Transient alterations in cellular permeability in cultured human proximal tubule cells: implications for transport studies.

Primary cultures of human proximal tubule (HPT) cells possess the characteristics of a tight epithelium and retain the characteristics of in vivo renal function. HPT cells form confluent monolayers when grown on collagen-coated polycarbonate inserts in a hormonally defined serum-free medium. However, initial studies of transepithelial transport observed large bidirectional fluxes of the paracellular probe inulin. The present studies were designed to assess the transformation of HPT cell tight junctions to a "leaky" state and subsequent recovery. The apparent transepithelial electrical resistance of HPT cells at confluence was 952.0 +/- 70.0 ohms*cm2, suggesting a well-developed tight junction-mediated paracellular pathway in this epithelium. However, replacement of the growth media produced an immediate 90% drop in the initial resistance, which was paralleled by an increased flux of inulin and of phenol red. This transient abolition of barrier function spontaneously reestablished over 1-2 h by a process that was dependent on the ionic composition of the added media. Complete recovery of cellular resistance was paralleled by markedly decreased fluxes of inulin and of phenol red. The recovery of cellular barrier function was inhibited by cytochalasin B suggesting an intracellular action, not a physical disruption of the monolayer. These results suggest that the tight junctions in these cells appear to transiently produce a leaky state during removal of the media, but rearrange to a "tight conformation" when incubated in the appropriate media.