Putative glutamate receptors in membranes obtained from heads of Drosophila melanogaster.

The specific binding of L-[3H]-glutamic acid (GLU) was examined in membrane preparations derived from heads of Drosophila melanogaster. L-[3H]-GLU bound to the membrane preparation with biphasic kinetics in a reversible and saturable way. The specific binding was inhibited by Cl- and Ca2+ ions. Saturation analysis of the data fit a model of two independent binding sites with dissociation constants (KD) of 29 nM and 249 nM and corresponding binding site densities (Bmax) of 5.7 and 24.6 pmol/mg protein. A series of excitatory amino acid receptor agonists and antagonists were tested as inhibitors of L-[3H]-GLU specific binding. Some compounds almost totally abolished the specific binding, whereas others reduced the binding to 45% over the concentration range used. Among the first type of inhibitors, L-GLU was the most potent, D-aspartate (D-ASP) and D-GLU were 10 times less effective than L-GLU, whereas quisqualic acid had the lowest potency. Among the second type of inhibitors, glutamate diethyl ester, D-alpha-amino adipate, and N-methyl-D-aspartate showed the highest potency, and DL-2-amino-4-phosphonobutyrate was the less effective. Kainic acid and gamma-amino butyric acid were not able to modify at any concentration used the specific binding of L-[3H]-GLU. These data suggest the presence of putative GLU receptors in the brain of Drosophila.