Angiotensin receptor

The angiotensin receptors are a class of G protein-coupled receptors with angiotensins as ligands. They are important in the renin-angiotensin system: they are responsible for the signal transduction of the main effector hormone.

Structure
The AT1 and AT2 receptors share a sequence identity of ~30%, but have a similar affinity for angiotensin II, which is their main ligand.

AT1
The AT1 receptor is the best elucidated angiotensin receptor. It is coupled to phospholipase C and angiotensin II increases the cytosolic Ca2+ level. It also inhibits adenylate cyclase and activate various tyrosine kinases. Effects mediated by the AT1 receptor include vasoconstriction, aldosterone synthesis and secretion, increased vasopressin secretion, cardiac hypertrophy, augmentation of peripheral noradrenergic activity, vascular smooth muscle cells proliferation, decreased renal blood flow, renal renin inhibition, renal tubular sodium reuptake, modulation of central sympathetic nervous system activity, cardiac contractility, central osmocontrol and extracellular matrix formation. It is encoded by the gene AGTR1.

AT2
AT2 receptors are more plentiful in the fetus and neonate. Effects mediated by the AT2 receptor include inhibition of cell growth, fetal tissue development, modulation of extracellular matrix, neuronal regeneration, apoptosis, cellular differentiation and maybe vasodilation.

AT3 and AT4
Other poorly characterized subtypes include the AT3 and AT4 receptors. The AT4 receptor is activated by the angiotensin II metabolite angiotensin IV, and may play a role in regulation of the CNS extracellular matrix.