Pharmacological and electrophysiological properties of the naturally occurring Pro391Arg variant of the human 5-HT3A receptor

Abstract

The 5-HT3A receptor, a ligand-gated ion channel, is involved in pain pathways, nausea and emesis, and irritable bowel syndrome, and may play a role in the pathogenesis of psychiatric diseases such as schizophrenia and depression. Recently, a naturally occurring variation (ProArg) in the second intracellular loop of the human (h) 5-HT3A receptor was identified in a schizophrenic patient. Because the substitution of proline, an alpha-imino acid, by arginine may affect the conformation of the whole receptor, the aim of the present study was to determine the pharmacological and functional properties of this variant compared to the wild-type receptor in stably transfected HEK293 cells. Studies of binding of [H]GR65630, a 5-HT3 receptor antagonist, to membranes (saturation and competition experiments with 5-HT3 receptor ligands) and patch-clamp studies of agonist-induced currents in outside-out patches were carried out. In comparison to the wild-type, the variant receptor exhibited no changes in the receptor density and the affinities for nine representative ligands (five agonists and four antagonists). The potencies and efficacies of three 5-HT3 receptor agonists in inducing currents through the ion channel and the potencies of two 5-HT3 receptor antagonists in blocking 5-HT-evoked currents did not differ between wild-type and variant receptors. In addition, there were no differences in the desensitization kinetics of both receptor isoforms. In conclusion, the ArgPro variation of the h5-HT3A receptor does not change ligand binding to the h5-HT3A receptor, nor does it modify current through the receptor channel.

The Human Serotonin Type 3 Receptor Gene (HTR3A-E) Allelic Variant Database

“…Functional studies of homomeric 5‐HT3A p.391Arg receptors revealed no striking changes in receptor properties compared to wildtype receptors [Kurzwelly et al., ]. It is still unclear whether the cell surface expression of the mutant receptor is reduced or not [Kurzwelly et al., ; Thompson et al., ]. Functional analyses of homomeric 5‐HT3A p.344His receptors also revealed no striking functional differences when compared with wild‐type receptors [Thompson et al., ; Krzywkowski et al., ; Combrink, ].…”

“…The p.Pro391Arg variant co-segregated with psychiatric disorders in the patient's family [Niesler et al, 2001b]. Functional studies of homomeric 5-HT3A p.391Arg receptors revealed no striking changes in receptor properties compared to wildtype receptors [Kurzwelly et al, 2004]. It is still unclear whether the cell surface expression of the mutant receptor is reduced or not [Kurzwelly et al, 2004;Thompson et al, 2006].…”

The 5-HT3receptor as a therapeutic target

“…The two mutations were located in a functionally important region, the M3 – M4 loop, which contains a number of potential phosphorylation sites and also has an important role in channel conductance and ion selectivity. However, the rarity of these mutations (single mutations in 2 individuals from a study of 428) and emerging electrophysiological evidence indicates that they are unlikely to be a major contributor to schizophrenia [78,79]. Association analysis of other polymorphisms has also revealed no link between 5-HT 3 receptor genes and polymorphisms [54,55].…”

Serotonin Type 3 Receptor Genes: HTR3A, B, C, D, E

“…Interestingly, this variant was reported to be associated with harm avoidance in women and increased amygdaloid activity, probably by regulation of 5-HT 3A subunit expression [20,21]. Furthermore, two missense mutations in HTR3A (c.1031G>A and c.1172C>G) were detected in schizophrenic patients and may be involved in the etiology of schizophrenia [17,[22][23][24][25]. The deletion c.-_100_102delAAG within the 5Ú TR of HTR3B seems to contribute to the etiology of BPAD [26] and the SNP c.386A>C in HTR3B was found to be associated with major depression [18], both of which have been shown to be functional and presumably predispose to the susceptibility of the respective condition [27,28].…”