Multiple histamine receptors: properties and functional characteristics.

Recent advances in molecular biological techniques have seen the cloning of the H2-receptor gene from canine parietal cells, and the structural identification and cloning of the H1- and H3-receptors should soon follow. This information will allow the elucidation of the mechanisms responsible for the species and tissue heterogeneity in the H1-receptor binding and functional characteristics. The mechanisms underlying the inhibitory effect of H3-receptor stimulation on neurotransmitter release remains to be established, but this receptor appears to be coupled to its effector system (perhaps an ion channel?) via a G-protein. Patch-clamp studies on histamine receptors in invertebrate neurones have identified a ligand-gated chloride channel at a photoreceptor synapse of the housefly and it remains an intriguing possibility that there is a counterpart in mammalian species.