • Humans
  • Hydrogen-Ion Concentration
  • Intestinal Absorption
  • Protons
  • Sodium
  • beta-Alanine

Cite this

Na(+)-independent, H(+)-coupled transepithelial beta-alanine absorption by human intestinal Caco-2 cell monolayers. / Thwaites, D T; McEwan, G T; Brown, C D; Hirst, B H; Simmons, N L.

In: The Journal of Biological Chemistry, Vol. 268, No. 25, 05.09.1993, p. 18438-41.

Research output: Contribution to journalArticle

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T1 - Na(+)-independent, H(+)-coupled transepithelial beta-alanine absorption by human intestinal Caco-2 cell monolayers

AU - Thwaites, D T

AU - McEwan, G T

AU - Brown, C D

AU - Hirst, B H

AU - Simmons, N L

PY - 1993/9/5

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N2 - beta-Alanine transport across intact human intestinal epithelial (Caco-2) cell layers has been investigated. In Na(+)-containing solutions, net absorptive flux of beta-alanine from apical-to-basal surfaces is small or absent, despite Na(+)-dependent intracellular beta-alanine accumulation across both apical and basal surfaces. Upon apical acidification (apical pH 6.0, basal pH 7.5), beta-alanine absorptive flux and accumulation across the apical surface are increased. In Na(+)-free conditions, a significant absorptive flux of beta-alanine is observed, which is markedly stimulated upon apical acidification (pH 6.0). Cellular accumulation of beta-alanine across the apical but not basal surface is observed in Na(+)-free conditions, and this is increased by acidic (pH 6.0) solutions. Absorptive beta-alanine flux in Na(+)-free conditions with acidic apical solutions displays saturation kinetics and competitive inhibition by alanine and glycine, but not valine or serine. Addition of 20 mM beta-alanine to the apical solution of epithelial monolayers loaded with the pH indicator 2',7'-bis(2-carboxyethyl-5(6)-carboxyfluorescein) causes a marked decrement in intracellular pH. beta-Alanine transport is also electrogenic, a concentration-dependent increase in an inward short circuit current being observed in voltage-clamped epithelial monolayers. We conclude that a proton-dependent, but Na(+)-independent, amino acid transporter is expressed at the apical membrane of human intestinal Caco-2 cells, and we provide direct evidence for amino acid-stimulated proton influx across the apical membrane in this intact epithelial cell system.

AB - beta-Alanine transport across intact human intestinal epithelial (Caco-2) cell layers has been investigated. In Na(+)-containing solutions, net absorptive flux of beta-alanine from apical-to-basal surfaces is small or absent, despite Na(+)-dependent intracellular beta-alanine accumulation across both apical and basal surfaces. Upon apical acidification (apical pH 6.0, basal pH 7.5), beta-alanine absorptive flux and accumulation across the apical surface are increased. In Na(+)-free conditions, a significant absorptive flux of beta-alanine is observed, which is markedly stimulated upon apical acidification (pH 6.0). Cellular accumulation of beta-alanine across the apical but not basal surface is observed in Na(+)-free conditions, and this is increased by acidic (pH 6.0) solutions. Absorptive beta-alanine flux in Na(+)-free conditions with acidic apical solutions displays saturation kinetics and competitive inhibition by alanine and glycine, but not valine or serine. Addition of 20 mM beta-alanine to the apical solution of epithelial monolayers loaded with the pH indicator 2',7'-bis(2-carboxyethyl-5(6)-carboxyfluorescein) causes a marked decrement in intracellular pH. beta-Alanine transport is also electrogenic, a concentration-dependent increase in an inward short circuit current being observed in voltage-clamped epithelial monolayers. We conclude that a proton-dependent, but Na(+)-independent, amino acid transporter is expressed at the apical membrane of human intestinal Caco-2 cells, and we provide direct evidence for amino acid-stimulated proton influx across the apical membrane in this intact epithelial cell system.

KW - Biological Transport

KW - Cell Line

KW - Electric Conductivity

KW - Epithelium

KW - Fluoresceins

KW - Fluorescent Dyes

KW - Humans

KW - Hydrogen-Ion Concentration

KW - Intestinal Absorption

KW - Protons

KW - Sodium

KW - beta-Alanine

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SP - 18438

EP - 18441

JO - The Journal of Biological Chemistry

JF - The Journal of Biological Chemistry

SN - 0021-9258

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