Characterization of the interaction between a novel convulsant agent, norbiphen, and GABA A and other ligand-gated ion channels

• Published in: Neuropharmacology 2002-09, Vol.43 (4), p.778-787
• Main Authors: Halliwell, R.F., Su, Jiping, Demuro, A., Martinez-Torres, A., Miledi, R.
• Format: Article
• Language: English
• Subjects: Animals; Convulsants - pharmacology; Electrophysiology; Fluoroquinolones; GABA receptors; Hippocampus - cytology; Hippocampus - drug effects; Hippocampus - metabolism; Humans; Ion Channel Gating - drug effects; Ion Channels - drug effects; Ligands; Membrane Potentials - physiology; Neurons - drug effects; Norfloxacin - analogs & derivatives; Norfloxacin - pharmacology; Norfloxacin-biphenyl acetic acid hybrid; NSAIDs; Oocytes - drug effects; Oocytes - metabolism; Patch-Clamp Techniques; Phenylacetates - pharmacology; Plasmids - genetics; Receptors, GABA-A - drug effects; Receptors, GABA-A - genetics; Recombinant Proteins; Xenopus
• ISSN: 0028-3908; 1873-7064
• DOI: 10.1016/S0028-3908(02)00173-9

A hybrid molecule composed of the antimicrobial, norfloxacin, linked to the non-steroidal anti-inflammatory drug (NSAID), biphenylacetic acid, which we have termed norbiphen, is a lethal convulsant in vivo and an antagonist of rodent GABA A receptors in vitro. In the present study, the selectivity, molecular site(s) and mechanism of action of this novel convulsant were investigated using electrophysiological techniques. Sub-maximal GABA-evoked currents recorded from rodent hippocampal neurons were reversibly inhibited by norbiphen (1 μM) to 5±2% of control whereas glutamate, NMDA and glycine activated responses were little or unaffected. Sub-maximal GABA-evoked currents recorded from oocytes expressing recombinant human α1β2γ2s or α1β2 GABA A receptors were also reversibly inhibited by norbiphen (1–1000 nM) with an IC 50 (±s.e.m.) of 5.7±1 and 8.8±1 nM, respectively. Similarly, GABA currents recorded from α1β1γ2s, α1β1 and β2γ2s receptors were inhibited with IC 50s of 16.1±1, 18.8±1 and 4.2±1 nM, respectively. In contrast, norbiphen (100 nM) had little or no effect at ρ1 GABA C homomers. At α1β2γ2s receptors, norbiphen had no affect on the GABA reversal potential, and inhibition was not voltage-dependent, suggesting that this compound does not act at the ion channel. The GABA concentration response curve was shifted in a competitive-like fashion by norbiphen (10–300 nM) and a Schild analysis of these data yielded a slope of 0.94±0.1 and a pA 2 of 7.77. Our data reveal a novel, selective and highly potent antagonist of GABA A receptors. Norbiphen should be a valuable agent in future studies of this receptor complex.