AMPA receptors are members of the glutamate receptor family of ion channels that also include the NMDA and Kainate receptors. The three subfamilies are named after the original synthetic agonists that were identified as selective ligands of each family.
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.
The 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.