GPR55 is an endocannabinoid receptor that belongs to group δ of the rhodopsin-like (class A) receptors. Like all other G-protein coupled receptors, it consists of seven trans-membrane helixes, intracellular C-terminal domain and extracellular N-terminal extension¹.

The other known cannabinoid receptors, CB1 and CB2 share low homology with GPR55 and have different ligand specificity and different downstream activated cascade. Thus, GPR55 consists on its own a class of cannabinoid receptor².

GPR55 is highly expressed in the striatum and binds a wide range of ligands, among which are endocannabinoids:  Anadanine and 2-Arachidonoyl Glycerol, and phytocannabinoids: Tetrahydrocannabinol (THC), abnormal cannabinoid (CBD) and cannabidiol³. Following ligand binding, GPR55 couples to Gα_12,13 proteins, which eventually lead to increased intracellular Ca²⁺ levels².

The endocannabinoid system has a tremendous potential for experimental and clinical research, based on their evolutionary conservation and role in fundamental physiological and pathological processes, including pain modulation, immune function, neuroprotection, cancer, cardiovascular diseases, fertility and appetite⁴. Clinical studies using cannabinoid receptor agonists and antagonists have suggested their possible use in modulating acute and/or chronic diseases such as hypertension, glaucoma, emesis, anxiety, depression, gastrointestinal and hepatic disorders, ulcerative colitis and neuropathic and inflammatory pain⁵.