title: Generation and analyses of R8L barttin knockin mouse.
abstract: Barttin, a gene product of BSND, is one of four genes responsible for Bartter syndrome. Coexpression of barttin with ClC-K chloride channels dramatically induces the expression of ClC-K current via insertion of ClC-K-barttin complexes into plasma membranes. We previously showed that stably expressed R8L barttin, a disease-causing missense mutant, is retained in the endoplasmic reticulum (ER) of Madin-Darby canine kidney (MDCK) cells, with the barttin β-subunit remaining bound to ClC-K α-subunits (Hayama A, Rai T, Sasaki S, Uchida S. Histochem Cell Biol 119: 485-493, 2003). However, transient expression of R8L barttin in MDCK cells was reported to impair ClC-K channel function without affecting its subcellular localization. To investigate the pathogenesis in vivo, we generated a knockin mouse model of Bartter syndrome that carries the R8L mutation. These mice display disease-like phenotypes (hypokalemia, metabolic alkalosis, and decreased NaCl reabsorption in distal tubules) under a low-salt diet. Immunofluorescence and immunoelectron microscopy revealed that the plasma membrane localization of both R8L barttin and the ClC-K channel was impaired in these mice, and transepithelial chloride transport in the thin ascending limb of Henle's loop (tAL) as well as thiazide-sensitive chloride clearance were significantly reduced. This reduction in transepithelial chloride transport in tAL, which is totally dependent on ClC-K1/barttin, correlated well with the reduction in the amount of R8L barttin localized to plasma membranes. These results suggest that the major cause of Bartter syndrome type IV caused by R8L barttin mutation is its aberrant intracellular localization.
authors: Department of Nephrology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Japan.
authors: Naohiro
authors: N
authors: Nomura
authors: Masato
authors: M
authors: Tajima
authors: Noriko
authors: N
authors: Sugawara
authors: Tetsuji
authors: T
authors: Morimoto
authors: Yoshiaki
authors: Y
authors: Kondo
authors: Mayuko
authors: M
authors: Ohno
authors: Keiko
authors: K
authors: Uchida
authors: Kerim
authors: K
authors: Mutig
authors: Sebastian
authors: S
authors: Bachmann
authors: Manoocher
authors: M
authors: Soleimani
authors: Eriko
authors: E
authors: Ohta
authors: Akihito
authors: A
authors: Ohta
authors: Eisei
authors: E
authors: Sohara
authors: Tomokazu
authors: T
authors: Okado
authors: Tatemitsu
authors: T
authors: Rai
authors: Thomas J
authors: TJ
authors: Jentsch
authors: Sei
authors: S
authors: Sasaki
authors: Shinichi
authors: S
authors: Uchida