Direct block of the cystic fibrosis transmembrane conductance regulator Cl(-) channel by niflumic acid

Mol Membr Biol. Jan-Feb 2004;21(1):27-38. doi: 10.1080/09687680310001597758.

Abstract

Niflumic acid is widely used to inhibit Ca(2+) -activated Cl(-) channels. However, the chemical structure of niflumic acid resembles that of diphenylamine-2-carboxylate, a drug that inhibits the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. To investigate how niflumic acid inhibits CFTR Cl(-) channel, we studied recombinant wild-type human CFTR in excised inside-out membrane patches. When added to the intracellular solution, niflumic acid caused a concentration- and voltage-dependent decrease of CFTR Cl(-) current with half-maximal inhibitory concentration (K(i)) of 253 microM and Hill co-efficient of approximately 1, at -50 mV. Niflumic acid inhibition of single CFTR Cl(-) channels was characterized by a very fast, flickery block that decreased dramatically current amplitude without altering open-probability. Consistent with these data, spectral analysis of CFTR Cl(-) currents suggested that channel block by niflumic acid was described by the closed <--> open <--> blocked kinetic scheme with blocker on rate (k(on)) = 13.9 x 10(6) M(-1)s(-1), off rate (k(off))=3348 s(-1) and dissociation constant (K(d)) = 241 microM, at -50 mV. Based on these data, we tested the effects of niflumic acid on transepithelial Cl(-) secretion and cyst growth using type I MDCK epithelial cells. Niflumic acid (200 microM) inhibited cAMP-stimulated, bumetanide-sensitive short-circuit current by 55%. Moreover, the drug potently retarded cyst growth. We conclude that niflumic acid is an open-channel blocker of CFTR that inhibits Cl(-) permeation by plugging the channel pore. It or related agents might be of value in the development of new therapies for autosomal dominant polycystic kidney disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anti-Inflammatory Agents, Non-Steroidal / pharmacology*
  • Cell Line
  • Chlorides / metabolism
  • Cystic Fibrosis Transmembrane Conductance Regulator / antagonists & inhibitors*
  • Cystic Fibrosis Transmembrane Conductance Regulator / chemistry
  • Cystic Fibrosis Transmembrane Conductance Regulator / genetics
  • Dogs
  • Electrophysiology
  • Humans
  • Ion Channel Gating / drug effects*
  • Ion Channel Gating / genetics
  • Membrane Potentials / drug effects
  • Molecular Structure
  • Niflumic Acid / pharmacology*
  • Patch-Clamp Techniques
  • Recombinant Proteins / antagonists & inhibitors*
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics

Substances

  • Anti-Inflammatory Agents, Non-Steroidal
  • CFTR protein, human
  • Chlorides
  • Recombinant Proteins
  • Cystic Fibrosis Transmembrane Conductance Regulator
  • Niflumic Acid