Storage of dopamine and acetylcholine in granules of PC12, a clonal pheochromocytoma cell line

Effects of latroeggtoxin-VI on dopamine and α-synuclein in PC12 cells and the implications for Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is characterized by death of dopaminergic neurons leading to dopamine deficiency, excessive α-synuclein facilitating Lewy body formation, etc. Latroeggtoxin-VI (LETX-VI), a proteinaceous neurotoxin discovered from the eggs of spider L. tredecimguttatus, was previously found to promote the synthesis and release of PC12 cells, showing a great potential as a drug candidate for PD. However, the relevant mechanisms have not been understood completely. The present study explored the mechanism underlying the effects of LETX-VI on dopamine and α-synuclein of PC12 cells and the implications for PD.

RESULTS

After PC12 cells were treated with LETX-VI, the level of dopamine was significantly increased in a dose-dependent way within a certain range of concentrations. Further mechanism analysis showed that LETX-VI upregulated the expression of tyrosine hydroxylase (TH) and L-dopa decarboxylase to enhance the biosynthesis of dopamine, and downregulated that of monoamine oxidase B to reduce the degradation of dopamine. At the same time, LETX-VI promoted the transport and release of dopamine through modulating the abundance and/or posttranslational modification of vesicular monoamine transporter 2 (VMAT2) and dopamine transporter (DAT). While the level of dopamine was increased by LETX-VI treatment, α-synuclein content was reduced by the spider toxin. α-Synuclein overexpression significantly decreased the dopamine level and LETX-VI efficiently alleviated the inhibitory action of excessive α-synuclein on dopamine. In the MPTP-induced mouse model of PD, application of LETX-VI ameliorated parkinsonian behaviors of the mice, and reduced the magnitude of MPTP-induced α-synuclein upregulation and TH downregulation. In addition, LETX-VI displayed neuroprotective effects by inhibiting MPTP-induced decrease in the numbers of TH-positive and Nissl-stained neurons in mouse brain tissues.

CONCLUSIONS

All the results demonstrate that LETX-VI promotes the synthesis and release of dopamine in PC12 cells via multiple mechanisms including preventing abnormal α-synuclein accumulation, showing implications in the prevention and treatment of PD.

Emodin ameliorates antioxidant capacity and exerts neuroprotective effect via PKM2-mediated Nrf2 transactivation

Pyruvate kinase M2 (PKM2) is overexpressed in neuronal cells. However, there are few studies on the involvement of PKM2 modulators in neurodegenerative diseases. Emodin, a dominating anthraquinone derivative extracting from the rhizome of rhubarb, has received expanding consideration due to its pharmacological properties. Our data reveal that emodin could resist hydrogen peroxide- or 6-hydroxydopamine-mediated mitochondrial fission and apoptosis in PC12 cells (a neuron-like rat pheochromocytoma cell line). Notably, emodin at nontoxic concentrations significantly inhibits PKM2 activity and promotes dissociation of tetrameric PKM2 into dimers in cells. The PKM2 dimerization enhances the interaction of PKM2 and NFE2-related factor 2 (Nrf2), which further triggers the activation of the Nrf2/ARE pathway to upregulate a panel of cytoprotective genes. Modulating the PKM2/Nrf2/ARE axis by emodin unveils a novel mechanism for understanding the pharmacological functions of emodin. Our findings indicate that emodin is a potential candidate for the treatment of oxidative stress-related neurodegenerative disorders.

Oxypeucedanin and isoimperatorin extracted from Prangos ferulacea (L.) Lindl protect PC12 pheochromocytoma cells from oxidative stress and apoptosis induced by doxorubicin

Background and purpose:

Doxorubicin (DOX) as a chemotherapeutic agent has been widely used in the treatment of various types of cancer. However, DOX exerts a toxic effect on normal tissues such as the brain. Furanocoumarins reduce the risk of cardiovascular and brain diseases because of their antioxidant activities. This study has been designed, for the first time, to evaluate the effect of known furanocoumarins oxypeucedanin and isoimperatorin extracted from Prangos ferulacea (L.) Lindl on oxidative stress and apoptosis induced by DOX toward pheochromocytoma cell line (PC12).

Experimental approach:

NMR and MASS spectrometers were used to characterize the isolated compounds. The protective effects of isolated compounds on DOX-induced cytotoxicity in PC12 cells were examined by MTT assay. PC12 cells were pretreated with oxypeucedanin and isoimperatorin for 2 and 21 h, respectively, subsequently exposure to DOX at IC₅₀ concentration. Then, mitochondrial membrane potential (MMP), Bax and Bcl2 mRNA expressions, caspase-3 activation, and the generation of intracellular reactive oxygen species (ROS) were measured after 24 h.

Findings/Results:

Pretreatment with oxypeucedanin and isoimperatorin significantly decreased DOX-induced apoptosis through reduction of caspase-3 activity and ROS generation and an increase in MMP. In addition, our finding showed pretreatment with these compounds leads to regulation of Bcl-2.

Conclusion and implications:

Taken together our observation indicated that oxypeucedanin and isoimperatorin have a protective effect against apoptosis induced by DOX in PC12 cells by inhibition of ROS production.

Sodium butyrate attenuates rotenone-induced toxicity by activation of autophagy through epigenetically regulating PGC-1α expression in PC12 cells

Short-chain fatty acids (SCFAs) are considered the key molecular link between gut microbiota and pathogenesis of Parkinson's disease (PD). However, the role of SCFAs in PD pathogenesis is controversial. Autophagy is important for the degradation of α-synuclein, which is critical to the development of PD. However, whether SCFAs can regulate autophagy in PD remains unknown. We aimed to investigate the role of SCFAs and explore the potential mechanisms in rat dopaminergic PC12 cells treated with rotenone. Expression levels of α-synuclein, peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and microtubule-associated protein 1 light chain 3 beta (LC3B)-II were detected by Western blot. Histone acetylation levels at PGC-1α promoter region were measured using chromatin immunoprecipitation-quantitative polymerase chain reaction (ChIP-qPCR). Among the three SCFAs, sodium butyrate (NaB) protected against rotenone-induced toxicity. NaB activated autophagy pathway and reduced rotenone-induced α-synuclein expression through the activation of autophagy. Notably, NaB activated autophagy pathway through upregulating PGC-1α expression. More importantly, NaB promoted the levels of histone 3 lysine 9 acetylation (H3K9Ac) and histone 3 lysine 27 acetylation (H3K27Ac) at PGC-1α promoter region, indicating that NaB promotes PGC-1α expression via histone acetylation modification. In conclusion, NaB can protect against rotenone-induced toxicity through activation of the autophagy pathway by upregulating PGC-1α expression via epigenetic modification.

