title: I-J loop involvement in the pharmacological profile of CLC-K channels expressed in Xenopus oocytes.
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.
authors: Istituto di Biofisica, CNR, Via De Marini 6, 16149 Genoa, Italy.
authors: Antonella
authors: A
authors: Gradogna
authors: Dipartimento di Farmacia-Scienze del farmaco, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy.
authors: Paola
authors: P
authors: Imbrici
authors: Istituto di Biofisica, CNR, Via De Marini 6, 16149 Genoa, Italy.
authors: Giovanni
authors: G
authors: Zifarelli
authors: Dipartimento di Farmacia-Scienze del farmaco, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy.
authors: Antonella
authors: A
authors: Liantonio
authors: Dipartimento di Farmacia-Scienze del farmaco, Università degli Studi di Bari, Via Orabona 4, 70125 Bari, Italy.
authors: Diana Conte
authors: DC
authors: Camerino
authors: Istituto di Biofisica, CNR, Via De Marini 6, 16149 Genoa, Italy. Electronic address: pusch@ge.ibf.cnr.it.
authors: Michael
authors: M
authors: Pusch
keywords: CLC-K1; CLC-Ka; Chloride channels; Niflumic acid