5-hydroxytryptamine receptor 5A, also known as HTR5A, is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 which in humans is encoded by the HTR5A gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

.

Function

The gene described in this record is a member of 5-hydroxytryptamine receptor

5-HT receptor

The serotonin receptors, also known as 5-hydroxytryptamine receptors or 5-HT receptors, are a group of G protein-coupled receptors and ligand-gated ion channels found in the central and peripheral nervous systems. They mediate both excitatory and inhibitory neurotransmission...

 family and encodes a multi-pass membrane protein that functions as a receptor for 5-hydroxytryptamine and couples to G protein

G protein

G proteins are a family of proteins involved in transmitting chemical signals outside the cell, and causing changes inside the cell. They communicate signals from many hormones, neurotransmitters, and other signaling factors. G protein-coupled receptors are transmembrane receptors...

s, negatively influencing cAMP levels via G_i and G_o. This protein has been shown to function in part through the regulation of intracellular Ca²⁺ mobilization.

Rodents have been shown to possess two functional 5-HT₅ receptor subtypes, 5-HT_5A and 5-HT_5B, however while humans possess a gene coding for the 5-HT_5B subtype, its coding sequence is interrupted by stop codons making the gene non-functional, and so only the 5-HT_5A subtype is expressed in human brain.

Clinical signficance

The neurotransmitter serotonin

Serotonin

Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...

 (5-hydroxytryptamine, 5-HT) has been implicated in a wide range of psychiatric conditions and also has vasoconstrictive and vasodilatory effects.

Selective Ligands

Few highly selective ligands are commercially available for the 5-HT_5A receptor. When selective activation of this receptor is desired in scientific research, the non-selective serotonin receptor agonist 5-Carboxamidotryptamine

5-Carboxamidotryptamine

5-Carboxamidotryptamine is a tryptamine derivative closely related to the neurotransmitter serotonin.5-CT acts as a non-selective, high-affinity full agonist at the 5-HT1A, 5-HT1B, 5-HT1D, 5-HT5A, and 5-HT7 receptors, as well as at the 5-HT2, 5-HT3, 5-HT6 receptors with lower affinity. It has...

 can be used in conjunction with selective antagonists for its other targets (principally 5-HT_1A, 5-HT_1B, 5-HT_1D and 5-HT₇). Research in this area is ongoing.

Agonists

• Valerenic acid
  Valerenic acid
  Valerenic acid is a sesquiterpenoid constituent of the essential oil of the Valerian plant. Not to be confused with valeric acid.Valerian is used as a herbal sedative which may be helpful in the treatment of insomnia....
  
  , a component of valerian
  Valerian (herb)
  Valerian is a hardy perennial flowering plant, with heads of sweetly scented pink or white flowers which bloom in the summer months. Valerian flower extracts were used as a perfume in the sixteenth century....
  
  , has been shown to act as a 5HT_5A partial agonist.

• Another ligand which has been recently disclosed is shown below, claimed be a selective 5-HT_5A agonist with K_i = 124 nM.

Further reading