Why is magnesium an NMDA antagonist?

  1. 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+?
     
  2. jcsd
  3. 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.
     
  4. Heres a quote from an abstract:
    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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