STIL: a multi-function protein required for dopaminergic neural proliferation, protection, and regeneration

Degeneration of dopaminergic (DA) neurons in the brain is the major cause for Parkinson’s disease (PD). While genetic loci and cellular pathways involved in DA neuron proliferation have been well documented, the genetic and molecular and cellular basis of DA cell survival remains to be elucidated. Recently, studies aimed to uncover the mechanisms of DA neural protection and regeneration have been reported. One of the most recent discoveries, i.e., multi-function of human oncogene SCL/TAL interrupting locus (Stil) in DA cell proliferation, neural protection, and regeneration, created a new field for studying DA cells and possible treatment of PD. In DA neurons, Stil functions through the Sonic hedgehog (Shh) pathway by releasing the inhibition of SUFU to GLI1, and thereby enhances Shh-target gene transcription required for neural proliferation, protection, and regeneration. In this review article, we will highlight some of the new findings from researches relate to Stil in DA cells using zebrafish models and cultured mammalian PC12 cells. The findings may provide the proof-of-concept for the development of Stil as a tool for diagnosis and/or treatment of human diseases, particularly those caused by DA neural degeneration.

Optical excitation and detection of neuronal activity

Optogenetics has emerged as an exciting tool for manipulating neural activity, which in turn, can modulate behavior in live organisms. However, detecting the response to the optical stimulation requires electrophysiology with physical contact or fluorescent imaging at target locations, which is often limited by photobleaching and phototoxicity. In this paper, we show that phase imaging can report the intracellular transport induced by optogenetic stimulation. We developed a multimodal instrument that can both stimulate cells with subcellular spatial resolution and detect optical pathlength (OPL) changes with nanometer scale sensitivity. We found that OPL fluctuations following stimulation are consistent with active organelle transport. Furthermore, the results indicate a broadening in the transport velocity distribution, which is significantly higher in stimulated cells compared to optogenetically inactive cells. It is likely that this label-free, contactless measurement of optogenetic response will provide an enabling approach to neuroscience.

Alzheimer's disease: Targeting the Cholinergic System

Acetylcholine (ACh) has a crucial role in the peripheral and central nervous systems. The enzyme choline acetyltransferase (ChAT) is responsible for synthesizing ACh from acetyl-CoA and choline in the cytoplasm and the vesicular acetylcholine transporter (VAChT) uptakes the neurotransmitter into synaptic vesicles. Following depolarization, ACh undergoes exocytosis reaching the synaptic cleft, where it can bind its receptors, including muscarinic and nicotinic receptors. ACh present at the synaptic cleft is promptly hydrolyzed by the enzyme acetylcholinesterase (AChE), forming acetate and choline, which is recycled into the presynaptic nerve terminal by the high-affinity choline transporter (CHT1). Cholinergic neurons located in the basal forebrain, including the neurons that form the nucleus basalis of Meynert, are severely lost in Alzheimer’s disease (AD). AD is the most ordinary cause of dementia affecting 25 million people worldwide. The hallmarks of the disease are the accumulation of neurofibrillary tangles and amyloid plaques. However, there is no real correlation between levels of cortical plaques and AD-related cognitive impairment. Nevertheless, synaptic loss is the principal correlate of disease progression and loss of cholinergic neurons contributes to memory and attention deficits. Thus, drugs that act on the cholinergic system represent a promising option to treat AD patients.

Osthole attenuates doxorubicin-induced apoptosis in PC12 cells through inhibition of mitochondrial dysfunction and ROS production

Doxorubicin (DOX) is a potent, broad-spectrum chemotherapeutic drug used for treatment of several types of cancers. Despite its effectiveness, it has a wide range of toxic side effects, many of which most likely result from its inherent prooxidant activity. It has been reported that DOX has toxic effects on normal tissues, including brain tissue. In the current study, we investigated the protective effect of osthole isolated from Prangos ferulacea (L.) Lindl. on oxidative stress and apoptosis induced by DOX in PC12 as a neuronal model cell line. PC12 cells were pretreated with osthole 2 h after treatment with different concentrations of DOX. 24 h later, the cell viability, mitochondrial membrane potential (MMP), the activity of caspase-3, the expression ratio of Bax/Bcl-2, and the generation of intracellular ROS were detected. We found that pretreatment with osthole on PC12 cells significantly reduced the loss of cell viability, the activity of caspase-3, the increase in Bax/Bcl-2 ratio, and the generation of intracellular ROS induced by DOX. Moreover, pretreatment with osthole led to an increase in MMP in PC12 cells. In conclusion, our results indicated that pretreatment with nontoxic concentrations of osthole protected PC12 cells from DOX-mediated apoptosis by inhibition of ROS production.

Characterization of the human oncogene SCL/TAL1 interrupting locus (Stil) mediated Sonic hedgehog (Shh) signaling transduction in proliferating mammalian dopaminergic neurons

The human oncogene SCL/TAL1 interrupting locus (Stil) is highly conserved in all vertebrate species. In humans, the expression of Stil is involved in cancer cell survival, apoptosis and proliferation. In this research, we investigated the roles of Stil expression in cell proliferation of mammalian dopaminergic (DA) PC12 cells. Stil functions through the Sonic hedgehog (Shh) signal transduction pathway. Co-immunoprecipitation tests revealed that STIL interacts with Shh downstream components, which include SUFU and GLI1. By examining the expression of Stil, Gli1, CyclinD2 (cell-cycle marker) and PCNA (proliferating cell nuclear antigen), we found that up-regulation of Stil expression (transfection with overexpression plasmids) increased Shh signaling transduction and PC12 cell proliferation, whereas down-regulation of Stil expression (by shRNA) inhibited Shh signaling transduction, and thereby decreased PC12 cell proliferation. Transient transfection of PC12 cells with Stil knockdown or overexpression plasmids did not affect PC12 cell neural differentiation, further indicating the specific roles of Stil in cell proliferation. The results from this research suggest that Stil may serve as a bio-marker for neurological diseases involved in DA neurons, such as Parkinson's disease.

The human oncogene SCL/TAL1 interrupting locus is required for mammalian dopaminergic cell proliferation through the Sonic hedgehog pathway

The human oncogene SCL/TAL1 interrupting locus (Stil) is highly conserved in all vertebrate species. In humans, the expression of Stil regulates cancer cell proliferation and survival. In this study, we examined the function of Stil in neural progenitor cell proliferation and neural differentiation using the mammalian dopaminergic (DA) PC12 cells. Stil is expressed in both proliferating and differentiated PC12 cells. The RNAi-mediated knockdown of Stil expression yielded a decreased proliferation rate of PC12 cells, whereas the overexpression of Stil transcript increased PC12 cell proliferation. The up- and down-regulation of the Sonic hedgehog (Shh) pathway by pharmacological approaches targeting Smoothened (Smo) demonstrated that Stil functions in the Shh pathway for PC12 proliferation. Smo antagonist cyclopamine decreased the proliferation rate of PC12 cells, whereas the overexpression of Stil rescued the cyclopamine-induced decrease in cell proliferation. Oppositely, the application of Smo agonist purmorphamine increased the rate of PC12 cell proliferation. However, the proliferation defect caused by Stil knockdown remained evident after activating the Shh pathway by purmorphamine. The expression of Stil is not required for PC12 cell neural differentiation. In PC12 cells transfected with Stil shRNA plasmids, the outgrowth of neurites persisted after treatment with nerve growth factor (NGF), whereas overexpression of Stil did not increase neurite growth in response to NGF induction. Together, the results from this study suggest a novel role for the oncogene Stil in neural progenitor cells through the Shh pathway, and further introduces Stil as a bio-marker for DA cells.

