GHB receptor

The existence of a specific GHB receptor was predicted by observing the action of GHB and related compounds that primarily act on the GABA_B receptor, but also exhibit a range of effects which were found not to be produced by GABA_B activity, and so were suspected of being produced by a novel and at the time unidentified receptor target. Following the discovery of the "orphan" G-protein coupled receptor GPR172A, it was subsequently found to be the GHB receptor whose existence had been previously predicted.[5] The rat GHB receptor was first cloned and characterised in 2003[6] followed by the human receptor in 2007.[7]

Due to its many functions, this gene has a history of multiple discovery. In 2002, data mining in the human genome found an incorrectly spliced form of this protein with eight transmembrane helices, and due to the presence of a G-protein binding site it was correctly assumed to be a GPCR (as GCPR41).[8] In 2003, it was first identified, in its 11-transmembrane-helice full length, as a receptor for porcine endogenous retrovirus.[9] The same protein was later identified as the GHB receptor in 2007.[7] In 2009 it was identified as a riboflavin transporter, and sorted into the SLC family 52 due to sequence similarity. The authors of the 2009 study were not aware of the 2007 study showing that it actually does function as a GPCR.[10]

The function of the GHB receptor appears to be quite different from that of the GABA_B receptor. It shares no sequence homology with GABA_B, and administration of mixed GHB/GABA_B receptor agonists along with a selective GABA_B antagonist or selective agonists for the GHB receptor which are not agonists at GABA_B, do not produce a sedative effect, instead causing a stimulant effect followed by convulsions at higher doses, thought to be mediated through increased Na⁺/K⁺ current and increased release of dopamine and glutamate.[11][12][13][14][15][16]