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

Acid-sensing ion channels contribute to the increase in vesicular release from SH-SY5Y cells stimulated by extracellular protons

Acid-sensing ion channels (ASICs) have been reported to play a role in the neuronal dopamine pathway, but the exact role in neurotransmitter release remains elusive. Human neuroblastoma SH-SY5Y is a dopaminergic neuronal cell line, which can release monoamine neurotransmitters. In this study, the expression of ASICs was identified in SH-SY5Y cells to further explore the role of ASICs in vesicular release stimulated by acid. We gathered evidence that ASICs could be detected in SH-SY5Y cells. In whole cell patch-clamp recording, a rapid decrease in extracellular pH evoked inward currents, which were reversibly inhibited by 100 μM amiloride. The currents were pH dependent, with a pH of half-maximal activation (pH(0.5)) of 6.01 ± 0.04. Furthermore, in calcium imaging and FM 1-43 dye labeling, it was shown that extracellular protons increased intracellular calcium levels and vesicular release in SH-SY5Y cells, which was attenuated by PcTx1 and amiloride. Interestingly, N-type calcium channel blockers inhibited the vesicular release induced by acidification. In conclusion, ASICs are functionally expressed in SH-SY5Y cells and involved in vesicular release stimulated by acidification. N-type calcium channels may be involved in the increase in vesicular release induced by acid. Our results provide a preliminary study on ASICs in SH-SY5Y cells and neurotransmitter release, which helps to further investigate the relationship between ASICs and dopaminergic neurons.

Amyloid-beta-induced ion flux in artificial lipid bilayers and neuronal cells: resolving a controversy

Understanding the pathogenicity of amyloid-beta (Abeta) peptides constitutes a major goal in research on Alzheimer's disease (AD). One hypothesis entails that Abeta peptides induce uncontrolled, neurotoxic ion flux through cellular membranes. The exact biophysical mechanism of this ion flux is, however, a subject of an ongoing controversy which has attenuated progress toward understanding the importance of Abeta-induced ion flux in AD. The work presented here addresses two prevalent controversies regarding the nature of transmembrane ion flux induced by Alphabeta peptides. First, the results clarify that Alphabeta can induce stepwise ion flux across planar lipid bilayers as opposed to a gradual increase in transmembrane current; they show that the previously reported gradual thinning of membranes with concomitant increase in transmembrane current arises from residues of the solvent hexafluoroisopropanol, which is commonly used for the preparation of amyloid samples. Second, the results provide additional evidence suggesting that Abeta peptides can induce ion channel-like ion flux in cellular membranes that is independent from the postulated ability of Alphabeta to modulate intrinsic cellular ion channels or transporter proteins.

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.

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.

Inhibition of depolarisation-evoked [(3)H]noradrenaline release from SH-SYFY human neuroblastoma cells by muscarinic (M1) receptors is not mediated by changes in [Ca(2+)]

The aim of this study was to obtain further understanding of the mechanism by which activation of muscarinic M(1) receptors inhibits K(+)-evoked noradrenaline (NA) release in the human neuroblastoma SH-SY5Y. Previous studies have found that muscarinic M(1) and M(3) receptors couple to the activation of phospholipase C in SH-SY5Y cells leading to an increase in (a) intracellular calcium ([Ca(2+)](i)) and (b) activation of protein kinase C (PKC). This study used specific inhibitors of PKC and conditions which deplete Ca(2+)(i) stores to examine the role of protein kinase C and changes in [Ca(2+)](i) in mediating the inhibition of K(+)-evoked NA release by muscarine. Our data show that pretreatment of SH-SY5Y cell layers with bisindolylmaleimide I (BIM-I) (i) failed to reverse inhibition of K(+)-evoked NA release by muscarine but (ii) did overcome the attenuation of muscarine inhibition following pretreatment with TPA. Furthermore pretreating cell layers with Ca(2+)-free Hepes buffered saline in the presence of thapsigargin, conditions which prevented muscarine induced increases in [Ca(2+)](i), failed to prevent inhibition of K(+)-evoked NA release by muscarine. The effect of muscarine on K(+)-evoked uptake of Ca(2+)(e) was examined in SH-SY5Y cells loaded with Fura-2. Muscarine inhibited Ca(2+)(e)-uptake by decreasing the rate at which Ca(2+) entered SH-SY5Y cells via voltage sensitive Ca(2+)-channels. Thus this study shows that muscarine inhibits depolarisation-evoked NA release by a mechanism which is not dependent on activation of PKC or release of Ca(2+) from internal stores.

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.

