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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.

Members

Overview table

Receptor	Mechanism
AT₁	G_q/11 G_i/o
AT₂	G_i2 / ₃
AT₃
AT₄

AT₁

The AT₁ receptor is the best elucidated angiotensin receptor.

Mechanism

The angiotensin receptor is activated by the vasoconstricting peptide angiotensin II. The activated receptor in turn couples to G_q/11 and G_i/o and thus activates phospholipase C and increases the cytosolic Ca²⁺ concentrations, which in turn triggers cellular responses such as stimulation of protein kinase C. Activated receptor also inhibits adenylate cyclase and activates various tyrosine kinases.

Effects

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.

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.