AP5 or APV ((2R)-amino-5-phosphonovaleric acid; (2R)-amino-5-phosphonopentanoate) is a selective NMDA receptor antagonist that competitively inhibits the ligand (glutamate) binding site of NMDA receptors. AP5 blocks NMDA receptors in micromolar concentrations (~50 µM).
AP5 blocks the cellular analog of classical conditioning in the sea slug Aplysia californica, and has similar effects on Aplysia long-term potentiation (LTP), since NMDA receptors are required for both. It is sometimes used in conjunction with the calcium chelator BAPTA to determine whether NMDARs are required for a particular cellular process. AP5/APV has also been used to study NMDAR-dependent LTP in the mammalian hippocampus.
In general, AP5 is very fast-acting within in vitro preparations, and can block NMDA receptor action at a reasonably small concentration. The active isomer of AP5 is considered to be the D configuration, although many preparations are available as a racemic mixture of D- and L-isomers. It is useful to isolate the action of other glutamate receptors in the brain, i.e., AMPA and kainate receptors.
AP5 can block the conversion of a silent synapse to an active one, since this conversion is NMDA receptor-dependent.
AP5 was developed by Jeff Watkins and Harry Olverman.