Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P46098 (5-HT3 receptor)
 2,290 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Chemical modification of the 5-HT3 receptors in membranes from NG108-15 hybridoma cells was achieved using protein modifying reagents specific for various amino acid residues: N-bromosuccinimide for tryptophan, dithiothreitol for cystine, sodium tetrathionate for cysteine, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline for aspartic and glutamic acids, diethylpyrocarbonate for histidine, tetranitromethane for tyrosine and 2,3-butanedione for arginine. Among all the reagents tested, N-bromosuccinimide produced the largest alteration in the specific binding of [3H]zacopride onto 5-HT3 receptors. A significant reduction in Bmax (approximately 50%) with no change in Kd were noted on [3H]zacopride specific binding to membranes which were incubated with 40 microM N-bromosuccinimide for 60 min at 25 degrees. The occupancy of 5-HT3 receptor binding sites by various 5-HT3 agonists and antagonists (phenylbiguanide, ondansetron, granisetron, MDL 72222) prevented, at least partially, any subsequent reduction in [3H]zacopride specific binding by N-bromosuccinimide treatment. However, neither m-chloro-phenylbiguanide, among the agonists, nor zacopride, among the antagonists, were able to prevent the effect of N-bromosuccinimide, suggesting that variations might exist in the molecular mechanisms implicated in the binding of 5-HT3 ligands to the recognition site on 5-HT3 receptors. Nevertheless, these data support the suggestion that tryptophan residue(s) are probably involved in the binding of agonists and antagonists onto 5-HT3 receptors in NG108-15 cell membranes.
 ...
PMID:Involvement of tryptophan residue(s) in the specific binding of agonists/antagonists to 5-HT3 receptors in NG108-15 clonal cells. 193 Feb 69

Hypothalamic slices (400 mu) from male Sprague-Dawley rats were perfused with a Mg+(+)-free medium containing nomifensine (10 microM) and tyrosine (50 microM). Spontaneous release of endogenous norepinephrine (NE), measured by high-performance liquid chromatography-electrochemical detection, averaged 102 +/- 13 (N = 76) fmol/mg of protein/3 min. L-Glutamic acid (L-GLU) (1 mM) more than doubled the rate of NE release. Preincubation with serotonin (5-HT) (0.1-10 microM) produced no change in spontaneous NE release but caused a concentration-dependent decrease of L-GLU-induced NE release with a maximal reduction of about 60 to 70%. 2-Methylserotonin, a 5-HT3 receptor agonist (0.07-10 microM), mimicked the 5-HT response. A highly selective 5-HT3 receptor antagonist, (3 alpha-tropanyl)1H-indole-3-carboxylic acid ester, 1 nM, inhibited the effect of both agonists. Neither ritanserin (1 microM) nor methylsergide (1 microM) modified either spontaneous or 1 mM L-GLU-evoked release of NE. However, if added to the superfusion medium simultaneously with 5-HT, they potentiated significantly the inhibition produced by 5-HT. Alpha-methylserotonin (1 microM) if added alone to the perfusion medium had no effect on 1 mM L-GLU-evoked release of NE but reversed the inhibition induced by 1 microM 2-methylserotonin. These observations provide direct evidence of a dual modulation by 5-HT of L-GLU-evoked release of endogenous NE from slices of rat hypothalamus: An inhibition mediated by 5-HT3 receptors and an opposing action mediated by receptors of the 5-HT1C/2 type.
 ...
PMID:Serotonergic modulation of L-glutamic acid-evoked release of endogenous norepinephrine from rat hypothalamus. 822 75

