Gut microbiota and neuropsychiatric disorders: Implications for neuroendocrine-immune regulation.

Recently, increasing evidence has shown gut microbiota dysbiosis might be implicated in the physiological mechanisms of neuropsychiatric disorders. Altered microbial community composition, diversity and distribution traits have been reported in neuropsychiatric disorders. However, the exact pathways by which the intestinal microbiota contribute to neuropsychiatric disorders remain largely unknown. Given that the onset and progression of neuropsychiatric disorders are characterized with complicated alterations of neuroendocrine and immunology, both of which can be continually affected by gut microbiota via "microbiome-gut-brain axis". Thus, we assess the complicated crosstalk between neuroendocrine and immunological regulation might underlie the mechanisms of gut microbiota associated with neuropsychiatric disorders. In this review, we summarized clinical and preclinical evidence on the role of the gut microbiota in neuropsychiatry disorders, especially in mood disorders and neurodevelopmental disorders. This review may elaborate the potential mechanisms of gut microbiota implicating in neuroendocrine-immune regulation and provide a comprehensive understanding of physiological mechanisms for neuropsychiatric disorders.

Bibliometrics Analysis of the Research Status and Trends of the Association Between Depression and Insulin From 2010 to 2020.

Depression is one of the common mental illnesses. Because it is an important complication of diabetes, its association with changes in insulin levels and insulin resistance, the causative factors of diabetes, has attracted widespread attention. However, the association between insulin and depression has not been systematically studied through bibliometric and visual analysis. This study is based on 3131 publications of Web of Science to identify the current research status and research trends in this field. The results show that since 2010, the number of publications has been growing rapidly. Cooperative network analysis shows that the United States, the University of Toronto and Roger S Mcintyre are the most influential countries, research institutes and scholars, respectively. Insulin resistance, obesity, and metabolic syndrome are hot topics in this field. Analysis of keywords and references reveals that "sex hormones," is new research area that constantly emerging. As far as we know, this study is the first one to visualize the association between depression and insulin and predict potential future research trends through bibliometric and visual analysis.

BmK NSPK, a Potent Potassium Channel Inhibitor from Scorpion Buthus martensii Karsch, Promotes Neurite Outgrowth via NGF/TrkA Signaling Pathway.

Scorpion toxins represent a variety of tools to explore molecular mechanisms and cellular signaling pathways of many biological functions. These toxins are also promising lead compounds for developing treatments for many neurological diseases. In the current study, we purified a new scorpion toxin designated as BmK NSPK (Buthus martensii Karsch neurite-stimulating peptide targeting Kv channels) from the BmK venom. The primary structure was determined using Edman degradation. BmK NSPK directly inhibited outward K+ current without affecting sodium channel activities, depolarized membrane, and increased spontaneous calcium oscillation in spinal cord neurons (SCNs) at low nanomolar concentrations. BmK NSPK produced a nonmonotonic increase on the neurite extension that peaked at ~10 nM. Mechanistic studies demonstrated that BmK NSPK increased the release of nerve growth factor (NGF). The tyrosine kinases A (TrkA) receptor inhibitor, GW 441756, eliminated the BmK NSPK-induced neurite outgrowth. BmK NSPK also increased phosphorylation levels of protein kinase B (Akt) that is the downstream regulator of TrkA receptors. These data demonstrate that BmK NSPK is a new voltage-gated potassium (Kv) channel inhibitor that augments neurite extension via NGF/TrkA signaling pathway. Kv channels may represent molecular targets to modulate SCN development and regeneration and to develop the treatments for spinal cord injury.

GABAergic System Dysfunction in Autism Spectrum Disorders.

