Potassium- and carbachol-evoked release of [3H]noradrenaline from human neuroblastoma cells, SH-SY5Y

Microglia cells treated with synthetic vasoactive intestinal peptide or transduced with LentiVIP protect neuronal cells against degeneration

A common pathological hallmark of neurodegenerative disorders is neuronal cell death, accompanied by neuroinflammation and oxidative stress. The vasoactive intestinal peptide (VIP) is a pleiotropic peptide that combines neuroprotective and immunomodulatory actions. The gene therapy field shows long-term promise for treating a wide range of neurodegenerative diseases (ND). In this study, we aimed to investigate the in vitro efficacy of transduction of microglia using lentiviral gene therapy vectors encoding VIP (LentiVIP). Additionally, we tested the protective effects of the secretome derived from LentiVIP-infected "immortalized human" microglia HMC3 cells, and cells treated with Synthetic VIP (SynVIP), against toxin-induced neurodegeneration. First, LentiVIP, which stably expresses VIP, was generated and purified. VIP secretion in microglial conditioned media (MG CM) for LentiVIP-infected HMC3 microglia cells was confirmed. Microglia cells were activated with lipopolysaccharide, and groups were formed as follows: 1) Control, 2) SynVIP-treated, or 3) LentiVIP-transduced. These MG CM were applied on an in vitro neurodegenerative model formed by differentiated (d)-SH-SY5Y cells. Then, cell survival analysis and apoptotic nuclear staining, besides measurement of oxidative/inflammatory parameters in CM of cells were performed. Activated MG CM reduced survival rates of both control and toxin-applied (d)-SH-SY5Y cells, whereas LentiVIP-infected MG CM and SynVIP-treated ones exhibited better survival rates. These findings were supported by apoptotic nuclear evaluations of (d)-SH-SY5Y cells, alongside oxidative/inflammatory parameters in their CM. LentiVIP seems worthy of further studies for the treatment of ND because of the potential of gene therapy to treat diseases effectively with a single injection.

Additive cell protective and oxidative stress reducing effects of combined treatment with cromolyn sodium and masitinib on MPTP-induced toxicity in SH-SY5Y neuroblastoma cells

The suppression of oxidative-stress induced neurotoxicity by antioxidants serves as a potential preventive strategy for neurodegenerative diseases. In this study, we aimed to investigate the cell protective and antioxidant effects of masitinib and cromolyn sodium against toxin-induced neurodegeneration. First, human neuroblastoma SH-SY5Y cells were differentiated into neuron-like (d)-SH-SY5Y cells. The differentiated cells were confirmed by immuno-staining with anti-PGP9.5 antibody, a neuronal marker. Cell culture groups were formed, and a neurotoxin, 1-methyl-4-phenyl1,2,3,6-tetrahydropyridine (MPTP) was applied on cells followed by masitinib and/or cromolyn sodium treatments. Survival rates of cells were detected by MTT assay. Anti-inflammatory Transforming Growth Factor-β1 (TGF-β1) and nitric oxide (NO) levels and total oxidant and antioxidant capacities (TOC and TAC) in cell conditioned media (CM) were measured. Morphological analysis and apoptotic nuclear assessment of cells were also noted. When (d)-SH-SY5Y cells were exposed to neurotoxin, cell viability rates of these cells were found to be decreased in a dose-dependent manner. CM of toxin applied groups displayed higher levels of TOC/TAC ratios and NO levels compared to control (p < 0.01). Both masitinib and cromolyn protected cells from toxin-induced cell death as revealed by ameliorated rates of viability and reversed toxin-induced elevation of TOC/TAC ratios and decreased NO levels in their CM. Combined treatment significantly reduced TOC/TAC ratios and NO levels more effectively compared to mono-treatments. Both drugs also increased TGF-β1 levels in cell CM. When these agents were tested for therapeutic effects against toxin-induced cell degeneration, better viability results were obtained by both masitinib and cromolyn sodium treatment, with significantly better amelioration provided by combined application of these drugs (p < 0.01). This study demonstrated new findings that combined treatment with cromolyn an FDA-approved drug of asthma, and masitinib, an orally administered drug with a low toxicity, exert neuroprotective and additive therapeutic effects. We propose combination therapy of masitinib and cromolyn may represent an innovative treatment in neurodegenerative diseases. Combination therapy may be more advantageous that it enables combined application of lower doses of both drugs, providing less side effects.

SH-SY5Y-derived neurons: a human neuronal model system for investigating TAU sorting and neuronal subtype-specific TAU vulnerability

The microtubule-associated protein (MAP) TAU is mainly sorted into the axon of healthy brain neurons. Somatodendritic missorting of TAU is a pathological hallmark of many neurodegenerative diseases, including Alzheimer's disease (AD). Cause, consequence and (patho)physiological mechanisms of TAU sorting and missorting are understudied, in part also because of the lack of readily available human neuronal model systems. The human neuroblastoma cell line SH-SY5Y is widely used for studying TAU physiology and TAU-related pathology in AD and related tauopathies. SH-SY5Y cells can be differentiated into neuron-like cells (SH-SY5Y-derived neurons) using various substances. This review evaluates whether SH-SY5Y-derived neurons are a suitable model for (i) investigating intracellular TAU sorting in general, and (ii) with respect to neuron subtype-specific TAU vulnerability. (I) SH-SY5Y-derived neurons show pronounced axodendritic polarity, high levels of axonally localized TAU protein, expression of all six human brain isoforms and TAU phosphorylation similar to the human brain. As SH-SY5Y cells are highly proliferative and readily accessible for genetic engineering, stable transgene integration and leading-edge genome editing are feasible. (II) SH-SY5Y-derived neurons display features of subcortical neurons early affected in many tauopathies. This allows analyzing brain region-specific differences in TAU physiology, also in the context of differential vulnerability to TAU pathology. However, several limitations should be considered when using SH-SY5Y-derived neurons, e.g., the lack of clearly defined neuronal subtypes, or the difficulty of mimicking age-related tauopathy risk factors in vitro. In brief, this review discusses the suitability of SH-SY5Y-derived neurons for investigating TAU (mis)sorting mechanisms and neuron-specific TAU vulnerability in disease paradigms.

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.

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.

