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Bicarbonate diffusion through mucus

E H Livingston1, J Miller, E Engel

  • 1Surgical and Research Services, West Los Angeles Veterans Affairs Medical Center, University of California 90073, USA.

The American Journal of Physiology
|September 1, 1995
PubMed
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The duodenal mucus layer maintains a neutral pH near the epithelium despite high acid. Bicarbonate (HCO3-) secretion and its diffusion through mucus are key to this pH gradient, with fluid flow also playing a role.

Area of Science:

  • Gastroenterology
  • Biophysics
  • Physiology

Background:

  • The duodenal epithelium is protected from high luminal acid by a mucus layer.
  • This mucus layer maintains a pH gradient, keeping the epithelial surface near neutral.
  • The precise mechanism of this pH gradient formation remains unclear.

Purpose of the Study:

  • To investigate the role of bicarbonate (HCO3-) diffusion in forming the duodenal pH gradient.
  • To quantify the diffusion coefficient of HCO3- in mucus.
  • To model the mucobicarbonate layer and its role in acid neutralization.

Main Methods:

  • Development of novel experimental and mathematical techniques for measuring ion diffusion coefficients.
  • Measurement of HCO3- diffusion coefficients in saline, mucin solutions, and rat duodenal mucus.

Related Experiment Videos

  • Mathematical modeling of the mucobicarbonate layer and simulation of acid neutralization.

    • Main Results:

    • Diffusion coefficients for HCO3- were determined: 20.2 x 10(-6) cm2/s in saline, 3.02 x 10(-6) cm2/s in 5% mucin, and 1.81 x 10(-6) cm2/s in rat duodenal mucus.
    • Modeling indicated that acid neutralization by HCO3- occurs directly above the epithelial surface.
    • A net luminal fluid flux of 5 µL/min/cm² was observed after acid perfusion, supporting the role of fluid convection.

    Conclusions:

    • Bicarbonate diffusion through mucus is crucial for maintaining the duodenal pH gradient.
    • Fluid convection towards the lumen may be essential for sustaining the pH gradient under high acid conditions.
    • These findings elucidate the protective mechanisms of the duodenal mucosa against acid injury.