DL-AP4, also known as 2-Amino-4-phosphonobutyric acid, is a competitive glutamate antagonist with defined binding affinity that is widely used to selectively inhibit glutamatergic neurotransmission, making it an essential experimental compound for probing synaptic signaling mechanisms and functional circuitry in central nervous system and visual system research.

DL-AP4 at a concentration of 500 µM reduces the tonic inward current by closing ion channels at a holding potential of -33 mV in isolated rod bipolar cells[1]. At a concentration of 0.1 M and after an hour of application, DL-AP4 counteracts glutamate's excitatory effects when iontophoretically applied to locust muscle membrane receptors[2]. Additionally, as compound 2, it opposes excitatory synapses in the rat hippocampal slice's lateral perforant path with an apparent Kd of 2.5 µM[3]. Furthermore, DL-AP4, at 50 µM, inhibits the light response to a series of 10 ms 405-nm flashes over 0-2 seconds at intensities ranging from 3 to 9900 photons µm^-2[4].

H2O: 4 mg/mL (21.85 mM), Sonication is recommended.