Search

The effect of mutating the conserved amino acid residue arginine 120 to lysine in the GABAA receptor alpha 1 subunit was studied. In electrophysiological experiments, the arginine 120 lysine (R120K) mutation in the alpha 1 subunit, when co-expressed with beta 2 and gamma 2 subunits in Sf-9 insect cells, induces a 180-fold rightward shift of the GABA dose-response curve compared with wild type alpha 1 beta 2 gamma 2s GABAA receptors. The diazepam potentiation of GABA-gated chloride ion currents was not affected. The binding of the GABAA ligands [3H]muscimol and [3H]SR 95531 to alpha 1 (R120K) beta 2 gamma 2s GABAA receptors was abolished but the binding affinity of the benzodiazepine receptor ligand [3H]flunitrazepam was unchanged. These results suggest that the arginine residue 120 in the alpha 1 subtype of the GABAA receptor is essential for GABA binding.

Molecular mechanics (MMP2) calculated geometries and conformational energies have been employed in an attempt to elucidate the molecular basis for presynaptic dopamine receptor selectivity of centrally acting agonists of the phenylpiperidine series. A receptor interaction model based on the McDermed receptor concept, on superimpositions of calculated structures, and on conformational analysis is presented. The model focuses on the interaction between N-alkyl substituents and the receptor. From comparisons with rigid structures having either agonistic or antagonistic properties it is concluded that the presynaptically selective compound (S)-3-(3-hydroxyphenyl)-N-n-propylpiperidine [S)-3PPP) is acting as an agonist in one rotameric form and as an antagonist in another one. The selectivity of (S)-3PPP and the nonselectivity of its enantiomer are suggested to be due to differences in the interactions between N-alkyl substituents and the receptor. The receptor model presented led to the hypothesis that the piperidine ring in the compounds studied should be equivalent to a N-methyl group in its receptor interactions. Examples are given in support of this idea. Presynaptic selectivity was predicted for an aminotetralin derivative and was also observed in subsequent testing.

(S)-CPW399 (2b) is a novel, potent, and subtype-selective AMPA receptor full agonist that, unlike (S)-willardiine and related compounds, in mouse cerebellar granule cells, stimulated an increase in [Ca(2+)](i), and induced neuronal cell death in a time- and concentration-dependent manner. Compound 2b appears to be a weakly desensitizing, full agonist at AMPA receptors and therefore represents a new pharmacological tool to investigate the role of AMPA receptors in excitotoxicity and their molecular mechanisms of desensitization.