Guanine nucleotides are competitive inhibitors of N-methyl-D-aspartate at its receptor site both in vitro and in vivo.
Guanine nucleotides were shown to alter N-methyl-d-aspartate (NMDA) receptor-effector coupling by competitive antagonism at the glutamate binding site, rather than via interaction with an intracellularly located GTP-binding protein. Thus, in contrast to known G-protein linked receptors, micromolar concentrations of guanine nucleotides and their analogs decreased both agonist [( 3H]glutamate) and antagonist [( 3H]-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid binding to the NMDA receptor complex. The most potent compound, the GDP analog guanosine-5'-O-(2-thiodiphosphate) (GDP beta S), was studied in detail. GDP beta S exhibited almost 200-fold selectivity for the glutamate recognition site vs. the strychnine-insensitive glycine binding site. IC50 values were 2.7 +/- 1.4 and 484 +/- 97 microM, respectively. GDP beta S also inhibited N-[1-(2-thienyl)cyclohexyl-3H]piperidine binding (IC50 was 28.0 +/- 3.7 microM) in an NMDA-reversible fashion. [3H]-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid saturation binding studies revealed an increase in Kd from 263 +/- 49 (control) to 552 +/- 134 nM (8 microM GDP beta S) without any change in maximum binding (4.94 +/- 0.34 and 5.19 +/- 0.58 pmol/mg of protein, respectively). GDP beta S was also a competitive inhibitor of the following NMDA-stimulated responses: elevation of cyclic GMP in neonatal rat cerebellar slices, release of preloaded [3H]norepinephrine from superfused rat hippocampal slices and elevation of cytosolic calcium concentration in fura-2-loaded cultured rat forebrain neurons. IC50 values were 78.4, 53.4 and 1.6 microM, respectively. Finally, GDP beta S resembled known NMDA receptor antagonists in its ability to block NMDA receptor-induced seizures after i.c.v. administration.(ABSTRACT TRUNCATED AT 250 WORDS)
Baron
B M
BM
Merrell Dow Research Institute, Cincinnati, Ohio.
Dudley
M W
MW
McCarty
D R
DR
Miller
F P
FP
Reynolds
I J
IJ
Schmidt
C J
CJ
D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D001667:Binding, Competitive; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002531:Cerebellum / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D006152:Cyclic GMP / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006624:Hippocampus / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D016202:N-Methylaspartate; D009474:Neurons / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*; D013574:Synaptosomes / Q000378:metabolism
D006150:Guanine Nucleotides; D016194:Receptors, N-Methyl-D-Aspartate; D017981:Receptors, Neurotransmitter; D001224:Aspartic Acid; D016202:N-Methylaspartate; D006152:Cyclic GMP; D002118:Calcium; D009638:Norepinephrine