AN IMPROVED DIFFUSION CELL DESIGN FOR DETERMINING DRUG TRANSPORT PARAMETERS ACROSS CULTURED-CELL MONOLAYERS

An improved two-chamber diffusion cell was developed for the study of drug transport across cultured cell monolayers. The cell monolayer was grown on a horizontal support membrane of polycarbonate, which could be rotated providing theoretically predictable thicknesses of the diff usion boundary layer in the donor and the receiver solution as a funct ion of rotation rate. Permeation measurements were performed using the support membrane with and without a cell monolayer. The Madin-Darby-B ovine-Kidney (MDBK) cell line was employed, and permeability coefficie nts of model solutes (salicylic acid, mannitol, testosterone) across t he three distinct mass transport barriers (i.e., the cell monolayer, t he support membrane, and the diffusion boundary layer) were determined . The permeability of the diffusion boundary layer followed the theore tical dependence on the rotation rate; absolute values, however, devia ted from predictions. Permeability coefficients for all three transpor t barriers varied substantially between solutes. This variation was th e strongest for the permeability coefficient for the cell monolayer an d resulted in a varying relative significance of these three barriers in controlling permeation kinetics. This improved diffusion apparatus permits the measurement of unbiased permeability values of solutes acr oss the cell monolayer, notably when the cell monolayer is not absolut ely the rate-determining barrier.