Neuroprotective effects of protocatechuic aldehyde against neurotoxin-induced cellular and animal models of Parkinson's disease

Protocatechuic aldehyde (PAL) has been reported to bind to DJ-1, a key protein involved in Parkinson's disease (PD), and exerts potential neuroprotective effects via DJ-1 in SH-SY5Y cells. In this study, we investigated the neuroprotective pharmacological effects of PAL against neurotoxin-induced cell and animal models of PD. In cellular models of PD, PAL markedly increased cell viability rates, mitochondrial oxidation-reduction activity and mitochondrial membrane potential, and reduced intracellular ROS levels to prevent neurotoxicity in PC12 cells. In animal models of PD, PAL reduced the apomorphine injection, caused turning in 6-OHDA treated rats, and increased the motor coordination and stride decreases in MPTP treated mice. Meanwhile, in an MPTP mouse model, PAL prevented a decrease of the contents of dopamine (DA) and its metabolites in the striatum and TH-positive dopaminergic neuron loss in the substantia nigra (SN). In addition, PAL increased the protein expression of DJ-1 and reduced the level of α-synuclein in the SN of MPTP lesioned mice. PAL also increased the spine density in hippocampal CA1 neurons. The current study demonstrates that PAL can efficiently protect dopaminergic neurons against neurotoxin injury in vitro and in vivo, and that the potential mechanisms may be related to its effects in increasing DJ-1, decreasing α-synuclein and its growth-promoting effect on spine density.

α-lipoic acid protects dopaminergic neurons against MPP+-induced apoptosis by attenuating reactive oxygen species formation

Reactive oxygen species (ROS) elicited by oxidative stress are widely recognized as a major initiator in the dege-neration of dopaminergic neurons distinctive of Parkinson's disease (PD). The interaction of ROS with mitochondria triggers sequential events in the mitochondrial cell death pathway, which is thought to be responsible for ROS-mediated neurodegeneration in PD. α-lipoic acid (LA) is a pleiotropic compound with potential pharmacotherapeutic value against a range of pathophysiological insults. Its protective actions against oxidative damage by scavenging ROS and reducing production of free radicals have been reported in various in vitro and in vivo systems. This study analyzed the ability of LA to protect PC12 neuronal cells from toxicity of 1-methyl-4-phenylpyridinium (MPP+), the neurotoxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) which is known to kill dopaminergic neurons selectively and to cause severe parkinsonism-like symptoms in humans and primate animals. Our results demonstrate that the apoptosis of PC12 cells elicited by MPP+ could be significantly prevented by pretreatment with LA for 1 h. In addition, LA inhibits intercellular ROS levels and the mitochondrial transmembrane permeability, the key players in the pathogenesis of PD, thereby protecting dopaminergic neuronal cells against oxidative damage.

3-O-demethylswertipunicoside protects against oxidative toxicity in PC12 cells

Xanthone compounds have been reported to inhibit cancer cell growth as well as possessing antioxidant properties. The xanthone compound 3-O-demethylswertipunicoside (3-ODS), extracted from Swertia punicea HEMSL, has not previously been demonstrated to have clear neuroprotective effects. In our study, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell death assay revealed that treatment of PC12 cells with 3-ODS ameliorated the decreased cell viability induced by exposure to 1-methyl-4-phenylpyridinium ion (MPP+), rotenone or H2O2. The acridine orange/ethidium bromide (AO/EB) apoptosis assay demonstrated a significant suppression of cell death in PC12 cells. by 3-ODS treatment. 3-ODS increased the protein expression of both tyrosine hydroxylase (TH) and DJ-1 expression in PC12 cells. The current study demonstrates that 3-ODS has potential neuroprotective effects mediated via the elevation of TH and DJ-1 protein levels.

Tempol attenuates cocaine-induced death of PC12 cells through decreased oxidative damage

The association between cocaine administration and induction of oxidative stress in different brain regions suggests that oxidative damage is an important factor participating in cocaine disruption of normal central nervous system functions. In order to deal with this topic, brain penetrating exogenous antioxidants were suggested as a tool to prevent cocaine-induced oxidative damage and behavioral changes. Lately, we have shown that Tempol, a stable nitroxide radical reduced oxidative damage and attenuated the development and expression of cocaine psychomotor sensitization. To examine whether nitroxides, represented by Tempol, can exhibit protective effects against cocaine-induced cell death and to elucidate the molecular mechanism of cocaine-induced oxidative damage, we used the well established PC12 cell line model. The results showed that (1) cocaine induced cell death in a dose-dependent manner (2) and that it was reduced significantly by the stable nitroxide radical Tempol. Furthermore, (3) Tempol significantly inhibited oxidative damage induced by cocaine as reflected by mitochondrial superoxide radical and peroxide enhancement. Finally, (4) Tempol restored the total scavenging capacity which was reduced by cocaine in PC12 cells. Cumulatively, these results suggest that nitroxides such as Tempol can attenuate oxidative damage and cell death induced by cocaine and that PC12 cells can be used as an in vitro model to further investigate the precise molecular mechanism of these compounds.

Exocytosis in islet beta-cells

The development of technologies that allow for live optical imaging of exocytosis from beta-cells has greatly improved our understanding of insulin secretion. Two-photon imaging, in particular, has enabled researchers to visualize the exocytosis of large dense-core vesicles (LDCVs) containing insulin from beta-cells in intact islets of Langerhans. These studies have revealed that high glucose levels induce two phases of insulin secretion and that this release is dependent upon cytosolic Ca(2+) and cAMP. This technology has also made it possible to examine the spatial profile of insulin exocytosis in these tissues and compare that profile with those of other secretory glands. Such studies have led to the discovery of the massive exocytosis of synaptic-like microvesicles (SLMVs) in beta-cells. These imaging studies have also helped clarify facets of insulin exocytosis that cannot be properly addressed using the currently available electrophysiological techniques. This chapter provides a concise introduction to the field of optical imaging for those researchers who wish to characterize exocytosis from beta-cells in the islets of Langerhans.

