Receptor Modulation
The NMDA receptor is a non-specific cation channel which can allow the passage of Ca2+ and Na+ into the cell and K+ out of the cell. The excitatory postsynaptic potential (EPSP) produced by activation of an NMDA receptor increases the concentration of Ca2+ in the cell. The Ca2+ can in turn function as a second messenger in various signaling pathways. However, the NMDA receptor cation channel is blocked by Mg2+ at resting membrane potential. To unblock the channel, the postsynaptic cell must be depolarized.
The NMDA receptor therefore functions as a "molecular coincidence detector". Its ion channel only opens when the following two conditions are met simultaneously: glutamate is bound to the receptor, and the postsynaptic cell is depolarized (which removes the Mg2+ blocking the channel). This property of the NMDA receptor explains many aspects of long term potentiation (LTP) and synaptic plasticity.
NMDA receptors are modulated by a number of endogenous and exogenous compounds and play a key role in a wide range of physiological (e.g. memory) and pathological processes (e.g. excitotoxicity).
Read more about this topic: NMDA Receptor
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