The kainate receptor subfamily consists of five members that have been further subdivided into two classes based upon structural homology and functional characteristics. GluR5, GluR6, and GluR7receptor subunits share a high degree of homology and are able to form functional channels when expressed in heterologous systems. The KA-1 and KA-2 receptors are unable to form functional channels on their own, but when coexpressed with GluR5-7 receptor subunits, they form channels with high affinity for kainate.