The paracellular permeability of opossum kidney cells, a proximal tubule cell line

Background. The regulation of the unusually leaky paracellular pathway of the proximal tubule is poorly understood partially because of the lack of an appropriate in vitro cell model. In this study, we determined whether the paracellular permeability of opossum kidney (OK) cells would resemble that of the in vivo proximal tubule epithelium. Methods. The parental and subclonal OK cells and, for comparison, LLC-PK1 cells were cultured on permeable Transwell supports. The apparent paracellular permeability coefficient (P-app) for the extracellular marker H-3 mannitol was determined. Results. The P-app of OK cell sheets (12.17 x 10(-6) cm/sec) was remarkably close to the previously reported P-app of rat proximal tubules. The P-app of LLC-PK1 cells, another proximal tubule cell line, however, was approximately 20-fold lower than that of both OK cells and the in vivo proximal tubule. Phorbol 12-myristate 13-acetate, a protein kinase C activator, enhanced the P-app of OK cell sheets. The characteristic response of paracellular permeability to Ca2+ switch was demonstrated in OK cell sheets. Slight variations of P-app among several OK subclones were observed. Basal to apical P-app was uniformly higher than apical to basal P-app, independent of cell subtype. This rectification was attenuated by inhibition of active transport. Conclusions. OK cell sheets cultured on Transwell supports possess a leaky paracellular pathway resembling that of the proximal tubule epithelium in vivo.