Nicotinic acetylcholine receptors in human neuroblastoma (SH-SY5Y) cells

Modulation of Gq/PLC-Mediated Signaling by Acute Lithium Exposure

Although lithium has long been one of the most widely used pharmacological agents in psychiatry, its mechanisms of action at the cellular and molecular levels remain poorly understood. One of the targets of Li+ is the phosphoinositide pathway, but whereas the impact of Li+ on inositol lipid metabolism is well documented, information on physiological effects at the cellular level is lacking. We examined in two mammalian cell lines the effect of acute Li+ exposure on the mobilization of internal Ca2+ and phospholipase C (PLC)-dependent membrane conductances. We first corroborated by Western blots and immunofluorescence in HEK293 cells the presence of key signaling elements of a muscarinic PLC pathway (M1AchR, Gq, PLC-β1, and IP3Rs). Stimulation with carbachol evoked a dose-dependent mobilization of Ca, as determined with fluorescent indicators. This was due to release from internal stores and proved susceptible to the PLC antagonist U73122. Li+ exposure reproducibly potentiated the Ca response in a concentration-dependent manner extending to the low millimolar range. To broaden those observations to a neuronal context and probe potential Li modulation of electrical signaling, we next examined the cell line SHsy5y. We replicated the potentiating effects of Li on the mobilization of internal Ca, and, after characterizing the basic properties of the electrical response to cholinergic stimulation, we also demonstrated an equally robust upregulation of muscarinic membrane currents. Finally, by directly stimulating the signaling pathway at different links downstream of the receptor, the site of action of the observed Li effects could be narrowed down to the G protein and its interaction with PLC-β. These observations document a modulation of Gq/PLC/IP3-mediated signaling by acute exposure to lithium, reflected in distinct physiological changes in cellular responses.

Functional alterations by a subgroup of neonicotinoid pesticides in human dopaminergic neurons

Neonicotinoid pesticides, originally developed to target the insect nervous system, have been reported to interact with human receptors and to activate rodent neurons. Therefore, we evaluated in how far these compounds may trigger signaling in human neurons, and thus, affect the human adult or developing nervous system. We used SH-SY5Y neuroblastoma cells as established model of nicotinic acetylcholine receptor (nAChR) signaling. In parallel, we profiled dopaminergic neurons, generated from LUHMES neuronal precursor cells, as novel system to study nAChR activation in human post-mitotic neurons. Changes of the free intracellular Ca²⁺ concentration ([Ca²⁺]_i) were used as readout, and key findings were confirmed by patch clamp recordings. Nicotine triggered typical neuronal signaling responses that were blocked by antagonists, such as tubocurarine and mecamylamine. Pharmacological approaches suggested a functional expression of α7 and non-α7 nAChRs on LUHMES cells. In this novel test system, the neonicotinoids acetamiprid, imidacloprid, clothianidin and thiacloprid, but not thiamethoxam and dinotefuran, triggered [Ca²⁺]_i signaling at 10-100 µM. Strong synergy of the active neonicotinoids (at low micromolar concentrations) with the α7 nAChR-positive allosteric modulator PNU-120596 was observed in LUHMES and SH-SY5Y cells, and specific antagonists fully inhibited such signaling. To provide a third line of evidence for neonicotinoid signaling via nAChR, we studied cross-desensitization: pretreatment of LUHMES and SH-SY5Y cells with active neonicotinoids (at 1-10 µM) blunted the signaling response of nicotine. The pesticides (at 3-30 µM) also blunted the response to the non-α7 agonist ABT 594 in LUHMES cells. These data show that human neuronal cells are functionally affected by low micromolar concentrations of several neonicotinoids. An effect of such signals on nervous system development is a toxicological concern.

Considerations for the Use of SH-SY5Y Neuroblastoma Cells in Neurobiology

The use of primary mammalian neurons derived from embryonic central nervous system tissue is limited by the fact that once terminally differentiated into mature neurons, the cells can no longer be propagated. Transformed neuronal-like cell lines can be used in vitro to overcome this limitation. However, several caveats exist when utilizing cells derived from malignant tumors. In this context, the popular SH-SY5Y neuroblastoma cell line and its use in in vitro systems is described. Originally derived from a metastatic bone tumor biopsy, SH-SY5Y (ATCC^® CRL-2266™) cells are a subline of the parental line SK-N-SH (ATCC^® HTB-11™). SK-N-SH were subcloned three times; first to SH-SY, then to SH-SY5, and finally to SH-SY5Y. SH-SY5Y were deposited to the ATCC^® in 1970 by June L. Biedler. Three important characteristics of SH-SY5Y cells should be considered when using these cells in in vitro studies. First, cultures include both adherent and floating cells, both types of which are viable. Few studies address the biological significance of the adherent versus floating phenotypes, but most reported studies utilize adherent populations and discard the floating cells during media changes. Second, early studies by Biedler's group indicated that the parental differentiated SK-N-SH cells contained two morphologically distinct phenotypes: neuroblast-like cells and epithelial-like cells (Ross et al., J Natl Cancer Inst 71(4):741-747, 1983). These two phenotypes may correspond to the "N" and "S" types described in later studies in SH-SY5Y by Encinas et al. (J Neurochem 75(3):991-1003, 2000). Cells with neuroblast-like morphology are positive for tyrosine hydroxylase (TH) and dopamine-β-hydroxylase characteristic of catecholaminergic neurons, whereas the epithelial-like counterpart cells lacked these enzymatic activities (Ross et al., J Natl Cancer Inst 71(4):741-747, 1983). Third, SH-SY5Y cells can be differentiated to a more mature neuron-like phenotype that is characterized by neuronal markers. There are several methods to differentiate SH-SY5Y cells and are mentioned below. Retinoic acid is the most commonly used means for differentiation and will be addressed in detail.

