NMDA receptors

Question

NMDA receptors

Quizplus · Accepted Answer

The correct answer is:
c) open with depolarized voltages when Mg2+ ions dissociate from the protein and permit ion influx
NMDA (N-methyl-D-aspartate) receptors are a type of ionotropic glutamate receptor that play a crucial role in synaptic plasticity, which is important for learning and memory. These receptors are unique in that their activation requires two conditions to be met: the binding of glutamate (or another agonist) and the depolarization of the postsynaptic membrane.
Under resting conditions, the NMDA receptor channel is blocked by Mg2+ ions, which sit inside the channel pore and prevent the flow of other ions. When the postsynaptic neuron is depolarized, the Mg2+ block is relieved because the positive charge inside the neuron repels the positively charged Mg2+ ions out of the channel. Once the Mg2+ ions are removed, and if glutamate is bound to the receptor, the channel opens, allowing the influx of Na+ and Ca2+ ions and the efflux of K+ ions.
The other options provided are incorrect for the following reasons:
a) NMDA receptors do not open in response to extracellular ATP. ATP can act as a signaling molecule in the nervous system, but it does not directly activate NMDA receptors.
b) While NMDA receptors do open with depolarized voltages, they do not have a voltage-sensing region with positively charged amino acids like some other voltage-gated ion channels (e.g., voltage-gated sodium or potassium channels).
d) NMDA receptors are not G protein-coupled receptors (GPCRs). They are ionotropic receptors, which means they form an ion channel pore and directly mediate changes in ion flow across the membrane upon activation.
e) Since only option c is correct, "all of the above" is not a valid answer.

NMDA Receptors