Decreased agonist sensitivity of human GABA(A) receptors by an amino acid variant, isoleucine to valine, in the alpha1 subunit

Eur J Pharmacol. 1997 Jun 25;329(2-3):253-7.

Abstract

Recombinant human GABA(A) receptors were investigated in vitro by coexpression of cDNAs coding for alpha1, beta2, and gamma2 subunits in the baculovirus/Sf-9 insect cell system. We report that a single amino acid exchange (isoleucine 121 to valine 121) in the N-terminal, extracellular part of the alpha1 subunit induces a marked decrease in agonist GABA(A) receptor ligand sensitivity. The potency of muscimol and GABA to inhibit the binding of the GABA(A) receptor antagonist [3H]SR 95531 (2-(3-carboxypropyl)-3-amino-6-(4-methoxyphenyl)pyridazinium bromide) was higher in receptor complexes of alpha1(ile 121) beta2gamma2 than in those of alpha1(val 121) beta2gamma2 (IC50 values were 32-fold and 26-fold lower for muscimol and GABA, respectively). The apparent affinity of the GABA(A) receptor antagonist bicuculline methiodide to inhibit the binding of [3H]SR 95531 did not differ between the two receptor complex variants. Electrophysiological measurements of GABA induced whole-cell Cl- currents showed a ten-fold decrease in the GABA(A) receptor sensitivity of alpha1 (val 121) beta2gamma2 as compared to alpha1(ile 121) beta2gamma2 receptor complexes. Thus, a relatively small change in the primary structure of the alpha1 subunit leads to a decrease selective for GABA(A) receptor sensitivity to agonist ligands, since no changes were observed in a GABA(A) receptor antagonist affinity and benzodiazepine receptor binding.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Baculoviridae / genetics
  • Cell Line
  • DNA Primers
  • GABA Agonists / pharmacology
  • GABA Antagonists / metabolism
  • GABA Antagonists / pharmacology
  • GABA-A Receptor Agonists*
  • Humans
  • Isoleucine / genetics*
  • Patch-Clamp Techniques
  • Point Mutation
  • Pyridazines / metabolism
  • Receptors, GABA-A / genetics
  • Receptors, GABA-A / metabolism
  • Recombinant Proteins / agonists
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Valine / genetics*

Substances

  • DNA Primers
  • GABA Agonists
  • GABA Antagonists
  • GABA-A Receptor Agonists
  • Pyridazines
  • Receptors, GABA-A
  • Recombinant Proteins
  • Isoleucine
  • gabazine
  • Valine