Hydrogen sulfide inhibits MPP(+)-induced apoptosis in PC12 cells

AIMS

Hydrogen sulfide (H2S) is a well-known cytotoxic gas. Recently it has been shown to protect neurons against oxidative stress caused by glutamate, hypochlorous acid (HOCl), and beta-amyloid. The aim of the present study is to explore the cytoprotection of H2S against 1-methyl-4-phenylpyridinium ion (MPP(+))-induced apoptosis and the molecular mechanisms underlying in PC12 cells, a rat cell line derived from pheochromocytoma cells.

MAIN METHODS

Cell viability was determined by the conventional 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. Apoptosis was assessed by Hoechst 33258 nuclear staining and flow cytometric (FCM) analysis after propidium iodide staining. The mitochondrial membrane potential (MMP) was measured by rhodamine 123 (Rh123) probe and reactive oxygen species (ROS) were measured by dihydrorhodamine probe using FCM analysis.

KEY FINDINGS

MPP(+) reduced the cell viability and induced apoptosis of PC12 cells along with dissipation of MMP as well as overproduction of ROS. Sodium hydrosulfide (NaHS), a H2S donor, protected PC12 cells against MPP(+)-induced cytotoxicity and apoptosis not only by reducing the loss of MMP, but also by attenuating an increase in intracellular ROS.

SIGNIFICANCE

H2S significantly protected PC12 cells against cytotoxicity and apoptosis induced by MPP(+), which was associated with the inhibition by H(2)S of MPP(+)-induced dissipation of MMP and overproduction of ROS. These findings can significantly advance therapeutic approaches to the neurodegenerative diseases which are associated with oxidative stress, such as Parkinson's disease.

Erythropoietin prevents PC12 cells from 1-methyl-4-phenylpyridinium ion-induced apoptosis via the Akt/GSK-3beta/caspase-3 mediated signaling pathway

Apoptosis is a contributing cause of dopaminergic neuron loss in Parkinson disease. Recent work has shown that erythropoietin (EPO) offers protection against apoptosis in a wide variety of tissues. We demonstrate that exposure of PC12 cells to 1-methyl-4-phenylpyridinium ion (MPP(+)) with recombinant human EPO, significantly decreased apoptosis as measured by TUNEL and caspase-3 activity when compared to MPP(+) treatment alone. EPO induced sustained phosphorylation of Akt and its substrate, GSK-3beta, reduced caspase-3 activities in PC12 cells. The anti-apoptotic effect of EPO was abrogated by co-treatment with LY294002, the specific blocker of phosphatidylinositol 3-kinase (PI3K). The effects of EPO on GSK-3beta and caspase-3 activities were also blocked by LY294002. LiCl, the inhibitor of GSK-3beta, downregulated the caspase-3 activity and blocked the apoptosis induced by MPP(+). Finally, we determined that EPO transiently activated the ERK signaling pathway, but PD98059, a specific inhibitor of ERK, does not alter the survival effect of EPO in this model system. Thus, these findings indicate that EPO protects against apoptosis in PC12 cells exposed to MPP(+), through the Akt/GSK-3beta/caspase-3 signaling pathway, but the ERK pathway is not involved in the EPO-dependent survival enhancing effect in this model system.

The Role of 3-O-Methyldopa in the Side Effects of l-dopa

Long-term treatment of L-dopa for Parkinson's disease (PD) patients induces adverse effects, including dyskinesia, on-off and wearing-off symptoms. However, the cause of these side effects has not been established to date. In the present study, therefore, 3-O-methyldopa (3-OMD), which is a major metabolite of L-dopa, was tested to determine whether it plays a role in the aforementioned adverse effects. The effects of 3-OMD on the dopaminergic nervous system in the brain were investigated, by examining behavioral, biochemical, and cellular changes in male Sprague-Dawley rats and catecholamine-producing PC12 neuronal cells. The results revealed that the intracerebroventricular (icv) injection of 1 micromol of 3-OMD impaired locomotor activities by decreasing movement time (MT), total distance (TD), and the number of movement (NM) by 70, 74 and 61%, respectively. The biochemical analysis results showed that a single administration of 1 micromole of 3-OMD decreased the dopamine turnover rate (DOPAC/DA) by 40.0% in the rat striatum. 3-OMD inhibited dopamine transporter and uptake in rat brain striatal membranes and PC12 cells. The subacute administration of 3-OMD (5 days, icv) also significantly impaired the locomotor activities and catecholamine levels. 3-OMD induced cytotoxic effects via oxidative stress and decreased mitochondrial membrane potential in PC12 cells, indicating that 3-OMD can damage neuronal cells. Furthermore, 3-OMD potentiated L-dopa toxicity and these toxic effects induced by both 3-OMD and L-dopa were blocked by vitamin E (alpha-tocopherol) in PC12 cells, indicating that 3-OMD may increase the toxic effects of L-dopa to some extent by oxidative stress. Therefore, the present study reveals that 3-OMD accumulation from long-term L-dopa treatment may be involved in the adverse effects of L-dopa therapy. Moreover, L-dopa treatment might accelerate the progression of PD, at least in part, by 3-OMD.

Protective effects of Ginkgo biloba extract on paraquat-induced apoptosis of PC12 cells

Previous studies have suggested that Ginkgo biloba extract (EGb761) has a protective potentiality against apoptosis of neurons or neuron-like cells induced by MPTP. In this study, the effects of EGb761 on PC12 cells injured by paraquat (PQ), a neurotoxin, were tested. The results showed that after incubation of PC12 cells with EGb761 prior to PQ exposure, the PQ-induced decrease of cell viability was significantly reversed, the collapse of mitochondrial membrane potential (MMP) was attenuated and the percentage of apoptotic cells was reduced. Moreover, EGb761 pretreatment evidently increased the numbers of tyrosine hydroxylase (TH) positive and bcl-2 positive cells and degraded the number of caspase-3 positive cells in PQ-injured PC12 cells, in comparison to the treatment with PQ alone. This study indicates that EGb761 has a neuroprotective effect on paraquat-induced apoptosis of PC12 cells. The mechanism underlying the protective effects of EGb761 in PQ-injured PC12 cells might be related to the increase of bcl-2 activation, maintenance of MMP stability and decrease of caspase-3 activation through mitochondria-dependent pathway. The results from this study provide an experimental basis for the potential use of EGb761 in treatment of Parkinson's disease.

