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

Pancreatic ganglia contain 5-hydroxytryptamine (5-HT)-immunoreactive axons, some of which are extensions of myenteric neurons located in the pyloric antrum and proximal duodenum. The present study investigated the effect of 5-HT on the membrane potential of cat pancreatic ganglion neurons by means of intracellular recordings in vitro. Pressure application of 5-HT evoked a fast depolarization in 29 of 147 neurons and a slow depolarization in 89 of 147 neurons. A biphasic response was observed in 10 of 108 neurons. The 5-HT-induced slow depolarizing response was not altered in a low Ca2+ (0.1 mM), high Mg2+ (15 mM) solution nor by hexamethonium (10(-4) M) or atropine (10(-6) M). The fast depolarizing response was associated with a decrease of membrane input resistance (-17.2%). The slow depolarizing response was associated with either a decrease (-19.6%) in 24, an increase (+25.0%) in 20, or without a detectable change of membrane input resistance in 10 out of 54 neurons tested. Conditioning hyperpolarization increased the amplitude of both fast and slow depolarizing responses. A low Na+ (68.5 mM) solution and a high K+ (23.5 mM) solution significantly reduced the amplitude of the slow depolarizing response. A low Cl- (9.6 mM) solution had no significant effect on the slow depolarization. The 5-HT3 receptor antagonist MDL 72222 (Bemesetron) blocked the 5-HT-evoked fast depolarizing response. BRL 24924 (Renzapride) and 5 HT-DP, antagonists for the putative 5-HT1P receptor, blocked the slow depolarizing response. The 5-HT3 receptor agonist 2-methyl-5-HT evoked a fast depolarizing response and MCPP, an agonist for the putative 5-HT1P receptor, evoked a slow depolarizing response. Spiperone (a 5-HT1A receptor antagonist) and mianserin (a 5-HT2 receptor antagonist) had no effect on either depolarizing response to 5-HT. The results show that pancreatic ganglion neurons responded to 5-HT with fast and slow depolarizing responses. The data suggest that these responses were mediated by the 5-HT3 receptor and the putative 5-HT1P receptor, respectively.
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PMID:5-Hydroxytryptamine depolarizes neurons of cat pancreatic ganglia. 886 89

In the present study, we investigated the effects of chronic in vitro administration of amitriptyline, a tricyclic antidepressant, on cyclic GMP formation stimulated by 5-hydroxytryptamine (5-HT) in the neuroblastoma x glioma hybrid cell line, NG 108-15, 5-HT (0.01-100 microM)-stimulated cyclic GMP formation was concentration-dependent and was sensitive to ICS 205-930, a 5-HT3 receptor antagonist. Exposure of NG 108-15 cells to 5 microM amitriptyline for 3 days significantly reduced 5-HT-stimulated cyclic GMP formation. Acute treatment with amitriptyline had no effect on 5-HT-stimulated cyclic GMP formation. The reduction by chronic amitriptyline exposure of 10 microM 5-HT-stimulated cyclic GMP formation was concentration-dependent over the concentration range examined (0.5 to 10 microM). The IC50 of amitriptyline was 1.9 microM. In contrast, amitriptyline exposure, even at a concentration of 8 microM, failed to modify cyclic GMP formation stimulated by bradykinin, sodium nitroprusside, or atrial natriuretic peptide. Increases in intracellular Ca2+ concentration ([Ca2+]i) evoked by 10 microM 5-HT were attenuated in amitriptyline-exposed cells, while 100 nM bradykinin-induced [Ca2+]i increases were not affected. In addition, chronic exposure to 5 microM amitriptyline caused a decrease in affinity (Kd) of [3H]zacopride specific binding to 5-HT3 recognition sites. The Bmax for the labelled ligand remained unchanged. These results suggest that chronic amitriptyline exposure reduces 5-HT-stimulated cyclic GMP formation and [Ca2+]i increases, and this may reflect the functional changes of 5-HT3 receptors.
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PMID:Chronic amitriptyline exposure reduces 5-HT3 receptor-mediated cyclic GMP formation in NG 108-15 cells. 900 9