Autism spectrum disorder (ASD) refers to a series of neurodevelopmental diseases characterized by two hallmark symptoms, social communication deficits and repetitive behaviors. Gamma-aminobutyric acid (GABA) is one of the most important inhibitory neurotransmitters in the central nervous system (CNS). GABAergic inhibitory neurotransmission is critical for the regulation of brain rhythm and spontaneous neuronal activities during neurodevelopment. Genetic evidence has identified some variations of genes associated with the GABA system, indicating an abnormal excitatory/inhibitory (E/I) neurotransmission ratio implicated in the pathogenesis of ASD. However, the specific molecular mechanism by which GABA and GABAergic synaptic transmission affect ASD remains unclear. Transgenic technology enables translating genetic variations into rodent models to further investigate the structural and functional synaptic dysregulation related to ASD. In this review, we summarized evidence from human neuroimaging, postmortem, and genetic and pharmacological studies, and put emphasis on the GABAergic synaptic dysregulation and consequent E/I imbalance. We attempt to illuminate the pathophysiological role of structural and functional synaptic dysregulation in ASD and provide insights for future investigation.

Airway relaxation mechanisms and structural basis of osthole for improving lung function in asthma.

Overuse of ß2-adrenoceptor agonist bronchodilators evokes receptor desensitization, decreased efficacy, and an increased risk of death in asthma patients. Bronchodilators that do not target ß2-adrenoceptors represent a critical unmet need for asthma management. Here, we characterize the utility of osthole, a coumarin derived from a traditional Chinese medicine, in preclinical models of asthma. In mouse precision-cut lung slices, osthole relaxed preconstricted airways, irrespective of ß2-adrenoceptor desensitization. Osthole administered in murine asthma models attenuated airway hyperresponsiveness, a hallmark of asthma. Osthole inhibited phosphodiesterase 4D (PDE4D) activity to amplify autocrine prostaglandin E2 signaling in airway smooth muscle cells that eventually triggered cAMP/PKA-dependent relaxation of airways. The crystal structure of the PDE4D complexed with osthole revealed that osthole bound to the catalytic site to prevent cAMP binding and hydrolysis. Together, our studies elucidate a specific molecular target and mechanism by which osthole induces airway relaxation. Identification of osthole binding sites on PDE4D will guide further development of bronchodilators that are not subject to tachyphylaxis and would thus avoid ß2-adrenoceptor agonist resistance.

Activation of voltage-gated sodium channels by BmK NT1 augments NMDA receptor function through Src family kinase signaling pathway in primary cerebellar granule cell cultures.

Voltage-gated sodium channels (VGSCs) are responsible for the generation and propagation of action potentials in excitable cells and are the molecular targets of an array of neurotoxins. BmK NT1, an α-scorpion toxin obtained from the scorpion Buthus martensii Karsch (BmK), produces neurotoxicity that is associated with extracellular Ca2+ influx through Na+-Ca2+ exchangers, N-methyl-d-aspartic acid (NMDA) receptors, and L-type Ca2+ channels in cultured cerebellar granule cells (CGCs). In the present study, we demonstrated that BmK NT1 triggered concentration-dependent release of excitatory neurotransmitters, glutamate and aspartate; both effects were eliminated by VGSC blocker, tetrodotoxin. More importantly, we demonstrated that a threshold concentration of BmK NT1 that produced marginal Ca2+ influx and neuronal death augmented glutamate-induced Ca2+ elevation and neuronal death in CGCs. BmK NT1-augmented glutamate-induced Ca2+ influx and neuronal death were suppressed by tetrodotoxin and MK-801 suggesting that the augmentation was through activation of VGSCs and NMDA receptors. Consistently, BmK NT1 also enhanced NMDA-induced Ca2+ influx. Further mechanistic investigations demonstrated that BmK NT1 increased the expression level of NMDA receptors on the plasma membrane and increased the phosphorylation level of NR2B at Tyr1472. Src family kinase inhibitor, 1-tert-butyl-3-(4-chlorophenyl)pyrazolo[3,4-d]pyrimidin-4-yl]amine (PP2), but not the inactive analogue, 4-amino-1-phenylpyrazolo[3,4-d]pyrimidine (PP3), eliminated BmK NT1-triggered NR2B phosphorylation, NMDA receptor trafficking, as well as BmK NT1-augmented NMDA Ca2+ response and neuronal death. Considered together, these data demonstrated that both presynaptic (excitatory amino acid release) and postsynaptic mechanisms (augmentation of NMDA receptor function) are critical for VGSC activation-induced neurotoxicity in primary CGC cultures.

