title: pH dependence of hydrochloric acid diffusion through gastric mucus: correlation with diffusion through a water layer using a membrane-mounted glass pH electrode.
abstract: Solute diffusion coefficients (D) can indicate a dependence upon actual solute concentrations. Here a single compartment has been utilized, in which effective HCl diffusion to a membrane-mounted glass pH electrode can be measured across the pH spectrum. The study has investigated HCl diffusion through both mucus and water layers as a function of HCl concentration. The observed dynamic responses of a liquid-film and mucus-coated electrodes over a range of HCl concentrations suggest that the speed at which equilibrium is attained is pH dependent; equilibrium was reached rapidly under more acidic and alkaline conditions. Estimated values of DHCl also indicate a strong pH dependence for both liquid film and mucus. In both instances, a greater than 10-fold reduction in DHCl at pH 7.5 as compared with that at pH 3.5 has been demonstrated. Furthermore, estimated values of DHCl are approximately 4-fold smaller through the mucus gel, as compared with a water layer. The findings indicate that the most powerful influence on diffusional resistance is pH itself, whereby a marked drop in H+ diffusion is likely to occur towards neutral pH irrespective of the composition of the gel barrier. Possible implications of the findings are discussed in relation to mucosal protection from acid.
authors.affiliation: Department of Medicine (Clinical Biochemistry), University of Manchester, Hope Hospital, Salford, UK.
authors.forename: C V
authors.initials: CV
authors.lastname: Nicholas
authors.forename: M
authors.initials: M
authors.lastname: Desai
authors.forename: P
authors.initials: P
authors.lastname: Vadgama
authors.forename: M B
authors.initials: MB
authors.lastname: McDonnell
authors.forename: S
authors.initials: S
authors.lastname: Lucas
mesh_terms: D000818:Animals; D004058:Diffusion; D004566:Electrodes; D005753:Gastric Mucosa / Q000737:chemistry*; D005898:Glass; D006851:Hydrochloric Acid / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008567:Membranes, Artificial; D013552:Swine; D014867:Water / Q000737:chemistry
chemical_list: D008567:Membranes, Artificial; D014867:Water; D006851:Hydrochloric Acid