The aim of the present study was to characterize the TR146 cell culture model as an in vitro model of human buccal epithelium with respect to the permeability of test substances with different molecular weights (M(w)). For this purpose, the apparent permeability (P(app)) values for mannitol and for fluorescein isothiocyanate (FITC)-labelled dextrans (FD) with various M(w) (4000-40000) were compared to the P(app) values obtained using porcine buccal mucosa as an in vitro model of the human buccal epithelium. The effect of 10 mM sodium glycocholate (GC) on the P(app) values was examined. To identify the pathways by which FD of M(w) 4000-40000 were transported, the confocal laser scanning microscope (CLSM) was used. The P(app) values obtained with the TR146 cell culture model in the absence of a permeability enhancer linearly decreased with increasing M(w) of the test substance from 0. 65+/-0.055x10(-8) to 44+/-7.5x10(-8) cm/s, as the P(app) values obtained with porcine buccal mucosa. In the presence of the permeability enhancer, GC, the permeability of the FD across the cultured TR146 cell culture model increased in a parabolic manner, reaching maximum at M(w) 10000. In the absence of the enhancer, only paracellular localization of FD was observed while, in the presence of GC, FD also could be detected in the cytosol of some of the superficial cells. The GC-induced enhancement of FD permeation may be partially attributed to changed permeation pathways. The present results indicate that the TR146 cell culture model is a suitable in vitro model for mechanistic permeability studies of human buccal drug permeability.