DL-AP4

Phenylglycines can evoke quisqualate-primed depolarizations in rat cingulate cortex: an effect associated with [3H]DL-AP4 uptake.[Pubmed:8996809]

Eur J Neurosci. 1996 Dec;8(12):2599-604.

Depolarization could be evoked in slices of rat cingulate cortex by the normally non-excitatory compound L-2-amino-4-phosphonobutyrate (L-AP4) if the slices had been sensitized by exposure to quisqualate. The magnitude of the response to L-AP4 was dependent on the concentrations of both L-AP4 and quisqualate and was inhibited by alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptor antagonism. A series of phenylglycine analogues were capable of evoking similar dose-dependent depolarizations in the rat cingulate cortex following quisqualate sensitization, the most potent being (S)-4-carboxy-3-hydroxyphenylglycine. If the superfusate collected during application of (S)-4-carboxy-3-hydroxyphenylglycine to a quisqualate-sensitized slice was administered to a slice not previously exposed to quisqualate, a small depolarization was obtained. All the compounds shown to be capable of evoking the quisqualate-sensitized response showed affinity for the L-AP4 uptake site whilst having no affinity at ionotropic glutamate receptors and different profiles of activity at metabotropic glutamate receptors. None of the compounds was active at the metabotropic glutamate 4a receptor. There was a statistically significant correlation between a compound's effectiveness in inhibiting [3H]DL-AP4 uptake into rat cortical synaptosomes and its potency in evoking quisqualate-sensitized depolarization. It is concluded that this response may be the result of hetero-exchange between L-AP4 ligands and quisqualate.

The effects of a series of omega-phosphonic alpha-carboxylic amino acids on electrically evoked and excitant amino acid-induced responses in isolated spinal cord preparations.[Pubmed:7042024]

Br J Pharmacol. 1982 Jan;75(1):65-75.

1 The depressant actions on evoked electrical activity and the excitant amino acid antagonist properties of a range of omega-phosphonic alpha-carboxylic amino acids have been investigated in the isolated spinal cord preparations of the frog or immature rat. 2 When tested on dorsal root-evoked ventral root potentials, members of the homologous series from 2- amino-5-phosphonovaleric acid to 2-amino-8-phosphonooctanoic acid showed depressant actions which correlated with the ability of the substances to antagonize selectivity motoneuronal depolarizations induced by N-methyl-D-aspartate. 3 2-Amino-5-phosphonovalerate was the most potent substance of the series giving an apparent KD of 1.4 microM for the antagonism of responses to N-methyl-D-aspartate. 4 A comparison of the (+)- and (-)-forms of 2-amino-5-phosphonovalerate indicated that the N-methyl-D-aspartate antagonist activity and the neuronal depressant action of this substance were both due mainly to the (-)-isomer. 5 The (-)- and (+)-forms of 2-amino-4-phosphonobutyrate had different actions. The (-)-forms of this substance had a relatively weak and non-selective antagonist action on depolarizations induced by N-methyl-D-aspartate, quisqualate and kainate and a similarly weak depressant effect when tested on evoked electrical activity. The (+)-form was more potent than he (-)-form in depressing electrically evoked activity but did not antagonize responses to amino acid excitants. At concentrations higher than those required to depress electrically evoked activity, the (+)-form produced depolarization. This action was blocked by 2-amino-5-phosphonovalerate.

Antagonism of excitatory amino acid-induced responses and of synaptic excitation in the isolated spinal cord of the frog.[Pubmed:316343]

Br J Pharmacol. 1979 Dec;67(4):591-603.

1. A range of compounds has been tested for excitatory amino acid agonist or antagonist activity and for effects on synaptic activity on isolated hemisected spinal cords of frogs. 2. L-Monoamino dicarboxylic acids of chain length up to 8 carbon atoms (L-alpha-aminosuberate) were all agonists. 3. Within a series of D-monoamino dicarboxylic acids, and with diamino dicarboxylic acids (mainly unresolved mixtures of diasteroisomers), there was a progression from agonist activity, for compounds of chain length equal to or shorter than glutamate, to antagonist activity, for compounds of longer chain length equal to or shorter than glutamate, to antagonist activity, for compounds of longer chain length, D-alpha-Aminosuberate (D alpha SD) was the most potent antagonist. 4. The antagonist actions of these substances showed a Mg2+--like selectivity with respect to depolarizations produced by different excitants. N-methyl-D-aspartate (NMDA) was the most susceptible agonist and quisqualate and kainate the least susceptible. Responses to other excitatory amino acids, including L-glutamate and L-aspartate, showed intermediate sensitivity to the antagonists. 5. A parallelism was observed between the relative potencies of mono- and diamino dicarboxylic acids as NMDA antagonists and their relative potencies as depressants of synaptic responses. 6. The results support the concept of different types of excitatory amino acid receptors, with NMDA and its antagonists acting predominantly on one type. These NMDA receptors are probably transmitter receptors activated by an excitatory amino acid transmitter.