RT Journal Article
SR Electronic
T1 Activation and Inhibition of Kidney CLC-K Chloride Channels by Fenamates
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 165
OP 173
DO 10.1124/mol.105.017384
VO 69
IS 1
A1 Antonella Liantonio
A1 Alessandra Picollo
A1 Elena Babini
A1 Giuseppe Carbonara
A1 Giuseppe Fracchiolla
A1 Fulvio Loiodice
A1 Vincenzo Tortorella
A1 Michael Pusch
A1 Diana Conte Camerino
YR 2006
UL http://molpharm.aspetjournals.org/content/69/1/165.abstract
AB 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 μM 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.