alpha-2 adrenergic receptors subtype D, member of the class A family of seven-transmembrane G protein-coupled receptors
The alpha-2 adrenergic receptors (or adrenoceptors) are a subfamily of the class A rhodopsin-like GPCRs that share a common architecture of seven transmembrane helices. This subfamily consists of three highly homologous receptor subtypes that have a key role in neurotransmitter release: alpha-2A, alpha-2B, and alpha-2C. In addition, a fourth subtype, alpha-2D is present in ray-finned fishes and amphibians, but is not found in humans. The alpha-2 receptors are found in both central and peripheral nervous system and serve to produce inhibitory functions through the G(i) proteins. Thus, the alpha-2 receptors inhibit adenylate cyclase, which decreases cAMP production and thereby decreases calcium influx during the action potential. Consequently, lowered levels of calcium will lead to a decrease in neurotransmitter release by negative feedback.