Beta-2 receptor

Beta-2 Adrenergic Receptor

The beta-2 adrenergic receptor (β2-adrenergic receptor) is a type of G protein-coupled receptor that is primarily found in the smooth muscles of the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, and skeletal muscle. It is one of the three types of beta adrenergic receptors, the others being beta-1 and beta-3.

Structure

The beta-2 adrenergic receptor is a member of the G protein-coupled receptor (GPCR) superfamily. It is composed of a single polypeptide chain that spans the cell membrane seven times, forming a characteristic seven-transmembrane domain structure. The receptor is coupled to a G protein, specifically the Gs protein, which activates the enzyme adenylate cyclase upon receptor activation.

Function

The primary function of the beta-2 adrenergic receptor is to mediate the effects of the sympathetic nervous system by binding to the endogenous ligand epinephrine (adrenaline) and, to a lesser extent, norepinephrine. Upon activation, the receptor stimulates the production of cyclic adenosine monophosphate (cAMP) from ATP, leading to various physiological responses.

Physiological Effects

• Bronchodilation: In the lungs, activation of beta-2 receptors causes relaxation of bronchial smooth muscle, leading to bronchodilation. This is particularly important in the treatment of asthma and chronic obstructive pulmonary disease (COPD).
• Vasodilation: In the vascular system, beta-2 receptor activation leads to vasodilation, which can decrease peripheral vascular resistance and lower blood pressure.
• Glycogenolysis: In the liver, beta-2 receptors stimulate glycogenolysis, increasing blood glucose levels.
• Uterine Relaxation: In the uterus, beta-2 receptor activation causes relaxation of uterine smooth muscle, which can be used therapeutically to delay premature labor.

Clinical Significance

Beta-2 adrenergic receptors are the target of several important classes of drugs, including:

• Beta-2 agonists: These drugs, such as albuterol and salmeterol, are used to treat asthma and COPD by inducing bronchodilation.
• Beta blockers: While primarily targeting beta-1 receptors, some beta blockers also affect beta-2 receptors, which can lead to side effects such as bronchoconstriction in susceptible individuals.

Genetic Variants

Polymorphisms in the beta-2 adrenergic receptor gene (ADRB2) can affect individual responses to beta-2 agonists and are a subject of pharmacogenomic research.

Also see

• Beta-1 adrenergic receptor
• Beta-3 adrenergic receptor
• G protein-coupled receptor
• Sympathetic nervous system
• Asthma
• Chronic obstructive pulmonary disease