Identification of gamma-aminobutyric acid and its binding sites in [formula omitted][formula omitted

Abstract

Gamma-aminobutyric acid (GABA), glutamate decarboxylase and GABA-transaminase were identified in the nematode Caenorhabditis elegans . The concentration of GABA in C. elegans (0.14 μg/mg protein) is approximately 10-fold lower than the concentration of GABA in rat brain. Glutamate decarboxylase and GABA-transaminase, the GABA anabolic and catabolic enzymes, are also present in C. elegans . Crude membrane fractions were prepared from C. elegans and used to study specific [ 3H] GABA binding sites. GABA binds to C. elegans membranes with high affinity (37 nM) and low capacity (Bmax = 2.25 pmol/mg protein). Muscimol is a competitive inhibitor of specific GABA binding with a K I value of 120 nM. None of the other GABA agonists or antagonists inhibited greater than 40% of the specific GABA binding at concentrations up to 10 −4 M. Thirteen spider venoms were examined as possible GABA agonists or antagonists, the venom from Calilena agelenidae inhibits specific GABA binding with a K I value of 6 nl/ml. These results suggest that GABA has a physiological role as a neurotransmitter in C. elegans .