3-Quinuclidinyl-α-methoxydiphenylacetate: A multi-targeted ligand with antimuscarinic and antinicotinic effects designed for the treatment of anticholinesterase poisoning

Racemic 3-quinuclidinyl-α-methoxydiphenylacetate (MB266) was synthesised. Its activity at muscarinic acetylcholine receptors (mAChRs), and muscle and neuronal nicotinic acetylcholine receptors (nAChRs), was compared to that of atropine and racemic 3-quinucidinyl benzilate (QNB) using a functional assay based on agonist-induced elevation of intracellular calcium ion concentration in CN21, Chinese Hamster Ovary (CHO) and SHSY5Y human cell lines. MB266 acted as an antagonist at acetylcholine receptors, displaying 18-fold selectivity for mAChR versus nAChR (compared to the 15,200-fold selectivity observed for QNB). Thus O-methylation of QNB reduced the affinity for mAChR antagonism and increased the relative potency at both muscle and neuronal nAChRs. Despite MB266 having a pharmacological profile potentially useful for the treatment of anticholinesterase poisoning, its administration did not improve the neuromuscular function in a soman-poisoned guinea-pig diaphragm preparation pretreated with the organophosphorus nerve agent soman. Consideration should be given to exploring the potential of MB266 for possible anticonvulsant action in vitro as part of a multi-targeted ligand approach.

Nicotine protects against manganese and iron-induced toxicity in SH-SY5Y cells: Implication for Parkinson's disease

Manganese (Mn) and iron (Fe) are trace elements that are essential for proper growth and physiological functions as both play critical role in a variety of enzymatic reactions. At high concentrations, however, they can be toxic and cause neurodegenerative disorders, particularly Parkinson-like syndromes. Nicotine, on the other hand, has been shown to have neuroprotective effects against various endogenous or exogenous toxins that selectively damage the dopaminergic cells. These cells include neuroblastoma-derived SH-SY5Y cells which express significant dopaminergic activity. However, practically no information on possible neuroprotective effects of nicotine against toxicity induced by trace elements is available. Therefore, in this study we investigated the effects of nicotine on toxicity induced by manganese or iron in these cells. Exposure of SH-SY5Y cells for 24 h to manganese (20 μM) or iron (20 μM) resulted in approximately 30% and 35% toxicity, respectively. Pretreatment with nicotine (1 μM) completely blocked the toxicities of Mn and Fe. The effects of nicotine, in turn, were blocked by selective nicotinic receptor antagonists. Thus, dihydro-beta erythroidine (DHBE), a selective alpha 4-beta 2 subtype antagonist and methyllycaconitine (MLA), a selective alpha7 antagonist, as well as mecamylamine, a non-selective nicotinic antagonist all dose-dependently blocked the protective effects of nicotine against both Mn and Fe. These findings provide further support for the potential utility of nicotine or nicotinic agonists in Parkinson's disease-like neurodegenerative disorders, including those that might be precipitated by trace elements, such as Fe and Mn. Moreover, both alpha4-beta2 and alpha7 nicotinic receptor subtypes appear to mediate the neuroprotective effects of nicotine against toxicity induced by these two trace metals.

The neuroprotective effect of nicotine in Parkinson's disease models is associated with inhibiting PARP-1 and caspase-3 cleavage

Clinical evidence points to neuroprotective effects of smoking in Parkinson’s disease (PD), but the molecular mechanisms remain unclear. We investigated the pharmacological pathways involved in these neuroprotective effects, which could provide novel ideas for developing targeted neuroprotective treatments for PD. We used the ETC complex I inhibitor methylpyridinium ion (MPP⁺) to induce cell death in SH-SY5Y cells as a cellular model for PD and found that nicotine inhibits cell death. Using choline as a nicotinic acetylcholine receptor (nAChR) agonist, we found that nAChR stimulation was sufficient to protect SH-SY5Y cells against cell death from MPP⁺. Blocking α7 nAChR with methyllycaconitine (MLA) prevented the protective effects of nicotine, demonstrating that these receptors are necessary for the neuroprotective effects of nicotine. The neuroprotective effect of nicotine involves other pathways relevant to PD. Cleaved Poly (ADP-ribose) polymerase-1 (PARP-1) and cleaved caspase-3 were decreased by nicotine in 6-hydroxydopamine (6-OHDA) lesioned mice and in MPP⁺-treated SH-SY5Y cells. In conclusion, our data indicate that nicotine likely exerts neuroprotective effects in PD through the α7 nAChR and downstream pathways including PARP-1 and caspase-3. This knowledge could be pursued in future research to develop neuroprotective treatments for PD.

