The histamine receptors are a class of G protein–coupled receptors which bind histamine as their primary endogenous ligand.
There are four known histamine receptors:
Comparison
There are several splice variants of H3 present in various species. Though all of the receptors are 7-transmembrane g protein coupled receptors, H1 and H2 are quite different from H3 and H4 in their activities. H1 causes an increase in PIP2 hydrolysis, H2 stimulates gastric acid secretion, and H3 mediates feedback inhibition of histamine.
References
Histamine receptor Wikipedia(Text) CC BY-SA