Figure 2.
Classification of histamine receptors (H1R–H4R) in relation to their functions. H1R–H3R transduce extracellular signals via Gαq/11, Gαis, and Gαi/o, respectively, while H4R acts through Gαi/o and β-arrestin. H1R and H2R are low-affinity receptors while H3R and H4R are high-affinity receptors towards histamine. Ligands of H1R–H4R have therapeutic applications in allergic inflammation, gastric acid secretion, neurotransmission, and immunomodulation, respectively. The information in the figure is partially based on [44].