MPTP-Induced Modulation of Neurotransmitters in SH-SY5Y Human Neuroblastoma Cells

Neurotoxic effects of MPTP(1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine) were evaluated in vitro using a human neuronal cell line, SH-SY5Y, that contained features contributing to expression of MPTP toxicity in vivo, namely, a transport system for dopam ine (DA) and monam ine oxidase (MAO) activity. In this model system, MPTP was found to reduce levels of catecholamines (DA, norepinephrine, epinephrine), serotonin (5-HT), and the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA). MPTP enhanced 3H-DA release, which could contribute to the reduction in DA concentrations seen in these cells. In addition, MPTP inhibited MAO activity (Ki 2.26 X 10-5 M). Pretreatment with the MAO inhibitor pargy-line protected the cells from MPTP-induced alterations of catecholamines and the decrease in 5-HT. In this in vitro model, the cholinergic antagonists atro-pine and A-tubocurarine also protected cells from MPTP-induced alterations of catecholamines. The capability of cholinergic antagonists to prevent the MPTP-induced alterations of catecholamine concentrations suggests a possible cholinergic contribution to MPTP neurotoxicity in this cell line.

Considerations for the use of SH-SY5Y neuroblastoma cells in neurobiology

The use of primary mammalian neurons derived from embryonic central nervous system tissue is limited by the fact that once terminally differentiated into mature neurons, the cells can no longer be propagated. Transformed neuronal-like cell lines can be used in vitro to overcome this limitation. However, several caveats exist when utilizing cells derived from malignant tumors. In this context, the popular SH-SY5Y neuroblastoma cell line and its use in in vitro systems is described. Originally derived from a metastatic bone tumor biopsy, SH-SY5Y (ATCC(®) CRL-2266™) cells are a subline of the parental line SK-N-SH (ATCC(®) HTB-11™). SK-N-SH were subcloned three times; first to SH-SY, then to SH-SY5, and finally to SH-SY5Y. SH-SY5Y were deposited to the ATCC(®) in 1970 by June L. Biedler.Three important characteristics of SH-SY5Y cells should be considered when using these cells in in vitro studies. First, cultures include both adherent and floating cells, both types of which are viable. Few studies address the biological significance of the adherent versus floating phenotypes, but most reported studies utilize adherent populations and discard the floating cells during media changes. Second, early studies by Biedler's group indicated that the parental differentiated SK-N-SH cells contained two morphologically distinct phenotypes: neuroblast-like cells and epithelial-like cells (Ross et al., J Nat Cancer Inst 71:741-747, 1983). These two phenotypes may correspond to the "N" and "S" types described in later studies in SH-SY5Y by Encinas et al. (J Neurochem 75:991-1003, 2000). Cells with neuroblast-like morphology are positive for tyrosine hydroxylase (TH) and dopamine-β-hydroxylase characteristic of catecholaminergic neurons, whereas the epithelial-like counterpart cells lacked these enzymatic activities (Ross et al., J Nat Cancer Inst 71:741-747, 1983). Third, SH-SY5Y cells can be differentiated to a more mature neuron-like phenotype that is characterized by neuronal markers. There are several methods to differentiate SH-SY5Y cells and are mentioned below. Retinoic acid is the most commonly used means for differentiation and will be addressed in detail.

Effect of cholinergic signaling on neuronal cell bioenergetics

Alzheimer's disease (AD) patients have reduced brain acetylcholine and reversing this deficit yields clinical benefits. In this study we explored how increased cholinergic tone impacts cell bioenergetics, which are also perturbed in AD. We treated SH-SY5Y neuroblastoma cells with carbachol, a cholinergic agonist, and tested for bioenergetic flux and bioenergetic infrastructure changes. Carbachol rapidly increased both oxidative phosphorylation and glycolysis fluxes. ATP levels rose slightly, as did cell energy demand, and AMPK phosphorylation occurred. At least some of these effects depended on muscarinic receptor activation, ER calcium release, and ER calcium re-uptake. Our data show that increasing cholinergic signaling enhances cell bioenergetics, and reveal mechanisms that mediate this effect. Phenomena we observed could potentially explain why cholinesterase inhibitor therapy increases AD brain glucose utilization and N-acetyl aspartate levels. The question of whether cholinesterase inhibitors have a disease modifying effect in AD has long been debated; our data suggest a theoretical mechanism through which such an effect could potentially arise.

From smoking to cancers: novel targets to neuronal nicotinic acetylcholine receptors

Cigarette smoking bears a strong etiological association with many neovascularization-related diseases, including cancer, cardiovascular disease, and age-related macular degeneration. Cigarette smoke is a complex mixture of many compounds, including nicotine, which is the major active and addictive component of tobacco. Nicotine and its specific metabolized carcinogens directly bind to nicotinic acetylcholine receptors (nAChRs) on cell membranes and trigger the nAChR signal cascade. The nAChRs were originally thought to be ligand-gated ion channels that modulate physiological processes ranging from neurotransmission to cancer signaling. For several decades, the nAChRs served as a prototypic molecule for neurotransmitter receptors; however, they are now important therapeutic targets for various diseases, including Alzheimer's and Parkinson's diseases, schizophrenia, and even cancer. This paper describes recent advances in our understanding of the assembly, activity, and biological functions of nicotinic receptors, as well as developments in the therapeutic application of nicotinic receptor ligands.