The profile of mephedrone on human monoamine transporters differs from 3,4-methylenedioxymethamphetamine primarily by lower potency at the vesicular monoamine transporter

Mephedrone (4-methylmethcathinone, MMC) and 3,4-methylenedioxymethamphetamine (MDMA) are constituents of popular party drugs with psychoactive effects. Structurally they are amphetamine-like substances with monoamine neurotransmitter enhancing actions. We therefore compared their effects on the human monoamine transporters using human cell lines stably expressing the human noradrenaline, dopamine and serotonin transporter (NET, DAT and SERT); preparations of synaptic vesicles from human striatum in uptake experiments; and a superfusion system where releasing effects can be reliably measured. MMC and MDMA were equally potent in inhibiting noradrenaline uptake at NET, with IC50 values of 1.9 and 2.1 µM, respectively. Compared to their NET inhibition potency, both drugs were weaker uptake inhibitors at DAT and SERT, with MMC being more potent than MDMA at DAT (IC50: 5.9 vs 12.6 µM) and less potent than MDMA at SERT (IC50: 19.3 vs 7.6 µM). MMC and MDMA both induced concentration-dependently [(3)H]1-methyl-4-phenylpyridinium-release from NET-, DAT or SERT-expressing cells which was clearly transporter-mediated release as demonstrated by the selective inhibitory effects of nmolar to low µmolar concentrations of desipramine, GBR 12909 and fluoxetine, respectively. MMC and MDMA differed most in their inhibition of [(3)H]dopamine uptake by synaptic vesicles from human striatum with MDMA being 10-fold more potent than MMC (IC50: 20 vs 223 µM) and their ability to release [(3)H]dopamine from human vesicular monoamine transporter expressing SH-SY5Y neuroblastoma cells in which MDMA seems to have a stronger effect. Our findings give a molecular explanation to the lower long-term neurotoxicity of MMC compared to MDMA.

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.

Dopamine D2 receptor activation leads to an up-regulation of glial cell line-derived neurotrophic factor via Gβγ-Erk1/2-dependent induction of Zif268

Glial cell line-derived neurotrophic factor (GDNF) is a potent growth factor essential to the development, survival, and function of dopaminergic neurons (Airaksinen and Saarma 2002). The molecular mechanisms underlying GDNF expression remain elusive; thus, we set out to identify a signaling pathway that governs GDNF levels. We found that treatment of both differentiated dopaminergic-like SH-SY5Y cells and rat midbrain slices with the dopamine D2 receptor (D2R) agonist, quinpirole, triggered an increase in the expression of GDNF that was temporally preceded by an increase in the levels of zinc-finger protein 268 (Zif268), a DNA-binding transcription factor encoded by an immediate-early gene. Moreover, the D2R inhibitor raclopride blocked the increase of both GDNF and Zif268 expression following potassium-evoked dopamine release in SH-SY5Y cells. We used adenoviral delivery of small hairpin RNA (shRNA) targeting Zif268 to down-regulate its expression and found that Zif268 is specifically required for the D2R-mediated up-regulation of GDNF. Furthermore, the D2R-mediated induction of GDNF and Zif268 expression was dependent on Gβγ-mediated signaling and activation of extracellular signal-regulated kinase 1/2. Importantly, using chromatin immunoprecipitation assay, we identified a direct association of Zif268 with the GDNF promoter. These results suggest that D2R activation induces a Gβγ- and extracellular signal-regulated kinase 1/2-dependent increase in the level of Zif268, which functions to directly up-regulate the expression of GDNF.

Lyn kinase regulates mesolimbic dopamine release: implication for alcohol reward

We report here that the Src family tyrosine kinase Lyn negatively regulates the release of dopamine (DA) in the mesolimbic system, as well as the rewarding properties of alcohol. Specifically, we show that RNA interference-mediated knockdown of Lyn expression results in an increase in KCl-induced DA release in DAergic-like SH-SY5Y cells, whereas overexpression of a constitutively active form of Lyn (CA-Lyn) leads to a decrease of DA release. Activation of ventral tegmental area (VTA) DAergic neurons results in DA overflow in the nucleus accumbens (NAc), and we found that the evoked release of DA was higher in the NAc of Lyn knock-out (Lyn KO) mice compared with wild-type littermate (Lyn WT) controls. Acute exposure of rodents to alcohol causes a rapid increase in DA release in the NAc, and we show that overexpression of CA-Lyn in the VTA of mice blocked alcohol-induced (2 g/kg) DA release in the NAc. Increase in DA levels in the NAc is closely associated with reward-related behaviors, and overexpression of CA-Lyn in the VTA of mice led to an attenuation of alcohol reward, measured in a conditioned place preference paradigm. Conversely, alcohol place preference was increased in Lyn KO mice compared with Lyn WT controls. Together, our results suggest a novel role for Lyn kinase in the regulation of DA release in the mesolimbic system, which leads to the control of alcohol reward.

The plasminogen activator system modulates sympathetic nerve function

Sympathetic neurons synthesize and release tissue plasminogen activator (t-PA). We investigated whether t-PA modulates sympathetic activity. t-PA inhibition markedly reduced contraction of the guinea pig vas deferens to electrical field stimulation (EFS) and norepinephrine (NE) exocytosis from cardiac synaptosomes. Recombinant t-PA (rt-PA) induced exocytotic and carrier-mediated NE release from cardiac synaptosomes and cultured neuroblastoma cells; this was a plasmin-independent effect but was potentiated by a fibrinogen cleavage product. Notably, hearts from t-PA–null mice released much less NE upon EFS than their wild-type (WT) controls (i.e., a 76.5% decrease; P < 0.01), whereas hearts from plasminogen activator inhibitor-1 (PAI-1)–null mice released much more NE (i.e., a 275% increase; P < 0.05). Furthermore, vasa deferentia from t-PA–null mice were hyporesponsive to EFS (P < 0.0001) but were normalized by the addition of rt-PA. In contrast, vasa from PAI-1–null mice were much more responsive (P < 0.05). Coronary NE overflow from hearts subjected to ischemia/reperfusion was much smaller in t-PA–null than in WT control mice (P < 0.01). Furthermore, reperfusion arrhythmias were significantly reduced (P < 0.05) in t-PA–null hearts. Thus, t-PA enhances NE release from sympathetic nerves and contributes to cardiac arrhythmias in ischemia/reperfusion. Because the risk of arrhythmias and sudden cardiac death is increased in hyperadrenergic conditions, targeting the NE-releasing effect of t-PA may have valuable therapeutic potential.

Neuroendocrine properties of intrinsic cardiac adrenergic cells in fetal rat heart

Intrinsic cardiac adrenergic (ICA) cells in developing rat heart constitute a novel adrenergic signaling system involved in cardiac regulation. Regulatory mechanisms of ICA cells remain to be defined. Immunohistochemical study of fetal rat hearts demonstrated ICA cells with catecholamine biosynthetic enzyme tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT). The mRNA of TH and PNMP was also detected in fetal rat hearts before sympathetic innervation. Immunoreactivity of norepinephrine transporter (NET) was localized to ICA cells in rat heart tissue and primary cell culture. For the functional study, the activity of intracellular Ca2+concentration ([Ca2+]i) transients was quantified by a ratio fluorescent spectrometer in cultured ICA cells and myocytes. ICA cells generated spontaneous [Ca2+]itransients that were eliminated by tetrodotoxin or Ca2+-free solutions and showed greatly reduced amplitude with the addition of L-type Ca2+channel blocker nifedipine. [3H]norepinephrine studies demonstrate release and uptake of norepinephrine. Functional interaction between catecholamines produced by the ICA cells and cocultured myocytes was evident by the effect of the β-adrenergic blocker atenolol eliciting a dose-dependent reduction in the amplitude and frequency of [Ca2+]itransients of beating myocytes. Hypoxia inhibited [Ca2+]itransient activity of ICA cells, which subsequently produced a reoxygenation-mediated rebound augmentation of [Ca2+]itransients. We conclude that ICA cells are capable of catecholamine synthesis, release, and uptake. They generate spontaneous [Ca2+]itransient activity that can be regulated by oxygen tension. ICA cells may provide an alternative adrenergic supply to maintain cardiac contractile and pacemaker function at rest and during stress in the absence of sympathetic innervation.

