Bicarbonate ion diffusion through mucus .
Livingston, Edward H., Jerry Miller, Eli Engel.
Surgical and Research Services, West Los Angeles VAMC, UCLA, and
Center for Ulcer Research and Education, Los Angeles, California,
90073
APStracts 2:0078G, 1995.
The mucus layer overlying duodenal epithelium maintains a pH gradient
against high luminal acid concentrations. Despite these adverse
conditions epithelial surface pH remains close to neutrality. The
exact nature of the gradient forming barrier remains unknown. The
barrier consists of mucus into which bicarbonate ion is secreted.
Quantification of bicarbonate ion's ability to establish and maintain
the gradient depends upon accurate measurement of this ion's
diffusion coefficient through mucus. We describe new experimental and
mathematical methods for diffusion measurement and report diffusion
coefficients for bicarbonate ion diffusion through saline, 5% mucin
solutions, and rat duodenal mucus. The diffusion coefficients were:
20.2 .10, 3.02 .31, and 1.8 .12 x 10-6 cm2 sec-1 respectively.
Modeling of the mucobicarbonatelayer with this latter value suggests
that for conditions of high luminal acid strength, the neutralization
of acid by bicarbonate occurs just above the epithelial surface.
Under these conditions the model predicts that fluid convection
towards the lumen could be important in maintaining the pH gradient.
In support of this we were able to demonstrate a net luminal fluid
flux of 5 {SYMBOL 109 \f "Symbol"}L/min/cm2 following
perfusion of .15 N HCl in the rat duodenum.
Received 20 May 1994; accepted in final form 7 April 1995.
APS Manuscript Number G191-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 2 May 1995.