urotensin-II receptor, member of the class A family of seven-transmembrane G protein-coupled receptors
The urotensin-II receptor (UII-R, also known as the hypocretin receptor) is a member of the class A rhodopsin-like G-protein coupled receptors, which binds the peptide hormone urotensin-II. Urotensin II (UII) is a vasoactive somatostatin-like or cortistatin-like peptide hormone. However, despite the apparent structural similarity to these peptide hormones, they are not homologous to UII. Urotensin II was first identified in fish spinal cord, but later found in humans and other mammals. In fish, UII is secreted at the back part of the spinal cord, in a neurosecretory centre called uroneurapophysa, and is involved in the regulation of the renal and cardiovascular systems. In mammals, urotensin II is the most potent mammalian vasoconstrictor identified to date and causes contraction of arterial blood vessels, including the thoracic aorta. The urotensin II receptor is a rhodopsin-like G-protein coupled receptor, which binds urotensin-II. The receptor was previously known as GPR14, or sensory epithelial neuropeptide-like receptor (SENR). The UII receptor is expressed in the CNS (cerebellum and spinal cord), skeletal muscle, pancreas, heart, endothelium and vascular smooth muscle. It is involved in the pathophysiological control of cardiovascular function and may also influence CNS and endocrine functions. Binding of urotensin II to the receptor leads to activation of phospholipase C, through coupling to G(q/11) family proteins. The resulting increase in intracellular calcium may cause the contraction of vascular smooth muscle.