Histamine H3-receptor-induced attenuation of norepinephrine exocytosis: a decreased protein kinase a activity mediates a reduction in intracellular calcium

We had reported that activation of presynaptic histamine H(3)-receptors inhibits norepinephrine exocytosis from depolarized cardiac sympathetic nerve endings, an action associated with a marked decrease in intraneuronal Ca(2+) that we ascribed to a decreased Ca(2+) influx. An H(3)-receptor-mediated inhibition of cAMP-dependent phosphorylation of Ca(2+) channels could cause a sequential attenuation of Ca(2+) influx, intraneuronal Ca(2+) and norepinephrine exocytosis. We tested this hypothesis in sympathetic nerve endings (cardiac synaptosomes) expressing native H(3)-receptors and in human neuroblastoma SH-SY5Y cells transfected with H(3)-receptors. Norepinephrine exocytosis was elicited by K(+) or by stimulation of adenylyl cyclase with forskolin. H(3)-receptor activation markedly attenuated the K(+)- and forskolin-induced norepinephrine exocytosis; pretreatment with pertussis toxin prevented this effect. Similar to forskolin, 8-bromo-cAMP elicited norepinephrine exocytosis but, unlike forskolin, it was unaffected by H(3)-receptor activation, demonstrating that inhibition of adenylyl cyclase is a pivotal step in the H(3)-receptor transductional cascade. Indeed, we found that H(3)-receptor activation attenuated norepinephrine exocytosis concomitantly with a decrease in intracellular cAMP and PKA activity in SH-SY5Y-H(3) cells. Moreover, pharmacological PKA inhibition acted synergistically with H(3)-receptor activation to reduce K(+)-induced peak intracellular Ca(2+) in SH-SY5Y-H(3) cells and norepinephrine exocytosis in cardiac synaptosomes. Furthermore, H(3)-receptor activation synergized with N- and L-type Ca(2+) channel blockers to reduce norepinephrine exocytosis in cardiac synaptosomes. Our findings suggest that the H(3)-receptor-mediated inhibition of norepinephrine exocytosis from cardiac sympathetic nerves results sequentially from H(3)-receptor-G(i)/G(o) coupling, inhibition of adenylyl cyclase activity, and decreased cAMP formation, leading to diminished PKA activity, and thus, decreased Ca(2+) influx through voltage-operated Ca(2+) channels.

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.

Muscarinic receptor-mediated phosphorylation of cyclic AMP response element binding protein in human neuroblastoma cells

This study describes the effect of signalling through muscarinic acetylcholine receptors on two transcription factors implicated in long-term synaptic plasticity and memory formation, EGR1 and the cyclic AMP response element binding protein (CREB). In SK-N-SH neuroblastoma cells, treatment with the cholinergic agonist carbachol led to maximal induction of EGR1 1 h after stimulation. This was preceded by the phosphorylation of CREB, which peaked as early as 5 minutes after carbachol treatment. The levels of both EGR1 and phosphorylated CREB (pCREB) slowly decayed over 4-8 h. CREB phosphorylation and EGR1 induction showed similar sensitivity to carbachol concentration, with EC(50) values in the range of 1-10 microM, and the changes in both transcription factors were blocked by the muscarinic antagonist atropine. As has been described elsewhere, EGR1 induction was dependent on activation of p42/44 MAP kinase, as it was blocked by the MEK inhibitor U0126. However, CREB phosphorylation by carbachol was largely unaffected by MAP kinase blockade. As both CREB phosphorylation and EGR1 induction have been linked to long-term potentiation and some forms of memory consolidation, these results may implicate CREB and EGR1 in independent or partially independent cholinergic signalling pathways involved in memory processes.

Decreased intracellular calcium mediates the histamine H3-receptor-induced attenuation of norepinephrine exocytosis from cardiac sympathetic nerve endings

Activation of presynatic histamine H(3) receptors (H(3)R) down-regulates norepinephrine exocytosis from cardiac sympathetic nerve terminals, in both normal and ischemic conditions. Analogous to the effects of alpha(2)-adrenoceptors, which also act prejunctionally to inhibit norepinephrine release, H(3)R-mediated antiexocytotic effects could result from a decreased Ca(2+) influx into nerve endings. We tested this hypothesis in sympathetic nerve terminals isolated from guinea pig heart (cardiac synaptosomes) and in a model human neuronal cell line (SH-SY5Y), which we stably transfected with human H(3)R cDNA (SH-SY5Y-H(3)). We found that reducing Ca(2+) influx in response to membrane depolarization by inhibiting N-type Ca(2+) channels with omega-conotoxin (omega-CTX) greatly attenuated the exocytosis of [(3)H]norepinephrine from both SH-SY5Y and SH-SY5Y-H(3) cells, as well as the exocytosis of endogenous norepinephrine from cardiac synaptosomes. Similar to omega-CTX, activation of H(3)R with the selective H(3)R-agonist imetit also reduced both the rise in intracellular Ca(2+) concentration (Ca(i)) and norepinephrine exocytosis in response to membrane depolarization. The selective H(3)R antagonist thioperamide prevented this effect of imetit. In the parent SH-SY5Y cells lacking H(3)R, imetit affected neither the rise in Ca(i) nor [(3)H]norepinephrine exocytosis, demonstrating that the presence of H(3)R is a prerequisite for a decrease in Ca(i) in response to imetit and that H(3)R activation modulates norepinephrine exocytosis by limiting the magnitude of the increase in Ca(i). Inasmuch as excessive norepinephrine exocytosis is a leading cause of cardiac dysfunction and arrhythmias during acute myocardial ischemia, attenuation of norepinephrine release by H(3)R agonists may offer a novel therapeutic approach to this condition.

Inhibition of depolarization-induced [3H]noradrenaline release from SH-SY5Y human neuroblastoma cells by some second-generation H(1) receptor antagonists through blockade of store-operated Ca(2+) channels (SOCs)