Genome-wide expression analysis reveals diverse effects of acute nicotine exposure on neuronal function-related genes and pathways

Previous human and animal studies demonstrate that acute nicotine exposure has complicated influences on the function of the nervous system, which may lead to long-lasting effects on the behavior and physiology of the subject. To determine the genes and pathways that might account for long-term changes after acute nicotine exposure, a pathway-focused oligoarray specifically designed for drug addiction research was used to assess acute nicotine effect on gene expression in the neuron-like SH-SY5Y cells. Our results showed that 295 genes involved in various biological functions were differentially regulated by 1 h of nicotine treatment. Among these genes, the expression changes of 221 were blocked by mecamylamine, indicating that the majority of nicotine-modulated genes were altered through the nicotinic acetylcholine receptors (nAChRs)-mediated signaling process. We further identified 14 biochemical pathways enriched among the nicotine-modulated genes, among which were those involved in neural development/synaptic plasticity, neuronal survival/death, immune response, or cellular metabolism. In the genes significantly regulated by nicotine but blocked by mecamylamine, 13 enriched pathways were detected. Nine of these pathways were shared with those enriched in the genes regulated by nicotine, including neuronal function-related pathways such as glucocorticoid receptor signaling, p38 MAPK signaling, PI3K/AKT signaling, and PTEN signaling, implying that nAChRs play important roles in the regulation of these biological processes. Together, our results not only provide insights into the mechanism underlying the acute response of neuronal cells to nicotine but also provide clues to how acute nicotine exposure exerts long-term effects on the nervous system.

Galantamine inhibits beta-amyloid aggregation and cytotoxicity

The ability of galantamine (Reminyl) to inhibit the aggregation and toxicity of the beta-amyloid peptide (Abeta) was investigated. Galantamine showed concentration-dependent inhibition of aggregation of both Abeta 1-40 and Abeta 1-42, as determined by an ELISA method. Electron microscope studies of Abeta 1-40 incubated in the presence of galantamine revealed fibrils that were disordered and clumped in appearance. MTT and lactate dehydrogenase assays, employing SH-SY5Y human neuroblastoma cells, showed that galantamine reduced the cytotoxicity induced by Abeta 1-40. Galantamine also dramatically reduced Abeta 1-40-induced cellular apoptosis in these cells. There is some evidence that galantamine may not be acting purely as a symptomatic treatment. Disease-modifying effects of the drug could be due to an additional effect on Abeta aggregation and/or toxicity.

Muscarinic receptor activation of AMP-activated protein kinase inhibits orexigenic neuropeptide mRNA expression

AMP-activated protein kinase (AMPK) plays a crucial role in both cellular and whole body energy homeostasis. Here we demonstrate that the muscarinic receptor agonist carbachol activates AMPKalpha1-containing complexes in the human SH-SY5Y cell line via a mechanism specific for the AMPK upstream kinase, Ca(2+)/calmodulin-dependent protein kinase kinase beta. Activation of AMPK inhibits mRNA expression of the orexigenic neuropeptides Agouti-related peptide and melanin-concentrating hormone but surprisingly has no effect on neuropeptide Y mRNA, a neuropeptide previously shown to be regulated by AMPK. Rather than restoring mRNA levels to baseline, pharmacological inhibition of Ca(2+)/calmodulin-dependent protein kinase kinase beta or AMPK greatly increases Agouti-related peptide and melanin-concentrating hormone mRNA expression. These data support a hypothesis that modulating basal AMPK activity in the hypothalamus is essential for maintaining tight regulation of pathways contributing to food intake.

Nicotinic component of galantamine in the regulation of amyloid precursor protein processing

Current therapies for Alzheimer's disease treatment rely mainly on acetylcholinesterase inhibitors, improving central cholinergic neurotransmission. Among these molecules, galantamine (GAL) has an interesting pharmacological profile as it is both a reversible acetylcholinesterase inhibitor and an allosteric potentiator of nicotinic cholinergic receptors. We investigated the effect of GAL on the metabolism of the amyloid precursor protein (APP) in differentiated SH-SY5Y neuroblastoma cells. The rationale was based on the suggestion that cholinergic activity may also be involved in the regulation of APP metabolism. We studied the acute effect on APP metabolism measuring the secretion of sAPPalpha in the conditioned medium of cells. Following 2h treatment, GAL 10microM promoted a strong increase in the release of sAPPalpha, the maximal effect approaching on average three-fold baseline value. The compound appeared to increase the release of sAPPalpha, with a mechanism dependent upon an indirect cholinergic stimulation. The effect of GAL was prevented by pre-treatment with alpha-bungarotoxin (40nM) but not low (nanomolar) atropine concentrations, suggesting the specific involvement of nicotinic cholinergic receptors.

Extracellular tau is toxic to neuronal cells

The degeneration of neurons in disorders such as Alzheimer's disease has an immediate consequence, the release of intracellular proteins into the extracellular space. One of these proteins, tau, has proven to be toxic when added to cultured neuronal cells. This toxicity varies according to the degree of protein aggregation. The addition of tau to cultured neuroblastoma cells provoked an increase in the levels of intracellular calcium, which is followed by cell death. We suggest that this phenomenon may be mediated by the interaction of tau with muscarinic receptors, which promotes the liberation of calcium from intracellular stores.

