Human HTR5A

5-Hydroxytryptamine receptors

5-HT receptors are, with the exception of the ionotropic 5-HT₃ class, GPCRs where the endogenous agonist is 5-hydroxytryptamine. The diversity of metabotropic 5-HT receptors is increased by alternative splicing... [read more] that produces isoforms of the 5-HT_2A (non-functional), 5-HT_2C (non-functional), 5-HT₄, 5-HT₆ (non-functional) and 5-HT₇ receptors. Unique amongst the GPCRs, RNA editing produces 5-HT_2C receptor isoforms that differ in function, such as efficiency and specificity of coupling to G_q/11 and also pharmacology [1,2]. Most 5-HT receptors (except 5-ht_1e and 5-ht_5b) play specific roles mediating functional responses in different tissues (reviewed by [3,4]).

References

1. Bockaert J, Claeysen S, Bécamel C, et al. Neuronal 5-HT metabotropic receptors: fine-tuning of their structure, signaling, and roles in synaptic modulation. Cell Tissue Res 2006;326:553-72.
2. Werry TD, Loiacono R, Sexton PM, et al. RNA editing of the serotonin 5HT2C receptor and its effects on cell signalling, pharmacology and brain function. Pharmacol Ther 2008;119:7-23.
3. Villalón CM, Centurión D. Cardiovascular responses produced by 5-hydroxytriptamine:a pharmacological update on the receptors/mechanisms involved and therapeutic implications. Naunyn Schmiedebergs Arch Pharmacol 2007;376:45-63.
4. Ramage AG, Villalón CM. 5-hydroxytryptamine and cardiovascular regulation. Trends Pharmacol Sci 2008;29:472-81.

5-HT5 Receptors

Two genes have been identified that give rise to 5-ht5a and 5-ht5b proteins with structures consistent with GPCRs although in humans the 5-ht5b gene is a pseudogene since a stop codon has evolved that would, if expressed, result in a truncated protein devoid of key functional moieties of the receptor. The predicted protein sequences display less than 38% amino acid sequence identity to other 5-HT GPCRs, thus clearly distinguishing the 5-ht5a protein from other 5-HT receptors.5-ht5a is yet to receive receptor status since no robust response signal in native tissue has been described. Native 5-ht5a protein would appear G-protein coupled and recombinant expression allows coupling via various transduction systems including the G-protein mediated inhibition of adenylate cyclase. A selective antagonist based on recombinant protein function has been identified (SB699551-A). [close]