Identification of gamma-aminobutyric acid and its binding sites in Caenorhabditis elegans.
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 micrograms/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 KI 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 KI value of 6 nl/ml. These results suggest that GABA has a physiological role as a neurotransmitter in C. elegans.
Schaeffer
J M
JM
Merck Sharp & Dohme Research Laboratories, Rahway, New Jersey 07065.
Bergstrom
A R
AR
D000612:4-Aminobutyrate Transaminase / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D002107:Caenorhabditis / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005968:Glutamate Decarboxylase / Q000378:metabolism; D007700:Kinetics; D009928:Organ Specificity; D051381:Rats; D011963:Receptors, GABA-A / Q000378:metabolism*; D013045:Species Specificity; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D000612:4-Aminobutyrate Transaminase; D005968:Glutamate Decarboxylase