Neuroblastoma-glioma Hybrid Cells Research Articles

Docosahexaenoic Acid Increases Vesicular Glutamate Transporter 2 Protein Levels in Differentiated NG108-15 Cells.

Docosahexaenoic acid (DHA; 22:6n-3), which is enriched in the neuronal membrane, plays a variety of roles in the brain. Vesicular glutamate transporters (VGLUTs) are responsible for incorporating glutamine into synaptic vesicles. We investigated the influence of DHA on the fatty acid profile and the levels of VGLUT1 and VGLUT2 proteins in differentiated NG108-15 cells, a neuroblastoma-glioma hybrid cell line. NG108-15 cells were plated and 24 h later the medium was replaced with Dulbecco's modified Eagle's medium supplemented with 1% fetal bovine serum, 0.2 mM dibutyryl cAMP, and 100 nM dexamethasone, which was added to induce differentiation. After 6 d, the amount of DHA in the cells was increased by addition of DHA to the medium. VGLUT2 levels were increased by the addition of DHA. These data indicate that DHA affected the levels of VGLUT2 in NG108-15 cells under differentiation-promoting conditions, suggesting that DHA affects brain functions involving VGLUT2.

Picosecond and Terahertz Perturbation of Interfacial Water and Electropermeabilization of Biological Membranes.

Non-thermal probing and stimulation with subnanosecond electric pulses and terahertz electromagnetic radiation may lead to new, minimally invasive diagnostic and therapeutic procedures and to methods for remote monitoring and analysis of biological systems, including plants, animals, and humans. To effectively engineer these still-emerging tools, we need an understanding of the biophysical mechanisms underlying the responses that have been reported to these novel stimuli. We show here that subnanosecond (≤500 ps) electric pulses induce action potentials in neurons and cause calcium transients in neuroblastoma-glioma hybrid cells, and we report complementary molecular dynamics simulations of phospholipid bilayers in electric fields in which membrane permeabilization occurs in less than 1 ns. Water dipoles in the interior of these model membranes respond in less than 1 ps to permeabilizing electric potentials by aligning in the direction of the field, and they re-orient at terahertz frequencies to field reversals. The mechanism for subnanosecond lipid electropore formation is similar to that observed on longer time scales-energy-minimizing intrusions of interfacial water into the membrane interior and subsequent reorganization of the bilayer into hydrophilic, conductive structures.

Abstract B01: Phosphorylation of pro-oncogenic c-Src at serine-17 by protein kinase G-Iα promotes chemoresistance/cell proliferation in human non-small cell lung cancer cells.

