Structure, function, and regulation of adrenergic receptors

Adrenergic receptors for adrenaline and noradrenaline belong to the large multigenic family of receptors coupled to GTP‐binding proteins. Three pharmacologic types have been identified: α 1 ‐, α 2 ‐, and β‐adrenergic receptors. Each of these has three subtypes, characterized by both structural and functional differences. The α 2 and β receptors are coupled negatively and positively, respectively, to adenylyl cyclase via G i or G s regulatory proteins, and the α 1 receptors modulate phospholipase C via the G o protein. Subtype expression is regulated at the level of the gene, the mRNA, and the protein through various transcriptional and postsynthetic mechanisms. Adrenergic receptors constitute, after rhodopsin, one of the best studied models for the other receptors coupled to G proteins that are likely to display similar structural and functional properties.