抄録
Mutations in the gene encoding for the renal tight junctional protein paracellin-1 cause familial hypomagnesemia with hypercalciuria and nephrocalcinosis, an autosomal recessive disorder of renal calcium and magnesium handling. To elucidate the magnesium and calcium permeability by paracellin-1, FLAG-tagged paracellin-1 was stably expressed in Madin-Darby canine kidney (MDCK) cells. Expression and localization of paracellin-1 were determined by immunoblotting and immunofluorescence microscopy. The protein co-localized with tight junctional proteins, occludin and ZO-1. Paracellin-1 expression affected neither the levels of occludin nor ZO-1. In vitro binding assay showed that the COOH-terminal domain of paracellin-1 was associated with ZO-1. In similar fashion, immunoprecipitation by anti-FLAG antibody showed that paracellin-1 was associated with ZO-1 in FLAG-tagged paracellin-1-expressing MDCK cells. Next, we examined the effect of paracellin-1 expression on transepithelial electrical resistance (TER) and calcium permeability. Paracellin-1 expression increased TER twice compared with non-expression cells. In contrast to TER, paracellin-1 expression increased calcium transport in the apical-to-basolateral direction. Increase of magnesium concentration diminished the calcium transport. These results suggest that paracellin-1 creates calcium- and magnesium-selective channels and has no relation to determination of TER. [Jpn J Physiol 54 Suppl:S66 (2004)]
