Oxygen diffusive barriers of rat distal colon - Role of subepithelial tissue, mucose, and mucus gel layer

The contributions of subepithelial tissue, mucosa, and mucus gel layer as r estraints for oxygen diffusion in rat distal colon in vitro were assessed b y comparing oxygen transfer through preparations of isolated submucosa, iso lated mucosa with and without the superficial mucus gel layer, and mucosa-s ubmucosa mounted as flat sheets in a diffusion chamber. One side of the cha mber was gassed with 95% O-2-5% CO2 while the time course of oxygen concent ration rise was measured in the continuously stirred opposite side, initial ly equilibrated with near-zero oxygen solution. The procedure does not affe ct epithelial viability. Diffusion in isolated mucosa was the same before a nd after KCN (5 mM) treatment, suggesting that epithelial oxygen consumptio n does not influence transfer rates. Subepithelial tissue, mucosa, and mucu s gel layer are roughly responsible, respectively, fur 12%, 56%, and 32% of oxygen diffusive hindrance. Diffusion coefficients range from 13% (mucosa- submucosa) to 54% (isolated submucosa) of that of water. Subepithelial tiss ue accounts for about 12% of total diffusive restraint.