PARACELLULAR DIFFUSION IN CACO-2 CELL MONOLAYERS - EFFECT OF PERTURBATION ON THE TRANSPORT OF HYDROPHILIC COMPOUNDS THAT VARY IN CHARGE ANDSIZE

We applied the principles of molecular-size-restricted diffusion withi n a negative electrostatic field of force to follow the changes in the aqueous pore radius of tight junctions (TJs) induced by perturbants a nd the accompanying influence on the permeation of neutral (urea and m annitol), cationic (methylamine acid atenolol), and anionic (formate a nd lactate) compounds that vary in size. The perturbants included palm itoyl-DL-carnitine (PC), which opens TJs by an unknown Ca++-independen t mechanism, and ethyleneglycol-bis-(beta-aminoethyl ether)-N,N,N',N'- tetraacetic acid (EGTA), a Ca++ chelator. Mass transfer resistances of the collagen-coated filter support and the aqueous boundary layers we re factored out to yield paracellular permeability coefficients (P-P). AS viewed from the P-P values of urea and mannitol, EGTA exhibited in significant effects on pore size at low concentrations compared with c ontrol, and then caused a dramatic opening of the TJs over a narrow co ncentration range (1.35-1.4 mM). The P-P values for urea and mannitol remained constant at >1.4 mM EGTA. However, PC produced dose-dependent responses from 0 to 0.15 mM that plateaued at >0.15 mM. In general, c ations permeated the cellular TJs faster and anions slower than their neutral images. The effects of changes in pore size (4.6 to 14.6 Angst rom in effective radius) on the ability of these solutes to permeate t he TJs were analyzed by the Renkin molecular sieving function. These s tudies established an experimental, theoretical, and quantitative temp late to assess perturbants of the TJ and define the limits, short of d etrimental effects, at which the TJs may be sufficiently perturbed for maximal enhancement of permeation of solutes varying in size and char ge.