Histamine Receptor
Four histamine receptor subtypes (H1-H4), encoded by the HRH1-HRH4 genes, transduce the signals of histamine through distinct G protein couplings. H1 couples to Gq and mobilizes calcium, driving allergic rhinitis, urticaria and bronchoconstriction, which first-generation and second-generation antihistamines such as cetirizine block. H2 couples to Gs and stimulates parietal cell acid secretion in the stomach, making it the target of acid-suppressive drugs like famotidine and cimetidine. H3 functions mainly as a Gi/o-coupled autoreceptor and heteroreceptor in the CNS regulating histamine and other transmitter release, whereas H4 is expressed on immune cells and shapes chemotaxis and inflammation, an emerging target for inflammatory disease.