Abstract We previously showed that PKG-Iα promotes cell survival in neural cells (N1E-115 neuroblastoma and NG108-15 neuroblastoma-glioma hybrid cells) and significantly contributes to serine-155 phosphorylation of BAD, an apoptosis-regulating protein (Johlfs and Fiscus 2010). We also found, by using both gene knockdown and pharmacological inhibitors (ODQ, DT-2 and DT-3) to decrease PKG-Iα kinase activity, that PKG-Iα promotes cell proliferation and chemoresistance in human ovarian cancer cells, involving a novel interaction between PKG-Iα and the oncogenic protein c-Src (Fiscus et al 2012, Leung et al 2010). PKG-Iα activity was dependent on c-Src-catalyzed tyrosine phosphorylation of PKG-Iα; and, reciprocally, c-Src activation was dependent on expression and kinase activity of PKG-Iα;. We hypothesized that activation of c-Src involves PKG-Iα-catalyzed phosphorylation at serine-17 of c-Src, because amino acids around serine-17 provide consensus sequence for PKG-I, and tαhat this plays an important role in proliferation and chemoresistance. As c-Src has been proposed to promote cell proliferation and chemoresistance in NSCLC cells, the present study aimed to: 1) determine if c-Src increases PKG-Iα kinase activity in NSCLC cells using our newly-developed near-infrared-fluorescence (NIRF)-kinase assay, 2) determine if serine-17-phosphorylation of c-Src, in intact cancer cells, is dependent on PKG-Iα expression and kinase activity (using siRNA gene knockdown and pharmacological inhibitors), and 3) determine if inhibition/knockdown of c-Src and PKG-Iα alters chemoresistance and proliferation of NSCLC cells. Protein expression of c-Src and PKG-Iα was determined by conventional Western blot analysis and new ultrasensitive capillary-electrophoresis-based NanoPro100/1000 (ProteinSimple, Santa Clara, CA, USA). NanoPro100/1000 allows clear separation and identification of different c-Src and PKG-Iαphospho-forms (a novel way of identifying the activation of c-Src and PKG-Iα). We found PKG-Iα was able to directly catalyze phosphorylation of serine-17 of c-Src, increasing autophosphorylation of c-Src at tyrosine-419, the activation site of c-Src. Inhibition of PKG-Iα kinase activity using DT-2 or silencing of PKG-Iα expression using siRNA dramatically reduced the intracellular phosphorylation of c-Src at serine-17. Both kinase-activity inhibition and knockdown of PKG-Iα caused significant increases in apoptosis, synergistically enhancing apoptosis induced by the chemotherapeutic agent cisplatin, and dramatically decreased cell proliferation/colony formation in NSCLC cells. This novel reciprocal relationship between c-Src and PKG-Iα provides a new target for the development of new anti-cancer therapeutic agents. Fiscus RR, Leung EL, Wong JC, Johlfs MG (2012). Nitric oxide/protein kinase G-Ialpha promote c-Src activation, proliferation and chemoresistance in ovarian cancer. In: Farghaly S (ed). Ovarian Cancer - Basic Science Perspective. Intech Open Access Publisher. pp 315-334. Johlfs MG, Fiscus RR (2010). Protein kinase G type-Ialpha phosphorylates the apoptosis-regulating protein Bad at serine 155 and protects against apoptosis in N1E-115 cells. Neurochem Int 56: 546-553. Leung EL, Wong JC, Johlfs MG, Tsang BK, Fiscus RR (2010). Protein kinase G type Ialpha activity in human ovarian cancer cells significantly contributes to enhanced Src activation and DNA synthesis/cell proliferation. Mol Cancer Res 8: 578-591. Citation Format: Mary G. Johlfs, Ronald R. Fiscus, Priyatham Gorjala, Renee Coffman, Harry Rosenberg. Phosphorylation of pro-oncogenic c-Src at serine-17 by protein kinase G-Iα promotes chemoresistance/cell proliferation in human non-small cell lung cancer cells. [abstract]. In: Proceedings of the AACR-IASLC Joint Conference on Molecular Origins of Lung Cancer; 2014 Jan 6-9; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2014;20(2Suppl):Abstract nr B01.

Protein kinase G type-I phosphorylates c-Src at serine-17 and promotes cell survival, proliferation and attachment in human mesothelioma and non-small cell lung cancer cells

Background Previously, we demonstrated that protein kinase G type-Ia (PKG-Ia) plays an important role in promoting cell survival in neural cells (N1E-115 neuroblastoma and NG10815 neuroblastoma-glioma hybrid cells) and significantly contributes to the serine-155 phosphorylation of BAD, an apoptosis-regulating protein [1]. We also found that PKGIa promotes cell survival and proliferation in mouse OP9 bone marrow stromal cells [2] and human ovarian cancer cells [3] [determined by using both pharmacological inhibitors (ODQ, DT-2 and DT-3) and gene knockdown (siRNA) to reduce PKG-Ia/b activity]. In the case of ovarian cancer cells, which predominantly express the PKG-Ia isoform, the pro-growth and pro-survival effects involved a novel interaction between PKG-Ia and the oncogenic protein c-Src [3]. For example, intracellular activation of PKG-Ia, assessed by VASP serine-239 phosphorylation, was dependent on c-Src-catalyzed tyrosine phosphorylation of PKG-Ia (i.e. VASP phosphorylation was blocked by Src inhibitors, SKI-1 or SU6656) and the intracellular activation of c-Src was (somehow) dependent on the kinase activity and expression levels of PKG-Ia (i.e. c-Src activation was decreased by DT-2 or siRNA-induced knockdown of PKG-Ia).