An investigation of noradrenaline uptake and release by the CATH.a cell line

The cell bodies of ascending noradrenergic neurons in the brain are located predominantly in the locus coeruleus. An in vitro model of locus coeruleus neurons could prove to be a useful tool in the investigation of noradrenergic neural networks and their associated pathophysiologies. The CATH.a cell line demonstrates some of the properties expected of locus coeruleus neurons, and the present study investigated the neurotransmitter uptake and release properties of the CATH.a cells. It was surprising that the CATH.a cells failed to accumulate [3H]noradrenaline ([3H]NA), suggesting the lack of a functional NA transporter. RT-PCR supported this finding by demonstrating the absence of NA transporter mRNA. Treatment of CATH.a cells with various differentiating agents failed to increase the [3H]NA uptake. Endogenous NA release was studied using HPLC detection, which revealed a lack of depolarisation-induced increases in endogenous NA release. A human NA transporter-transfected CATH.a cell line was generated (termed RUNT), and a study of the [3H]NA uptake revealed that the RUNT cells displayed significant uptake that could be blocked by cocaine (10 microM). Furthermore, the uptake capacity could be dramatically increased by differentiation of the cells with dibutyryl cyclic AMP (1 mM) for 24 h. Using dibutyryl cyclic AMP-differentiated RUNT cells, high K+ concentrations (50 mM) significantly increased [3H]NA release above basal levels.

Competition between Li+ and Mg2+ in neuroblastoma SH-SY5Y cells: a fluorescence and 31P NMR study

Because Mg2+ and Li+ ions have similar chemical properties, we have hypothesized that Li+/Mg2+ competition for Mg2+ binding sites is the molecular basis for the therapeutic action of lithium in manic-depressive illness. By fluorescence spectroscopy with furaptra-loaded cells, the free intracellular Mg2+ concentration within the intact neuroblastoma cells was found to increase from 0. 39 +/- 0.04 mM to 0.60 +/- 0.04 mM during a 40-min Li+ incubation in which the total intracellular Li+ concentration increased from 0 to 5.5 mM. Our fluorescence microscopy observations of Li+-free and Li+-loaded cells also indicate an increase in free Mg2+ concentration upon Li+ incubation. By 31P NMR, the free intracellular Mg2+ concentrations for Li+-free cells was 0.35 +/- 0. 03 mM and 0.80 +/- 0.04 mM for Li+-loaded cells (final total intracellular Li+ concentration of 16 mM). If a Li+/Mg2+ competition mechanism is present in neuroblastoma cells, an increase in the total intracellular Li+ concentration is expected to result in an increase in the free intracellular Mg2+ concentration, because Li+ displaces Mg2+ from its binding sites within the nerve cell. The fluorescence spectroscopy, fluorescence microscopy, and 31P NMR spectroscopy studies presented here have shown this to be the case.

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.

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.

A comparative study of L-type voltage sensitive Ca2+ channels in rat brain regions and cultured neuronal cells

Radioligand binding studies using the L-type voltage sensitive Ca2+ channel (VSCC) antagonist (+)-[3H]PN200-110 revealed the following rank order channel density in rat brain and cultured neuronal cell homogenates: striatum > or = cerebrocortex > > cerebellum = brainstem > SH-SY5Y cell line > NG108-15 cell line > 1321N1 cell line > PC12 cell line. There were no significant differences in the equilibrium dissociation constant, Kd for (+)-[3H]PN200-110 or pK50 for nifedipine. K+ depolarization in SH-SY5Y cells and NG108-15 cells evoked a biphasic and monophasic increase in [Ca2+]i. The L-type Ca2+ channel antagonist nifedipine (1 microM) produced a 66 and 87% inhibition of the K(+)-evoked rise in the peak and plateau phase [Ca2+]i in SH-SY5Y cells and abolished the monophasic response in NG108-15 cells. The L-channel activator S(-)Bay K 8644 (1 microM) enhanced the K(+)-evoked increase in [Ca2+]i in both cell lines. These data demonstrate a comparatively low density of L-VSCC in undifferentiated SH-SY5Y cells, NG108-15 cells, 1321N1 cells and PC12 cells that are functionally active in at least SH-SY5Y cells and NG108-15 cells.

Microsphere embolism-induced changes in presynaptic function of the cerebral cortex in rats

The present study was undertaken to elucidate pathophysiological changes in the cortical presynaptic function, K(+)-stimulated calcium influx, noradrenaline release and noradrenaline uptake, on the 1st and 3rd days after microsphere embolism in rats. Voltage-dependent calcium channels were characterized pharmacologically using three types of calcium channel blockers, L-type (nifedipine and diltiazem), N-type (omega-conotoxin GVIA), and P-type channel (omega-agatoxin IVA) blockers. K(+)-stimulated calcium influx of the normal rat synaptosome was inhibited by 100 nM omega-agatoxin IVA, but not by 10 microM nifedipine, 10 microM diltiazem and 100 nM omega-conotoxin GVIA. Calcium influx of the cortical nerve terminals of the right hemisphere was decreased on the 1st and 3rd days after the embolism. Noradrenaline release and uptake were also decreased on the 1st and 3rd days after the embolism. However, the percent release of noradrenaline was not altered. The results suggest that P-type channels are predominant in the cerebrocortical nerve terminals in rats and that calcium influx, noradrenaline release and uptake in the cerebrocortical nerve terminals are decreased by microsphere embolism. The decrease in noradrenaline release may be mainly due to a reduction in the activity of noradrenaline uptake in cerebrocortical nerve terminals of the microsphere-embolized rat.

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 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.

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.