Browsing by Author "FIEDLER, JL"

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    PUTATIVE GLUTAMATE RECEPTORS IN MEMBRANES OBTAINED FROM HEADS OF DROSOPHILA-MELANOGASTER
    (1986) FIEDLER, JL; INESTROSA, NC; BUSTOS, G
    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.
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    SPECIFIC BINDING OF L-[H-3]-GLUTAMIC ACID TO RAT SUBSTANTIA-NIGRA SYNAPTIC-MEMBRANES
    (1986) FIEDLER, JL; ARQUEROS, L; BUSTOS, G
    The specific binding of L-[3H]-glutamic acid (GLU) was investigated in synaptic membranes from rat substantia nigra. L-[3H]-GLU binding to the membrane preparations occurred in a reversible and saturable way. The specific binding was stimulated by the presence of CaCl2 and was reduced by freezing and thawing the membranes. Scatchard analysis of the saturation isotherms yielded a non-linear plot suggesting that the binding reaction does not occur through a simple biomolecular association. Assuming non-interacting binding sites, a high (KD1, 139 nM; Bmax1, 3.5 pmoles/mg protein) and a low (KD2, 667 nM; Bmax2, 15.1 pmoles/mg protein) affinity L-[3H]-GLU binding site were obtained. The kinetics of dissociation of bound L-[3H]-GLU was biphasic; the respective dissociation rate constant (k-1) being 0.20 min-1 and 0.013 min-1. A series of amino acid receptor agonists and antagonists were tested as inhibitors of L-[3H]-GLU specific binding. Quisqualic acid, L-GLU and D-.alpha.-aminoadipate (D-.alpha.-AA) were the most potent inhibitors. DL-2-amino-4-phosphonobutyrate (APB), N-Methyl-D-aspartate (NMDA) and D-GLU were moderate inhibitors, whereas diaminopimelic acid (DAPA) and glutamate diethyl ester (GDEE) exhibited the lowest relative potency. Kainic acid (KA), .gamma.-aminobutyric acid (GABA) and bicuculline were not able to modify at any concentration used the specific binding of L-[3H]-GLU. These data demonstrate the presence of specific GLU binding sites in synaptic structures at substantia nigra level and support the idea that excitatory amino acids may play a role in synaptic transmission in this brain region.