Changes in the regulation of heat shock gene expression in neuronal cell differentiation

Neuronal differentiation of the NG108-15 neuroblastoma-glioma hybrid cells is accompanied by a marked attenuation in the heat shock induction of the Hsp70-firefly luciferase reporter gene activity. Analysis of the amount and activation of heat shock factor 1, induction of mRNA(hsp), and the synthesis and accumulation of heat shock proteins (HSPs) in the undifferentiated and differentiated cells suggest a transcriptional mechanism for this attenuation. Concomitant with a decreased induction of the 72-kDa Hsp70 protein in the differentiated cells, there is an increased abundance of the constitutive 73-kDa Hsc70, a protein known to function in vesicle trafficking. Assessment of sensitivity of the undifferentiated and differentiated cells against stress-induced cell death reveals a significantly greater vulnerability of the differentiated cells toward the cytotoxic effects of arsenite and glutamate/glycine. This study shows that changes in regulation of the HSP and HSC proteins are components of the neuronal cell differentiation program and that the attenuated induction of HSPs likely contributes to neuronal vulnerability whereas the increased expression of Hsc70 likely has a role in neural-specific functions.

Ammonium-induced calcium mobilization in 1321N1 astrocytoma cells

High blood levels of ammonium/ammonia (NH 4 +/NH 3) are associated with severe neurotoxicity as observed in hepatic encephalopathy (HE). Astrocytes are the main targets of ammonium toxicity, while neuronal cells are less vulnerable. In the present study, an astrocytoma cell line 1321N1 and a neuroblastoma glioma hybrid cell line NG108-15 were used as model systems for astrocytes and neuronal cells, respectively. Ammonium salts evoked a transient increase in intracellular calcium concentrations ([Ca 2+] i) in astrocytoma (EC 50 = 6.38 mM), but not in NG108-15 cells. The ammonium-induced increase in [Ca 2+] i was due to an intracellular effect of NH 4 +/NH 3 and was independent of extracellular calcium. Acetate completely inhibited the ammonium effect. Ammonium potently reduced calcium signaling by G q protein-coupled receptors (H 1 and M3) expressed on the cells. Ammonium (5 mM) also significantly inhibited the proliferation of 1321N1 astrocytoma cells. While mRNA for the mammalian ammonium transporters RhBG and RhCG could not be detected in 1321N1 astrocytoma cells, both transporters were expressed in NG108-15 cells. RhBG and RhBC in brain may promote the excretion of NH 3/NH 4 + from neuronal cells. Cellular uptake of NH 4 +/NH 3 was mainly by passive diffusion of NH 3. Human 1321N1 astrocytoma cells appear to be an excellent, easily accessible human model for studying HE, which can substitute animal studies, while NG108-15 cells may be useful for investigating the role of the recently discovered Rhesus family type ammonium transporters in neuronal cells. Our findings may contribute to the understanding of pathologic ammonium effects in different brain cells, and to the treatment of hyperammonemia.

Neuroprotective actions of pyridoxine

Electroencephalographic recordings in cerebral cortex of mice given a single sub-convulsive dose of domoic acid exhibited typical spike and wave discharges. Administration of the anti-epileptic drugs sodium valproate, nimodipine, or 5α-pregnan 3α-ol-20-one as well as pyridoxine simultaneously with or after domoic acid treatment resulted in significantly less spike and wave activity. Administration of these same drugs 45 min prior to the administration of domoic acid also significantly reduced EEG background. Mechanistically, sodium valproate and pyridoxine significantly attenuated domoic acid-induced increase in levels of glutamate, increase in levels of calcium influx, decrease in levels of γ-aminobutyric acid and increase in levels of the protooncogenes c- fos, jun-B and jun-D. In hippocampal cells, domoic acid-induced increases in glutamate and calcium influx were significantly decreased by pyridoxal phosphate or nimodipine. Similarly in neuroblastoma–glioma hybrid cells (NG 108/15), pyridoxine attenuated domoic acid-induced increases in glutamate, influx of extracellular calcium, and enhanced induction of oncoproteins regardless of whether cells were undifferentiated, differentiated or de-differentiated. Pyridoxine has anti-seizure and neuroprotective actions mediated through mechanisms similar to those targeted by current therapeutic strategies.

Single-cell analysis by a scanning thermal lens microscope with a microchip: direct monitoring of cytochrome c distribution during apoptosis process.

