Histamine is a ubiquitous messenger molecule released from mast cells, enterochromaffin-like cells, and neurons. The histamine H1 receptor is an integral membrane protein and belongs to the family 1 of G protein-coupled receptors. It mediates the contraction of smooth muscles, increase in capillary permeability due to contraction of terminal venules, catecholamine release from adrenal medulla, and mediates neurotransmission in the central nervous system.
Regulator of G protein signaling 4 (RGS4) negatively regulates G protein coupled receptor signaling. RGS4 belongs to a family of regulatory molecules that act as GTPase activating proteins (GAPs) for G alpha subunits of heterotrimeric G proteins. RGS proteins are able to deactivate G protein subunits of the Gi alpha, Go alpha and Gq alpha subtypes. They drive G proteins into their inactive GDP bound forms. All RGS proteins share a conserved 120 amino acid sequence termed the RGS domain. Regulator of G protein signaling 4 protein is 37% identical to RGS1 and 97% identical to rat Rgs4. This protein negatively regulate signaling upstream or at the level of the heterotrimeric G protein and is localized in the cytoplasm. The antihypertrophic effects of RGS4 in the myocardium is well characterized. RGS4 may also have a potential role in the pathogenesis of cardiac arrhythmias.