Nicotine regulates SH-SY5Y neuroblastoma cell proliferation through the release of brain-derived neurotrophic factor

Nicotine has been shown to produce some beneficial effects in neurodegenerative disorders, and several studies have suggested that these effects may be mediated in part through the action of the neurotrophic factor BDNF. To further elucidate the interaction between nicotine and BDNF, we examined the effect of nicotine on the proliferation of the neuroblastoma cell line SH-SY5Y, which, following differentiation with retinoic acid, expresses both nicotinic receptors and the receptor for BDNF, TrkB. Both nicotine and the nicotinic alpha-7 selective agonist AR-17779 significantly increased cell proliferation albeit with bell-shaped dose-response kinetics. The blockade of this effect with either the alpha-7 nicotinic antagonist methyllycaconitine or the non-selective nicotinic antagonist mecamylamine indicated that the effect was mediated by nicotinic receptors. Prior addition of neutralising BDNF antibodies or of the tyrosine kinase inhibitor K252A (200 nM) completely blocked nicotine-induced proliferation, suggesting the involvement of TrkB signalling in the mediation of the effect. Nicotine also enhanced both the secretion of BDNF from the SH-SY5Y and cell surface density of TrkB receptors. These effects were abolished by pretreatment with MLA. These data indicate that activation of nicotinic receptors has effects upon the BDNF-TrkB pathway, inducing cell proliferation by promoting the release of BDNF, which in turn activates TrkB receptors.

Oxidative mechanisms contributing to the developmental neurotoxicity of nicotine and chlorpyrifos

Nicotine and chlorpyrifos are developmental neurotoxicants that, despite their differences in structure and mechanism of action, share many aspects for damage to the developing brain. Both are thought to generate oxidative radicals; in the current study, we evaluated their ability to produce lipid peroxidation in two in vitro models of neural cell development (PC12 and SH-SY5Y cells) and for nicotine, with treatment of adolescent rats in vivo. Nicotine and chlorpyrifos, in concentrations relevant to human exposures, elicited an increase in thiobarbituric-acid-reactive species (TBARS) in undifferentiated cells, an effect that was prevented by addition of the antioxidant, Vitamin E. Initiating differentiation with nerve growth factor, which enhances nicotinic acetylcholine receptor expression, increased the TBARS response to nicotine but not chlorpyrifos, suggesting that the two agents act by different originating mechanisms to converge on the endpoint of oxidative damage. Furthermore, nicotine protected the cells from oxidative damage evoked by chlorpyrifos and similarly blocked the antimitotic effect of chlorpyrifos. Treatment of adolescent rats with nicotine elicited increases in TBARS in multiple brain regions when given in doses that simulate plasma nicotine concentrations found in smokers or at one-tenth the dose. Our results indicate that nicotine and chlorpyrifos elicit oxidative damage to developing neural cells both in vitro and in vivo, a mechanism that explains some of the neurodevelopmental endpoints that are common to the two agents. The balance between neuroprotectant and neurotoxicant actions of nicotine may be particularly important in situations where exposure to tobacco smoke is combined with other prooxidant insults.

Suppression by phthalates of the calcium signaling of human nicotinic acetylcholine receptors in human neuroblastoma SH-SY5Y cells

Phthalates are widely used in industry and cause public concern since they have genomic estrogenic-like effects via estrogen receptors. We previously found that some phthalates have nongenomic effects, exerting inhibitory effects on the functional activities of nicotinic acetylcholine receptors (nAChRs) in bovine chromaffin cells. In this study, we investigated the effects of eight phthalates on the calcium signaling of human nAChR by using human neuroblastoma SH-SY5Y cells. All eight phthalates, with different potency, have inhibitory roles on the calcium signaling coupled with human nAChR, but not muscarinic acetylcholine receptors (mAChRs). For inhibition of human nAChR, the strongest to weakest potencies were observed as di-n-pentyl phthalate (DPP) --> butyl benzyl phthalate (BBP) --> di-n-butyl phthalate (DBP) --> dicyclohexyl phthalate (DCHP) --> di-n-hexyl phthalate (DHP) --> di-(2-ethyl hexyl) phthalate (DEHP) --> di-n-propyl phthalate (DPrP) --> diethyl phthalate (DEP). The potencies of phthalates were associated with their structures such that the most effective ones had dialkyl group carbon numbers of C4 or C5, with shorter or longer numbers resulting in decreased potency. At as low as 0.1 microM, DPP, DBP, BBP, DCHP and DHP significantly inhibited the calcium signaling of human nAChR. The IC50 of phthalates on human nAChR, ranging from 0.32 to 7.96 microM, were 10-50 lower than those for bovine nAChR. We suggest that some phthalates effectively inhibit the calcium signaling of human nAChR, and these nongenomic effects are cause for concern.

Galantamine prevents apoptosis induced by beta-amyloid and thapsigargin: involvement of nicotinic acetylcholine receptors

Galantamine is currently used to treat Alzheimer's disease patients; it behaves as a mild blocker of acetylcholinesterase (AChE) and has an allosteric modulating action on nicotinic acetylcholine receptors (nAChRs). In this study, we observed that galantamine prevented cell death induced by the peptide beta-amyloid(1-40) and thapsigargin in the human neuroblastoma cell line SH-SY5Y, as well as in bovine chromaffin cells. The protective effect of galantamine was concentration-dependent in both cell types; maximum protection was produced at 300 nM. The antiapoptotic effect of galantamine at 300 nM, against beta-amyloid(1-40) or thapsigargin-induced toxicity, was reversed by alpha-bungarotoxin. At neuroprotective concentrations, galantamine caused a mild and sustained elevation of the cytosolic concentration of calcium, [Ca2+]c, measured in single cells loaded with Fura-2. Incubation of the cells for 48 h with 300 nM galantamine doubled the density of alpha7 nicotinic receptors and tripled the expression of the antiapoptotic protein Bcl-2. These results strongly suggest that galantamine can prevent apoptotic cell death by inducing neuroprotection through a mechanism related to that described for nicotine, i.e. activation of nAChRs and upregulation of Bcl-2. These findings might explain the long-term beneficial effects of galantamine in patients suffering of Alzheimer's disease.