We developed a microsystem for cell experiments consisting of a scanning thermal lens microscope detection system and a cell culture microchip. The microchip system was good for liquid control in microspace, and this results in secure cell stimulation and coincident in vivo observation of the cell responses. The system could detect nonfluorescent biological substances with extremely high sensitivity without any labeling materials and had a high spatial resolution of approximately 1 microm. This system was applied to monitoring of cytochrome c distribution in a neuroblastoma-glioma hybrid cell cultured in the microflask (1 mm x 10 mm x 0.1 mm; 1 microL) fabricated in a glass microchip. Cytochrome c release from mitochondria to cytosol during the apoptosis process was successfully monitored with this system. The cytochrome c detected with this system was estimated to be approximately 10 zmol. We concluded that the system was suitable for measuring the distribution of chemical substances in a single cell because the microchip is good for liquid handling in microspace and the thermal lens microscope has high sensitivity and spatial resolution.

Opioid receptor types selectively cointernalize with G protein-coupled receptor kinases 2 and 3.

Activation of G protein-coupled receptors (GPCRs) may bring about their disappearance from the cell membrane, and it is commonly accepted that G protein-coupled receptor kinases (GRKs) play a key function in this mechanism. Opioid receptors belong to the family of GPCRs and are substrates of GRKs. We examined the fate of delta- and mu-opioid receptors and GRK2 and 3 in living cells during the process of receptor sequestration, using laser scanning microscopy. For visualization purposes, receptors and kinases were tagged at their respective C terminus with a fluorophore. The opioid receptors were fused to enhanced green fluorescence protein (EGFP), and the GRKs were linked to red fluorescence protein (DsRed). The cDNAs of these constructs served for transfection of human embryonic kidney 293 cells and neuroblastoma-glioma hybrid cells (NG 108-15), respectively. We report that activation of delta-opioid-EGFP receptors triggers a rapid translocation of cytosolic GRK-DsRed toward the cell membrane, which in turn releases vesicles carrying both green fluorescent delta-receptors and red fluorescent GRKs. Phosducin, a Gbetagamma scavenger, completely prevents translocation of GRKs and the formation of vesicles. In analogous experiments with mu-opioid receptors fused to EGFP, we observed that receptor activation also discharges green fluorescent vesicles. In contrast to delta-receptors, mu-receptors failed to trigger accumulation of GRK2 or 3 at the membrane, and no cointernalization of mu-opioid receptors with GRK2 or 3 was observed. The results suggest that delta-opioid receptors, but not mu-receptors, cointernalize with GRK2 or 3.

Increased Resistance to Nitric Oxide Cytotoxicity Associated with Differentiation of Neuroblastoma-Glioma Hybrid (NG108-15) Cells

Nitric oxide (NO), synthesized by the enzyme nitric oxide synthase (NOS), acts as an intercellular messenger associated with various physiological and pathological events. In this study, we investigated whether there exits a difference in the vulnerability to NO-induced cytotoxicity between undifferentiated and differentiated NG108-15 cells, and if so, the mechanisms responsible for the difference. Following a 7- to 8-day exposure to dibutyryl cAMP (dbcAMP), NG108-15 cells exhibited a neuron-like morphology associated with the expression of the neuronal protein, synaptophysin, and with increased NADPH-d activity. Neuron-like differentiated NG108-15 cells acquired resistance to exogenously applied NO. This increased resistance to NO toxicity in differentiated cells was almost completely cancelled out by inhibiting the activity of superoxide dismutase (SOD), but not by inhibiting the activity of NOS. The present study suggested that the activity of SOD increased in parallel with the activity of NOS associated with differentiation and was crucial for the acquired resistance to NO toxicity in differentiated cells.

Selectivity of blocking of low- versus high-voltage activated calcium currents by the dihydropyridine derivatives Bay E5759 and Bay A4339 in neuroblastoma–glioma NG 108-15 cells

Beneficial therapeutic effects of dihydropyridine derivatives in cardiovascular and neurological disorders are often associated with selective L-type Ca2+channel blockade. Here the new dihydropyridine derivatives Bay E5759 (1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic acid ethyl-1-methylethyl ester) and Bay A4339 (1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic acid dimethyl-ester) were tested for their potency and selectivity of blocking of Ba2+currents mediated by low-(LVACC)vs high-voltage activated Ca2+channels (HVACC) in neuroblastoma–glioma hybrid cells. Nisoldipine and mibefradil served as reference compounds. Bay E5759 and Bay A4339 blocked HVACC at low nanomolar concentrations, whereas LVACC was hardly reduced at up to 10 μ M. The order of potency for blockade of HVACC was Bay E5759 (IC50: 0.4 nM) > Bay A4339 (2.5 nM) ∼= nisoldipine (4 nM) ⪢ mibefradil (3.8 μ M). Thus Bay E5759 and Bay A4339 are highly potent and selective blockers of HVACC, presumably L-type Ca2+channels.

