Alpha-1 adrenergic receptor
The alpha-1 (α1) adrenergic receptor is a G protein-coupled receptor (GPCR) associated with the Gq heterotrimeric G-protein. It consists of three highly homologous subtypes, including α1A-, α1B-, and α1D-adrenergic. Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α1-adrenergic receptor in the central and peripheral nervous systems.
Effects
The α1-adrenergic receptor has several general functions in common with the α2-adrenergic receptor, but also has specific effects of its own. α1-receptors primarily mediate smooth muscle contraction, but have important functions elsewhere as well. The neurotransmitter noradrenaline has higher affinity for the α1 receptor than does adrenaline (which is a hormone).
Smooth muscle
In smooth muscle cells of blood vessels the principal effect of activation of these receptors is vasoconstriction. Blood vessels with α1-adrenergic receptors are present in the skin, the sphincters of gastrointestinal system, kidney (renal artery) and brain. During the fight-or-flight response vasoconstriction results in decreased blood flow to these organs. This accounts for the pale appearance of the skin of an individual when frightened.
Beta-1 adrenergic receptor
The beta-1 adrenergic receptor (β1 adrenoreceptor), also known as ADRB1, is a beta-adrenergic receptor, and also denotes the human gene encoding it. It is a G-protein coupled receptor associated with the Gs heterotrimeric G-protein and is expressed predominantly in cardiac tissue.
Receptor
Actions
Actions of the β1 receptor include:
- 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.
- Increases conduction and automaticity of atrioventricular node (AV node)
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