What role do AMPA receptors play at synapses that exhibit NMDA mediated long-term potentiation?
AMPA 受体在表现出 NMDA 介导的长时程增强作用的突触中发挥什么作用？

Question

BlackTom AI · Accepted Answer

AMPA receptors are ionotropic glutamate receptors that open non-selective cation channels permitting Na+ influx and K+ efflux; this produces fast excitatory postsynaptic depolarization.

1) Relevant knowledge points and concepts
- AMPA receptors (AMPARs) are ligand-gated ion channels permeable mainly to Na+ and K+ (and in some cases Ca2+ when lacking the GluA2 subunit).  
- NMDA receptors (NMDARs) are voltage- and ligand-gated channels that allow Ca2+ entry when the Mg2+ block is relieved by depolarization.  
- NMDA-mediated LTP: high synaptic activity → initial AMPAR-mediated depolarization → relief of NMDAR Mg2+ block → Ca2+ influx through NMDARs → intracellular signaling (e.g., CaMKII) → increased AMPAR number/function at the synapse.

2) Step-by-step reasoning
- At baseline, glutamate activates AMPARs to produce fast EPSPs by allowing Na+ in and K+ out, depolarizing the postsynaptic membrane.  
- Strong stimulation increases NMDAR Ca2+ entry (because AMPAR-mediated depolarization relieves the Mg2+ block).  
- Ca2+-dependent signaling cascades then increase AMPAR insertion and/or conductance at that synapse.  
- After LTP, the synapse has more functional AMPARs, so subsequent glutamate release produces larger cation currents and greater depolarization.

3) Intermediate “calculation” steps
- No numeric calculations are required; mechanistic steps are: glutamate → AMPAR current (↑) → depolarization → NMDAR Ca2+ influx → signaling → ↑ AMPAR expression → larger cation currents.

4) Why the correct answer is correct
- The stated choice (“After LTP they conduct cation currents that depolarize the post‑synaptic neuron”) captures the core role of AMPARs after NMDA-dependent LTP: increased AMPAR-mediated cation conductance produces stronger depolarizing EPSPs that underlie the potentiated synapse.

5) Why the other options are incorrect
- “They conduct a significant part of the depolarizing calcium ion current”: incorrect because most synaptic Ca2+ influx driving NMDA‑dependent LTP is through NMDARs, not AMPARs (AMPARs are mainly Na+/K+ permeable; only some GluA2‑lacking AMPARs are Ca2+ permeable, which is not the general mechanism here).  
- “They conduct a significant depolarizing sodium current”: partially true but incomplete/less accurate—AMPARs are nonselective cation channels (Na+ and K+), so the best description is that they conduct cation currents that depolarize.  
- “They are the main mechanism for glutamate reuptake into the presynaptic terminal”: false—glutamate reuptake is performed by transporters (EAATs), not AMPARs.

6) Conclusion
This explanation supports and confirms the provided correct answer: After LTP they conduct cation currents that depolarize the post‑synaptic neuron.

What role do AMPA receptors play at synapses that exhibit NMDA mediated long-term potentiation? AMPA 受体在表现出 NMDA 介导的长时程增强作用的突触中发挥什么作用？单项选择题

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