In the present study, the effect of the blockade of membrane calcium channels activated by intracellular Ca(2+) store depletion on basal and depolarization-induced [3H]norepinephrine ([3H]NE) release from SH-SY5Y human neuroblastoma cells was examined. The second-generation H(1) receptor blockers astemizole, terfenadine, and loratadine, as well as the first-generation compound hydroxyzine, inhibited [3H]NE release induced by high extracellular K(+) concentration ([K(+)](e)) depolarization in a concentration-dependent manner (the IC(50)s were 2.3, 1.7, 4.8, and 9.4 microM, respectively). In contrast, the more hydrophilic second-generation H(1) receptor blocker cetirizine was completely ineffective (0.1-30 microM). The inhibition of high [K(+)](e)-induced [3H]NE release by H(1) receptor blockers seems to be related to their ability to inhibit Ca(2+) channels activated by Ca(i)(2+) store depletion (SOCs). In fact, astemizole, terfenadine, loratadine, and hydroxyzine, but not cetirizine, displayed a dose-dependent inhibitory action on the increase in intracellular Ca(2+) concentrations ([Ca(2+)](i)) obtained with extracellular Ca(2+) reintroduction after Ca(i)(2+) store depletion with thapsigargin (1 microM), an inhibitor of the sarcoplasmic-endoplasmic reticulum calcium ATPase (SERCA) pump. The rank order of potency for SOC inhibition by these compounds closely correlated with their inhibitory properties on depolarization-induced [3H]NE release from SH-SY5Y human neuroblastoma cells. Nimodipine (1 microM) plus omega-conotoxin (100 nM) did not interfere with the present model for SOC activation. In addition, the inhibition of depolarization-induced [3H]NE release does not seem to be attributable to the blockade of the K(+) currents carried by the K(+) channels encoded by the human Ether-a-Gogo Related Gene (I(HERG)) by these antihistamines. In fact, whole-cell voltage-clamp experiments revealed that the IC(50) for astemizole-induced hERG blockade is about 300-fold lower than that for the inhibition of high K(+)-induced [3H]NE release. Furthermore, current-clamp experiments in SH-SY5Y cells showed that concentrations of astemizole (3 microM) which were effective in preventing depolarization-induced [3H]NE release were unable to interfere with the cell membrane potential under depolarizing conditions (100 mM [K(+)](e)), suggesting that hERG K(+) channels do not contribute to membrane potential control during exposure to elevated [K(+)](e). Collectively, the results of the present study suggest that, in SH-SY5Y human neuroblastoma cells, the inhibition of SOCs by some second-generation antihistamines can prevent depolarization-induced neurotransmitter release.

The mood stabilizer valproic acid activates mitogen-activated protein kinases and promotes neurite growth

The mood-stabilizing agents lithium and valproic acid (VPA) increase DNA binding activity and transactivation activity of AP-1 transcription factors, as well as the expression of genes regulated by AP-1, in cultured cells and brain regions involved in mood regulation. In the present study, we found that VPA activated extracellular signal-regulated kinase (ERK), a kinase known to regulate AP-1 function and utilized by neurotrophins to mediate their diverse effects, including neuronal differentiation, neuronal survival, long term neuroplasticity, and potentially learning and memory. VPA-induced activation of ERK was blocked by the mitogen-activated protein kinase/ERK kinase inhibitor PD098059 and dominant-negative Ras and Raf mutants but not by dominant-negative stress-activated protein kinase/ERK kinase and mitogen-activated protein kinase kinase 6 mutants. VPA also increased the expression of genes regulated by the ERK pathway, including growth cone-associated protein 43 and Bcl-2, promoted neurite growth and cell survival, and enhanced norepinephrine uptake and release. These data demonstrate that VPA is an ERK pathway activator and produces neurotrophic effects.

Hypoxic enhancement of evoked noradrenaline release from the human neuroblastoma SH-SY5Y

The effects of chronic hypoxia (2.5% O(2), 24 h) on [3H]noradrenaline ([3H]NA) release evoked from human neuroblastoma SH-SY5Y cells by depolarisation and by activation of muscarinic receptors was investigated. Depolarization of cells with 100 mM K(+) evoked [3H]NA release, and chronic hypoxia enhanced this release significantly. In fluorimetric studies, the K(+)-evoked rises of [Ca(2+)](i) observed in response to 100 mM K(+) were also significantly enhanced. Muscarine-evoked [3H]NA release was also dramatically enhanced by chronic hypoxia. However, muscarine-induced release of Ca(2+) from intracellular stores and subsequent capacitative Ca(2+) entry was unaffected. The protein kinase C inhibitors GF 109 203X and RO-31-8220 did not prevent the enhancement of muscarine-evoked release caused by chronic hypoxia. These findings indicate that chronic hypoxia increases release of [3H]NA from human neuroblastoma SH-SY5Y cells. Enhancement of K(+)-evoked release was attributable to an enhancement of depolarisation-mediated Ca(2+) influx. In contrast, the larger enhancement of muscarine-evoked [3H]NA release was not due to greater release of Ca(2+) from internal stores, nor due to enhanced Ca(2+) influx. Furthermore, it was not attributable to activation of protein kinase C. These findings suggest that enhancement of sympathetic output, known to occur following prolonged hypoxia, may be mediated in part by enhancement of exocytosis.

Overexpression of the myristoylated alanine-rich C kinase substrate decreases uptake and K(+)-evoked release of noradrenaline in the human neuroblastoma SH-SY5Y

The aim of this study was to investigate a possible role of the myristoylated alanine-rich C kinase substrate (MARCKS) in the mechanism of noradrenaline uptake and release in the human neuroblastoma cell line SH-SY5Y. A stable cell line showing a twofold overexpression of MARCKS was prepared by transfecting SH-SY5Y with pCEP4 containing MARCKS cDNA in the sense orientation. This cell line showed no changes in the expression of neurofilaments or markers of noradrenergic large dense-cored vesicles compared with both untransfected SH-SY5Y and SH-SY5Y transfected with pCEP4 only (mock transfected). Similarly, no differences in the rate of cell growth could be detected between these three cell lines. In contrast, specific uptake and depolarization-evoked (100 mM K(+)) release of noradrenaline from the cell line overexpressing MARCKS was inhibited by approximately 50% compared with mock-transfected SH-SY5Y. K(+)-evoked noradrenaline release enhanced by pretreatment with 12-O-tetradecanoylphorbol 13-acetate (100 nM) was also inhibited by 50%. In contrast, carbachol-evoked noradrenaline release was unaffected. Thus, in SH-SY5Y cells, overexpression of MARCKS leads to a decrease in the K(+)-evoked noradrenaline release possibly by increased actin cross-linking preventing the movement of noradrenaline containing large dense-cored vesicles to the plasma membrane in response to depolarization.

SH-SY5Y cells as a model for sigma receptor regulation of potassium-stimulated dopamine release

Previous studies in our laboratory using rat brain tissue have shown that neuropeptide Y (NPY) can enhance NMDA- and potassium-stimulated dopamine release from various brain regions and that this enhancement is reversed by sigma (sigma) receptor antagonists. In the current study, we sought to determine whether SH-SY5Y cells are suitable for investigating sigma receptor effects and whether any sigma receptors present are of the subtype responsive to NPY. We compare mechanisms by which the prototypical sigma receptor agonist (+)-pentazocine, and the proposed endogenous sigma receptor ligand NPY regulate potassium-stimulated [(3)H]dopamine release from SH-SY5Y cells. Both (+)-pentazocine and NPY inhibit potassium-stimulated [(3)H]dopamine release. Unlike our studies in rat brain tissue, the effect of NPY on [(3)H]dopamine release is not reversed by sigma receptor antagonists. SH-SY5Y cells appear to be an appropriate model to study the regulation of dopamine release by sigma receptors or by NPY receptors, but this population is not identical to that population identified in brain slices.

