Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract Purpose. To investigate concentration dependent permeabilities andmetabolism kinetics of thymotrinan (TP3) versus thymocartin (TP4)in nasal epithelium in vitro. Methods. Excised bovine nasal mucosa was used as an in vitro model.Permeabilities were studied in a diffusion chamber, metabolism kineticsin a reflection kinetics set-up. Studies were performed at various TP3and TP4 concentrations. The 3H-mannitol flux was measured to monitorjunctional permeability. Potential Ca2+-complexation was investigatedusing a Ca2+-selective electrode. Results. Permeability of TP3 was negligible at 0.1 and 0.2 mM andincreased drastically above 0.4 mM up to ∼2 × 10−5 cm s−1. In thepresence of 2 mM TP4 the TP3 permeabilites were significantly above(∼4 × 10−5 cm s−1) the level of TP3 without TP4, and TP3 metabolismwas totally inhibited. TP3 and TP4 showed a significant concentrationdependent effect on the permeability of 3H-mannitol. Ahyperosmolarity effect of the peptide solutions was excluded. Transepithelialelectrical resistance (TEER; ∼30 Ω cm2) was unchanged by either TP3 orTP4. At 1 mM TP3 the mucosal-to-serosal permeability was four timeshigher than serosal-to-mucosal, indicating enzyme polarization. Inreflection kinetics studies, TP3 degradation was slightly higher on themucosal than on the serosal side. TP3 and TP4 followed the samenon-linear metabolism kinetics. Conclusions. Increase in permeability at high TP concentrationsinvolves competitive enzyme saturation combined with self-enhancedparacellular permeation.
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