BmK NSP, a new sodium channel activator from Buthus martensii Karsch, promotes neurite outgrowth in primary cultured spinal cord neurons.

Scorpion venom is a rich source of bioactive compounds that affect neuronal excitability by modulating the activities of various channels/receptors. In the current study, guided by a Ca2+ mobilization assay, we purified a new neuroactive peptide designated as BmK NSP (Buthus martensii Karsch neurite-stimulating peptide, MW: 7064.30 Da). The primary structure of BmK NSP was determined by Edman degradation. BmK NSP concentration-dependently elevated intracellular Ca2+ concentration ([Ca2+]i) with an EC50 value of 4.18 µM in primary cultured spinal cord neurons (SCNs). Depletion of extracellular Ca2+ abolished BmK NSP-triggered Ca2+ response. Moreover, we demonstrated that BmK NSP-induced Ca2+ response was partially suppressed by the inhibitors of L-type Ca2+ channels, Na+-Ca2+ exchangers and NMDA receptors and was abolished by voltage-gated sodium channel (VGSC) blocker, tetrodotoxin. Whole-cell patch clamp recording demonstrated that BmK NSP delayed VGSC inactivation (EC50 = 1.10 µM) in SCNs. BmK NSP enhanced neurite outgrowth in a non-monotonic manner that peaked at ~30 nM in SCNs. BmK NSP-promoted neurite outgrowth was suppressed by the inhibitors of L-type Ca2+ channels, NMDA receptors, and VGSCs. Considered together, these data demonstrate that BmK NSP is a new α-scorpion toxin that enhances neurite outgrowth through main routes of Ca2+ influx. Modulation of VGSC activity by α-scorpion toxin might represent a novel strategy to regulate the neurogenesis in SCNs.

Effects of Electroconvulsive Therapy on Depression and Its Potential Mechanism.

Depression is one of the most common disorders causing mortality around the world. Although electroconvulsive therapy (ECT) is, along with antidepressants and psychotherapy, one of the three major treatments of depression, it is still considered as the last resort for depressed patients. This situation is partially due to limited studies and uncertainty regarding its mechanism. However, decades of increased research have focused on the effects of ECT on depression and its potential mechanism. Furthermore, these investigations may suggest that ECT should be a first-line therapy for depression due to its profound effects in relieving desperation in certain situations. Here, we outline recent clinical and preclinical studies and summarize the advantages and disadvantages of ECT. Thus, this review may provide some hints for clinical application.

Role of Leptin in Mood Disorder and Neurodegenerative Disease.

The critical regulatory role of leptin in the neuroendocrine system has been widely reported. Significantly, leptin can improve learning and memory, affect hippocampal synaptic plasticity, exert neuroprotective efficacy and reduce the risk of several neuropsychiatric diseases. In terms of depression, leptin could modulate the levels of neurotransmitters, neurotrophic factors and reverse the dysfunction in the hypothalamic-pituitary-adrenal axis (HPA). At the same time, leptin affects neurological diseases during the regulation of metabolic homeostasis. With regards to neurodegenerative diseases, leptin can affect them via neuroprotection, mainly including Alzheimer's disease and Parkinson's disease. This review will summarize the mechanisms of leptin signaling within the neuroendocrine system with respect to these diseases and discuss the therapeutic potential of leptin.

BmK NT1-induced neurotoxicity is mediated by PKC/CaMKâ ¡-dependent ERK1/2 and p38 activation in primary cultured cerebellar granule cells.