Granulocyte-colony stimulating factor is neuroprotective in a model of Parkinson's disease

We have recently shown that the hematopoietic Granulocyte-Colony Stimulating Factor (G-CSF) is neuroprotective in rodent stroke models, and that this action appears to be mediated via a neuronal G-CSF receptor. Here, we report that the G-CSF receptor is expressed in rodent dopaminergic substantia nigra neurons, suggesting that G-CSF might be neuroprotective for dopaminergic neurons and a candidate molecule for the treatment of Parkinson's disease. Thus, we investigated protective effects of G-CSF in 1-methyl-4-phenylpyridinium (MPP+)-challenged PC12 cells and primary neuronal midbrain cultures, as well as in the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease. Substantial protection was found against MPP+-induced dopaminergic cell death in vitro. Moreover, subcutaneous application of G-CSF at a dose of 40 microg/Kg body weight daily over 13 days rescued dopaminergic substantia nigra neurons from MPTP-induced death in aged mice, as shown by quantification of tyrosine hydroxylase-positive substantia nigra cells. Using HPLC, a corresponding reduction in striatal dopamine depletion after MPTP application was observed in G-CSF-treated mice. Thus our data suggest that G-CSF is a novel therapeutic opportunity for the treatment of Parkinson's disease, because it is well-tolerated and already approved for the treatment of neutropenic conditions in humans.

Selective alterations of transcription factors in MPP+-induced neurotoxicity in PC12 cells

MPP(+) (1-methyl-4-phenylpyridinium; the active metabolite of the neurotoxin MPTP (1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine)) depletes dopamine (DA) content and elicits cell death in PC12 cells. However, the mechanism of MPP(+)-induced neurotoxicity is still unclear. In this study, the dose response and time-course of MPP(+)-induced DA depletion and decreased cell viability were determined in nerve growth factor (NGF)-differentiated PC12 cells. The alteration of transcription factors (TFs) induced by MPP(+) from a selected dose level and time point was then evaluated using protein/DNA-binding arrays. K-means clustering analysis identified four patterns of protein/DNA-binding changes. Three of the 28 TFs identified in PC12 cells increased by 100% (p53, PRE, Smad SBE) and 2 decreased by 50% (HSE, RXR(DR1)) of control with MPP(+) treatment. In addition, three TFs decreased within the range of 33-50% (TFIID, E2F1, CREB) and two TFs increased within the range of 50-100% (PAX-5, Stat4). An electrophoretic mobility shift assay (EMSA) was used to confirm the changes of p53 and HSE. The observed changes in TFs correlated with the alterations of DA and cell viability. The data indicates that selective transcription factors are involved in MPP(+)-induced neurotoxicity and it provides mechanistic information that may be applicable to animal studies with MPTP and clinical studies of Parkinson's disease.

A microarray study of MPP+-treated PC12 Cells: Mechanisms of toxicity (MOT) analysis using bioinformatics tools

Background

This paper describes a microarray study including data quality control, data analysis and the analysis of the mechanism of toxicity (MOT) induced by 1-methyl-4-phenylpyridinium (MPP⁺) in a rat adrenal pheochromocytoma cell line (PC12 cells) using bioinformatics tools. MPP⁺ depletes dopamine content and elicits cell death in PC12 cells. However, the mechanism of MPP⁺-induced neurotoxicity is still unclear.

Results

In this study, Agilent rat oligo 22K microarrays were used to examine alterations in gene expression of PC12 cells after 500 μM MPP⁺ treatment. Relative gene expression of control and treated cells represented by spot intensities on the array chips was analyzed using bioinformatics tools. Raw data from each array were input into the NCTR ArrayTrack database, and normalized using a Lowess normalization method. Data quality was monitored in ArrayTrack. The means of the averaged log ratio of the paired samples were used to identify the fold changes of gene expression in PC12 cells after MPP⁺ treatment. Our data showed that 106 genes and ESTs (Expressed Sequence Tags) were changed 2-fold and above with MPP⁺ treatment; among these, 75 genes had gene symbols and 59 genes had known functions according to the Agilent gene Refguide and ArrayTrack-linked gene library. The mechanism of MPP⁺-induced toxicity in PC12 cells was analyzed based on their genes functions, biological process, pathways and previous published literatures.

Conclusion

Multiple pathways were suggested to be involved in the mechanism of MPP⁺-induced toxicity, including oxidative stress, DNA and protein damage, cell cycling arrest, and apoptosis.

PC12 cells as a model for studies of regulated secretion in neuronal and endocrine cells

Pheochromocytoma-derived cell lines such as PC12 cells maintain a differentiated neuroendocrine phenotype and have been widely used as a convenient model system for a wide variety of cell biological studies on neurotrophin action, monoamine biogenesis, protein trafficking, and secretory vesicle dynamics. This chapter reviews a number of methods that are useful for studies of the regulated dense core vesicle secretory pathway. This includes protocols for maintaining cells and preserving their phenotype. A variety of assays are discussed for monitoring secretion in intact or permeable cells and in transfected cells. Specific methods for immunocytochemical studies in permeable cells are discussed. Finally, protocols for high-efficiency PC12 cell transfections and the isolation of stably transfected cell lines are provided.

Mechanisms of nicotine mediated communication between NGF-differentiated PC12 and HEL cells

HEL 92.1.7 cells were immobilized among nerve growth factor (NGF)-differentiated PC12 cells. Nicotine caused an immediate Ca2+ mobilisation in the PC12 cells followed by a delayed secondary Ca2+ response in the HEL 92.1.7 cells. The Ca2+ elevation in response to nicotine in PC12 cells was abolished by Na+ removal. The response was diminished by omega-contoxin GVIA (omega-CTx-GVIA) in PC12 cell neurites and by nifedipine in the cell bodies, respectively. The secondary response in HEL 92.1.7 cells was blocked by omega-CTx-GVIA. The results suggest that nicotinic receptor-mediated depolarisation and subsequent activation of voltage dependent Ca2+ channels (VDCC) are sufficient to induce transmitter release from NGF-differentiated PC12 cell varicosities without requirement for additional Ca2+ influx via nicotinic receptor ion channels.

The fetal and neonatal brain protein neuronatin protects PC12 cells against certain types of toxic insult

The protein neuronatin is expressed in the nervous system of the fetus and neonate at a much higher level than in the adult. Its function is unknown. As a result of variable splicing, neuronatin mRNA exists in two forms, alpha and beta. Wild type PC12 cells express neuronatin-alpha. We have isolated a PC12 variant, called 1.9, that retains many of the neuron-like properties of wild type PC12 cells, but it does not express neuronatin and it exhibits markedly increased sensitivity to the toxic effects of nigericin, rotenone and valinomycin. Pretreatment of the 1.9 cells with alpha-methyltyrosine, which inhibits dopamine synthesis, had little effect on the cells' sensitivity to nigericin, rotenone or valinomycin indicating that dopamine-induced oxidative stress was not involved in the toxicity of these compounds. However, flattened cell subvariants of the 1.9 cells, which do not have any neuron-specific characteristics, did not exhibit increased sensitivity to nigericin indicating that some neuronal characteristic of the 1.9 cells contributed to the toxicity of nigericin. After the neuronatin-beta gene was transfected into and expressed in the 1.9 cells, they regained wild type PC12 levels of resistance to nigericin, rotenone and valinomycin. These studies suggest that the function of neuronatin during development could be to protect developing cells from toxic insult occurring during that period.

