Alpha-2-adrenergic receptors are members of the G protein-coupled receptor superfamily. They include 3 highly homologous subtypes: alpha 2A, alpha 2B, and alpha 2C. These receptors have a critical role in regulating neurotransmitter release from sympathetic nerves and from adrenergic neurons in the central nervous system. Studies in mouse revealed that both the alpha 2A and alpha 2C subtypes were required for normal presynaptic control of transmitter release from sympathetic nerves in the heart and from central noradrenergic neurons; the alpha 2A subtype inhibited transmitter release at high stimulation frequencies, whereas the alpha 2C subtype modulated neurotransmission at lower levels of nerve activity. This gene encodes alpha 2A subtype and it contains no introns in either its coding or untranslated sequences. [provided by RefSeq].