Alpha-1 adrenergic receptor
G protein-coupled receptor
The alpha-1 (α1) adrenergic receptor (or adrenoceptor) is a G protein-coupled receptor (GPCR) associated with the Gq heterotrimeric G protein. It consists of three highly homologous subtypes, α1A-, α1B-, and α1D-adrenergic. There is no α1C receptor. At one time, there was a subtype known as α1C, but it was found to be identical to the previously discovered α1A receptor subtype. To avoid confusion, naming was continued with the letter D. Catecholamines like norepinephrine (noradrenaline) and epinephrine (adrenaline) signal through the α1-adrenergic receptors in the central and peripheral nervous systems. The crystal structure of the α1B-adrenergic receptor subtype has been determined in complex with the inverse agonist (+)-cyclazosin.
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 norepinephrine has higher affinity for the α1 receptor than does the hormone epinephrine.
Smooth muscle
In smooth muscle cells of blood vessels the principal effect of activation of these receptors is vasoconstriction.
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