Conversion of cellular sialic acid expression from N-acetyl- to N-glycolylneuraminic acid using a synthetic precursor, N-glycolylmannosamine pentaacetate: inhibition of myelin-associated glycoprotein binding to neural cells.

Sialic acids are prominent termini of mammalian glycoconjugates and are key binding determinants for cell-cell recog-nition lectins. Binding of the sialic acid-dependent lectin, myelin-associated glycoprotein (MAG), to nerve cells is implicated in the inhibition of nerve regeneration after injury. Therefore, blocking MAG binding to nerve cell sialoglycoconjugates might enhance nerve regeneration. Previously, we reported that certain sialoglycoconjugates bearing N-acetylneuraminic acid (NeuAc) but not N-glycolylneuraminic acid (NeuGc) support MAG binding (Collins et al., 1997a). We now report highly efficient conversion of sialic acids on living neural cells from exclusively NeuAc to predominantly NeuGc using a novel synthetic metabolic precursor, N-glycolylmannosamine pentaacetate (Man-NGc-PA). When NG108-15 neuroblastoma-glioma hybrid cells, which normally express only NeuAc (and bind to MAG), were cultured in the presence of 1 mM ManNGcPA, they expressed 80-90% of their sialic acid precursor pool as NeuGc within 24 h. Within 5 days, 80% of their ganglioside-associated sialic acids and 70% of their glycoprotein-associated sialic acids were converted to NeuGc. Consistent with this result, treatment of NG108-15 cells with ManNGcPA resulted in nearly complete abrogation of MAG binding. These results demonstrate that ManNGcPA treatment efficiently alters the sialic acid structures on living cells, with a commensurate change in recognition by a physiologically important lectin.

High-voltage-activated calcium channel messenger RNA expression in the 140-3 neuroblastoma–glioma cell line

Expression of calcium channel α 1 subunits in oocytes or cell lines has proven to be a powerful method in the analysis of structure–function relations, but these experimental systems are of limited value in the examination of neuron-specific functions such as transmitter release. Cell lines derived from neurons are often capable of these functions, but their intrinsic calcium channel α 1 subunits are complicating factors in experimental design. We have examined the biophysical and molecular properties of calcium channels in a little studied neuroblastoma–glioma hybrid cell line, 140-3, a close relative of the NG108-15 cell line, to test whether this cell line might serve a role as an expression system for neural mechanisms. This cell was selected as it contains an intact transmitter release mechanism yet secretes little in response to depolarization. Patch-clamp recording revealed only a prominent low-threshold, rapidly inactivating calcium current with a single-channel conductance of ∼7 pS that was identified as T type. A search for calcium channel α 1 subunit messenger RNA in the 140-3 cells with three different tests only revealed α 1C, whereas α 1A–α 1C were present in the parent NG108-15 line. We made a particular effort to search for α 1E, since this subunit has been associated with a low-voltage-activated current. Our findings suggest that, since the principal nerve terminal-associated calcium channels (α 1A, α 1B, α 1E) are absent in the 140-3 cell, this cell line may prove a particularly useful model for the analysis of the role of high-voltage-activated calcium channels in complex functions of neuronal cells.

Different potencies of dihydropyridine derivatives in blocking T-type but not L-type Ca 2+ channels in neuroblastoma-glioma hybrid cells