Methamphetamine-induced dopaminergic neurotoxicity and production of peroxynitrite are potentiated in nerve growth factor differentiated pheochromocytoma 12 cells

Methamphetamine (METH) is a widely abused psychomotor stimulant known to cause dopaminergic neurotoxicity in rodents, nonhuman primates, and humans. METH administration selectively damages the dopaminergic nerve terminals, which is hypothesized to be due to release of dopamine from synaptic vesicles within the terminals. This process is believed to be mediated by the production of free radicals. The current study evaluates METH-induced dopaminergic toxicity in pheochromocytoma 12 (PC12) cells cultured in the presence or absence of nerve growth factor (NGF). Dopaminergic changes and the formation of 3-nitrotyrosine (3-NT), a marker for peroxynitrite production, were studied in PC12 cell cultures grown in the presence or absence of NGF after different doses of METH (100-1,000 microM). METH exposure did not cause significant alterations in cell viability and did not produce significant dopaminergic changes or 3-NT production in PC12 cells grown in NGF-negative media after 24 hours. However, cell viability of PC12 cells grown in NGF-positive media was decreased by 45%, and significant dose-dependent dopaminergic alteration and 3-NT production were observed 24 hours after exposure to METH. The current study supports the hypothesis that METH acts at the dopaminergic nerve terminals and produces dopaminergic damage by the production of free radical peroxynitrite.

Electron microscopic evidence for multiple types of secretory vesicles in bovine chromaffin cells

It has been previously shown that the neuron-like chromaffin cells from the bovine adrenal medulla are heterogeneous. Among other differences, the cells also differed in secretory vesicles represented in their cytoplasm. The present study investigates the types of secretory vesicles in bovine chromaffin cells by electron microscopy. Morphometric analysis revealed five types of electron-dense secretory vesicles in chromaffin cells. These were as follows: elementary large catecholamine-storing chromaffin granules of rounded shape, large dense core vesicles of ovoid and rod-like shapes, small dense core vesicles as well as ribosome-coated vesicles of intermediate density. Among the electron-lucent vesicles there were small synaptic-like microvesicles, endocytotic clathrin-coated vesicles, growth cone vesicles, and emptied large light core vesicles. The structural and functional backgrounds of different types of secretory vesicles are described, focusing on their formation and potential role.

Cell death induced by MPTP, a substrate for monoamine oxidase B

MPTP is known to cause PD symptoms in primates and in rodents. In order to exert its neurotoxicity MPTP must be converted by monoamine oxidase B into MPP(+) which is the true toxic agent. MPP(+) is taken up by the dopaminergic neurons of the substantia nigra in which it induces cell death. The present work reviews and discusses papers in which specific methods were used to determine whether cell death induced by MPTP/MPP(+) should be considered as apoptosis or necrosis. These two cell death modes may be distinguished using morphological and biochemical criteria. The effect of MPTP/MPP(+) was studied in vitro and in vivo. The results show that no univocal answer is possible. The most widespread interpretation is that MPTP/MPP(+) causes apoptosis when its neurotoxic effect is only sligh and necrosis when it is stronger. Similar considerations may be made also concerning the type of cell death occurring in the dopaminergic neurons in the substantia nigra of PD patients.

Death by a dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP+) and protection by EGF in GH3 cells

In this study we investigated the uptake and effect of a dopaminergic neurotoxin, 1-methyl-4-phenylpyridinium ion (MPP+) on a clonal strain, GH3 cells, established from rat anterior pituitary. Although the level was very low compared with that in PC12 cells, a clonal rat pheochromocytoma cell line, there was a detectable amount of tyrosine hydroxylase protein in GH3 cells. The levels of monoamines including dopamine in GH3 cells were also very low compared with those in PC12 cells. [3H]MPP+ was incorporated to GH3 cells in a concentration-dependent manner and the uptake was inhibited by nomifensine, an inhibitor of dopamine transporter. Addition of 200 microM MPP+ stimulated the leakage of lactate dehydrogenase (LDH) after a lag of 24 h. Pretreatment with 50 ng/ml of epidermal growth factor (EGF), but not nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF), protected against MPP+-induced cell death. These findings show that: (1) MPP+ uptake to GH3 cells was via an effective dopamine transport system and causes delayed cell death, and (2) EGF protects against MPP+-induced cell death. A possible role for GH3 cells as dopaminergic neurons is discussed.

The cytoplasmic tail of the vesicular acetylcholine transporter contains a synaptic vesicle targeting signal

The human homologue of the vesicular acetylcholine transporter (hVAChT) and the neuronal isoform of the vesicular monoamine transporter (hVMAT2) are differentially targeted to two populations of regulated secretory organelles when expressed in PC12 cells. Western blot analysis of subcellular fractions from sucrose equilibrium density gradients and glycerol velocity gradients of homogenates from stably transfected cells revealed hVAChT immunoreactivity in fractions that contain synaptophysin, a marker of synaptic vesicles, while hVMAT2 immunoreactivity was confined to heavy fractions containing chromogranin B, a marker of large dense core vesicles. In cells treated with nerve growth factor, hVAChT immunoreactivity alone co-localized with synaptophysin and was abundantly expressed on synaptic vesicle clusters. Chimeras between hVMAT2 and hVAChT were utilized to identify the domain of hVAChT required for its expression on synaptic vesicles and which would shift the expression of hVMAT2 from large dense core vesicles to synaptic vesicles. Biochemical, immunocytochemical, and electron microscopic analyses revealed that a chimera in which the cytoplasmic tail of hVMAT2 was replaced with hVAChT sequences was now preferentially targeted to synaptic vesicles. In addition, hVAChT expression on synaptic vesicles was nearly abolished when the hVMAT2 cytoplasmic tail was present. Thus, structural information resides within the terminal cytoplasmic domain of VAChT, which specifically targets it to synaptic vesicles.

Elevated expression of glutathione peroxidase in PC12 cells results in protection against methamphetamine but not MPTP toxicity

In vivo administration of either 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or methamphetamine (MA) produces damage to the dopaminergic nervous system which may be due in part to the generation of reactive oxygen species (ROS). The resistance of superoxide dismutase (SOD) over-expressing transgenic mice to the effects of both MPTP and MA suggests the involvement of superoxide in the resulting neurotoxicity of both compounds. Superoxide can be converted by SOD to hydrogen peroxide, which itself can cause cellular degeneration by reacting with free iron to produce highly reactive hydroxyl radicals resulting in damage to proteins, nucleic acids and membrane phospholipids. Hydrogen peroxide has also been reported to be produced via inhibition of NADH dehydrogenase by MPP + formed during oxidation of MPTP by MAO-B and by dopamine auto-oxidation following MA-induced dopamine release from synaptic vesicles within nerve terminals. To test whether hydrogen peroxide is an important factor in the toxicity of either of these two neurotoxins, we created clonal PC12 lines expressing elevated levels of the hydrogen peroxide-reducing enzyme glutathione peroxidase (GSHPx). Elevation of GSHPx levels in PC12 was found to diminish the rise in ROS levels and lipid peroxidation resulting from MA but not MPTP treatment. Elevated levels of GSHPx also appeared to prevent decreases in transport-mediated dopamine uptake produced via MA administration as well as to attenuate toxin-induced cell loss as measured by either MTT reduction or LDH release. Our data, therefore, suggest that hydrogen peroxide production likely contributes to MA toxicity in dopaminergic neurons.

