H2 receptors are positively coupled to adenylate cyclase via Gs alpha subunit. It is a potent stimulant of cAMP production, which leads to activation of protein kinase A. [5] PKA functions to phosphorylate certain proteins, affecting their activity. The drug betazole is an example of a histamine H2 receptor agonist.
Histamine is a ubiquitous messenger molecule released from mast cells, enterochromaffin-like cells, and neurons. [5] Its various actions are mediated by histamine receptors H1, H2, H3 and H4. The histamine receptor H2 belongs to the rhodopsin-like family of G protein-coupled receptors. It is an integral membrane protein and stimulates gastric acid secretion. It also regulates gastrointestinal motility and intestinal secretion and is thought to be involved in regulating cell growth and differentiation. [6] Histamine may play a role in penile erection. [7]
Histamine H2 receptors are expressed in the following tissues:
Activation of the H2 receptor results in the following physiological responses:
Gastrin is a peptide hormone that stimulates secretion of gastric acid (HCl) by the parietal cells of the stomach and aids in gastric motility. It is released by G cells in the pyloric antrum of the stomach, duodenum, and the pancreas.
The histamine receptors are a class of G protein–coupled receptors which bind histamine as their primary endogenous ligand.
Histamine H3 receptors are expressed in the central nervous system and to a lesser extent the peripheral nervous system, where they act as autoreceptors in presynaptic histaminergic neurons and control histamine turnover by feedback inhibition of histamine synthesis and release. The H3 receptor has also been shown to presynaptically inhibit the release of a number of other neurotransmitters (i.e. it acts as an inhibitory heteroreceptor) including, but probably not limited to dopamine, GABA, acetylcholine, noradrenaline, histamine and serotonin.
The H1 receptor is a histamine receptor belonging to the family of rhodopsin-like G-protein-coupled receptors. This receptor is activated by the biogenic amine histamine. It is expressed in smooth muscles, on vascular endothelial cells, in the heart, and in the central nervous system. The H1 receptor is linked to an intracellular G-protein (Gq) that activates phospholipase C and the inositol triphosphate (IP3) signalling pathway. Antihistamines, which act on this receptor, are used as anti-allergy drugs. The crystal structure of the receptor has been determined (shown on the right/below) and used to discover new histamine H1 receptor ligands in structure-based virtual screening studies.
The enzyme histidine decarboxylase is transcribed on chromosome 15, region q21.1-21.2, and catalyzes the decarboxylation of histidine to form histamine. In mammals, histamine is an important biogenic amine with regulatory roles in neurotransmission, gastric acid secretion and immune response. Histidine decarboxylase is the sole member of the histamine synthesis pathway, producing histamine in a one-step reaction. Histamine cannot be generated by any other known enzyme. HDC is therefore the primary source of histamine in most mammals and eukaryotes. The enzyme employs a pyridoxal 5'-phosphate (PLP) cofactor, in similarity to many amino acid decarboxylases. Eukaryotes, as well as gram-negative bacteria share a common HDC, while gram-positive bacteria employ an evolutionarily unrelated pyruvoyl-dependent HDC. In humans, histidine decarboxylase is encoded by the HDC gene.
The secretin receptor is a protein that in humans is encoded by the SCTR gene. This protein is a G protein-coupled receptor which binds secretin and is the leading member of the secretin receptor family, also called class B GPCR subfamily.
Antihistamines are drugs which treat allergic rhinitis, common cold, influenza, and other allergies. Typically, people take antihistamines as an inexpensive, generic drug that can be bought without a prescription and provides relief from nasal congestion, sneezing, or hives caused by pollen, dust mites, or animal allergy with few side effects. Antihistamines are usually for short-term treatment. Chronic allergies increase the risk of health problems which antihistamines might not treat, including asthma, sinusitis, and lower respiratory tract infection. Consultation of a medical professional is recommended for those who intend to take antihistamines for longer-term use.
The urotensin-2 receptor (UR-II-R) also known as GPR14 is a class A rhodopsin family G protein coupled-receptor (GPCR) that is 386 amino acids long which binds primarily to the neuropeptide urotensin II.[1] The receptor quickly rose to prominence when it was found that when activated by urotensin II it induced the most potent vasoconstriction effect ever seen. While the precise function of the urotensin II receptor is not fully known it has been linked to cardiovascular effects, stress, and REM sleep.
P2Y purinoceptor 1 is a protein that in humans is encoded by the P2RY1 gene.
Pituitary adenylate cyclase-activating polypeptide type I receptor also known as PAC1, is a protein that in humans is encoded by the ADCYAP1R1 gene. This receptor binds pituitary adenylate cyclase activating peptide.
The Cholecystokinin A receptor is a human protein, also known as CCKAR or CCK1, with CCK1 now being the IUPHAR-recommended name.
Galanin receptor 1 (GAL1) is a G-protein coupled receptor encoded by the GALR1 gene.
Angiotensin II receptor type 2, also known as the AT2 receptor is a protein that in humans is encoded by the AGTR2 gene.
Probable G-protein coupled receptor 12 is a protein that in humans is encoded by the GPR12 gene.
Melanocortin 5 receptor (MC5R) is a protein that in humans is encoded by the MC5R gene. It is located on the chromosome 18 in the human genome. When the MC5R was disrupted in transgenic mice, it induced disruption of their exocrine glands and resulted in decreased production of sebum.
P2Y purinoceptor 6 is a protein that in humans is encoded by the P2RY6 gene.
Somatostatin receptor type 1 is a protein that in humans is encoded by the SSTR1 gene.
Neurotensin receptor type 2 is a protein that in humans is encoded by the NTSR2 gene.
Vasoactive intestinal polypeptide receptor 1 also known as VPAC1, is a protein, that in humans is encoded by the VIPR1 gene. VPAC1 is expressed in the brain (cerebral cortex, hippocampus, amygdala), lung, prostate, peripheral blood leukocytes, liver, small intestine, heart, spleen, placenta, kidney, thymus and testis.
G protein-activated inward rectifier potassium channel 3 is a protein that in humans is encoded by the KCNJ9 gene.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.