Chronic treatment with nicotine or potassium attenuates depolarisation-evoked noradrenaline release from the human neuroblastoma SH-SY5Y

Chronic treatment, of SH-SY5Y cells, with KCl (20 mM) for 4 days decreased 100 mM KCl-evoked noradrenaline (NA) release by 50% and nicotine (100 microM)-evoked NA release by 55%. Pretreatment with the L-type calcium channel antagonist, nifedipine, prevented this inhibitory effect of chronic exposure to 20 mM KCl on NA release. In contrast pretreatment with 10 microM nicotine for 4 days had no effect on 100 mM KCl -evoked secretion and decreased nicotinic -evoked NA release by only 25%. Inclusion of nifedipine prevented the inhibition of NA release by chronic nicotine treatment. These data are discussed in relation to effects of chronic moderate, depolarisation by either K(+) or nicotine on influx of Ca(2+) via L-type voltage sensitive calcium channels.

Modulatory role of presynaptic nicotinic receptors in synaptic and non-synaptic chemical communication in the central nervous system

Neuronal nicotinic acetylcholine receptors (nAChRs) belong to a family of ligand-gated channels closely related to but distinct from the muscle nAChRs. Recent progress in neurochemical and pharmacological methods supports the hypothesis of presynaptically located nAChRs on axon terminals and indicates that the major effect of nAChR is the modulation rather than processing of fast synaptic transmission. Strong neurochemical evidence indicate that the most important function of presynaptic nAChRs in either synaptic or non-synaptic localization is to increase transmitter release initiated by axonal firing, or directly induce Na(+) and Ca(2+) influx followed by a depolarization sufficient to activate local voltage-sensitive Ca(2+) channels, as a result transmitter of vesicular origin will be released. Therefore, it is somewhat expected that nicotine-induced transmitter release of different monoamines including norepinephrine (NE), dopamine (DA), serotonin (5-HT) can be tetrodotoxin (TTX)- and [Ca(2+)](o)-sensitive. However, some of the nAChR agonists at higher concentrations (1, 1-dimethyl-4-phenylpiperazinium (DMPP) and lobeline), besides their effects on presynaptic nAChRs, are able to inhibit the uptake of NE and 5-HT into nerve terminals, thereby their transmitter releasing effects are extended in time and space. The effect on the uptake process is different from classical nicotinic actions, not being sensitive to nAChR antagonism, but can be prevented by selective uptake blockers or reduced temperature. Considering neurochemical, pharmacological and electrophysiological evidence it seems likely that presynaptic nAChRs on monoaminergic fibers are composed of alpha3 or alpha4 subunits in combination with the beta2 subunit. This is supported by the observation that nicotinic agonists have no presynaptic effect on transmitter release in knockout mice lacking the beta2 nAChR subunit gene. The essential brain function lies not only in impulse transmission within a hard-wired neuronal circuitry but also within synaptic and non-synaptic communication subjected to presynaptic modulation. Since the varicose noradrenergic, dopaminergic, serotonergic, glutamatergic and cholinergic axon terminals mainly do not make synaptic contact, but their varicosities are equipped with nAChRs and these non-synaptically localized receptors are of high affinity, it is suggested that nicotine inhaled during smoking might exert its behavioral, psychological, neurological and neuroendocrinological effects via these receptors.

Human neuronal nicotinic receptors

Nicotine is a very widely used drug of abuse, which exerts a number of neurovegetative, behavioural and psychological effects by interacting with neuronal nicotinic acetylcholine receptors (NAChRs). These receptors are distributed widely in human brain and ganglia, and form a family of ACh-gated ion channels of different subtypes, each of which has a specific pharmacology and physiology. As human NAChRs have been implicated in a number of human central nervous system disorders (including the neurodegenerative Alzheimer's disease, schizophrenia and epilepsy), they are suitable potential targets for rational drug therapy. Much of our current knowledge about the structure and function of NAChRs comes from studies carried out in other species, such as rodents and chicks, and information concerning human nicotinic receptors is still incomplete and scattered in the literature. Nevertheless, it is already evident that there are a number of differences in the anatomical distribution, physiology, pharmacology, and expression regulation of certain subtypes between the nicotinic systems of humans and other species. This review will attempt to survey the major achievements reached in the study of the structure and function of NAChRs by examining the molecular basis of their functional diversity viewed mainly from pharmacological and biochemical perspectives. It will also summarize our current knowledge concerning the structure and function of the NAChRs expressed by other species, and the newly discovered drugs used to classify their numerous subtypes. Finally, the role of NAChRs in behaviour and pathology will be considered.

