affect the paracellular permeability in Caco-2 cells. Cells were cultured on Transwell polycarbonate filters and the TJ functionality was analyzed by the ruthenium red technique (A) and by measuring the Transepithelial electrical resistance (TER) (B). A: Representative images of thin sections of control cells showing the ruthenium red in the apical region in control cells and in cells treated with PGE2, as indicated. Cells incubated with the prostanoid revealed extensive spaces in the junctional complex area and permeation of the marker between the intercellular spaces. Bar: 0.8 μm. Arrowheads: ruthenium red. B. TER was measured in different conditions as indicated. Observe that PGE2 and its analogue, PGE2 16-16 dm PGE2, caused a significant drop of the TER (*P < 0.01 compared with untreated cells). The effect was visible at 15 and 30 min, however at 60 and 120 min a recovery of the TER was observed.