Role of Membrane Components, Glycocalyx and Lipid in Absorption of Water-soluble Dyes from the Rat Small Intestine

Role of membrane components in the absorption from the rat small intestine of four water-soluble dyes, methylene blue (MB), bromthymol blue (BTB), bromphenol blue (BPB), and phenol red (PR) was investigated. Uptake by the isolated epithelial cells, binding to the brush borders, and uptake by the everted sac of BTB and BPB, anionic dyes, were significantly reduced by digestion with papain, but in PR no effect was found. Binding of the dyes to the components released by the cellulose papain complex digestion from the brush borders was examined using the method of equilibrium dialysis. More MB and BTB bound to the components than BPB and PR, poorly absorbable dyes. These results suggested that membrane component contributing to the dye binding to the brush borders may be glycocalyx (surface coat). Lipids, other major membrane components, were extracted from rat intestinal mucosa and separated to neutral lipid (NL), glycolipid (GL), phosphatidylcholine (PC), and phosphatidylethanolamine (PE) fractions. Each fraction was dissolved in chloroform and partitioning behavior of the dyes was examined using a non-emulsifying system. Extent of transfer of the dyes from aqueous phase into chloroform containing GL and total lipid (TL) was well correlated to the extent of net absorption and tissue accumulation respectively.