bemesetron and Neuroblastoma

The present study investigated the functional antagonism of different antidepressants on 5-HT (3) receptor function and the role of lipid rafts for these modulatory effects. Electrophysiological recordings of 5-HT evoked cation currents were recorded with N1E-115 and HEK-5-HT (3A) cells and hippocampal neurons. The characterization of the antagonism of antidepressants was made by the displacement of [ (3)H]GR65630 binding. For membrane fractionation, sucrose density gradient centrifugation was used. Gradient fractions were assayed for antidepressant concentrations by HPLC; 5-HT (3) receptor membrane distribution was determined by Western blot. Colocalization experiments were performed by means of immunocytochemistry. Most antidepressants acted as non-competitive antagonists at the 5-HT (3) receptor. Moreover, some of these compounds were enriched within lipid rafts. Cholesterol depletion impaired lipid raft integrity thereby affecting 5-HT (3) receptor function, whereas the antagonistic effects of antidepressants were not altered.In conclusion, most antidepressants directly antagonize 5-HT (3) receptor activity. 5-HT (3) receptor function PER SE appears to depend on lipid raft integrity, which is, however, not a prerequisite for the modulatory potency of antidepressants at this receptor.

Topics: Animals; Antidepressive Agents; Cell Line; Cell Line, Tumor; HEK293 Cells; Hippocampus; Humans; Imidazoles; Indoles; Ligand-Gated Ion Channels; Membrane Microdomains; Mice; Neuroblastoma; Patch-Clamp Techniques; Rats; Receptors, Serotonin, 5-HT3; Serotonin Antagonists; Tropanes

The 5-HT3-receptor antagonist, ondansetron, has been shown to have positive effects in selected in-vivo models of memory impairment and anxiety. The exact mechanisms underlying such bioactivities are unknown. In the present work, an 86Rb efflux bioassay was used to show that ondansetron has a unique ability to block voltage-gated potassium channels in TE671 human neuroblastoma cells. This intrinsic potassium-channel-blocking (KCB) property is relatively weak (IC50 20 microM), but is not shared by other 5-HT3-receptor ligands including zatosetron, MDL 72222, LY 278, 584, zacopride, 1-phenylbiguanide, and ICS 205-930 (tropisetron). Pre-incubation of the target neuroblastoma cells with several 5-HT-receptor ligands including 5-hydroxytryptamine, 8-OH-DPAT, ketanserin, 2-methyl-5-HT, as well as a number of potent 5-HT3 agonists and antagonists and two selective neurotoxins, failed to abolish the KCB action of ondansetron. A preliminary structure-activity relationship analysis indicates that the KCB activity of ondansetron is almost entirely attributable to its structural nucleus, 2,3-dihyro-9-methyl-4(1H)-carbazolone. It is hypothesized that the KCB action of ondansetron is mediated through receptors other than 5-HT3 receptors. The KCB activity of ondansetron may be a significant factor in the in-vivo cognition-enhancing activities of this compound, conceivably due to depolarization of the hippocampal synaptic membranes and a consequent augmentation of neurotransmission.

Topics: Anti-Anxiety Agents; Benzamides; Benzofurans; Biguanides; Bridged Bicyclo Compounds, Heterocyclic; Humans; Hypoglycemic Agents; Indazoles; Indoles; Neuroblastoma; Neurotoxins; Ondansetron; Potassium Channels; Receptors, Serotonin; Receptors, Serotonin, 5-HT3; Rubidium Radioisotopes; Serotonin Antagonists; Serotonin Receptor Agonists; Structure-Activity Relationship; Tropanes; Tropisetron; Tumor Cells, Cultured

In order to resolve single channel events underlying the 5-HT3 receptor-gated ion current in N1E-115 neuroblastoma cells patch clamp experiments have been performed on excised outside-out membrane patches under optimized experimental conditions. When the driving force for Na+ through the 5-HT3 receptor-gated ion channel is enhanced by raising the external Na+ concentration to 180 mM and by substituting internal K+ with the relatively impermeable cation N-methyl-D-glucamine, a single conductance level is observed in the presence of 5-HT. Single channel activity is observed only in the presence of the agonist and is blocked by 50 nM of the selective 5-HT3 receptor antagonist MDL 72222 in a reversible manner. At membrane potentials more negative than -60 mV discrete single channel events can be resolved with a conductance of 5.6 +/- 1.2 pS.

Topics: Animals; Cell Membrane; Electric Conductivity; In Vitro Techniques; Ion Channel Gating; Membrane Potentials; Mice; Neuroblastoma; Receptors, Serotonin; Serotonin; Tropanes; Tumor Cells, Cultured

Both substance P and, to a lesser degree, serotonin activate cation permeability in neuroblastoma x glioma hybrid cells, as determined by measurement of [14C]guanidinium uptake. Serotonin potentiates the action of substance P by shifting the concentration-effect curve of substance P to the left. The EC50 value for the synergistic effect of serotonin was around 0.3 microM. Dopamine and noradrenaline displayed comparable activity, albeit only at 50 and 130 times higher concentrations, respectively. The order of potency of various substance P-analogues was not changed by serotonin, indicating that the specificity of the substance P site on the hybrid cells was not affected by serotonin. Various other neurotransmitters and peptides had no effect on the response of the hybrid cells to substance P. The serotonin receptor interacting with the substance P receptor may be classified as a 5-HT3-receptor since methysergide, cimetidine, and ketanserin were ineffective, but two inhibitors specific for 5-HT3-receptors, ICS 205-930 (3 alpha-tropanyl-1H-indole-3-carboxylic acid ester) and MDL 72222 (1 alpha H,3 alpha,5 alpha H-tropan-3-yl-3,5-dichlorobenzoate), blocked the effect of serotonin at nanomolar concentrations. However, the two serotonin antagonists might also be blocking the ion permeability, since at higher concentrations they fully inhibited the stimulation of guanidinium uptake by substance P or by substance P plus serotonin. The synergism between substance P and serotonin on the hybrid cells offers the opportunity to study the mechanism of interaction of neurotransmitter receptors on a permanent neuronal cell line.

Topics: Catecholamines; Cations; Cell Line; Cell Membrane Permeability; Drug Interactions; Glioma; Guanidine; Guanidines; Indoles; Neuroblastoma; Neurons; Serotonin; Substance P; Tropanes; Tropisetron; Tumor Cells, Cultured