Leakiness and Size Exclusion of Paracellular Channels in Cultured Epithelial Cell Monolayers-Interlaboratory Comparison

To determine and compare the paracellular characteristics of permeability (P-app) of Caco-2, MDCK, and 2/4/A1 cell lines. The P-app data from 14 studies were analyzed by weighted nonlinear regression in terms of the paracellular parameters: porosity-pathlength (epsilon/delta), pore radius (R), and electrostatic potential drop (Delta phi). Aqueous diffusivities, D-aq, for the analysis, were empirically determined. The required hydrodynamic radii, r(HYD), were estimated without knowledge of compound density. Mannitol iso-paracellular profiles allowed comparisons of "leakiness" across labs. D-aq (37A degrees C) was predicted as 9.9 x 10(-5) MW-0.453; r(HYD) = (0.92 + 21.8 MW-1)I double dagger r(SE), where r(SE) is the Stokes-Einstein radius. Values of pore radius ranged from 4.0(+/- 0.1) to 18(+/- 3) , with the 2/4/A1 indicating the largest pores. The epsilon/delta capacity factor ranged from 0.2 (+/- 0.1) to 69 (+/- 5) cm(-1), with most values < 1.5 cm(-1). The average potential drop for Caco-2 models was Delta phi (wt avg) (Caco-2) = -43 +/- 20 mV. The paracellular model predicted measured log P-app values with pooled r (2) = 0.93 and s = 0.17 (n = 108). R and epsilon/delta are negatively correlated to a large extent. P-app can be rate-limited by either factor, with a wide range of possible combinations still indicating nearly constant leakiness for a given marker.