Sequential treatment of SH-SY5Y cells with retinoic acid and brain-derived neurotrophic factor gives rise to fully differentiated, neurotrophic factor-dependent, human neuron-like cells

A rapid and simple procedure is presented to obtain nearly pure populations of human neuron-like cells from the SH-SY5Y neuroblastoma cell line. Sequential exposure of SH-SY5Y cells to retinoic acid and brain-derived neurotrophic factor in serum-free medium yields homogeneous populations of cells with neuronal morphology, avoiding the presence of other neural crest derivatives that would normally arise from those cells. Cells are withdrawn from the cell cycle, as shown by 5-bromo-2'-deoxyuridine uptake and retinoblastoma hypophosphorylation. Cell survival is dependent on the continuous presence of brain-derived neurotrophic factor, and removal of this neurotrophin causes apoptotic cell death accompanied by an attempt to reenter the cell cycle. Differentiated cells express neuronal markers, including neurofilaments, neuron-specific enolase, and growth-associated protein-43 as well as neuronal polarity markers such as tau and microtubule-associated protein 2. Moreover, differentiated cultures do not contain glial cells, as could be evidenced after the negative staining for glial fibrillary acidic protein. In conclusion, the protocol presented herein yields homogeneous populations of human neuronal differentiated cells that present many of the characteristics of primary cultures of neurons. This model may be useful to perform large-scale biochemical and molecular studies due to its susceptibility to genetic manipulation and the availability of an unlimited amount of cells.

The Na+-Ca2+ exchange inhibitor KB-R7943 inhibits high K+-induced increases in intracellular Ca2+ concentration and [3H]noradrenaline release in the human neuroblastoma SH-SY5Y

The effects of the Na+-Ca2+ exchange inhibitor 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate (KB-R7943) on depolarization-induced Ca2+ signal and [3H]noradrenaline release were examined in SH-SY5Y cells. KB-R7943 at 10 microM significantly inhibited high K+-induced increase in intracellular Ca2+ concentration. KB-R7943 also inhibited high K+-evoked release of [3H]noradrenaline from the cells. These findings suggest that the Na+-Ca2+ exchanger in the reverse mode is involved at least partly in depolarization-induced transmitter release.

Organophosphorus compound-induced modification of SH-SY5Y human neuroblastoma mitochondrial transmembrane potential

Organophosphorus (OP) compounds inhibit mitochondrial enzymes, respiration, and ATP generation, in addition to inducing structural changes such as matrix swelling. This implicates mitochondria as primary subcellular targets for these compounds. In this study, the health and function of cellular mitochondria following OP compound exposure were assessed by evaluating the mitochondrial transmembrane potential (DeltaPsi(m)). This was done by measuring the changes in DeltaPsi(m) in SH-SY5Y human neuroblastoma cells incubated with the cationic fluorochrome, rhodamine 123 (5 microg/ml), and the OP compounds tri-ortho-tolyl phosphate (TOTP), triphenyl phosphite (TPPi), or parathion for 7.5 to 960 minutes. OP compounds (100 microM to 1 mM) induced significant concentration-dependent mitochondrial hyperpolarization with peak maxima occurring at 60 (TOTP, TPPi) or 120 (parathion) min. Following this, the mitochondrial membranes gradually depolarized. Pretreatment with cyclosporin A (500 nM, 30 h), a mitochondrial permeability transition pore (PTP) inhibitor, decreased the hyperpolarization. In contrast, 30-h pretreatment with the muscarinic receptor agonist carbachol (1 mM) significantly increased DeltaPsi(m) and delayed subsequent depolarization. Hyperpolarization and subsequent depolarization of mitochondrial membranes occurred 16 to 24 h prior to a loss of substrate adhesion or an increase in DNA fragmentation, indicating that mitochondria were a primary target in OP compound-initiated cytotoxicity.

Redistribution of F-actin and large dense-cored vesicles in the human neuroblastoma SH-SY5Y in response to secretagogues and protein kinase Calpha activation

Our previous studies have shown that noradrenaline release is enhanced by activation of protein kinase Calpha in SH-SY5Y cells. In the present study, we report that activation of protein kinase Calpha leads to (a) partial redistribution of the F-actin cytoskeleton and (b) a 2.5-fold increase in the number of large dense-cored vesicles within 100 nm of the plasma membrane. This redistribution can be prevented by down-regulation of protein kinase Calpha by up to 48 h exposure to phorbol dibutyrate. Treatment with the secretagogues 100 mM KCl, the Ca2+ ionophore A23187 (20 microM) and 1 mM carbachol also leads to a partial disassembly of the F-actin cytoskeleton. This is accompanied by an increase in the number of large dense cored vesicles at the plasma membrane following exposure to KCl and A23187 but not following exposure to carbachol. These results are discussed in relation to the hypothesis that a key step in the enhancement of noradrenaline release following activation of protein kinase Calpha and elevation of intracellular calcium is the movement of large dense cored vesicles to the plasma membrane following partial disassembly of the F-actin cytoskeleton.

The regulation of neurotransmitter secretion by protein kinase C

The effect of protein kinase C (PKC) on the release of neurotransmitters from a number preparations, including sympathetic nerve endings, brain slices, synaptosomes, and neuronally derived cell lines, is considered. A comparison is drawn between effects of activation of PKC on neurotransmitter release from small synaptic vesicles and large dense-cored vesicles. The enhancement of neurotransmitter release is discussed in relation to the effect of PKC on: 1. Rearrangement of the F-actin-based cytoskeleton, including the possible role of MARCKS in this process, to allow access of large dense-cored vesicles to release sites on the plasma membrane. 2. Phosphorylation of key components in the SNAP/SNARE complex associated with the docking and fusion of vesicles at site of secretion. 3. Ion channel activity, particularly Ca2+ channels.

Stimulation of Na+-K+-2Cl- cotransporter in neuronal cells by excitatory neurotransmitter glutamate

Na+-K+-2Cl- cotransporters are important in renal salt reabsorption and in salt secretion by epithelia. They are also essential in maintenance and regulation of ion gradients and cell volume in both epithelial and nonepithelial cells. Expression of Na+-K+-2Cl- cotransporters in brain tissues is high; however, little is known about their function and regulation in neurons. In this study, we examined regulation of the Na+-K+-2Cl- cotransporter by the excitatory neurotransmitter glutamate. The cotransporter activity in human neuroblastoma SH-SY5Y cells was assessed by bumetanide-sensitive K+ influx, and protein expression was evaluated by Western blot analysis. Glutamate was found to induce a dose- and time-dependent stimulation of Na+-K+-2Cl- cotransporter activity in SH-SY5Y cells. Moreover, both the glutamate ionotropic receptor agonist N-methyl-D-aspartic acid (NMDA) and the metabotropic receptor agonist (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (trans-ACPD) significantly stimulated the cotransport activity in these cells. NMDA-mediated stimulation of the Na+-K+-2Cl- cotransporter was abolished by the selective NMDA-receptor antagonist (+)-MK-801 hydrogen maleate. trans-ACPD-mediated effect on the cotransporter was blocked by the metabotropic receptor antagonist (+)-alpha-methyl-(4-carboxyphenyl)glycine. The results demonstrate that Na+-K+-2Cl- cotransporters in neurons are regulated by activation of both ionotropic and metabotropic glutamate receptors.

