Salt-losing nephropathy in mice with a null mutation of the Clcnk2 gene.

Abstract

The basolateral chloride channel ClC-Kb facilitates Cl reabsorption in the distal nephron of the human kidney. Functional mutations in CLCNKB are associated with Bartter's syndrome type 3, a hereditary salt-losing nephropathy. To address the function of ClC-K2 invivo, we generated ClC-K2-deficient mice. ClC-K2-deficient mice were generated using TALEN technology. ClC-K2-deficient mice were viable and born in a Mendelian ratio. ClC-K2-/- mice showed no gross anatomical abnormalities, but they were growth retarded. The 24-h urine volume was increased in ClC-K2-/- mice (4.4±0.6 compared with 0.9±0.2mL per 24h in wild-type littermates; P=0.001). Accordingly, ambient urine osmolarity was markedly reduced (590±39 vs. 2216±132mosmolL-1 in wild types; P<0.0001). During water restriction (24h), urinary osmolarity increased to 1633±153 and 3769±129mosmolL-1 in ClC-K2-/- and wild-type mice (n=12; P<0.0001), accompanied by a loss of body weight of 12±0.4 and 8±0.2% respectively (P<0.0001). ClC-K2-/- mice showed an increased renal sodium excretion and compromised salt conservation during a salt-restricted diet. The salt-losing phenotype of ClC-K2-/- mice was associated with a reduced plasma volume, hypotension, a slightly reduced glomerular filtration rate, an increased renal prostaglandin E2 generation and a massively stimulated renin-angiotensin system. Clckb-/- mice showed a reduced sensitivity to furosemide and were completely resistant to thiazides. Loss of ClC-K2 compromises TAL function and abolishes salt reabsorption in the distal convoluted tubule. Our data suggest that ClC-K2 is crucial for renal salt reabsorption and concentrating ability. ClC-K2-deficient mice in most aspects mimic patients with Bartter's syndrome type 3.