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. This gene encodes one of the histamine receptors (H3) which belongs to the family 1 of G protein-coupled receptors. It is an integral membrane protein and can regulate neurotransmitter release. This receptor can also increase voltage-dependent calcium current in smooth muscles and innervates the blood vessels and the heart in cardiovascular system.