title: Structure and function of alpha-adrenergic receptors.
abstract: Alpha 1- and alpha 2-adrenergic receptors are the initial recognition sites on a wide variety of catecholamine-responsive target cells. This article addresses several major questions related to subtypes, structure, signal transduction mechanisms, and regulation of alpha 1- and alpha 2-adrenergic receptors. The application of biochemical and cell and molecular biologic techniques has provided many new insights regarding alpha-adrenergic receptors. Two (and perhaps three) distinct alpha 2-adrenergic receptor subtypes have been identified, and subtypes may exist for alpha 1-adrenergic receptors as well. These multiple subtypes imply much greater diversity among alpha-adrenergic receptors than among beta-adrenergic receptors. Alpha-adrenergic receptors are membrane glycoproteins with several common structural features (including seven membrane-spanning domains with extracellular amino terminus and intracellular carboxyl terminus) that are shared with other types of membrane receptors linked to guanine nucleotide-binding regulatory (G) proteins. These G proteins appear to link alpha-adrenergic receptors to multiple effector systems, including enzymes such as adenylate cyclase and phospholipases, and ion channels. The receptors themselves are dynamic entities, the number of which is regulated as a consequence of a poorly understood life cycle. Although unproven, it seems likely that several important clinical disorders represent alterations in alpha-adrenergic receptors themselves or in the G proteins or effector systems to which these receptors couple. New tools for studying receptor structure and function should help clarify the numerous, inadequately understood issues regarding alpha-adrenergic receptors and their possible alteration in disease states.
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla, California 92093.
authors.forename: P A
authors.initials: PA
authors.lastname: Insel
mesh_terms: D000345:Affinity Labels; D000818:Animals; D006801:Humans; D015394:Molecular Structure; D011942:Receptors, Adrenergic, alpha / Q000145:classification / Q000502:physiology*
chemical_list: D000345:Affinity Labels; D011942:Receptors, Adrenergic, alpha