Voltage-gated sodium channels (VGSCs) represent molecular targets for a number of potent neurotoxins that affect the ion permeation or gating kinetics. BmK NT1, an α-scorpion toxin purified from Buthus martensii Karch (BMK), induces excitatory neurotoxicity by activation of VGSCs with subsequent overloading of intracellular Ca2+ in cerebellar granule cells (CGCs). In the current study, we further investigated signaling pathways responsible for BmK NT1-induced neurotoxicity in CGCs. BmK NT1 exposure induced neuronal death in different development stages of CGCs with similar potencies ranging from 0.21-0.48 µM. The maximal neuronal death induced by BmK NT1 gradually increased from 25.6% at 7 days in vitro (DIVs) to 42.1%, 47.8%, and 67.2% at 10, 13, and 16 DIVs, respectively, suggesting that mature CGCs are more vulnerable to BmK NT1 exposure. Application of Ca2+/calmodulin-dependent protein kinase Ⅱ (CaMKⅡ) inhibitors, KN-62 or KN-93, but not Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) inhibitor, STO-609, completely abolished BmK NT1-induced neuronal death. Moreover, BmK NT1 exposure stimulated CaMKⅡ phosphorylation. BmK NT1 also stimulated extracellular regulated protein kinases 1/2 (ERK1/2) and p38 phosphorylation which was abolished by tetrodotoxin demonstrating the role of VGSCs on BmK NT1-induced ERK1/2 and p38 phosphorylation. However, BmK NT1 didn't affect c-Jun N-terminal kinase (JNK) phosphorylation. In addition, both ERK1/2 inhibitor, U0126 and p38 inhibitor, SB203580 attenuated BmK NT1-induced neuronal death. Both PKC inhibitor, Gö 6983 and CaMKⅡ inhibitor, KN-62 abolished BmK NT1-induced ERK1/2 and p38 phosphorylation. Considered together, these data demonstrate that BmK NT1-induced neurotoxicity is through PKC/CaMKⅡ mediated ERK1/2 and p38 activation.

Dehydrocrenatidine Inhibits Voltage-Gated Sodium Channels and Ameliorates Mechanic Allodia in a Rat Model of Neuropathic Pain.

Picrasma quassioides (D. Don) Benn, a medical plant, is used in clinic to treat inflammation, pain, sore throat, and eczema. The alkaloids are the main active components in P. quassioides. In this study, we examined the analgesic effect of dehydrocrenatidine (DHCT), a ß-carboline alkaloid abundantly found in P. quassioides in a neuropathic pain rat model of a sciatic nerve chronic constriction injury. DHCT dose-dependently attenuated the mechanic allodynia. In acutely isolated dorsal root ganglion, DHCT completely suppressed the action potential firing. Further electrophysiological characterization demonstrated that DHCT suppressed both tetrodotoxin-resistant (TTX-R) and sensitive (TTX-S) voltage-gated sodium channel (VGSC) currents with IC50 values of 12.36 µM and 4.87 µM, respectively. DHCT shifted half-maximal voltage (V1/2) of inactivation to hyperpolarizing direction by ~16.7 mV in TTX-S VGSCs. In TTX-R VGSCs, DHCT shifted V1/2 of inactivation voltage to hyperpolarizing direction and V1/2 of activation voltage to more depolarizing potential by ~23.9 mV and ~12.2 mV, respectively. DHCT preferred to interact with an inactivated state of VGSCs and prolonged the repriming time in both TTX-S and TTX-R VGSCs, transiting the channels into a slow inactivated state from a fast inactivated state. Considered together, these data demonstrated that the analgesic effect of DHCT was likely though the inhibition of neuronal excitability.

BmK AEP, an Anti-Epileptic Peptide Distinctly Affects the Gating of Brain Subtypes of Voltage-Gated Sodium Channels.

