Diffusion coefficient in native mucus gel of rat small intestine

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Abstract
The diffusion coefficients of [3H] water, urea, benzoic acid, antipyrine, aminopyrine, α-methyl-glucoside, L-phenylalanine and of hydrogen ions were measured at 38 °C in native mucus gel from rat small intestine. The diffusion in the gel was reduced to 37–53% (for hydrogen ions to 7%) compared with buffer solution. In addition, the buffering capacity of the gel retarded the permeation of hydrogen ions before a steady state flux was attained. A model calculation revealed that in the preparation a gel layer of 80 μm thickness represents 23% of the total permeation resistance for substances with high epithelial permeability. The aqueous part of the pre-epithelial diffusion resistance amounts to 77% of the total resistance.