serotonin receptor subtype 4, member of the class A family of seven-transmembrane G protein-coupled receptors
The 5-HT4 subtype is a member of the serotonin receptor family that belongs to the class A G protein-coupled receptors, and binds the neurotransmitter serotonin (5HT; 5-hydroxytryptamine) in the mammalian central nervous system (CNS). 5-HT4 receptors are selectively linked to G proteins of the G(s) family, which positively stimulate adenylate cyclase, causing cAMP formation and activation of protein kinase A. 5-HT4 receptor-specific agonists have been shown to enhance learning and memory in animal studies. Moreover, hippocampal 5-HT4 receptor expression has been reported to be inversely correlated with memory performance in humans. All GPCRs have a common structural architecture comprising of seven-transmembrane (TM) alpha-helices interconnected by three extracellular and three intracellular loops. A general feature of GPCR signaling is agonist-induced conformational changes in the receptors, leading to activation of the heterotrimeric G proteins, which consist of the guanine nucleotide-binding G-alpha subunit and the dimeric G-beta-gamma subunits. The activated G proteins then bind to and activate numerous downstream effector proteins, which generate second messengers that mediate a broad range of cellular and physiological processes.