Why is magnesium an NMDA antagonist?

  • #1

Main Question or Discussion Point

The NMDA receptor is a ligand gated non selective cation channel. It allows Na+ and to a lesser extent Ca2+ and K+ to pass through. I read that Mg2+ clogs up the pore. Why would Mg2+ block the channel but not Ca2+? Ca2+ is larger so I'd expect that to be more likely to block an ion channel. Is it because Mg2+ is more electronegative than Ca2+?
 

Answers and Replies

  • #2
901
3
The NMDA receptor is a ligand gated non selective cation channel. It allows Na+ and to a lesser extent Ca2+ and K+ to pass through. I read that Mg2+ clogs up the pore. Why would Mg2+ block the channel but not Ca2+? Ca2+ is larger so I'd expect that to be more likely to block an ion channel. Is it because Mg2+ is more electronegative than Ca2+?
I'd say its because Mg2+ is the smallest charge 2 ion and is more reactive than Ca2+; clogging up the pore might just mean that it deactivates the protein, not actually block the pore, right? Just my opinion, I'm no expert.
 
  • #3
Heres a quote from an abstract:
Physiological concentrations of magnesium reduce responses to N M D A by blocking the NMDA-associated ionophore in a voltage-dependent manner [2].
deepblue.lib.umich.edu/bitstream/2027.42/28723/1/0000544.pdf

In a voltage dependent manner so what you said must be correct. Magnesiums size-charge ratio is behind it. I read something about NMDA receptors being partially voltage gated.
 

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