Colon, selective permeability

TEER, normalized to surface, was 188-221 Ohm/cm2 in CACO-2 cells and 78-125 Ohm/cm2 in colon (Rubas et al. 1996). The presence of villi and crypts in vivo with a higher surface and a different cellular composition (goblet cells, M cells, higher permeability in crypts) compared to a cell mono-layer might lead to higher permeability. Tanaka et al. (1995) compared permeability of FITC-Dextran (MW 4000) in CACO-2 cells and rat jejunum and colon the permeability was 10 fold decreased in CACO-2 compared to jejunum and 5 fold lower than in colon. TEER in CACO-2 was 470 Ohm x cm2 in this study, 40 Ohm x cm2 in rat jejunum and 80 Ohm x cm2 in rat colon. Permeability of standard markers like PEG was compared between CACO-2 cells and colon (Artursson et al. 1993). The conclusion for cellular studies is to select cells with acceptable TEER and permeability values and to perform quality assurance tests on a regular basis. 

Thus, the apparent membrane permeability characteristics of hydrophilic compounds listed in Table 3.4 indicate that colonic epithelium is different from small intestinal epithelium in selectivity, or size or density distribution of the paracellular pathway. This is further complicated because of the possible involvement of unidentified carriers or channels for some compounds, as suggested for glycerol and D-xylose. However, the colon-to-SI ratios of the apparent membrane permeability are generally comparable with (or lower than) those calculated considering the morphological surface area, suggesting that such factors are not in favor for colonic absorption in most cases. Matching... 

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