Several human Mendelian diseases, including the long-QT syndrome, malignant hyperthermia, and episodic ataxia/myokymia syndrome, have recently been demonstrated to be due to mutations in ion channel genes. Systematic mapping of ion channel genes may therefore reveal candidates for other heritable disorders. In this study, the GenBank and dbEST databases were used to identify members of several ion channel families (voltage-gated calcium and sodium, cardiac chloride, and all classes of potassium channels). Genes and ESTs without prior map localization were identified based on GDB and OWL database information and 15 genes and ESTs were selected for mapping. Of these 15, only the serotonin receptor 5HT3R had been previously mapped to a chromosome. A somatic cell hybrid panel (SCH) was screened with an STS from each gene and, if necessary the results verified by a second SCH panel. For three ESTs, rodent derived PCR products of the same size as the human STS precluded SCH mapping. For these three, human P1 clones were isolated and the genomic location was determined by metaphase FISH. These genes and ESTs can now be further evaluated as candidate genes for inherited cardiac, neuromuscular and psychiatric disorders mapped to these chromosomes. Furthermore, the ESTs developed in this study can be used to isolate genomic clones, enabling the determination of each transcript's genomic structure and physical map location. This approach may also be applicable to other gene families and may aid in the identification of candidate genes for groups of related heritable disorders.
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PMID:Chromosomal localization of 15 ion channel genes. 903 51

In the present study, we identified the serotonergic receptor of type 3 (5-HT3) on the lymphocytes of a teleost fish, Oncorhynchus mykiss. In the pharmacological studies on the binding of [3H]serotonin to membrane receptor sites, 2-methyl-5-HT, an agonist of 5-HT3 receptors, displaced the binding of [3H]serotonin to fish lymphocytes, indicating the presence of 5-HT3 receptors on these cells. The known antagonists of the mammalian 5-HT3 receptor, ICS-205-930 and metoclopramide, failed to displace [3H]serotonin binding to lymphocytes during the period of association equilibrium (8 min); however, these antagonists progressively displaced [3H]serotonin binding from 10 to 40 min of incubation. These results suggest that fish 5-HT3 lymphocyte receptors may differ pharmacologically from mammalian receptors. As mammalian 5-HT3 receptors are coupled with Na+ inward movements, we undertook a study on Na+ influx by using SBFI/AM, a fluorescent probe. In SBFI/AM loaded fish lymphocytes, 2-methyl-5-HT leaked Na+ inward movements. Prior incubation of lymphocytes for 30 min in the presence of 5-HT3 antagonists, ICS-205-930, metoclopramide and MDL-72222, curtailed significantly the Na+ influx evoked by 2-methyl-5-HT, demonstrating that Na+ is leaked into fish lymphocytes via the 5-HT3 receptor-channel whose functioning is blocked by these antagonists. Furthermore, 2-methyl-5-HT exerted immunosuppressive effects in a dose dependent manner on fish T-lymphocytes stimulated by phytohaemagglutinin (PHA). Serotonin and 2-methyl-5-HT blocked the cell cycle progression of PHA-stimulated T-cells from G0/G1 to S phase. The immunosuppressive effects of 2-methyl-5-HT on T-cells were partially reversed by the antagonists, metoclopramide and ICS-205-930; however, the latter antagonist at high concentrations synergized with the immunosuppressive effects of 2-methyl-5-HT. These results demonstrate that the fish lymphocyte 5-HT3 receptor, which may be pharmacologically different from mammalian receptor subtype, is functionally implicated in fish T-cell proliferation.
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PMID:Identification of lymphocyte 5-HT3 receptor subtype and its implication in fish T-cell proliferation. 916 81

