Correlation between in vitro Papp (apical to basal direction) for P.1 PBEC and calculated Log Poctanol. P.1 PBEC were grown on Transwell Clear inserts and were used after treatment with cAMP, RO-20-1724 and hydrocortisone for 24 h (n=3 experiments, 9–12 inserts for each compound). Permeability assays were performed as described in Section 4.8 and 4.15. Calculated Log Poctanol was obtained from http://www.syrres.com/eSc/est_kowdemo.htm. Solute permeation: open circles, passive; closed squares, uptake; closed triangles, ABC-mediated efflux; open square, glutamate – subject to both uptake and efflux, see Section 2.5.