Polyamine and ifenprodil interactions with the NMDA receptor's glycine site.

Ifenprodil partially inhibited [3H]glycine binding to the N-methyl-D-aspartate (NMDA) receptor in rat telencephalic membranes. The polyamine spermine significantly enhanced [3H]glycine binding and decreased ifenprodils inhibitory potency. However, ifenprodil was unable to completely reverse the stimulation of binding produced by spermine. Also, ifenprodil was found to reduce the maximum degree to which spermine enhanced binding but had no effect on the polyamine's potency. These results show that ifenprodil and spermine do not competitively interact with respect to their abilities to modify [3H]glycine binding to the NMDA receptor complex.