The effects of changes in external K+, Ca2+, and Mg2+ concentrations on 5-HT2- and 5-HT3 receptor-mediated depolarizations of the resting membrane potential in rat dorsal root ganglion (DRG) cells was studied. In cells exhibiting a 5-HT2-mediated response, 5-HT and alpha-methyl 5-HT depolarized the resting membrane potential (RMP) and increased the slope of the current-voltage (I/V) relationship. The equilibrium potential (Er) for the depolarization was linearly related to the logarithm of the [K+]o, indicating the depolarization resulted from a decrease in resting K+ conductance. In a subpopulation of large-diameter acutely dissociated DRG neurons recorded from using the whole-cell patch-clamp configuration, 5-HT produced an inward shift in the current required to hold cells at -60 mV. This inward shift in holding current was associated with a reduction in membrane conductance and reversed near Ek. This data suggests that the 5-HT2 receptor-mediated depolarization and increase in R(in) seen in intact DRG preparation is produced by blockade of an outward K+ leak current. Increases in [K+]o reduced the increase in R(in) and depolarization induced by 5-HT with 50% inhibition of the depolarization occurring at 8.3 mM of [K+]o. Half-normal Ca2+ (1.2 mM) produced a downward shift of the 5-HT concentration-response curve, reducing the maximal response by 40%, with minimal effect on the half-maximal response. Mg2+ ions did not affect this 5-HT response. In cells exhibiting a 5-HT3 receptor response, 5-HT and 2-methyl-5-HT produced depolarization with decreased R(in). The Er for this depolarizing response (-30.2 +/- 1.8 mV) became less negative (-11.5 mV) in 10 mM [K+]o with minimal effect on the amplitude of the depolarization. In Na(+)-free superfusate, the 5-HT-induced depolarization was converted to hyperpolarization. This indicated the 5-HT3 response increased a mixed Na+/K+ conductance. Elevated Ca2+ or Mg2+ markedly reduced the 5-HT3 response. Incubation with 3.5 mM Ca2+ shifted the 5-HT concentration-response curve downward and to the right, decreasing the maximal response by 49% and increasing the EC50 by 10-fold. Elevated Mg2+ produced similar effects. In cells where both 5-HT2- and 5-HT3-mediated responses could be demonstrated, the elevation of K+ or the reduction of Ca2+ converted a 5-HT2 response to a 5-HT3 response. The above data suggest that elevation of [K+]o or reduction of [Ca2+]o produced by rapid firing rates of sensory neurons will favor the expression of 5-HT3 responses over 5-HT2 responses.
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PMID:Cationic modulation of 5-HT2 and 5-HT3 receptors in rat sensory neurons: the role of K+, Ca2+ and Mg2+. 931 2

We report an improved synthesis of unlabeled (S)-iodozacopride, the radiolabeling of (S)-[125I]iodozacopride via deschloro-(S)-zacopride, and a re-evaluation of its affinity for the 5-HT3 receptor. Unlabeled (S)-iodozacopride was prepared in seven steps from 4-aminosalicylic acid via alkaline hydrolysis of its 4-acetamide derivative. Catalytic hydrogenation of (S)-iodozacopride gave deschloro-(S)-zacopride, identical to that obtained from (S)-3-amino-quinuclidine and 4-amino-2-methoxybenzoic acid via its corresponding 1-imidazole derivative. Radioiodination to produce (S)-[125I]iodozacopride was accomplished by treatment of deschloro-(S)-zacopride with 5 mCi sodium 125iodide and chloramine-T in hydrochloric acid. Purification of the reaction products using an HPLC system capable of detecting chlorinated side-products revealed a mixture of 2.1 mCi (1.3 nmol) (S)-[125I]iodozacopride and (S)-zacopride (1.5 nmol). Saturation analysis of the binding of the purified (S)-[125I]iodozacopride to whole rat brain homogenates gave an estimated KD of 1.10 +/- 0.07 nM. As anticipated, this is approximately half the KD reported for binding of racemic [125I]iodozacopride, and differs from the previously reported value by an order of magnitude. Analysis of the apparent binding affinity of a 1:1 mixture of (S)-[125I]iodozacopride and (S)-zacopride suggests that the previous result may have been confounded by contamination of the product with unlabeled (S)-zacopride. Competition analysis of the displacement of (S)-[125I]iodozacopride binding by unlabeled (S)-iodozacopride and (S)-zacopride gave Ki values of 0.95 and 0.21 nM, respectively.
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PMID:Synthesis and radiolabeling of (S)-4-amino-5-iodo-2-methoxy-N-(1-azabicyclo[2.2.2]oct-3-yl)benzamide, the active enantiomer of [125I]iodozacopride, and re-evaluation of its 5-HT3 receptor affinity. 943 79

