RESUMO
Epithelia can adjust the permeability of their paracellular permeation route to physiological requirements, pathological conditions, and pharmacological challenges. This is reflected by a transepithelial electrical resistance (TER) ranging from a few tenth to several thousands Omega.cm(2), depending on the degree of sealing of the tight junction (TJ). The present work is part of an effort to understand the causes and mechanisms underlying these adaptations. We observed that an extract of human urine (hDLU) increases TER in a concentration- and time-dependent manner and is more effective when added from the basolateral side of cultured monolayers of Madin-Darby canine kidney cells than from the apical one. We found that its main TER-increasing component is epidermal growth factor (hEGF), as depletion of this peptide with specific antibodies, or inhibition of its receptor with PD153035, abolishes its effect. Since the permeability of the TJ depends on the expression of several species of membrane proteins, chiefly claudins, we explored whether hDLU can affect five members of the claudin family, the three known members of the ZO family, and occludin. EGF present in hDLU decreases the content of claudins-1 and -2 as well as delocalizes them from the TJ and increases the content of claudin-4. As expected from the fact that the degree of sealing of the TJ must be a physiologically regulated parameter, besides of hEGF, we also found that hDLU appears to contain also other components that decrease TER, claudin-4 and -7, and that seem to act with different kinetics than the TER-increasing ones.