UTILIZATION OF ENDOTHELIAL-CELL MONOLAYERS OF LOW TIGHTNESS FOR ESTIMATION OF TRANSCELLULAR TRANSPORT CHARACTERISTICS OF HYDROPHILIC COMPOUNDS

The determination of transcellular transport characteristics using fil ter-grown brain capillary endothelial cells in conventional permeation studies requires extremely tight cell layers, exhibiting electrical r esistance values of more than 500 ohm.cm(2), for avoiding interference s with the paracellular flux. The present investigations demonstrate t hat rate and asymmetry of transcellular transport processes can be eva luated sufficiently reliably for orientation and comparison purposes a lso by use of more easily obtainable leaky cell layers exhibiting elec trical resistance values of about 20 ohm.cm(2) only. The studies, rely ing on measurements of rates for influx and efflux into and out of the cells, respectively, of the cell barrier were performed with aortic e ndothelial cell monolayers grown on permeable supports. Alanine, leuci ne, 3-(O-methyl)-D-glucose served as representative hydrophilic substr ates being transported actively or by facilitated diffusion. HPLC, com bined with a simple precolumn benzoylation appropriate for a simultane ous analysis of both substance groups, was used for the quantitation.