Serotoninergic neurones originating in the dorsal and median raphe nuclei project to mesolimbic structures, including the nucleus accumbens (NAcb) and the ventral tegmental area (VTA), where they may have an important regulatory role. Some evidence from dopamine release, behavioural and binding studies directly implicates involvement of 5-HT3 and 5-HT4 receptors in the NAcb. Other in vivo dopamine release and behavioural experiments in rats have provided evidence for 5-HT3 receptor-mediated enhancement of mesolimbic dopaminergic activity, although the location of the 5-HT3 receptors involved is unknown because the selective 5-HT3 receptor agents used were administered systemically or intracerebroventricularly. This raises the possibility of a VTA site of action; as yet, however, relatively little is specifically known about 5-HT receptors and function in the VTA. Mesolimbic dopamine release in rats, measured in-vivo with microdialysis probes in the NAcb, can be inhibited by tropisetron administered directly into the VTA. In our laboratory, behavioural studies in rats have shown that a sustained hyperlocomotion is produced by 2-methyl-5-HT administered into the VTA via stereotactically implanted guide cannulae. Mesolimbic dopaminergic activation is involved, because pretreatment with the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine abolishes 2-methyl-5-HT-induced hyperlocomotion. The 2-methyl-5-HT hyperlocomotor response is blocked by prior intra-VTA injection of ondansetron but is not affected by methiothepin, and intra-VTA 5-carboxamidotryptamine, alpha-methyl-5-HT or renzapride were without effect, thus a 5-HT3 receptor in the VTA mediates the 2-methyl-5-HT response. These in vivo dopamine release and behavioural studies therefore confirm that 5-HT3 receptors in the VTA can mediate increased locomotor activity, by modulating the firing of mesolimbic dopaminergic cell bodies.
 ...
PMID:Ventral tegmental area 5-HT receptors: mesolimbic dopamine release and behavioural studies. 878 68

5-Hydroxytryptamine (5-HT) is involved in the modulation of dopaminergic activity in the mesolimbic system, but its sites of action and the receptors involved are not well understood. Locomotor activity responses in rats were monitored in Animex automated activity boxes following injection of 5-HT3 receptor-selective agents directly into two mesolimbic nuclei, the nucleus accumbens and the ventral tegmental area, via stereotactically implanted injection guide cannulae. Neither spontaneous nor dexamphetamine-stimulated locomotor activity was changed by bilateral intra-nucleus accumbens injection of the selective agonist 2-methyl-5-HT or the selective antagonists ondansetron or granisetron. In contrast, intra-ventral tegmental area injection of 2-methyl-5-HT produced significant long-lasting (approximately 240 min) increases in locomotor activity; intra-ventral tegmental area injection of ondansetron elicited an initial inhibition of spontaneous and dexamphetamine-stimulated locomotor activity (for the 0-30 min period), but granisetron had no effect. The hyperlocomotor response to intra-ventral tegmental area 2-methyl-5-HT was abolished by pretreatment with the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine, or by pretreatment with ondansetron. Methiothepin pretreatment had no effect on the hyperlocomotor response to 2-methyl-5-HT, although methiothepin itself produced an initial increase in spontaneous locomotor activity (for the 60-120 min period). Intra-ventral tegmental area injection of 5-carboxamidotryptamine, alpha-methyl-5-HT or renzapride produced no changes in spontaneous locomotor activity. In some of the ventral tegmental area experiments, other behaviours were also monitored. 2-Methyl-5-HT produced forward locomotion, rearing, and increased wakefulness, but did not appreciably alter circling, grooming or sniffing. Ondansetron alone had no effect on any of these behaviours, but it opposed the 2-methyl-5-HT-induced changes. Methiothepin alone increased forward locomotion and wakefulness but did not alter the other behaviours; it had no effect on the responses to 2-methyl-5-HT. These observations show that 5-HT3 receptors may mediate increased locomotor activity by modulating firing of mesolimbic dopaminergic cell bodies in the ventral tegmental area rather than terminals in the nucleus accumbens.
 ...
PMID:Effects of 5-HT3 receptor-selective agents on locomotor activity in rats following injection into the nucleus accumbens and the ventral tegmental area. 880 5

The nicotinic acetylcholine receptor (AChR) and the serotonin type 3 receptor (5HT3R) are members of the ligand-gated ion channel gene family. Both receptors are inhibited by nanomolar concentrations of d-tubocurarine (curare) in a competitive fashion. Chemical labeling studies on the AChR have identified tryptophan residues on the gamma (gammaTrp-55) and delta (deltaTrp-57) subunits that interact with curare. Comparison of the sequences of these two subunits with the 5HT3R shows that a tryptophan residue is found in the homologous position in the 5HT3R (Trp-89), suggesting that this residue may be involved in curare-5HT3R interactions. Site-directed mutagenesis at position Trp-89 markedly reduces the affinity of the 5HT3R for the antagonists curare and granisetron but has little effect on the affinity for the agonist serotonin. To further examine the role of this region of the receptor in ligand-receptor interactions, alanine-scanning mutagenesis analysis of the region centered on Trp-89 (Thr-85 to Trp-94) was carried out, and the ligand binding properties of the mutant receptors were determined. Within this region of the receptor, curare affinity is reduced by substitution only at Trp-89, whereas serotonin affinity is reduced only by substitution at Arg-91. On the other hand, granisetron affinity is reduced by substitutions at Trp-89, Arg-91, and Tyr-93. This differential effect of substitutions on ligand affinity suggests that different ligands may have different points of interaction within the ligand-binding pocket. In addition, the every-other-residue periodicity of the effects on granisetron affinity strongly suggests that this region of the ligand-binding site of the 5HT3R (and by inference, other members of the ligand-gated ion channel family) is in a beta-strand conformation.
 ...
PMID:Structural features of the ligand-binding domain of the serotonin 5HT3 receptor. 1002 68