Kinetic diversity in the fusion of exocytotic vesicles

The speed at which secretory vesicles fuse with the plasma membrane is a key parameter for neuronal and endocrine functions. We determined the precise time courses for fusion of small clear and large dense-core vesicles in PC12 and chromaffin cells by simultaneously measuring both plasma membrane areas and release of vesicular contents. We found that instantaneous increases in cytosolic Ca2+ concentration evoked vesicle fusion, but with time constants that varied over four orders of magnitude among different types of vesicles and cells. This indicates that the molecular machinery for the final Ca2+-dependent fusion steps of exocytosis is highly variable and is as critical as Ca2+ signalling processes in determining the speed and amount of secretion of neurotransmitters and hormones. Our results suggest a new possibility that the molecules responsible for the final fusion reaction that leads to vesicle fusion are key determinants for neuronal plasticity and hormonal disorders.

Active transport of acetylcholine by the human vesicular acetylcholine transporter

The characteristics of ATP-dependent transport of acetylcholine (ACh) in homogenates of pheochromocytoma (PC-12) cells stably transfected with the human vesicular acetylcholine transporter (VAChT) cDNA are described. The human VAChT protein was abundantly expressed in this line and appeared as a diffuse band with a molecular mass of approximately 75 kDa on Western blots. Vesicular [3H]ACh accumulation increased approximately 20 times over levels attained by the endogenous rat VAChT, expressed at low levels in control PC-12 cells. The transport of [3H]ACh by human VAChT was dependent upon the addition of exogenous ATP at 37 degrees C. Uptake was abolished by low temperature (4 degrees C), the proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone (2.5 microM) and bafilomycin A1 (1 microM), a specific inhibitor of the vesicular H+-ATPase. The kinetics of [3H]ACh uptake by human VAChT were saturable, exhibiting an apparent Km of 0.97 +/- 0.1 mM and Vmax of 0.58 +/- 0.04 nmol/min/mg. Maximal steady-state levels of vesicular [3H]ACh accumulation were directly proportional to the concentration of substrate present in the medium with saturation occurring at approximately 4 mM. Uptake was stereospecifically inhibited by L-vesamicol with an IC50 of 14.7 +/- 1.5 nM. The apparent affinity (Kd) of [3H]vesamicol for human VAChT was 4.1 +/- 0.5 nM, and the Bmax was 8.9 +/- 0.6 pmol/mg. The turnover (Vmax/Bmax) of the human VAChT was approximately 65/min. This expression system should prove useful for the structure/function analysis of VAChT.

Two components of exocytosis and endocytosis in phaeochromocytoma cells studied using caged Ca2+ compounds

1. Changes in membrane capacitance evoked by the rapid photolysis of a caged Ca2+ compound, DM-nitrophen or nitrophenyl-EGTA, were investigated in undifferentiated PC12 cells. They were interpreted as representing exocytosis and endocytosis. 2. The Ca2+ jumps evoked two components of exocytosis. Slow exocytosis was selectively evoked with small increases in intracellular Ca2+ concentration between 5 and 10 microM, while fast exocytosis preceded the slow one at [Ca2+]i greater than 10 microM. 3. The release rates of the two components of exocytosis depended steeply on [Ca2+]i. A half-maximal release rate was achieved at 8 and 24 microM for the slow and fast exocytoses, respectively. 4. Prior Ca2+ rises did not augment the fast exocytosis. 5. The fast exocytosis was often followed by a rapid decrease in membrane capacitance, representing endocytosis, after a delay of 0.5-2 s. The speed and delay in the fast endocytosis were Ca2+ dependent. Amounts of the fast endocytosis tended to balance with those of the fast exocytosis evoked by the same Ca2+ jumps. 6. The slow exocytosis was followed by a sluggish endocytosis that was associated with large capacitance steps indicative of secretory processes involving large dense-core vesicles. The onset of the slow endocytosis exhibited a complex Ca2+ dependence. The amounts of the slow endocytosis appeared to parallel those of the slow exocytosis. Prior induction of the slow exocytosis gave rise to selective excess retrieval of membrane during the slow endocytosis. 7. These data indicate the existence of two distinct populations of secretory vesicles in PC12 cells. They seem to couple selectively with specific endocytotic mechanisms. Our data suggest that the two vesicles belong to two distinct secretory pathways.

Role of endocrine cell microvesicles in intercellular chemical transduction

Microvesicles (MVs) in endocrine cells are morphologically similar to neuronal synaptic vesicles. MVs were shown to contain proteins involved in neurotransmitter storage such as vacuolar H(+)-ATPase and neurotransmitter transporters, and ones in vesicular trafficking such as synaptobrevins and N-ethylmaleimide-sensitive fusion protein. Isolated MVs accumulate cell-specific neurotransmitters in an energy-dependent manner. Upon stimulation, the MVs may fuse with the plasma membrane and secrete the internal neurotransmitters. Thus, endocrine cells possess an MV-mediated secretion system as an intercellular signal transducing system.

Biphasic effects of MPP+, a possible parkinsonism inducer, on dopamine content and tyrosine hydroxylase mRNA expression in PC12 cells

When PC12 cells were treated with 1-methyl-4-phenylpyridinium ion (MPP+) at various concentrations for 1 week, the dopamine (DA) content was increased compared to the control at 1-30 microM but was decreased to less than the control at concentrations above 100 microM. Cell death was caused by 300 microM MPP+, indicating that decrease in DA content proceeds cell death. When the cells were treated with 100 microM MPP+ for various periods, DA content was transiently increased (6 h-2 days) and then gradually decreased below the control (4-7 days). These results suggest that MPP+ possesses biphasic effects on DA content, being dependent on both concentrations and treatment periods. Moreover, by treatment with 100 microM MPP+, tyrosine hydroxylase (TH) mRNA expression was also transiently increased and then gradually decreased below the control, suggesting that MPP+ also possesses biphasic effects on TH mRNA expression.