Acute effects of interleukin-1 beta on noradrenaline release from the human neuroblastoma cell line SH-SY5Y

Interleukins are potent intercellular messenger peptides, initially found in cells of the immune system and best known for producing chronic, genomic effects in target cells. Here, interleukin-1beta (IL-1beta) was tested for acute effects on neurotransmitter release. The human neuroblastoma-derived cell-line SH-SY5Y is a model for mature post-ganglionic sympathetic neurones and release of tritiated noradrenaline from these cells was measured, in response to stimulation with either elevated extracellular K+ concentration (100 K+) orveratridine. Pre-incubation for 15-25 min with 60 pM (but not 0.06 pM) IL-1beta significantly reduced 100 K+-evoked release (by approximately 75%). The interleukin was without effect on basal or veratridine-evoked noradrenaline release. The present data suggest two distinct stimulatory pathways: one that is activated by 100 K+ and veratridine and is unaffected by IL-1beta and another that is activated by 100 K+ but not veratridine and is inhibited by IL-1beta. The acute depression of 100 K+-evoked transmitter release may be involved in immune system-nervous system interactions.

Stimulatory effects of opioids on transmitter release and possible cellular mechanisms: overview and original results

Opiates and opioid peptides carry out their regulatory effects mainly by inhibiting neuronal activity. At the cellular level, opioids block voltage-dependent calcium channels, activate potassium channels and inhibit adenylate cyclase, thus reducing neurotransmitter release. An increasing body of evidence indicates an additional opposite, stimulatory activity of opioids. The present review summarizes the potentiating effects of opioids on transmitter release and the possible cellular events underlying this potentiation: elevation of cytosolic calcium level (by either activating Ca2+ influx or mobilizing intracellular stores), blockage of K+ channels and stimulation of adenylate cyclase. Biochemical, pharmacological and molecular biology studies suggest several molecular mechanisms of the bimodal activity of opioids, including the coupling of opioid receptors to various GTP-binding proteins, the involvement of different subunits of these proteins, and the activation of several intracellular signal transduction pathways. Among the many experimental preparations used to study the bimodal opioid activity, the SK-N-SH neuroblastoma cell line is presented here as a suitable model for studying the complete chain of events leading from binding to receptors down to regulation of transmitter release, and for elucidating the molecular mechanism involved in the stimulatory effects of opioid agonists.

Ionomycin induced changes in intracellular free calcium in SH-SY5Y human neuroblastoma cells: sources of calcium and effects on [3H]-noradrenaline release

In adherent SH-SY5Y human neuroblastoma cells cultured for 14 days to promote uptake and release of [3H]-noradrenaline, ionomycin induced a biphasic elevation of the intracellular [Ca2+] ([Ca2+]i). This consisted of a rapid transient elevation followed by a marked, persistent secondary elevation. Further study indicated that the peak [Ca2+]i elevation was dependent upon intracellular Ca2+ whilst the secondary elevation was dependent upon extracellular Ca2+. This profile of response and dependence upon intracellular and extracellular sources of Ca2+ was similar to that evoked by the muscarinic agonist, methacholine but was independent of inositol 1,4,5-trisphosphate generation. Ionomycin also stimulated the release of [3H]-noradrenaline from preloaded cells. Both intracellular and extracellular sources of Ca2+ were needed for the full response and synergised to effect release. Thus, in adherent SH-SY5Y cells, ionomycin elevates [Ca2+]i in a complex way in a manner partly analogous to the elevation of [Ca2+]i by agonists of phosphoinositidase C-linked receptors. Furthermore the effects of [Ca2+]i elevation on [3H]-noradrenaline release by these two processes are similar. Such functional consequences may, however, differ under circumstances where the profile and source of Ca2+ for ionomycin-mediated changes differs to that of receptor agonists.

Effects of propofol and thiopentone on potassium- and carbachol-evoked [3H]noradrenaline release and increased [Ca2+]i from SH-SY5Y human neuroblastoma cells

We have examined the effects of two intravenous anaesthetic induction agents, propofol and thiopentone, on K+ and carbachol evoked [3H]noradrenaline release from a human neuroblastoma cell line, SH-SY5Y. In this model, we have previously demonstrated that K+ evoked [3H]noradrenaline release was dependent on Ca2+ entry and carbachol evoked release was extracellular Ca(2+)- independent. Propofol inhibited K+ (100 mM)-evoked (IC50 of 42 +/- 11 microM), but not carbachol (1 mM)-evoked, [3H]noradrenaline release. Thiopentone inhibited both K+- and carbachol-evoked release with IC50 values of 116 +/- 15 microM and 169 +/- 39 microM, respectively. These inhibitory effects were not due to changes in the release dynamics, as assessed using perfused cells. Furthermore, thiopentone inhibition of carbachol-evoked release was not due to muscarinic receptor antagonism. Both propofol and thiopentone caused noncompetitive inhibition of K+-stimulated Ca2+ influx, with IC50 values of 127 +/- 7 microM and 121 +/- 10 microM, respectively. These effects were not due to interaction with GABAA receptors, but suggest that both compounds block voltage-sensitive Ca2+ channels. Thiopentone, but not propofol, inhibited carbachol-stimulated increased intracellular Ca2+ concentrations in the presence and absence of extracellular Ca2+. However, thiopentone had no effect on carbachol-stimulated inositol (1,4,5)-triphosphate formation, suggesting that thiopentone may directly inhibit Ca2+ release from intracellular stores.

Inhibition of Ca2+ channel currents in human neuroblastoma (SH-SY5Y) cells by neuropeptide Y and a novel cyclic neuropeptide Y analogue

Whole-cell Ca2+ channel currents were recorded in human neuroblastoma (SH-SY5Y) cells, using conventional and perforated-patch techniques. Neuropeptide Y (NPY, 10-1000 nM) caused concentration-dependent inhibition of Ca2+ channel current amplitudes which was pertussis toxin-sensitive, voltage-dependent and associated with slowing of channel activation kinetics, regardless of which recording configuration was used. Inhibition was observed in all cells tested. Similar current inhibitions were observed with NPY (18-36) and peptide YY, but not with [Leu31, Pro34]NPY, indicating that the effects were mediated by Y2 receptors. Pancreatic polypeptide (100 nM) was without effect on Ca2+ channel currents. The effects of NPY were additive with nifedipine (at a supramaximal concentration of 5 microM), suggesting that NPY predominantly inhibits N-type Ca2+ channels present in these cells, and not L-type. The effects of NPY were mimicked by a novel, cyclic analogue of NPY which is 40-fold more selective for Y2 receptors than other commonly used Y2-selective peptides. The cyclic analogue was also more potent than NPY itself, causing maximal current inhibition at approx 300 nM, whereas the response to NPY was not fully saturated at 1 microM. Our results indicate that SH-SY5Y cells represent an excellent model system for studying the coupling of Y2 receptors to N-type channel inhibition. Furthermore, in the absence of selective antagonists for NPY receptor subtypes, the highly selective Y2 agonist cyclic NPY derivative may prove a useful tool for probing the various roles of Y2 receptors in the nervous system.