Evidence has accumulated that classic L-type Ca 2+ channel blockers with a dihydropyridine structure also inhibit T-type Ca 2+ channels in certain types of central and peripheral neurons and in smooth muscle cells, albeit with a lower potency. Thus beneficial therapeutic effects of dihydropyridines in cardiovascular and neurological diseases may not only be associated with L-type but also with T-type Ca 2+ channel blockade. Little is known about the exact order of potency of dihydropyridine derivatives at T-type Ca 2+ channels. Here we investigate the efficacy and potency of four therapeutically used compounds, i.e. nifedipine, nimodipine, nicardipine, niguldipine, in the neuroblastoma-glioma cell line NG108-15. For comparative purposes the Ca 2+ channel agonist Bay K 8644 was included. Ca 2+ channel currents were measured with the whole-cell voltage clamp technique. Subtype Ca 2+ channel currents were separated by clamp protocol and selective blockers. T-type Ca 2+ channel currents were inhibited with decreasing potency in the order niguldipine>nicardipine>nimodipine>nifedipine (IC 50-values 244 nM, 2.5 μM, 9.8 μM, 39 μM), whereas L-type Ca 2+ channel currents were blocked with similar potency (IC 50 for nicardipine 75 nM). Bay K 8644 increased T-type Ca 2+ channel current at nanomolar concentrations (i.e. 95±16% increase by 300 nM). T-type Ca 2+ channel block was completely reversible with exception of the block by niguldipine. Our results indicate a variability of two orders of magnitude in potency of T-type Ca 2+ channel block by the dihydropyridine derivatives investigated. It is speculated that the relation between the L- and T-type Ca 2+ channel block may determine the therapeutic profile of a dihydropyridine derivative.

Effects of carbamazepine on nerve activity and transmitter release in neuroblastoma-glioma hybrid cells and the frog neuromuscular junction.

Effects of the antiepileptic drug carbamazepine on nerve action potential and transmitter release in mouse neuroblastoma-glioma hybrid cells (NG108-15) and the frog neuromuscular junction were studied. Carbamazepine within a concentration range of 0.1-0.5 mmol/L reduced the peak height of the action potential of the NG108-15 cells, whereas the membrane potential and membrane resistance were unaffected. Voltage clamp revealed that the decrease in the action was due to the blockage of the Na+, delayed K+ and transient Ca2+ currents. Carbamazepine did not affect Ca(2+)-activated and A type K+ currents and long-lasting Ca2+ current. In the frog neuromuscular junction, carbamazepine decreased the mean quantal content by a parallel shift in the frequency augmentation-potentiation (FAP) relation. It is concluded that carbamazepine blocks the voltage-dependent Na+, delayed K+, and transient Ca2+ currents and quantal transmitter release through a decrease of nerve excitation.

The Monomeric G-Proteins Rac1 and/or Cdc42 Are Required for the Inhibition of Voltage-Dependent Calcium Current by Bradykinin

Although regulation of voltage-dependent calcium current (ICa,V) by neurotransmitters is a ubiquitous mechanism among nerve cells, the signaling pathways involved are not well understood. We have determined previously that in a neuroblastoma-glioma hybrid cell line (NG108-15), the heterotrimeric G-protein G13 mediates the inhibition of ICa,V produced by bradykinin (BK) via an unknown mechanism. Various reports indicate that G13 can couple to RhoA, Rac1, and Cdc42, which are closely related members of the Rho family of monomeric G-proteins. We have investigated their role as signaling intermediates in the pathway used by BK to inhibit ICa,V. Using immunoblot analysis and the PCR, we found evidence that RhoA, Rac1, and Cdc42 all are expressed in NG108-15 cells. Intracellularly perfused recombinant Rho-GDI (an inhibitor of guanine nucleotide exchange specific for the Rho family) attenuated the inhibition of ICa,V by BK. These findings indicate that activation of RhoA, Rac1, or Cdc42 may be required for the response to BK. To determine whether any of these monomeric G-proteins mediate the response to BK, we have intracellularly applied blocking antibodies specific for each of the candidate proteins. Only the anti-Rac1 antibody blocked the response to BK. In parallel experiments, peptides corresponding to the C-terminal regions of Rac1 and Cdc42 blocked the same response. These data indicate a novel functional contribution of Rac1 and possibly also of Cdc42 to the inhibition of ICa,V by neurotransmitters.

Mechanism of cellular swelling induced by extracellular lactic acidosis in neuroblastoma-glioma hybrid (NG108-15) cells.

