Molecular analysis of the interaction of the pyrazine derivatives RPR119990 and RPR117824 with human AMPA-type glutamate receptor channels.

Antagonizing glutamatergic neurotransmission by blockade of AMPA-type glutamate receptors is a promising pharmacological strategy in the treatment of neurodegenerative diseases. We investigated the interaction of two new pyrazine derivatives (RPR119990 and RPR117824) with recombinant AMPA-type glutamate receptors. Recombinant homooligomeric GluR1flop, GluR2flip, GluR2flop, GluR6, non-desensitizing GluR2 L504Y channels and heterooligomeric GluR1/2 channels were expressed in HEK293 cells. AMPA-type channels were competitively inhibited by RPR119990 or RPR117824 with an IC(50) around 10 nM, at GluR6 channels the dose-response relation of the inhibition was shifted to higher concentrations. Non-desensitizing GluR2 L504Y channels were used to further characterize the inhibition. After equilibration with the agonist a marked dose-dependent current decay upon coapplication of glutamate and RPR119990 and a dose-independent time course of recovery from block was observed. The extents of current inhibition as well as the time constant of current decay upon addition of the blocker to the test solution were dependent on agonist concentration, pointing to a competitive inhibition. Quantitative analysis of the experimental data using computerized simulations are compatible with a competitive block mechanism and provides hints to binding sites at unliganded and liganded closed states of the receptor.