The effect of the angiotensin II (AT1A) receptor stably transfected into human neuroblastoma SH-SY5Y cells on noradrenaline release and changes in intracellular calcium

A stable cell line expressing the angiotensin II (AII) receptor has been obtained by transfecting the human neuroblastoma SH-SY5Y with the plasmid pCEP4 containing the entire coding region of the rat angiotensin AII receptor AT1A. Angiotensin II (AII; 1-100 nM) evokes the release of [3H]noradrenaline ([3H]NA) in this cell line. Pretreatment with 100 nM 12-O-tetradecanoylphorbol-13-acetate (TPA) enhances the AII-evoked release of [3H]NA approximately two-fold. Removal of extracellular Ca2+ ([Ca2+]o) decreases 100 nM AII-evoked release of [3H]NA by over 50% both in the presence and absence of TPA. AII increases intracellular Ca2+ ([Ca2+]i) in this cell line which is consistent with the AT1A receptor being coupled to phospholipase C. Pretreatment with 100 nM TPA for 8 min attenuated the effect of AII on [Ca2+]i. The effects of AT1A receptor stimulation are therefore regulated differently in this cell line by activation of protein kinase C (PKC). Thus a useful cell line has been obtained from the human neuroblastoma SH-SY5Y in which to study at the molecular level the mechanism(s) by which AII regulates NA release.

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.

The effect of barium on [3H]noradrenalin release from the human neuroblastoma SH-SY5Y

Replacement of Ca2+ with Ba2+ in HEPES-buffered saline stimulated [3H]noradrenalin release in the human neuroblastoma clone SH-SY5Y by up to 20% of the cell content in the absence of other secretory stimuli. The Ba(2+)-evoked release was inhibited by 85% by 3 microM tetrodotoxin and 95% by 5 microM nifedipine. Ba2+ also increased the potency of K(+)-evoked release of [3H]noradrenalin, as maximal release was observed with 60 mM K+ compared with the 100 mM K+ necessary to achieve maximal release in the presence of Ca2+. In contrast, replacing Ca2+ with Ba2+ had little effect on carbachol- and bradykinin-evoked release of [3H]noradrenalin. No evidence was obtained from studies on changes in [Ca2+]i (in response to 100 microM carbachol) using fura-2 that Ba2+ could enter intracellular stores in SH-SY5Y cells. Whole-cell patch-clamp studies showed that Ba2+ depolarizes SH-SY5Y cells as well as enhancing inward Ca2+ channel currents and shifting their voltage dependence to more negative values. These results are discussed in terms of the hypothesis that Ba2+ blocks K+ channels, leading to depolarization followed by opening of voltage-sensitive Na+ channels. This in turn opens voltage-sensitive L-type Ca2+ channels, which are coupled to the release of [3H]noradrenalin in SH-SY5Y cells.

Enhancement of Ca2+ channel currents in human neuroblastoma (SH-SY5Y) cells by phorbol esters with and without activation of protein kinase C

The effects of phorbol esters on Ca2+ channel currents in human neuroblastoma SH-SY5Y cells were studied using whole-cell patch-clamp recordings. Bath application of 12-O-tetradecanoylphorbol-13-acetate (TPA) or phorbol 12,13-dibutyrate (PDBu; 100 nM to 1 microM), known activators of protein kinase C (PKC), enhanced Ca2+ channel currents in a voltage-dependent manner similar to that of Bay K 8644. TPA also enhanced Ca2+ channel currents during cell dialysis with the PKC pseudosubstrate, PKC(19-36), and in cells which had been pre-incubated with 500 nM staurosporine, and which were exposed to staurosporine during recordings. Application of 4 alpha-phorbol-12,13-didecanoate (4 alpha-PDD; 100 nM), which does not activate PKC, caused current enhancement similar to the effects of TPA. However, intracellular dialysis of TPA was without effect on Ca2+ channel currents. Residual Ca2+ channel currents recorded after exposure to 1 microM omega-conotoxin GVIA were still enhanced by TPA, but in the presence of either Bay K 8644 (5 microM) or nifedipine (5 microM), TPA was without effect. When cells were pre-incubated for 10 min at 37 degrees C with 100 nM TPA, currents subsequently recorded in its absence were enhanced as compared to untreated cells; 5 microM nifedipine still inhibited currents to the same degree. This enhancement was not mimicked by 4 alpha-PDD, and was inhibited by staurosporine. Our results indicate that acute applications of phorbol esters (at concentrations commonly used to activate PKC) enhance L-type Ca2+ channel currents in SH-SY5Y cells via a PKC-independent mechanism which appears similar to that induced by Bay K 8644. By contrast, pre-incubation with TPA enhances both L- and N-type currents via activation of PKC.

Muscarinic (M1) receptor-mediated inhibition of K(+)-evoked [3H]-noradrenaline release from human neuroblastoma (SH-SY5Y) cells via inhibition of L- and N-type Ca2+ channels

1. Human neuroblastoma (SH-SY5Y) cells were preincubated with [3H]-noradrenaline ([3H]-NA) in the presence of 0.2 mM pargyline to examine the modulation of K(+)-evoked [3H]-NA release by muscarinic agonists. 2. Release of [3H]-NA evoked by 4 min exposure to 100 mM K+ could be partially inhibited by 5 microM nifedipine and partially inhibited by 100 nM omega-conotoxin GVIA (omega-CgTx). When nifedipine and omega-CgTx were added together, evoked release was inhibited by approximately 93%. 3. K(+)-evoked [3H]-NA release was inhibited by > 90% by pretreatment of cells for 2 min with muscarine, carbachol or oxotremorine methiodide (each at 300 microM). For muscarine, inhibition of evoked release was both time- and concentration-dependent and was reversible. Muscarine also inhibited [3H]-NA release evoked by veratridine (28 microM) and replacement of extracellular Ca2+ with Ba2+, but not that evoked by the Ca2+ ionophore, A23187 (19 microM). 4. Residual K(+)-evoked [3H]-NA release measured in the presence of either nifedipine (5 microM) or omega-CgTx (100 nM) was inhibited by muscarine with a similar potency as release evoked in the absence of either Ca2+ channel blocker. Pretreatment of cells for 16-24 h with pertussis toxin (200 ng ml-1) did not affect K(+)-evoked release per se or the ability of muscarine to inhibit such release. 5. Muscarinic inhibition of K(+)-evoked [3H]-NA release was potently antagonized by pirenzepine (pA2 8.14) and by hexahydrosiladiphenidol (pA2 9.03), suggesting the involvement of an M1 receptor. 6. Our results demonstrate that 100 mM K+-evoked release of [3H]-NA from the human neuroblastoma is mediated by activation of both L- and N-type Ca2+ channels. Activation of muscarinic Ml receptors can inhibit release via a pertussis toxin-insensitive mechanism which involves non-selective inhibition of L- and N-type Ca2+ channels.

