prostaglandin E2 receptor EP3 subtype, member of the class A family of seven-transmembrane G protein-coupled receptors
Prostaglandin E2 receptor EP3, also called prostanoid EP3 receptor, is one of four receptor subtypes whose endogenous physiological ligand is prostaglandin E2 (PGE2). Each of these subtypes (EP1-EP4) have unique but overlapping tissue distributions that activate different intracellular signaling pathways. Stimulation of the EP3 receptor by PGE2 preferentially couples to G(i) protein. This leads to a decrease in adenylate cyclase activity, thereby decreasing cAMP levels, which subsequently produces smooth muscle contraction. Knockout mice studies suggest that the EP3 receptor may act as a systemic vasopressor. Prostanoids are the cyclooxygenase (COX) metabolites of arachidonic acid, which include the prostaglandins (PGD2, PGE2, PGF2alpha), prostacyclin (PGI2), and thromboxane A2 (TxA2). These five major bioactive prostanoids acts as mediators or modulators in a wide range of physiological and pathophysiological processes within the kidney and play important roles in inflammation, platelet aggregation, and vasoconstriction/relaxation, among many others. They act locally by preferentially interacting with G protein-coupled receptors designated DP, EP. FP, IP, and TP, respectively. The phylogenetic tree suggests that the prostanoid receptors can be grouped into two major branches: G(s)-coupled (DP1, EP2, EP4, and IP) and G(i)- (EP3) or G(q)-coupled (EP1, FP, and TP), forming three clusters.