Histamine H2 receptor

H2 receptors are positively coupled to is_associated_with::adenylate cyclase via Gs. It is a potent stimulant of cAMP production, which leads to activation of is_associated_with::Protein Kinase A. PKA functions to phosphorylate certain proteins, affecting their activity. The drug is_associated_with::betazole is an example of a is_associated_with::Histamine H2 receptor agonist.

Function
is_associated_with::Histamine is a ubiquitous messenger molecule released from is_associated_with::mast cells, is_associated_with::enterochromaffin-like cells, and is_associated_with::neurons. Its various actions are mediated by histamine receptors H1, H2, H3 and H4. The histamine receptor H2 belongs to the is_associated_with::rhodopsin-like family of is_associated_with::G protein-coupled receptors. It is an is_associated_with::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.

Tissue distribution
It is found here:
 * Gastric parietal cells (oxyntic cells)
 * is_associated_with::Vascular smooth muscle
 * is_associated_with::Neutrophils
 * is_associated_with::Central nervous system
 * is_associated_with::Heart
 * is_associated_with::Uterus

Physiological responses
Activation of the H2 receptor results in the following physiological responses:


 * Stimulation of is_associated_with::gastric acid secretion (Target of anti-histaminergics (H2 receptors) for is_associated_with::peptic ulcer disease and is_associated_with::GERD)
 * is_associated_with::Smooth muscle relaxation (Experimental histamine H2 receptor agonist used for asthma and COPD)
 * Inhibit is_associated_with::antibody synthesis, is_associated_with::T-cell proliferation and is_associated_with::cytokine production
 * is_associated_with::Vasodilation – PKA activity causes phosphorylation of MLCK, decreasing its activity, resulting in MLC of is_associated_with::myosin being dephosphorylated by MLCP and thus inhibiting contraction. The smooth muscle relaxation leads to vasodilation.