The angiotensin receptors are G protein-coupled cell surface receptors responsible for the signal transduction of the main effector hormone. The AT1 and AT2 receptors have a sequence identity of ~30%, but have a similar affinity for angiotensin II, their main ligand.
angiotensin II receptor, type 1
|Locus||Chr. 3 q21-q25|
angiotensin II receptor, type 2
|Locus||Chr. X q22-q23|
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.
AT2 receptors are more plentiful in the foetus 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.
Other poorly characterized subtypes include AT3 receptor and AT4 receptor. The AT4 receptor is activated by angiotensin IV, and may play a role in regulating the CNS extracellular matrix.