In this study, we examined the effect of n-methylquipazine (NMQ), which is a putative 5-hydroxytryptamine3(5-HT3)receptor agonist, on the extracellular concentrations of dopamine (DA) and one of its metabolites, dihydroxyphenylacetic acid (DOPAC), in the anterior medial prefrontal cortex (AmPFc) of awake, freely moving rats. The administration of NMQ via the perfusion fluid produced a concentration-dependent (10-1,000 microM) increase in extracellular DA levels in the AmPFc. In contrast, NMQ produced a decrease in the extracellular concentrations of DOPAC. The increase in extracellular DA levels returned to baseline after the removal of NMQ from the perfusate. The increase in extracellular DA levels in the AmPFc produced by 100 microM of NMQ was markedly attenuated by either the coadministration of tetrodotoxin (1 microM), which inhibits axonal impulse flow, or the depletion of extracellular Ca2+ by removing CaCl2 and adding EDTA to the perfusate. The intradialysate administration of the 5-HT3 antagonist BRL 46470A produced a concentration-dependent (10-1,000 microM) decrease in extracellular DA levels, and this effect was reversible on removal from the perfusate. In contrast, ondansetron (500 and 1,000 microM), which is another 5-HT3 receptor antagonist, produced a transient increase followed by a sustained decrease in extracellular DA levels. The preinfusion of 10 microM of BRL 46470 followed by coperfusion of BRL 46470A with 50 or 100 microM of NMQ via the dialysis probe did not significantly attenuate the increase of NMQ in extracellular DA levels in the AmPFc. The administration of the selective 5-HT2 receptor MDL 100907 (1 mg/kg, i.p.) also did not alter the increase in basal DA levels produced by 100 microM of NMQ. The pretreatment of rats with alpha-methyl-p-tyrosine produced a significant attenuation in the NMQ-induced increase in extracellular DA levels, suggesting that the elevation by NMQ of DA levels is dependent on newly synthesized stores of DA. Overall, these results suggest that the increase in AmPFc DA levels by NMQ is probably not mediated by its interaction with the 5-HT3 receptor.
 ...
PMID:The characterization of the effect of locally applied N-methylquipazine, a 5-HT3 receptor agonist, on extracellular dopamine levels in the anterior medial prefrontal cortex in the rat: an in vivo microdialysis study. 1063 22

5-HT3 receptors possess a number of highly conserved proline residues. We changed each of these to alanine, expressed the mutants as homomeric 5-HT3A receptors in HEK293 cells, and analyzed them with radioligand binding, electrophysiology, and immunocytochemistry. Mutation of Pro56, Pro104, Pro123, and Pro170 resulted in ablation of radioligand binding, whereas mutation of Pro257 and Pro301 did not. Only the latter were expressed at the plasma membrane but were non-functional. Thus the former, which are in the N-terminal domain, may be involved in forming correct receptor structure, while those in the transmembrane region (Pro257 and Pro301) are necessary for the function of the protein. To explore the conformational preference (propensity) of these residues we examined the proportion of cis-prolines and the influence of adjacent residues in known protein structures. 4.7% of prolines in the protein data base were in the cis conformation, and the distribution of amino acids adjacent to cis-prolines was not randomly distributed. Comparison of the proportion of each amino acid residue adjacent to a cis-proline revealed that aromatic and bend-facilitating residues were favored while those with beta-branched chains were not. Thus five residues (Gly, Pro, Tyr, Trp, Phe) and three residues (Pro, Tyr, Phe) were found more frequently than expected before and after cis-prolines respectively, whereas five residues (Val, Ile, Leu, Asp, Thr) and two residues (Asp, Glu) were found less frequently. Of the 20 proline residues in the 5-HT3A receptor subunit only Pro170 has adjacent residues that are favorable. Mutating these to non-favorable residues resulted in ablation of ligand binding, whereas replacement with alternative favorable residues did not. We therefore propose that Pro170, which is part of the characteristic cys-loop found in this family of proteins, may be in the cis conformation.
 ...
PMID:The role and predicted propensity of conserved proline residues in the 5-HT3 receptor. 1149 6

