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1 Division of Nephrology, Department of Medicine, University of Southern California Keck School of Medicine, Los Angeles, California, United States
2 Division of Nephrology, University of Southern California Keck School of Medicine, Los Angeles, California, United States
* To whom correspondence should be addressed. E-mail: alanyu{at}usc.edu.
Claudins form a large family of transmembrane tight junction proteins that play a key role in control and selectivity of paracellular transport. Mutations in claudin-19, which is expressed in kidney, retina and myelinated peripheral neurons, were identified in familial hypomagnesemia with hypercalciuria and nephrocalcinosis, a hereditary disease causing renal Mg2+ and Ca2+ wasting. Here, we studied the distribution and possible functional role of claudin-19 in the renal tubule. By immunofluorescence staining of mouse kidney, claudin-19 was found to be expressed at the tight junction of the cortical thick ascending limb of Henle, the major site of paracellular Mg2+ reabsorption, where it colocalized with claudin-16, as well as in the thin ascending limb. The role of claudin-19 in paracellular transport was tested by stable transfection into MDCK II TetOff cells to generate inducible cell lines. Claudin-19 increased the transepithelial electrical resistance and decreased permeability to monovalent and divalent cations, while anion and urea permeability were not affected. Our data suggests that claudin-19 acts as a selective cation barrier at the tight junction. This would be consistent with its physiological role to electrically seal myelinated peripheral neurons. The normal role of claudin-19 in renal tubule function remains to be determined.
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