Figure 7.

Permeability of the mucosal epithelium probed with TRD and FM. Sections of mucosal explants cultured for 1 h with TRD or FM in the absence or presence of 2 mM NaC or DDM, respectively. In the control, TRD bound to the enterocyte brush border, but only few and weakly-stained TRD-positive supapical punctae were observed. In addition, a faint labeling of the lamina propria was detectable. NaC and DDM both greatly increased the lateral TRD-labeling and accumulation of the probe in the lamina propria without affecting TRD-binding at the brush border, but little if any leakage was seen into the cytosol of the enterocytes. Like TRD, FM strongly labeled the enterocyte brush border, and also appeared in bright subapical punctae in the control. The brush border labeling was generally unaffected by both surfactants, but subapical punctae were sparse. Occasionally, FM was absent from the brush border, but leaked into the cytosol of enterocytes, as shown for DDM, but no staining of the lamina propria was observed. (Asterisks show goblet cells labeled by FM and inserts show enlarged image details.) Bars: 20 µm.