Selective storage of acetylcholine, but not catecholamines, in neuroendocrine synaptic-like microvesicles of early endosomal origin

We have defined, in the neuroendocrine cell line PC12, the catecholamine- and acetylcholine-storing organelles in the context of the biogenesis of secretory granules and synaptic-like microvesicles (SLMVs). SLMVs were found to originate directly from early endosomes. Both early endosomes and SLMVs exhibited uptake and storage of biosynthetic acetylcholine. Surprisingly, however, despite the presence of a reserpine-sensitive vesicular amine transporter in early endosomes, SLMVs lacked detectable uptake and storage of catecholamines. This was confined to two populations of mature secretory granules, referred to as small and large mature secretory granules, which both derived from immature secretory granules. Our result show that PC12 cells lack small dense core vesicles, i.e., the catecholamine-storing, but secretory protein-lacking, vesicles found in sympathetic neurons and imply that the biogenesis of these vesicles requires the expression of a distinct type of vesicular amine transporter and/or a change in endosomal protein sorting.

Acetylcholine transport, storage, and release

ACh is released from cholinergic nerve terminals under both resting and stimulated conditions. Stimulated release is mediated by exocytosis of synaptic vesicle contents. The structure and function of cholinergic vesicles are becoming known. The concentration of ACh in vesicles is about 100-fold greater than the concentration in the cytoplasm. The AChT exhibits the lowest binding specificity among known ACh-binding proteins. It is driven by efflux of protons pumped into the vesicle by the V-type ATPase. A potent pharmacology of the AChT based on the allosteric VR has been developed. It has promise for clinical applications that include in vivo evaluation of the density of cholinergic innervation in organs based on PET and SPECT. The microscopic kinetics model that has been developed and the very low transport specificity of the vesicular AChT-VR suggest that the transporter has a channel-like or multidrug resistance protein-like structure. The AChT-VR has been shown to be tightly associated with proteoglycan, which is an unexpected macromolecular relationship. Vesamicol and its analogs block evoked release of ACh from cholinergic nerve terminals after a lag period that depends on the rate of release. Recycling quanta of ACh that are sensitive to vesamicol have been identified electrophysiologically, and they constitute a functional correlate of the biochemically identified VP2 synaptic vesicles. The concept of transmitter mobilization, including the observation that the most recently synthesized ACh is the first to be released, has been greatly clarified because of the availability of vesamicol. Differences among different cholinergic nerve terminal types in the sensitivity to vesamicol, the relative amounts of readily and less releasable ACh, and other aspects of the intracellular metabolism of ACh probably are more apparent than real. They easily could arise from differences in the relative rates of competing or sequential steps in the complicated intraterminal metabolism of ACh rather than from fundamental differences among the terminals. Nonquantal release of ACh from motor nerve terminals arises at least in part from the movement of cytoplasmic ACh through the AChT located in the cytoplasmic membrane, and it is blocked by vesamicol. Possibly, the proteoglycan component of the AChT-VR produces long-term residence of the macromolecular complex in the cytoplasmic membrane through interaction with the synaptic matrix. The preponderance of evidence suggests that a significant fraction of what previously, heretofore, had been considered to be nonquantal release from the motor neuron actually is quantal release from the neuron at sites not detected electrophysiologically.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of cocaine-sensitive dopamine uptake in PC12 cells

Dopamine uptake in rat pheochromocytoma (PC12) cells is a carrier-mediated process which follows Michaelis-Menten kinetics. Uptake was saturable with an apparent Km of 0.71 microM for dopamine and a Vmax of 3.2 pmol/2 x 10(5) cells/min. The rank order of potency for various amines was norepinephrine > or = dopamine > epinephrine. Uptake increased with increasing temperature and showed a sharp break in the Arrhenius plot at 27.5 degrees C. The Q10 was 1.39 above and 2.95 below 27.5 degrees C. Cocaine inhibited uptake in a dose-dependent manner with a Ki of 0.97 microM. The presence of cocaine lowered the apparent Km but did not affect the Vmax, indicating competitive inhibition. Tunicamycin inhibited [3H]dopamine accumulation in a dose- and time-dependent fashion suggesting the dopamine uptake site in PC12 cells is an asparagine-linked glycoprotein. Kinetic analysis showed a decrease in Vmax but not in the apparent Km after tunicamycin treatment, consistent with the notion that tunicamycin treatment results in the loss of a substantial amount of active carrier molecules.

The pharmacology of vesamicol: an inhibitor of the vesicular acetylcholine transporter

1. Vesamicol (2-[4-phenylpiperidino] cyclohexanol) inhibits the transport of acetylcholine into synaptic vesicles in cholinergic nerve terminals. 2. Recent pharmacological studies of the effects of vesamicol on skeletal neuromuscular transmission have revealed a pattern of activity for the compound consistent with the neurochemical observation of the mechanism of action of the compound. 3. Pharmacological manipulation of vesicular acetylcholine transport has been used to investigate the recycling and mobilization of synaptic vesicles within cholinergic nerve terminals. 4. In addition to its effects on vesicular acetylcholine transport, vesamicol also possesses some sodium channel and alpha-adrenoceptor blocking activity. 5. Vesamicol clearly represents a unique tool for investigating presynaptic mechanisms in cholinergic nerve terminals.

1-Methyl-4-(2'-ethylphenyl)-1,2,3,6-tetrahydropyridine-induced toxicity in PC12 cells is enhanced by preventing glycolysis

The effects of 1-methyl-4-(2'-ethylphenyl)-1,2,3,6-tetrahydropyridine (2'Et-MPTP), 1-methyl-4-(2'-ethylphenyl)pyridinium (2'Et-MPP+), and the classic complex 1 inhibitor, rotenone, on toxicity as well as on rates of glucose use and lactate production were studied using the pheochromocytoma PC12 cell line. PC12 cells are neoplastic in nature and have a high rate of glycolysis accompanied by a large production of lactate and a low use of glucose carbon through the Krebs cycle. 1-Methyl-4-phenylpyridinium (MPP+) and analogues such as 2'Et-MPP+ are actively accumulated by mitochondrial preparations in vitro and block NADH dehydrogenase of complex 1. This blockade results in biochemical sequelae that are ultimately cytotoxic. In this study, untreated PC12 cells used glucose and concomitantly accumulated lactate in a time-dependent manner at all concentrations of glucose studied. Treatment with 50 microM 2'Et-MPP+ or 50 nM rotenone increased both rates significantly, indicating a shift toward increased glycolysis. Cell death caused by the neurotoxins was also time and concentration dependent and markedly enhanced by glucose depletion in the medium. The increase in 2'Et-MPTP-induced toxicity in low glucose-supplemented cells was not due to an increase in pyridinium formation from the tetrahydropyridine, but rather to the lack of glucose for glycolysis. Moreover, inhibition of glycolysis with 2-deoxyglucose or iodoacetic acid also enhanced the lethality of the neurotoxins to the cells. The data in this study provide additional support to the hypothesis that 2'Et-MPP+ or related analogues act to kill cells by inhibiting mitochondrial respiration.(ABSTRACT TRUNCATED AT 250 WORDS)