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Identification of sites responsible for the potentiating effect of niflumic acid on ClC-Ka kidney chloride channels.

TitleIdentification of sites responsible for the potentiating effect of niflumic acid on ClC-Ka kidney chloride channels.
Publication TypeJournal Article
Year of Publication2010
AuthorsZifarelli G, Liantonio A, Gradogna A, Picollo A, Gramegna G, De Bellis M, Murgia AR, Babini E, D Camerino C, Pusch M
JournalBr J Pharmacol
Volume160
Issue7
Pagination1652-61
Date Published2010 Aug
ISSN1476-5381
KeywordsAmino Acid Sequence, Animals, Anti-Inflammatory Agents, Non-Steroidal, Binding Sites, Chloride Channels, Dose-Response Relationship, Drug, Humans, Ion Channel Gating, Kidney, Models, Molecular, Molecular Sequence Data, Mutagenesis, Site-Directed, Niflumic Acid, Oocytes, Patch-Clamp Techniques, Sequence Alignment, Transfection, Xenopus
Abstract

BACKGROUND AND PURPOSE: ClC-K kidney Cl(-) channels are important for renal and inner ear transepithelial Cl(-) transport, and are potentially interesting pharmacological targets. They are modulated by niflumic acid (NFA), a non-steroidal anti-inflammatory drug, in a biphasic way: NFA activates ClC-Ka at low concentrations, but blocks the channel above approximately 1 mM. We attempted to identify the amino acids involved in the activation of ClC-Ka by NFA.

EXPERIMENTAL APPROACH: We used site-directed mutagenesis and two-electrode voltage clamp analysis of wild-type and mutant channels expressed in Xenopus oocytes. Guided by the crystal structure of a bacterial CLC homolog, we screened 97 ClC-Ka mutations for alterations of NFA effects.

KEY RESULTS: Mutations of five residues significantly reduced the potentiating effect of NFA. Two of these (G167A and F213A) drastically altered general gating properties and are unlikely to be involved in NFA binding. The three remaining mutants (L155A, G345S and A349E) severely impaired or abolished NFA potentiation.

CONCLUSIONS AND IMPLICATIONS: The three key residues identified (L155, G345, A349) are localized in two different protein regions that, based on the crystal structure of bacterial CLC homologs, are expected to be exposed to the extracellular side of the channel, relatively close to each other, and are thus good candidates for being part of the potentiating NFA binding site. Alternatively, the protein region identified mediates conformational changes following NFA binding. Our results are an important step towards the development of ClC-Ka activators for treating Bartter syndrome types III and IV with residual channel activity.

DOI10.1111/j.1476-5381.2010.00822.x
Alternate JournalBr. J. Pharmacol.
PubMed ID20649569
PubMed Central IDPMC2936838
Grant ListGGP08064 / / Telethon / Italy