title: CLCNKB mutations causing mild Bartter syndrome profoundly alter the pH and Ca2+ dependence of ClC-Kb channels.
abstract: ClC-Kb, a member of the ClC family of Cl(-) channels/transporters, plays a major role in the absorption of NaCl in the distal nephron. CLCNKB mutations cause Bartter syndrome type 3, a hereditary renal salt-wasting tubulopathy. Here, we investigate the functional consequences of a Val to Met substitution at position 170 (V170M, α helix F), which was detected in eight patients displaying a mild phenotype. Conductance and surface expression were reduced by ~40-50 %. The regulation of channel activity by external H(+) and Ca(2+) is a characteristic property of ClC-Kb. Inhibition by external H(+) was dramatically altered, with pKH shifting from 7.6 to 6.0. Stimulation by external Ca(2+) on the other hand was no longer detectable at pH 7.4, but was still present at acidic pH values. Functionally, these regulatory modifications partly counterbalance the reduced surface expression by rendering V170M hyperactive. Pathogenic Met170 seems to interact with another methionine on α helix H (Met227) since diverse mutations at this site partly removed pH sensitivity alterations of V170M ClC-Kb. Exploring other disease-associated mutations, we found that a Pro to Leu substitution at position 124 (α helix D, Simon et al., Nat Genet 1997, 17:171-178) had functional consequences similar to those of V170M. In conclusion, we report here for the first time that ClC-Kb disease-causing mutations located around the selectivity filter can result in both reduced surface expression and hyperactivity in heterologous expression systems. This interplay must be considered when analyzing the mild phenotype of patients with type 3 Bartter syndrome.
authors.affiliation: UPMC Université Paris 06, UMR_S 872, Team 3, 75006, Paris, France.
authors.forename: Olga
authors.initials: O
authors.lastname: Andrini
authors.forename: Mathilde
authors.initials: M
authors.lastname: Keck
authors.forename: Sébastien
authors.initials: S
authors.lastname: L'Hoste
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Briones
authors.forename: Lamisse
authors.initials: L
authors.lastname: Mansour-Hendili
authors.forename: Teddy
authors.initials: T
authors.lastname: Grand
authors.forename: Francisco V
authors.initials: FV
authors.lastname: Sepúlveda
authors.forename: Anne
authors.initials: A
authors.lastname: Blanchard
authors.forename: Stéphane
authors.initials: S
authors.lastname: Lourdel
authors.forename: Rosa
authors.initials: R
authors.lastname: Vargas-Poussou
authors.forename: Jacques
authors.initials: J
authors.lastname: Teulon
mesh_terms: D000328:Adult; D001477:Bartter Syndrome / Q000235:genetics* / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D018118:Chloride Channels / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008875:Middle Aged; D018408:Patch-Clamp Techniques; D010641:Phenotype; D017354:Point Mutation; D055815:Young Adult
chemical_list: C412733:CLCNKB protein, human; D018118:Chloride Channels; D002118:Calcium