[mycotheologist]

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⁺?