Muscarinic depolarization of SH-SY5Y human neuroblastoma cells as determined using oxonol V

Membrane potential was measured in the suspension of SH-SY5Y cells using the anionic potentiometric probe, oxonol V. The relation of fluorescence to membrane potential was assessed by increasing the external [K+] in the presence of the K+ ionophore valinomycin. The response was linear in the range of 5 to 30 mM K+ (membrane potential change of approximately 40 mV). Muscarine increased the fluorescence indicating a depolarization. The competitive inhibitory constant (112 nM) of the muscarinic antagonist pirenzepine (5,11-dihydro-11-([4-methyl-1-piperazinyl]acetyl)-6H-pyrido[2,3-b] (1,4)benzodiazepin-6-one-dihydrochloride) suggests that Hm1 receptors are not involved. The protein kinase C inhibitor, GF 109203X (3-[1-(3-demethylaminopropyl)-indol-3-yl]-3-(indol-3-yl)-maleimide ), and a reduction of extracellular Na+ both produced an additive partial inhibition. The results suggest that muscarinic receptors depolarize these cells by separate Na(+)-dependent and -independent mechanisms, the Na(+)-independent mechanism being protein kinase C-dependent.

Potential-dependent block of human delayed rectifier K+ channels by internal Na+

The delayed rectifier K+ currents in differentiated human SH-SY5Y neuroblastoma cells were characterized with tight-seal recording techniques. Activation and inactivation parameters were measured. At high positive potentials, the current showed a marked rectification, causing a region of negative slope conductance in the current vs. potential curve. The rectification depended markedly on the pipette Na+ concentration. Without Na+, no rectification was observed, whereas with high Na+ (20-60 mM), a marked rectification was always observed. Tail current measurements showed a fast ( < 400 microseconds) block of K+ currents in the presence of internal Na+. With 60 mM Na+ in the pipette 8% of the K+ current was blocked at 0 mV, 27% at +20 mV, and 82% at +100 mV. Similar degrees of block were often seen with 30 mM Na+ in the pipette. The submembrane Na+ concentration in intact cells was estimated, on the basis of the reversal of Na+ current, to be approximately 15 mM. Single-channel K+ currents, in the cell-attached configuration, showed a conductance of approximately 20 pS at 40-60 mV above rest but showed rectification at high potentials.

The use of the human neuroblastoma SH-SY5Y to study the effect of second messengers on noradrenaline release

1. Recent data suggesting that the human neuroblastoma SH-SY5Y is a suitable cell line in which to study the effect of second messengers on NA release are discussed in the context of current views on exocytosis. 2. Release of NA is evoked by depolarization, as well as activation of muscarinic (M3) and bradykinin (B2) receptors in SH-SY5Y cells which have not been differentiated by the addition of growth factors. 3. Evoked release is enhanced by activation of protein kinase C. 4. Activation of protein kinase C decreases the changes in intracellular calcium evoked by carbachol, bradykinin and 100 mM K+. 5. SH-SY5Y express N-type and L-type voltage sensitive Ca2+ channels. L-Type Ca(2+)-channels are coupled to NA release under conditions of weak depolarization. However with strong depolarization (100 mM K+) both L-type and N-type channels are involved. 6. Muscarinic- and neuropeptide Y receptors are coupled to the inhibition of Ca2+ channel activity.

Differences of the electrical and nicotinic receptor stimulation-evoked liberation of norepinephrine from chicken sympathetic neurons in culture: possible involvement of different pools of the transmitter

We studied the release of [3H]norepinephrine from chicken sympathetic neurons in culture evoked by nicotinic and electrical stimulation with an intention to establish functional identity or nonidentity of the two stimuli in investigations of neurotransmitter release. Nicotinic stimulation evoked extracellular calcium dependent release of [3H]norepinephrine and the rise of intracellular calcium concentration. The release was completely blocked by nicotinic antagonists hexamethonium (100 mumol/l) and mecamylamine (10 mumol/l), and decreased by tetrodotoxin (0.3 mumol/l) and omega-conotoxin (0.1 mumol/l) to 17% and 27%, resp. The intracellular calcium response was decreased by nicotinic antagonists and tetrodotoxin, but not changed by omega-conotoxin. The electrical stimulation-evoked release was blocked by both tetrodotoxin and omega-conotoxin, and decreased by previous electrical, but not nicotinic, stimulation. The differential sensitivity to omega-conotoxin and tetrodotoxin,and the inability of nicotinic stimulation to decrease the liberation by following electrical stimulation may suggest the mobilization of different pools of the transmitter.

Functional expression of nicotinic acetylcholine receptors containing rat alpha 7 subunits in human SH-SY5Y neuroblastoma cells

Neuronal nicotinic acetylcholine receptors (nAChR) are made from different combinations of subunits encoded by a diverse family of genes. However, the recently cloned alpha 7 gene codes for subunits that can form homooligomeric nAChR complexes when expressed in Xenopus oocytes. Electrophysiological studies reveal that these alpha 7-nAChR function as alpha-bungarotoxin (Bgt)-sensitive, quickly activating/inactivating ion channels with a unique pharmacological profile and an unusually high permeability to calcium ions. Although similar observations have been made in studies of Bgt-sensitive, functional nAChR subtypes that are naturally expressed in neuronal cells, all attempts until now to reconstitute functional alpha 7-nAChR in cell lines have failed. Here we report the successful use of SH-SY5Y human neuroblastoma cells, which naturally express low levels of endogenous alpha 7 transcripts, to stably overexpress heterologous rat nAChR alpha 7 transgenes. These transgenes are expressed as the appropriately-sized alpha 7 messages and protein, and stably transfected SH-SY5Y cells have over 30-times higher levels of specific Bgt binding sites than do wild-type cells. Whole cell current recordings confirm that transfected cells express functional nAChR that are sensitive to blockade by Bgt and display the typical physiological and pharmacological profiles of alpha 7-nAChR. We conclude that stable, functional expression of alpha 7 transgenes in a mammalian cell line has been achieved for the first time.

