Some forms of synaptic potentiation require calcium ion entry into the post-synaptic neuron via NMDA receptors. Which of the following is NOT a direct action of this increased post-synaptic calcium?

Question

BlackTom AI · Accepted Answer

Calcium entering through NMDA receptors primarily acts as an intracellular second messenger that binds proteins and regulates enzymes and ion fluxes; it does not itself bind DNA promoter regions to control gene expression.

1) Relevant knowledge points and concepts
- NMDA receptor-mediated Ca2+ entry supplies intracellular Ca2+ that acts via Ca2+-binding proteins (e.g., calmodulin) to activate kinases and phosphatases, and can contribute to membrane depolarization because Ca2+ is a positively charged ion.  
- CaMKII (calcium/calmodulin-dependent protein kinase II) is activated when Ca2+-calmodulin binds and thereby triggers phosphorylation events important for synaptic potentiation.  
- Protein Phosphatase 2B (PP2B, calcineurin) is a Ca2+-calmodulin-dependent phosphatase activated directly by rising Ca2+.  
- Regulation of gene expression by Ca2+ is indirect: Ca2+-dependent kinases/phosphatases modify transcription factors (e.g., CREB), which then bind promoter regions; Ca2+ itself does not directly bind DNA.

2) Step-by-step reasoning
- Increased post-synaptic Ca2+ first binds calmodulin. This Ca2+-calmodulin complex directly activates CaMKII (so option A is a direct action).  
- The same Ca2+-calmodulin complex directly activates calcineurin (PP2B) (so option C is a direct action).  
- Ca2+ influx through NMDA receptors contributes directly to membrane depolarization because the ion carries positive charge and increases inward current; additionally, downstream Ca2+-dependent modulation of AMPA receptors and ion channels further alters membrane potential (so option B is a direct/physiologically immediate effect).  
- While Ca2+ influences transcription, it does so by activating intracellular signaling cascades and transcription factors that then bind promoter regions. Ca2+ ions do not themselves bind promoter DNA to control gene expression; thus this is not a direct action.

3) Why the correct answer is correct
- "Binding to gene promoter regions to control gene expression" describes a direct DNA-binding action by Ca2+, which does not occur. Gene regulation is mediated indirectly via Ca2+-dependent proteins.

4) Why the other options are incorrect
- Binding to calmodulin to activate CaMKII: correct direct action.  
- Depolarization of the post-synaptic compartment: Ca2+ influx contributes directly to depolarization.  
- Activation of Protein Phosphatase 2B: calcineurin is directly activated by Ca2+/calmodulin.

Conclusion: The statement that is NOT a direct action of increased post-synaptic calcium is "Binding to gene promoter regions to control gene expression," which matches the provided answer.

Some forms of synaptic potentiation require calcium ion entry into the post-synaptic neuron via NMDA receptors. Which of the following is NOT a direct action of this increased post-synaptic calcium?Single choice

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