Gradogna A, Imbrici P, Zifarelli G, Liantonio A, Camerino DC, Pusch M. I-J loop involvement in the pharmacological profile of CLC-K channels expressed in Xenopus oocytes.
Biochim Biophys Acta 2014;
1838:2745-56. [PMID:
25073071 PMCID:
PMC4331650 DOI:
10.1016/j.bbamem.2014.07.021]
[Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 07/13/2014] [Accepted: 07/21/2014] [Indexed: 12/19/2022]
Abstract
CLC-K chloride channels and their subunit, barttin, are crucial for renal NaCl reabsorption and for inner ear endolymph production. Mutations in CLC-Kb and barttin cause Bartter syndrome. Here, we identified two adjacent residues, F256 and N257, that when mutated hugely alter in Xenopus oocytes CLC-Ka's biphasic response to niflumic acid, a drug belonging to the fenamate class, with F256A being potentiated 37-fold and N257A being potently blocked with a KD~1μM. These residues are localized in the same extracellular I-J loop which harbors a regulatory Ca(2+) binding site. This loop thus can represent an ideal and CLC-K specific target for extracellular ligands able to modulate channel activity. Furthermore, we demonstrated the involvement of the barttin subunit in the NFA potentiation. Indeed the F256A mutation confers onto CLC-K1 a transient potentiation induced by NFA which is found only when CLC-K1/F256A is co-expressed with barttin. Thus, in addition to the role of barttin in targeting and gating, the subunit participates in the pharmacological modulation of CLC-K channels and thus represents a further target for potential drugs.
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