Presynaptic alpha 2-adrenoceptors inhibit calcium influx in terminals of chicken sympathetic neurons and noradrenaline release evoked by nicotinic stimulation

The changes of intracellular calcium concentration evoked by stimulation of nicotinic receptors and its modulation by alpha 2-adrenoceptors were investigated in chicken sympathetic neurons grown in culture. Stimulation of nicotinic receptors increased the intracellular calcium both in the area of cell bodies and processes. In normal extracellular calcium (1.3 mmol/l), the specific alpha 2-adrenoreceptor agonist UK 14,304 (10 mumol/l) diminished the response in cell bodies but not in processes. The same treatment in medium with reduced calcium (0.13 mmol/l) resulted in the decrease of the response evoked by nicotinic stimulation in the area of processes but not in the cell bodies. The effect of UK 14,304 on evoked noradrenaline release paralleled its influence on intracellular calcium in processes. These data indicate that nicotine stimulation-induced influx of calcium is inhibited by alpha 2-adrenoceptor stimulation both in cell bodies and in processes. It is concluded that the nicotinic stimulation-evoked release of noradrenaline is triggered by influx of calcium through alpha 2-adrenoreceptor sensitive as well as insensitive pathways.

Inhibition of neuronal nicotinic acetylcholine receptors by imipramine and desipramine

The actions of two structurally related tricyclic antidepressants on neuronal nicotinic acetylcholine receptors were investigated in human neuroblastoma (SY-SY5Y) cells, using whole-cell patch-clamp recordings. Both desipramine and imipramine reversibly inhibited inward currents evoked by application of the nicotinic receptor agonist dimethylphenylpiperazinium iodide (30-300 microM) with IC50 values of 0.17 microM and 1.0 microM respectively (holding potential -70 mV). The degree of current inhibition caused by either tricyclic compound was unaffected by agonist concentration (30-300 microM). The effects of desipramine were voltage-independent over the range -40 mV to -100 mV, and inhibition caused by imipramine only increased very slightly with membrane hyperpolarization over the same range. These results indicate that tricyclic antidepressants can inhibit neuronal nicotinic acetylcholine receptors by mechanisms which are distinct from their actions at non-neuronal nicotinic acetylcholine receptors.

Nicotinic receptor-mediated release of noradrenaline in the human neuroblastoma SH-SY5Y

Dimethylphenylpiperazinium iodide (a nicotinic agonist) evokes noradrenaline release from human neuroblastoma SH-SY5Y cells that have been pretreated with 12-O-tetradecanoylphorbol 13-acetate for 8 min. This effect of dimethylphenylpiperazinium iodide was inhibited by 1 microM mecamylamine but not by 1 microM atropine, which suggests that SH-SY5Y cells express nicotinic receptors coupled to the release of noradrenaline. Dimethylphenylpiperazinium iodide-evoked release was enhanced by 5 microM Bay K 8644 (an L-type calcium agonist) and inhibited by 1 microM nifedipine. Dimethylphenylpiperazinium iodide depolarised SH-SY5Y cells and enhanced the level of intracellular calcium in cells loaded with fura 2. The effects of dimethylphenylpiperazinium iodide on noradrenaline release, depolarisation, and intracellular calcium levels were all inhibited by 1 microM desmethylimipramine. The results of this study show that nicotinic receptors in SH-SY5Y cells stimulate noradrenaline release by activation of L-type calcium channels.

Nicotinic acetylcholine receptors in isolated type I cells of the neonatal rat carotid body

Electrophysiological responses of enzymatically isolated type I cells from the neonatal rat carotid body to cholinergic agonists were examined using the whole-cell patch-clamp technique. Inward currents were evoked in cells clamped at -70 mV in response to bath-applied carbachol and two selective nicotinic agonists, nicotine and dimethylphenylpiperazinium. Muscarine failed to produce any change in membrane current. Responses to nicotine were concentration-dependent and also voltage-dependent, showing strong rectification positive to -40 mV. Currents evoked by nicotine were reduced or abolished in the presence of mecamylamine and also by high concentrations of atropine (10 or 100 microM). Under "current-clamp", nicotine was shown to depolarize type I cells, an effect which was only slowly reversible, but which could be rapidly attenuated by introduction of mecamylamine to the perfusate. In voltage-clamped cells, nicotine could evoke inward currents when extracellular Na+ was replaced by Ca2+. Our results demonstrate the presence of functional nicotinic acetylcholine receptors on type I cells of the neonatal rat carotid body. Activation of these receptors could lead to excitation of the intact carotid body by either of two possible mechanisms: depolarization of type I cells sufficient to open voltage-gated Ca2+ channels, or Ca2+ influx through the receptor pore itself. Either (or both) mechanisms could trigger catecholamine release from type I cells, which is a fundamental step in chemotransmission.