GLC-3: a novel fipronil and BIDN-sensitive, but picrotoxinin-insensitive, L-glutamate-gated chloride channel subunit from Caenorhabditis elegans

Br J Pharmacol. 2001 Mar;132(6):1247-54. doi: 10.1038/sj.bjp.0703937.

Abstract

1. We report the cloning and expression of a novel Caenorhabditis elegans polypeptide, GLC-3, with high sequence identity to previously cloned L-glutamate-gated chloride channel subunits from nematodes and insects. 2. Expression of glc-3 cRNA in XENOPUS oocytes resulted in the formation of homo-oligomeric L-glutamate-gated chloride channels with robust and rapidly desensitizing currents, an EC(50) of 1.9+/-0.03 mM and a Hill coefficient of 1.5+/-0.1. GABA, glycine, histamine and NMDA all failed to activate the GLC-3 homo-oligomer at concentrations of 1 mM. The anthelminthic, ivermectin, directly and irreversibly activated the L-glutamate-gated channel with an EC(50) of 0.4+/-0.02 microM. 3. The GLC-3 channels were selective for chloride ions, as shown by the shift in the reversal potential for L-glutamate-gated currents after the reduction of external Cl(-) from 107.6 to 62.5 mM. 4. Picrotoxinin failed to inhibit L-glutamate agonist responses at concentrations up to 1 mM. The polycyclic dinitrile, 3,3-bis-trifluoromethyl-bicyclo[2,2,1]heptane-2,2-dicarbonitrile (BIDN), completely blocked L-glutamate-induced chloride currents recorded from oocytes expressing GLC-3 with an IC(50) of 0.2+/-0.07 microM. The phenylpyrazole insecticide, fipronil, reversibly inhibited L-glutamate-gated currents recorded from the GLC-3 receptor with an IC(50) of 11.5+/-0.11 microM. 5. In this study, we detail the unusual antagonist pharmacology of a new GluCl subunit from C. elegans. Unlike all other native and recombinant nematode GluCl reported to date, the GLC-3 receptor is insensitive to picrotoxinin, but is sensitive to two other channel blockers, BIDN and fipronil. Further study of this receptor may provide insights into the molecular basis of non-competitive antagonism by these compounds.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Antinematodal Agents / pharmacology
  • Antiparasitic Agents / pharmacology
  • Bridged Bicyclo Compounds / pharmacology*
  • Caenorhabditis elegans / drug effects*
  • Caenorhabditis elegans / genetics
  • Chloride Channels / classification
  • Chloride Channels / drug effects
  • Chloride Channels / genetics*
  • Convulsants / antagonists & inhibitors
  • DNA, Complementary / analysis
  • Insecticides / pharmacology
  • Ivermectin / pharmacology
  • Molecular Sequence Data
  • Nitriles / pharmacology*
  • Oocytes / drug effects
  • Oocytes / metabolism
  • Picrotoxin / analogs & derivatives
  • Picrotoxin / pharmacology*
  • Polymerase Chain Reaction
  • Pyrazoles / pharmacology*
  • Sequence Homology, Amino Acid
  • Transfection
  • Xenopus laevis

Substances

  • Antinematodal Agents
  • Antiparasitic Agents
  • Bridged Bicyclo Compounds
  • Chloride Channels
  • Convulsants
  • DNA, Complementary
  • Insecticides
  • Nitriles
  • Pyrazoles
  • glutamate-gated chloride channels
  • Picrotoxin
  • Ivermectin
  • 3,3-bis(trifluoromethyl)bicyclo(2.2.1)heptane-2,2-dicarbonitrile
  • picrotoxinin
  • fipronil