BmK AEP, a scorpion peptide purified form the venom of Buthus martensii Karsch, has been reported to display anti-epileptic activity. Voltage-gated sodium channels (VGSCs) are responsible for the rising phase of action potentials (APs) in neurons and, therefore, controlling neuronal excitability. To elucidate the potential molecular mechanisms responsible for its anti-epileptic activity, we examined the influence of BmK AEP on AP firing in cortical neurons and how BmK AEP influences brain subtypes of VGSCs (Nav1.1⁻1.3 and Nav1.6). BmK AEP concentration-dependently suppresses neuronal excitability (AP firing) in primary cultured cortical neurons. Consistent with its inhibitory effect on AP generation, BmK AEP inhibits Na⁺ peak current in cortical neurons with an IC50 value of 2.12 µM by shifting the half-maximal voltage of activation of VGSC to hyperpolarized direction by ~7.83 mV without affecting the steady-state inactivation. Similar to its action on Na⁺ currents in cortical neurons, BmK AEP concentration-dependently suppresses the Na⁺ currents of Nav1.1, Nav1.3, and Nav1.6, which were heterologously expressed in HEK-293 cells, with IC50 values of 3.20, 1.46, and 0.39 µM with maximum inhibition of 82%, 56%, and 93%, respectively. BmK AEP shifts the voltage-dependent activation in the hyperpolarized direction by ~15.60 mV, ~9.97 mV, and ~6.73 mV in Nav1.1, Nav1.3, and Nav1.6, respectively, with minimal effect on steady-state inactivation. In contrast, BmK AEP minimally suppresses Nav1.2 currents (~15%) but delays the inactivation of the channel with an IC50 value of 1.69 µM. Considered together, these data demonstrate that BmK AEP is a relatively selective Nav1.6 gating modifier which distinctly affects the gating of brain subtypes of VGSCs.

Saikosaponin d causes apoptotic death of cultured neocortical neurons by increasing membrane permeability and elevating intracellular Ca2+ concentration.

Saikosaponins (SSs) are a class of naturally occurring oleanane-type triterpenoid saponins found in Radix bupleuri that has been widely used in traditional Chinese medicine. As the main active principals of Radix bupleuri, SSs have been shown to suppress mouse motor activity, impair learning and memory, and decrease hippocampal neurogenesis. In the present study, we investigated the effect of five SSs (SSa, SSb1, SSb2, SSc, and SSd) on neuronal viability and the underlying mechanisms in cultured murine neocortical neurons. We demonstrate that SSa, SSb1 and SSd produce concentration-dependent apoptotic neuronal death and induce robust increase in intracellular Ca2+ concentration ([Ca2+]i) at low micromolar concentrations with a rank order of SSd > SSa > SSb1, whereas SSb2 and SSc have no detectable effect on both neuronal survival and [Ca2+]i. Mechanistically, SSd-induced elevation in [Ca2+]i is the primary result of enhanced extracellular Ca2+ influx, which likely triggers Ca2+-induced Ca2+ release through ryanodine receptor activation, but not SERCA inhibition. SSd-induced Ca2+ entry occurs through a non-selective mechanism since blockers of major neuronal Ca2+ entry pathways, including L-type Ca2+ channel, NMDA receptor, AMPA receptor, Na+-Ca2+ exchanger, and TRPV1, all failed to attenuate the Ca2+ response to SSd. Further studies demonstrate that SSd increases calcein efflux and induces an inward current in neocortical neurons. Together, these data demonstrate that SSd elevates [Ca2+]i due to its ability to increase membrane permeability, likely by forming pores in the surface of membrane, which leads to massive Ca2+ influx and apoptotic neuronal death in neocortical neurons.

Recent Advances in Herbal Medicines for Digestive System Malignancies.

Herbal medicines, as an important part of traditional Chinese medicine (TCM), have been used to treat digestive system malignancies (DSM) for many years, and have gradually gained recognition worldwide. The role of herbal medicines in the comprehensive treatment of DSM is being improved from adjuvant treatment of the autologous immune function in cancer patients, to the treatment of both the symptoms and disease, direct inhibition of tumor cell growth and proliferation, and induction of tumor cell autophagy and apoptosis. Their specific mechanisms in these treatments are also being explored. The paper reviews the current anti-tumor mechanisms of TCM, including single herbal medicines, Chinese herbal formulations, Chinese medicine preparations and TCM extract, and their application in the comprehensive treatment of digestive system tumors, providing a reference for clinical application of TCM.

The Role of KLF4 in Alzheimer's Disease.

