Pre-exposure to L-homocysteinesulfinic acid blocks quisqualate-induced sensitization to L-2-amino-4-phosphonobutanoic acid.

Quisqualic acid sensitizes hippocampal CA1 neurons to depolarization by L-2-amino-4-phosphonobutanoic acid (L-AP4). This sensitization to L-AP4 is known to be blocked by simultaneous exposure to L-homocysteinesulfinic acid, L-alpha-aminoadipic acid and L-serine-O-sulfate during exposure to quisqualate. We report here that these compounds also act as 'pre-blockers' which, when added and removed from the medium prior to exposure to quisqualate, prevent subsequent induction of sensitization to L-AP4 by quisqualate. This pre-blockade suggests that simple competitive inhibition of extracellular receptor or uptake sites may not be the mechanism by which these compounds attenuate the action of quisqualate in this 'Quis-effect'.