Background：

Histamine is a ubiquitous messenger molecule released from mast cells， enterochromaffin-like cells， and neurons. Its various actions are mediated by histamine receptors H1， H2， H3 and H4. Histamine receptor H2 belongs to the family 1 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. Alternatively spliced transcript variants encoding different isoforms have been found for this gene.