Each AMPA receptor subunit binds one glutamate molecule in the ligand binding site in the N terminus. Each receptor is capable of binding four glutamate molecules however, channel opens when two sites are occupied by the ligand and the current increases with increased ligand binding. Ca impermeable AMPA receptors containing GluR2 subunit conduct Na currents upon activation by either glutamate binding or agonist, AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) binding. The Na currents mainly lead to depolarization of the membrane leading to activation of voltage gated channels such as NMDA receptors that require both agonist binding and depolarization for their activation.