Experimental analysis of hydrogen ion diffusion in gastrointestinal mucus glycoprotein

Experiments were undertaken to test the hypothesis that mucus glycoproteins retard the diffusion of hydrogen ions, a possible protective action of gastric mucus. Mucus and mucus glycoproteins (visible mucus, crude mucin, mucus glycoprotein fractions) were evaluated in two devices designed for this test, a linear diffusion chamber and a hydrogen ion flux chamber. The linear diffusion chamber assessed ion diffusion from a point source through mucus glycoproteins to a H+ detector. A mathematical model of diffusion, based on Fick's law, was adapted to characterize diffusion in this chamber. The H+ flux chamber assessed H+ flux rates across a steep concentration gradient through controlled amounts of mucus glycoprotein. With the exception of human sulfomucin, tested only at dilute concentrations and only in the flux chamber, both procedures indicated that mucosubstances retarded, in a dose-related manner, diffusion of hydrogen ions. Experiments on buffering by crude porcine gastric mucin did not demonstrate significant buffering under physiological conditions. Thus, the present experimental data, the principles of which should be extrapolative to the mucous barrier at the biological level, suggest that mucus glycoproteins can in fact inhibit the diffusion of hydrogen ions.