Bradykinin-evoked release of [3H]noradrenaline from the human neuroblastoma SH-SY5Y

Bradykinin (BK) evoked [3H]noradrenaline ([3H]NA) release from the human neuroblastoma SH-SY5Y and this was enhanced by pre-treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) for 8 min. This effect of BK was inhibited by 500 microM [D-Phe7]BK and 100 microM [Thi5,8,D-Phe7]BK but not by 500 microM [Des-Arg9,Leu8]BK. The BK (B1)-agonist [Des-Arg9]BK did not evoke [3H]NA release. This suggested that SH-SY5Y expressed BK (B2)-receptors coupled to the release of [3H]NA. BK acting at B2-receptors, also elevated intracellular calcium and depolarized SH-SY5Y cells. Although pre-treatment of SH-SY5Y cells with TPA enhanced BK-evoked [3H]NA release, the elevation of intracellular calcium [Ca2+]; was decreased by about 50%. BK-evoked release of [3H]NA in cells not pre-treated with phorbol ester was only 23% dependent on extracellular calcium. In comparison, following phorbol ester treatment approximately 40% of [3H]NA release was dependent on extracellular calcium. Nifedipine (5 microM), CoCl2 (1 mM) and NiCl2 (1 mM) inhibited NA release in SH-SY5Y cells pre-treated with TPA by 16.0, 47 and 44%, respectively. The results of this study showed that BK, acting at B2-receptors, activated [3H]NA release in SH-SY5Y. Part of this effect appeared to be due to activation of L-type calcium channels but the majority of BK-evoked [3H]NA release in SH-SY5Y cells appeared to depend on [Ca2+]i.

Calcium channel currents in undifferentiated human neuroblastoma (SH-SY5Y) cells: actions and possible interactions of dihydropyridines and omega-conotoxin

Ca2+ channel currents were recorded in undifferentiated human neuroblastoma (SH-SY5Y) cells with the whole-cell patch-clamp technique, using 10 mM Ba2+ as charge carrier. Currents were only evoked by depolarizations to -30 mV or more positive (holding potential -80 mV), inactivated partially during 200 ms depolarizing steps, and were abolished by 150 microM Cd2+. Currents could be enhanced by Bay K-8644 and partially inhibited by nifedipine, suggesting that they arose in part due to activation of L-type Ca2+ channels. Currents were also inhibited by the marine snail peptide omega-conotoxin GVIA (omega-CgTx). At a concentration of 10 nM inhibition by omega-CgTx was reversible, but at higher concentrations blockade was always irreversible. Although current inhibition by nifedipine was maximal at 1 microM, supramaximal concentrations reduced the inhibitory actions of omega-CgTx in a concentration-dependent manner. Ca2+ channel currents evoked from a holding potential of -50 mV showed no inactivation during 200 ms depolarizations but declined in amplitude with successive depolarizing steps (0.2 Hz). Current amplitudes could be restored by returning the holding potential to -80 mV. Currents evoked from -50 mV were inhibited by nifedipine and omega-CgTx to a similar degree as those evoked from -80 mV. Our results indicate that undifferentiated SH-SY5Y cells possess L- and N-type Ca2+ channels which can be distinguished pharmacologically but cannot be separated by using depolarized holding potentials. Furthermore, these data suggest that nifedipine has a novel action to inhibit blockade of N-type channels by omega-CgTx.

Dual regulation by opioids of 3H-norepinephrine release in the human neuroblastoma cell-line SK-N-SH

Depolarization-evoked 3H-norepinephrine release from SK-N-SH cells was found to be regulated by opioid ligands. Opioids exerted either inhibition or augmentation of 3H-norepinephrine release. Both effects were mediated by opioid receptors. In addition, a nonopioid inhibitory effect of opiates on release was observed. The SK-N-SH cell-line provides a suitable model for studying the various mechanisms underlying the opioid regulatory pathways within single cells.

Studies on the mechanism of [3H]-noradrenaline release from SH-SY5Y cells: the role of Ca2+ and cyclic AMP

1. The roles of both Ca2+ and adenosine 3':5'-cyclic monophosphate (cyclic AMP) in carbachol and K(+)-stimulated [3H]-noradrenaline release from SH-SY5Y human neuroblastoma cells were examined. 2. Both carbachol and K+ caused a time- and dose-related stimulation of [3H]-noradrenaline release. The release event in perfused cells was monophasic. Half-maximum stimulation measured in statically incubated (3 min) cells was 38 +/- 4 microM and 63 +/- 4 mM respectively. K+ (100 mM, added)-evoked release was greater than that produced by carbachol (1 mM). 3. Both carbachol and K+ caused a time- and dose (measured at 3 min)-related stimulation of cyclic AMP formation with half-maximum stimulation occurring at 5 +/- 1 microM and 49 +/- 2 mM respectively. In contrast to its effects on release, carbachol produced a greater stimulation of cyclic AMP formation than K+. 4. K(+)-stimulated [3H]-noradrenaline release was entirely dependent on Ca2+ entry as 2.5 mM Ni2+ abolished release. However, carbachol-evoked (1 mM) release appeared to be unaffected by Ni2+ pretreatment. 5. These data suggest that in SH-SY5Y cells, elevated cyclic AMP levels are not directly involved in [3H]-noradrenaline release. In addition, carbachol-stimulated release is largely independent of extracellular Ca2+ possibly implying a role for intracellular stored Ca2+ in the release process.

A role for protein kinase C subtypes alpha and epsilon in phorbol-ester-enhanced K(+)- and carbachol-evoked noradrenaline release from the human neuroblastoma SH-SY5Y

Protein kinase C (PKC) consists of a family of closely related subtypes which differ in their localization and activation properties. Our previous studies have suggested a role for PKC in the regulation of noradrenaline (NA) release from the human neuroblastoma SH-SY5Y. Here we have used two approaches to characterize the PKC subtypes present in SH-SY5Y cells. Firstly, the PCR was used to show that SH-SY5Y cells contain mRNA encoding PKC subtypes alpha, beta, gamma, delta, epsilon and zeta. Secondly, immunoblotting showed that SH-SY5Y cells express PKC subtypes alpha, epsilon and zeta at the protein level. Prolonged (48 h) exposure of cells to the phorbol ester phorbol 12-myristate 13-acetate (PMA; 100 nM) resulted in a marked decrease in the amounts of PKC-alpha and PKC-epsilon, with no change in levels of PKC-zeta. Prolonged PMA treatment had no significant effect on K(+)-evoked NA release from SH-SY5Y cells, whereas carbachol-evoked release was increased 2.2-fold. However, prolonged exposure to PMA completely inhibited the ability of acute (12 min) PMA treatment to enhance both K(+)- and carbachol-evoked NA release. The specific PKC inhibitor RO 31-7459 (10 microM) was found to inhibit K(+)- and carbachol-evoked release by 27% and 68% respectively. RO 31-7549 also completely inhibited the ability of acute PMA treatment to enhance release. These data suggest that PKC-alpha and/or PKC-epsilon play an essential role in the regulation of PMA-enhanced K(+)- and carbachol-evoked NA release in SH-SY5Y cells.

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.