Beta-2 adrenergic receptor

Overview
The beta-2 adrenergic receptor (β2 adrenoreceptor), also known as ADRB2, is an beta-adrenergic receptor, and also denotes the human gene encoding it.

Gene
The gene is intronless. Different polymorphic forms, point mutations, and/or downregulation of this gene are associated with nocturnal asthma, obesity and type 2 diabetes.

Structure
The 3D crystallographic structure (see figure to the right) of the β2-adrenergic receptor has been determined.

Mechanism
This receptor is directly associated with one of its ultimate effectors, the class C L-type calcium channel CaV1.2. This receptor-channel complex also contains a G protein - Gs, which activate an adenylyl cyclase, cAMP-dependent kinase, and the counterbalancing phosphatase, PP2A. The assembly of the signaling complex provides a mechanism that ensures specific and rapid signaling by this G protein-coupled receptor. A two-state biophysical and molecular model has been proposed to account for the pH and REDOX sensitivity of this and other GPCRs.

Function
Actions of the β2 receptor include:

Circulatory system

 * Increase cardiac output (minor degree compared to β1).
 * Increase heart rate in sinoatrial node (SA node) (chronotropic effect).
 * Increase atrial cardiac muscle contractility. (inotropic effect).
 * Increases contractility and automaticity of ventricular cardiac muscle.
 * Dilate hepatic artery.
 * Dilate arteries to skeletal muscle.

Digestive system

 * Glycogenolysis and gluconeogenesis in liver.
 * Glycogenolysis and lactate release in skeletal muscle.
 * Contract sphincters of GI tract.
 * Insulin secretion from pancreas.
 * Thickened secretions from salivary glands.

Other

 * Inhibit histamine-release from mast cells.
 * Increase protein content of secretions from lacrimal glands.
 * Increase renin secretion from kidney.
 * Receptor also present in cerebellum.

Agonists
(Short/long)
 * spasmolytics in asthma and COPD
 * salbutamol (albuterol in USA)
 * bitolterol mesylate
 * isoproterenol
 * levalbuterol
 * metaproterenol
 * salmeterol
 * terbutaline
 * ritodrine (tocolytic)

Antagonists
(Beta blockers)
 * butoxamine*
 * propranolol (antihypertensive)

* denotes selective agonists to the receptor.

Related Chapters

 * Other adrenergic receptors
 * Alpha-1 adrenergic receptor
 * Alpha-2 adrenergic receptor
 * Beta-1 adrenergic receptor
 * Beta-3 adrenergic receptor