The α-amino-3-hydroxy-5-methyl-4-isoazolepropionic acid (AMPA) receptor subfamily includes four members AMPA1-AMPA4 that are also known as GluR1-GluR4 respectively.nThe functional AMPA channel is believed to be a tetramer, with most neuronal AMPA receptors being actually heterotetramers composed of AMPA1 plus AMPA2 or AMPA2 plus AMPA3, although homotetramers can also be found.nAMPA receptors are permeable to cations Na+ and K+ and Ca2+. The Ca2+ permeability is dependent on the presence of AMPA2: whenever this subunit is present, the channel will be impermeable to Ca2+. The Ca2+ permeability of the AMPA2 subunit is determined by the presence of an arginine (R) at a critical site in the pore loop instead of a glutamine (Q) present in the same site in the other AMPA subunits. A post-transcriptional process known as RNA editing determines the presence of this R. Since most AMPA2 subunits in the adult brain have undergone RNA editing and most AMPA receptors contain the AMPA2 subunit, most native AMPA receptors will be impermeable to Ca2+.
