Ex Vivo Models Ussing Chambers Technique

Extracellular marker molecules, such as mannitol, inulin, Na-fluorescein, and PEG-400, have been used to verify a tight epithelium they have also been used for testing the effects of enhancers and increased fluid absorption [159], 

The more viable the segment is the better is the quality of the results. Based on the tissue viability data, extremes in permeability values can be discarded from the data set, resulting in better and more reliable results and a better overall understanding of drug transport [108], 

In an attempt to increase the biorelevance of the Ussing chambers technique even further, the use of simulated intestinal fluids (FaSSIF and FeSSIF) as transport media was recently evaluated [105], However, the potential difference collapsed to zero after 120 min when exposed to FaSSIF solution and permeability for mannitol was increased twofold. Electron micrographs revealed erosion of the villi tips and substantial denudation of the microvilli after exposure of the ileal tissue to FaSSIF and FeSSIF [105], 

Similar to the PAMPA and the Caco-2 models, the experimental pH of the buffer solution can be changed in the Ussing chambers model. However, it seems that the impact of changing the pH of the mucosal (= apical) buffer solution is lower than for the other two systems [82], This is probably due to the presence of the mucus layer retaining the microclimate pH regardless of the luminal pH using the Ussing chambers technique [82], 

Recently, more importance is given to the link between the integrity of the mucosal epithelium on one side and the immune system on the 

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