Krüppel-like factor 4 (KLF4), a member of the family of zinc-finger transcription factors, is widely expressed in range of tissues that play multiple functions. Emerging evidence suggest KLF4's critical regulatory effect on the neurophysiological and neuropathological processes of Alzheimer's disease (AD), indicating that KLF4 might be a potential therapeutic target of neurodegenerative diseases. In this review, we will summarize relevant studies and illuminate the regulatory role of KLF4 in the neuroinflammation, neuronal apoptosis, axon regeneration and iron accumulation to clarify KLF4's status in the pathogenesis of AD.

Selective Voltage-Gated Sodium Channel Peptide Toxins from Animal Venom: Pharmacological Probes and Analgesic Drug Development.

Voltage-gated sodium channels (Navs) play critical roles in action potential generation and propagation. Nav channelopathy as well as pathological sensitization contribute to allodynia and hyperalgesia. Recent evidence has demonstrated the significant roles of Nav subtypes (Nav1.3, 1.7, 1.8, and 1.9) in nociceptive transduction, and therefore these Navs may represent attractive targets for analgesic drug discovery. Animal toxins are structurally diverse peptides that are highly potent yet selective on ion channel subtypes and therefore represent valuable probes to elucidate the structures, gating properties, and cellular functions of ion channels. In this review, we summarize recent advances on peptide toxins from animal venom that selectively target Nav1.3, 1.7, 1.8, and 1.9, along with their potential in analgesic drug discovery.

Activation of sodium channel by a novel α-scorpion toxin, BmK NT2, stimulates ERK1/2 and CERB phosphorylation through a Ca2+ dependent pathway in neocortical neurons.

Neuronal excitability controls the expression of a variety of genes and proteins and therefore regulates neurite outgrowth and synapse formation, fundamental physiological processes controlling learning and memory. Scorpion venom contains many neurotoxins which alter ion channel activities that influence neuronal excitability. In this study, a novel scorpion peptide termed BmK NT2 was purified from venom of Chinese scorpion Buthus martensii Karsch by combining mass spectrum mapping and intracellular Ca2+ concentration measurement in primary cultured neocortical neurons. Electrophysiological experiments demonstrated that BmK NT2 concentration-dependently delayed inactivation of voltage-gated sodium channels (VGSCs) with an EC50 value of 0.91µM, and shifted the steady-state activation and inactivation of VGSCs to hyperpolarized direction. The effects of BmK NT2 on electrophysiological characteristics of VGSCs were similar to that of α-scorpion toxins. BmK NT2 altered Ca2+ dynamics and increased phosphorylation of extracellular-regulated protein kinases (ERK) 1/2 and cAMP-response element binding (CREB) proteins, which were eliminated by the VGSC blocker, tetrodotoxin. These data demonstrate that BmK NT2 is a novel VGSC α-scorpion toxin which is sufficient to increase the phosphorylation of ERK1/2 and CREB proteins, suggesting that modulation of VGSC function by α-scorpion toxin exerts neurotrophic effect in primary cultured neocortical neurons.

Allergens in red ginseng extract induce the release of mediators associated with anaphylactoid reactions.

BACKGROUND: Anaphylactoid reactions induced by preparations containing red ginseng have been reported. The aim of this study is to evaluate the allergenicity and screen potential allergens in red ginseng extract thoroughly. METHODS: Red ginseng extract (RGE) and different fractions of RGE were prepared and evaluated by measuring the degranulation and viability of rat basophilic leukemia 2H3 (RBL-2H3) cells. Potential allergens were screened by RBL-2H3 cell extraction and allergenicity verified in RBL-2H3 cells, mouse peritoneal mast cells, Laboratory of Allergic Disease 2 (LAD2) human mast cells and mice, respectively. RESULTS: 80% ethanol extract of red ginseng extract induced mast cell degranulation with less cytotoxicity, but 40% ethanol extract could not. Ginsenoside Rd and 20(S)-Rg3 could induce a significant increase in ß-hexosaminidase release, histamine release and translocation of phosphatidylserine in RBL-2H3 cells. Ginsenoside Rd and 20(S)-Rg3 also increased ß-hexosaminidase release and the intracellular Ca2+ concentration in mouse peritoneal mast cells and LAD2 cells. In addition, histamine levels in serum of mice were elevated dose-dependently. CONCLUSIONS: Ginsenoside Rd and 20(S)-Rg3 are potential allergens that induce the release of mediators associated with anaphylactoid reactions. Our study could guide optimization of methods associated with Rd/20(S)-Rg3-containing preparations and establishment of quality standards for safe application of Traditional Chinese Medicines.