The effects of phorbol 12-myristate, 13-acetate (PMA) on 5-hydroxytryptamine (5-HT)-evoked ion currents in the mouse 5-HT3A receptor were examined. Perfusion with PMA caused a concentration dependent potentiation of 5-HT mediated currents and increased both potency and efficacy of 5-HT at the 5-HT3A receptor expressed in Xenopus oocytes. Enhancement of receptor function was partially blocked by injection of oocytes with PKCI, the peptide inhibitor of protein kinase C (PKC). Mutation of all 12 intracellular serine and threonine residues to alanine was without effect on PMA-induced potentiation of 5-HT elicited currents. Mutation of tyrosine 458 in the 5-HT3A receptor lacking intracellular serines and threonines reduced the PMA-induced potentiation of 5-HT evoked currents by approximately 55%. In contrast, mutation of tyrosine 458 in the wild-type receptor did not alter PMA-induced enhancement. The tyrosine kinase inhibitor, lavendustin A, reduced the enhancement of 5-HT3A receptor mediated currents by PMA in the mutant 5-HTA3A receptor containing no intracellular serine or threonine residues, but not in the wild-type receptor. Thus, the role of intracellular serines and threonines is redundant with that of tyrosine, suggesting that these two components act through a similar pathway in response to PMA treatment.
 ...
PMID:Enhancement of 5-hydroxytryptamine3A receptor function by phorbol 12-myristate, 13-acetate is mediated by protein kinase C and tyrosine kinase activity. 1244 87

The mechanism by which agonist binding triggers pore opening in ligand-gated ion channels is poorly understood. Here, we used unnatural amino acid mutagenesis to introduce subtle changes to the side chains of tyrosine residues (Tyr141, Tyr143, Tyr153, and Tyr234), which dominate the 5-HT3 receptor binding site. Heterologous expression in oocytes, combined with radioligand binding data and a model of 5-HT (serotonin) computationally docked into the binding site, has allowed us to determine which of these residues are responsible for binding and/or gating. We have shown that Tyr 143 forms a hydrogen bond that is essential for receptor gating but does not affect binding, whereas a hydrogen bond formed by Tyr153 is involved in both binding and gating of the receptor. The aromatic group of Tyr234 is essential for binding and gating, whereas its hydroxyl does not affect binding but plays a steric role in receptor gating. Tyr141 is not involved in agonist binding or receptor gating but is important for antagonist interactions. These data, combined with a new model of the nonliganded 5-HT3 receptor, lead to a mechanistic explanation of the interactions that initiate the conformational change leading to channel opening. Thus, we suggest that agonist entry into the binding pocket may displace Tyr143 and Tyr153 and results in their forming new hydrogen bonds. These bonds may form part of the network of bond rearrangements that trigger the conformational change leading to channel opening. Similar rearrangements may initiate gating in all Cys-loop receptors.
 ...
PMID:Tyrosine residues that control binding and gating in the 5-hydroxytryptamine3 receptor revealed by unnatural amino acid mutagenesis. 1548 28

The 5-HT3 receptor is a typical ligand-gated ion channel of the Cys-loop superfamily, which is activated by binding of serotonin (5-HT). Models of the binding site of this protein reveal potential interactions between 5-HT and Tyr143, Tyr153, and Tyr234. Here we describe a series of ab initio calculations, based on density functional theory, to assess the effects of mutating these tyrosine residues on the binding of 5-HT. A series of mutations to these tyrosines, previously studied experimentally, were tested, and the binding energies compared with the available experimental data. Our results show that Tyr153 could form a hydrogen bond with the tertiary amine of 5-HT, and that mutation in this location revealed binding energies broadly in line with experimentally determined EC50s. Tyr143 could also form a hydrogen bond, but as EC50s do not relate to binding energies, it is unlikely that such a bond is formed here. Tyr234 is quite distinct in that it may interact with 5-HT via a mixed hydrogen bond/cation-pi interaction.
 ...
PMID:Exploring the binding of serotonin to the 5-HT3 receptor by density functional theory. 1718 Dec 90


1 2 Next >>