title: Activation and inhibition of kidney CLC-K chloride channels by fenamates.
abstract: CLC-K Cl(-) channels are selectively expressed in kidney and ear, where they are pivotal for salt homeostasis, and loss-of-function mutations of CLC-Kb produce Bartter's syndrome type III. The only ligand known for CLC-K channels is a derivative of the 2-p-chlorophenoxypropionic acid (CPP), 3-phenyl-CPP, which blocks CLC-Ka, but not CLC-Kb. Here we show that in addition to this blocking site, CLC-K channels bear an activating binding site that controls channel opening. Using the voltage-clamp technique on channels expressed in Xenopus laevis oocytes, we found that niflumic acid (NFA) increases CLC-Ka and CLC-Kb currents in the 10 to 1000 microM range. Flufenamic acid (FFA) derivatives or high doses of NFA produced instead an inhibitory effect on CLC-Ka, but not on CLC-Kb, and on blocker-insensitive CLC-Ka mutants, indicating that the activating binding site is distinct from the blocker site. Evaluation of the sensitivity of CLC-Ka to derivatives of NFA and FFA together with a modeling study of these ligands allow us to conclude that one major characteristic of activating compounds is the coplanarity of the two rings of the molecules, whereas block requires a noncoplanar configuration. These molecules provide a starting point for identification of diuretics or drugs useful in the treatment of Bartter's syndrome.
authors.affiliation: Unità di Farmacologia, Dipartimento Farmacobiologico, Facoltà di Farmacia, Università di Bari, Bari, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Liantonio
authors.forename: Alessandra
authors.initials: A
authors.lastname: Picollo
authors.forename: Elena
authors.initials: E
authors.lastname: Babini
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Carbonara
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Fracchiolla
authors.forename: Fulvio
authors.initials: F
authors.lastname: Loiodice
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Tortorella
authors.forename: Michael
authors.initials: M
authors.lastname: Pusch
authors.forename: Diana Conte
authors.initials: DC
authors.lastname: Camerino
mesh_terms: D000818:Animals; D001477:Bartter Syndrome / Q000188:drug therapy; D065101:Chloride Channel Agonists; D018118:Chloride Channels / Q000037:antagonists & inhibitors*; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D014982:Xenopus laevis; D062367:ortho-Aminobenzoates / Q000494:pharmacology* / Q000627:therapeutic use
chemical_list: C489932:CLCNKA protein, human; D065101:Chloride Channel Agonists; D018118:Chloride Channels; D062367:ortho-Aminobenzoates; C001209:fenamic acid