The mechanism of cellular swelling induced by extra-cellular lactic acidosis and the effect of diuretics were studied using neuroblastoma-glioma hybrid (NG108-15) cells. The cells were incubated in one of three lactate concentrations (0, 15, or 30 mM), each of which was randomized to one of three pH groups (7.4, 6.2, or 5.0). Analysis of the swelling was measured using a Coulter counter technique. Cellular swelling was most prominent at pH 6.2 at all lactate levels. Cellular swelling was noted to be pH dependent but not lactate dependent. The addition of 1 mM amiloride completely blocked cellular swelling, suggesting that the main mechanism of neuronal cellular swelling induced by extracellular lactic acidosis was the activation of Na+/H+ exchange. Second, three dissimilar diuretic drugs were used for cellular swelling: amiloride (Na+/H+ exchange inhibitor), mannitol (osmotic diuretic), and bumetanide (loop diuretic). Amiloride and mannitol were found effective in reducing the lactic acidosis-induced cellular swelling. Furthermore, the combination of these drugs had additive effects. However, bumetanide was not effective. The results indicate that the direct inhibition of Na+/H+ exchange and/or removal of water from the cell by mannitol was effective against cellular swelling induced by the activation of Na+/H+ exchange in NG108-15 cells.

Mechanism of Cellular Swelling Induced by Extracellular Lactic Acidosis in Neuroblastoma-Glioma Hybrid (NG108-15) Cells

Mechanism of Cellular Swelling Induced by Extracellular Lactic Acidosis in Neuroblastoma-Glioma Hybrid (NG108-15) Cells

D2L, D2S, and D3 dopamine receptors stably transfected into NG108-15 cells couple to a voltage-dependent potassium current via distinct G protein mechanisms.

The D2-like dopamine (DA) receptor family has continued to expand and now includes the D2-short (D2S) and D2-long (D2L) receptor isoforms and the D3 and D4 receptors. The D2 receptor isoforms differ in length by 29 amino acids within the third cytoplasmic loop, a region of the receptor believed to be important for G protein coupling. This observation has led to the hypothesis that the two isoforms of the D2 receptor may utilize different signal transduction pathways when present in the same cell. The D2 and D3 receptors, although mostly different, show some common amino acid sequences within the third cytoplasmic loop. Thus, it is possible that the D2 and D3 receptors may employ similar signal transduction pathways. To test these hypotheses directly, NG108-15 neuroblastoma-glioma hybrid cells were stably transfected to express either the D2S, D2L, or D3 DA receptors. All transfected but not untransfected NG108-15 cells demonstrated a dose-dependent reduction in the peak whole-cell potassium (K+) current in response to receptor activation by DA or the DA receptor agonists quinpirole (QUIN) and apomorphine (APO). The modulation of K+ current by D2S receptor stimulation was prevented by pretreatment of the cells with cholera toxin (20 micrograms/ml for 18 h), whereas pertussis toxin pretreatment (500 ng/ml for 4 h) completely blocked the effects of D2L and D3 receptor activation. These observations suggest that the signal transduction mechanisms involved in coupling the two isoforms of the D2 receptor to the K+ current are different, whereas the D2L and D3 receptor coupling mechanisms may be similar. In direct support of this hypothesis, it was observed that the intracellular application of a polyclonal antibody that is specific for the GO alpha subunit completely blocked the ability of D2L and D3 receptors to modulate outward K+ currents. In contrast, the D2S-mediated modulation of K+ currents was blocked by intracellular application of an antibody recognizing GS alpha but not GO alpha. These findings demonstrate that D2S and D2L receptors are able to couple to a common effector in a cell via two G protein pathways.

Human central nervous system myelin inhibits neurite outgrowth

In vitro and animal studies have identified molecules in mammalian CNS myelin which inhibit neuritic extension and which may be responsible, at least in part, for the lack of axonal regeneration after injury in the injured brain, optic nerve and spinal cord. To determine whether such inhibitory activity may be present in human CNS myelin, we used a bioassay to characterize neurite outgrowth on this substrate. Human CNS myelin strongly inhibited neuritic outgrowth from newborn rat dorsal root ganglion neurons and NG-108-15 cells, a neuroblastoma-glioma hybrid cell line. Similar but less potent inhibitory activity was identified in human gray matter. The CNS myelin inhibition of neuritic outgrowth appeared to be dependent on direct contact between the myelin substrate and neuntes. The inhibitory activity in human CNS myelin closely resembled that described in adult rodents. Inhibition of neurite growth by human CNS myelin in this in vitro bioassay mirrors the lack of regeneration in vivo and can be used as a model to develop strategies designed to enhance axonal regeneration and neural recovery.