A serotonin 5-HT3 receptor was functionally expressed to high levels and on a large scale in mammalian cells with the Semliki Forest virus system. Conditions were optimized to maximize detergent solubilization of the receptor, while preserving ligand binding activity. An efficient one-step purification yielding approximately 50% of the histidine-tagged 5-HT3 receptor was achieved with immobilized metal ion chromatography. The expressed receptor, in both membranes and purified preparations, exhibited wild-type ligand binding properties, characterized by one class of binding sites. The purity of the receptor was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, yielding a single band at 65 kDa, and was confirmed by the specific ligand binding activity of approximately 5 nmol/mg of protein. Deglycosylation of the receptor reduced the estimated relative molecular mass to 49 kDa. The apparent molecular mass of the functional receptor complex was determined by size exclusion chromatography to be 280 kDa, suggesting that the 5-HT3 receptor is a pentameric homooligomer. The secondary structure of the 5-HT3 receptor as determined by circular dichroism appeared to consist of mainly alpha-helices (50%) and beta-strands (24%), with minor contributions from nonregular structure (9%). The binding of either agonist or antagonist did not alter the secondary structure of the receptor.
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PMID:Characterization of a mouse serotonin 5-HT3 receptor purified from mammalian cells. 945 79

The serotonin 5-HT3 receptor, a ligand-gated ion channel, has previously been shown to be present on a subpopulation of brain nerve terminals, where, on activation, the 5-HT3 receptors induce Ca2+ influx. Whereas postsynaptic 5-HT3 receptors induce depolarization, being permeant to Na+ and K+, the basis of presynaptic 5-HT3 receptor-induced calcium influx is unknown. Because the small size of isolated brain nerve terminals (synaptosomes) precludes electrophysiological measurements, confocal microscopic imaging has been used to detect calcium influx into them. Application of 100 nM 1-(m-chlorophenyl)biguanide (mCPBG), a highly specific 5-HT3 receptor agonist, induced increases in internal free Ca2+ concentration ([Ca2+]i) and exocytosis in a subset of corpus striatal synaptosomes. mCPBG-induced increases in [Ca2+]i ranged from 1.3 to 1.6 times over basal values and were inhibited by 10 nM tropisetron, a potent and highly specific 5-HT3 receptor antagonist, but were insensitive to the removal of external free Na+ (substituted with N-methyl-D-glucamine), to prior depolarization induced on addition of 20 mM K+, or to voltage-gated Ca2+ channel blockade by 10 microM Co2+/Cd2+ or by 1 microM omega-conotoxin MVIIC/1 microM oemga-conotoxin GVIA/200 nM agatoxin TK. In contrast, the Ca2+ influx induced by 5-HT3 receptor activation in NG108-15 cells by 1 microM mCPBG was substantially reduced by 10 microM Co2+/Cd2+ and was completely blocked by 1 microM nitrendipine, an L-type Ca2+ channel blocker. We conclude that in contrast to the perikaryal 5-HT3 receptors, presynaptic 5-HT3 receptors appear to be uniquely calcium-permeant.
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PMID:High calcium permeability of serotonin 5-HT3 receptors on presynaptic nerve terminals from rat striatum. 948 30