Modification of distinct ion channels differentially modulates Ca2+ dynamics in primary cultured rat ventricular cardiomyocytes.

Primary cultured cardiomyocytes show spontaneous Ca2+ oscillations (SCOs) which not only govern contractile events, but undergo derangements that promote arrhythmogenesis through Ca2+ -dependent mechanism. We systematically examined influence on SCOs of an array of ion channel modifiers by recording intracellular Ca2+ dynamics in rat ventricular cardiomyocytes using Ca2+ specific fluorescence dye, Fluo-8/AM. Voltage-gated sodium channels (VGSCs) activation elongates SCO duration and reduces SCO frequency while inhibition of VGSCs decreases SCO frequency without affecting amplitude and duration. Inhibition of voltage-gated potassium channel increases SCO duration. Direct activation of L-type Ca2+ channels (LTCCs) induces SCO bursts while suppressing LTCCs decreases SCO amplitude and slightly increases SCO frequency. Activation of ryanodine receptors (RyRs) increases SCO duration and decreases both SCO amplitude and frequency while inhibiting RyRs decreases SCO frequency without affecting amplitude and duration. The potencies of these ion channel modifiers on SCO responses are generally consistent with their affinities in respective targets demonstrating that modification of distinct targets produces different SCO profiles. We further demonstrate that clinically-used drugs that produce Long-QT syndrome including cisapride, dofetilide, sotalol, and quinidine all induce SCO bursts while verapamil has no effect. Therefore, occurrence of SCO bursts may have a translational value to predict cardiotoxicants causing Long-QT syndrome.

Activation of sodium channels by α-scorpion toxin, BmK NT1, produced neurotoxicity in cerebellar granule cells: an association with intracellular Ca2+ overloading.

Voltage-gated sodium channels (VGSCs) are responsible for the action potential generation in excitable cells including neurons and involved in many physiological and pathological processes. Scorpion toxins are invaluable tools to explore the structure and function of ion channels. BmK NT1, a scorpion toxin from Buthus martensii Karsch, stimulates sodium influx in cerebellar granule cells (CGCs). In this study, we characterized the mode of action of BmK NT1 on the VGSCs and explored the cellular response in CGC cultures. BmK NT1 delayed the fast inactivation of VGSCs, increased the Na+ currents, and shifted the steady-state activation and inactivation to more hyperpolarized membrane potential, which was similar to the mode of action of α-scorpion toxins. BmK NT1 stimulated neuron death (EC50 = 0.68 µM) and produced massive intracellular Ca2+ overloading (EC50 = 0.98 µM). TTX abrogated these responses, suggesting that both responses were subsequent to the activation of VGSCs. The Ca2+ response of BmK NT1 was primary through extracellular Ca2+ influx since reducing the extracellular Ca2+ concentration suppressed the Ca2+ response. Further pharmacological evaluation demonstrated that BmK NT1-induced Ca2+ influx and neurotoxicity were partially blocked either by MK-801, an NMDA receptor blocker, or by KB-R7943, an inhibitor of Na+/Ca2+ exchangers. Nifedipine, an L-type Ca2+ channel inhibitor, slightly suppressed both Ca2+ response and neurotoxicity. A combination of these three inhibitors abrogated both responses. Considered together, these data ambiguously demonstrated that activation of VGSCs by an α-scorpion toxin was sufficient to produce neurotoxicity which was associated with intracellular Ca2+ overloading through both NMDA receptor- and Na+/Ca2+ exchanger-mediated Ca2+ influx.