1. A human recombinant homo-oligomeric 5-HT3 receptor (h5-HT3A) expressed in a human embryonic kidney cell line (HEK 293) was characterized using the whole-cell recording configuration of the patch clamp technique. 2. 5-HT evoked transient inward currents (EC50 = 3.4 microM; Hill coefficient = 1.8) that were blocked by the 5-HT3 receptor antagonist ondansetron (IC50 = 103 pM) and by the non-selective agents metoclopramide (IC50 = 69 nM), cocaine (IC50 = 459 nM) and (+)-tubocurarine (IC50 = 2.8 microM). 3. 5-HT-induced currents rectified inwardly and reversed in sign (E5-HT) at a potential of -2.2 mV. N-Methyl-D-glucamine was finitely permeant. Permeability ratios PNa/PCs and PNMDG/PCs were 0.90 and 0.083, respectively. 4. Permeability towards divalent cations was assessed from measurements of E5-HT in media where Ca2+ and Mg2+ replaced Na+. PCa/PCs and PMg/PCs were calculated to be 1.00 and 0.61, respectively. 5. Single channel chord conductance (gamma) estimated from fluctuation analysis of macroscopic currents increased with membrane hyperpolarization from 243 fS at -40 mV to 742 fS at -100 mV. 6. Reducing [Ca2+]o from 2 to 0.1 mM caused an increase in the whole-cell current evoked by 5-HT. A concomitant reduction in [Mg2+]o produced further potentiation. Fluctuation analysis indicates that a voltage-independent augmentation of gamma contributes to this phenomenon. 7. The data indicate that homo-oligomeric receptors composed of h5-HT3A subunits form inwardly rectifying cation-selective ion channels of low conductance that are permeable to Ca2+ and Mg2+.
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PMID:Ion permeation and conduction in a human recombinant 5-HT3 receptor subunit (h5-HT3A). 950 27

1. Recordings were made from a total of sixty-four vagal preganglionic neurones in the dorsal vagal motor nucleus (DVMN) of pentobarbitone sodium anaesthetized rats. The effects of ionophoretic administration of Mg2+ and Cd2+, inhibitors of neurotransmitter release, and the selective NMDA and non-NMDA receptor antagonists (+/-)-2-amino-5-phosphono-pentanoic acid (AP5) and 6,7-dinitroquinoxaline-2,3-dione (DNQX) on the excitatory actions of the 5-HT3 receptor agonist 1-phenylbiguanide (PBG) were studied. 2. In extracellular recording experiments, PBG (0-40 nA) increased the firing rate of thirty-five of the thirty-nine neurones tested. The PBG-evoked excitation was attenuated by application of Mg2+ (1-10 nA) in sixteen of seventeen neurones or Cd2+ (2-10 nA) in seven of eight neurones tested. At these low ejection currents neither Mg2+ nor Cd2+ altered baseline firing rates and Mg2+ had no effect on the excitations evoked by DL-homocysteic acid (n = 4), NMDA (n = 4) or (AMPA; n = 2). 3. Ionophoresis of AP5 (2-10 nA), at currents which selectively inhibited NMDA-evoked excitations, attenuated PBG-evoked excitations in all eight neurones tested. DNQX (5-20 nA), at currents which selectively inhibited AMPA-evoked excitations, also attenuated PBG-evoked excitations (n = 3). 4. Intracellular activity was recorded in nine DVMN neurones. In six neurones ionophoretic application of PBG (10-200 nA) depolarized the membrane and increased firing rate whilst in the other three neurones, PBG had no effect on membrane potential though it increased synaptic noise (n = 3) and firing rate (n = 2). In all six neurones tested, ionophoresis of Mg2+ (10-120 nA) attenuated the PBG-evoked increases in synaptic noise and firing rate. 5. In conclusion, the data are consistent with the hypothesis that 5-HT3 receptor agonists activate DVMN neurones partly by acting on receptors located at sites presynaptic to the neurones. Activation of these receptors appears to facilitate release of glutamate, which, in turn, acts on postsynaptic NMDA and non-NMDA receptors to activate the neurones.
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PMID:Presynaptic 5-HT3 receptors evoke an excitatory response in dorsal vagal preganglionic neurones in anaesthetized rats. 959 91


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