Histamine Excites Rat GABAergic Ventral Pallidum Neurons via Co-activation of H1 and H2 Receptors / 神经科学通报·英文版

The ventral pallidum (VP) is a crucial component of the limbic loop of the basal ganglia and participates in the regulation of reward, motivation, and emotion. Although the VP receives afferent inputs from the central histaminergic system, little is known about the effect of histamine on the VP and the underlying receptor mechanism. Here, we showed that histamine, a hypothalamic-derived neuromodulator, directly depolarized and excited the GABAergic VP neurons which comprise a major cell type in the VP and are responsible for encoding cues of incentive salience and reward hedonics. Both postsynaptic histamine H1 and H2 receptors were found to be expressed in the GABAergic VP neurons and co-mediate the excitatory effect of histamine. These results suggested that the central histaminergic system may actively participate in VP-mediated motivational and emotional behaviors via direct modulation of the GABAergic VP neurons. Our findings also have implications for the role of histamine and the central histaminergic system in psychiatric disorders.

Antiarrhythmic ionic mechanism of Guanfu base A--Selective inhibition of late sodium current in isolated ventricular myocytes from guinea pigs / 中国天然药物

The present study was designed to determine the effects of Guanfu base A (GFA) on the late sodium current (INa.L), transient sodium current (INa.T), HERG current (IHERG), and Kv1.5 current (IKv1.5). The values of INa.L, INa.T, IHERG and IKv1.5 were recorded using the whole-cell patch clamp technique. Compared with other channels, GFA showed selective blocking activity in late sodium channel. It inhibited INa.L in a concentration-dependent manner with an IC50 of (1.57 ± 0.14) μmol · L(-1), which was significantly lower than its IC50 values of (21.17 ± 4.51) μmol · L(-1) for the INa.T. The inhibitory effect of GFA on INa,L was not affected by 200 μmol · L(-1) H2O2. It inhibited IHERG with an IC50 of (273 ± 34) μmol · L(-1) and has slight blocking effect on IKv1.5, decreasing IKv1.5 by only 20.6% at 200 μmol · L(-1). In summary, GFA inhibited INa.L selectively and remained similar inhibition in presence of reactive oxygen species. These findings may suggest a novel molecular mechanism for the potential clinical application of GFA in the treatment of cardiovascular disorders.

Scorpion toxin BmK I directly activates Nav1.8 in primary sensory neurons to induce neuronal hyperexcitability in rats

Voltage-gated sodium channels (VGSCs) in primary sensory neurons play a key role in transmitting pain signals to the central nervous system. BmK I, a site-3 sodium channel-specific toxin from scorpion Buthus martensi Karsch, induces pain behaviors in rats. However, the subtypes of VGSCs targeted by BmK I were not entirely clear. We therefore investigated the effects of BmK I on the current amplitude, gating and kinetic properties of Nav1.8, which is associated with neuronal hyperexcitability in DRG neurons. It was found that BmK I dose-dependently increased Nav1.8 current in small-sized (<25 μm) acutely dissociated DRG neurons, which correlated with its inhibition on both fast and slow inactivation. Moreover, voltage-dependent activation and steady-state inactivation curves of Nav1.8 were shifted in a hyperpolarized direction. Thus, BmK I reduced the threshold of neuronal excitability and increased action potential firing in DRG neurons. In conclusion, our data clearly demonstrated that BmK I modulated Nav1.8 remarkably, suggesting BmK I as a valuable probe for studying Nav1.8. And Nav1.8 is an important target related to BmK I-evoked pain.

Lipid bilayer modification alters the gating properties and pharmacological sensitivity of voltage-gated sodium channel / 生理学报

Voltage-gated sodium channels (VGSCs) are widely distributed in most cells and tissues, performing many physiological functions. As one kind of membrane proteins in the lipid bilayer, whether lipid composition plays a role in the gating and pharmacological sensitivity of VGSCs still remains unknown. Through the application of sphingomyelinase D (SMaseD), the gating and pharmacological sensitivity of the endogenous VGSCs in neuroblastoma ND7-23 cell line to BmK I and BmK AS, two sodium channel-specific modulators from the venom of Buthus martensi Karsch (BmK), were assessed before and after lipid modification. The results showed that, in ND7-23 cells, SMaseD did not change the gating properties of VGSCs. However, SMaseD application altered the slope factor of activation with the treatment of 30 nmol/L BmK I, but caused no significant effects at 100 and 500 nmol/L BmK I. With low concentration of BmK I (30 and 100 nmol/L) treatment, the application of SMaseD exerted hyperpolarizing effects on both slow-inactivation and steady-state inactivation, and increased the recovery time constant, whereas total inactivation and recovery remained unaltered at 500 nmol/L BmK I. Meanwhile, SMaseD modulation hyperpolarized the voltage dependence of slow-inactivation at 0.1 nmol/L BmK AS and altered the slope factor of slow-inactivation at 10 nmol/L BmK AS, whereas other parameters remained unchanged. These results indicated a possibility that the lipid bilayer would disturb the pharmacological sensitivity of VGSCs for the first time, which might open a new way of developing new drugs for treating sodium channelopathies.

Estudo do efeito de mutações no gene do canal de sódio de aedes aegypti: distribuição em populações naturais, correlação com resistência a piretroide e custo evolutivo / Studies of the effects of mutations in voltage gated sodium channel of aedes aegypti: distribution in natural populations, correlation with resistance to pyrethroid and adaptive cost

Aedes aegypti é o principal vetor de dengue. Uma das formas mais adotadas de controle é o uso de inseticidas, notadamente da classe dos piretroides, contra o mosquito no estágio alado. Estes compostos são prediletos, pois apresentam um menor impacto ambiental e conferem atuação rápida no sistema nervoso dos insetos, conhecida como efeito knockdown. O intenso uso de inseticidas tem selecionado populações de mosquitos resistentes em todo o mundo. Uma das principais formas fisiológicas de resistência é a alteração no canal de sódio regulado por voltagem (NaV), sítio alvo dos piretroides. Substituições de aminoácido no NaV, que conferem resistência ao efeito knockdown, são chamadas de mutações kdr (knockdown resistance). Em Ae. aegypti, há pelo menos duas mutações kdr descritas na América Latina: Val1016Ile e Phe1534Cys, respectivamente, nos domínios IIS6 e IIIS6 do NaV. Nesta dissertação, estudamos a distribuição das mutações kdr em populações naturais de Ae. aegypti do Brasil. Para tanto, genotipamos cerca de 30 indivíduos de cada uma de 30 populações para os sítios 1016 e 1534, via PCRs alelo-específicas. Considerando ambos os sítios para configuração alélica de um único locus, identificamos três alelos: NaVS (selvagem), NaVR1 (mutante no sítio 1534) e NaVR2 (mutante em ambos os sítios). O alelo kdr NaVR1 encontrou-se distribuído em todas as regiões do Brasil, porém o NaVR2 apenas na região centro-sul, ou em baixa frequência em algumas localidades do norte-nordeste, com exceção do estado de Roraima...

In order to acomplish this, we isolated an homozygous lineage for the mutation in both 1016 and 1534 sites, starting from a natural population. Following, the mutant allele was inserted into a genetic background gold-standard for vigour and susceptibility, through retro crosses with Rockefeller (Rock) strain. This lineage, called Rock-kdr, developed longer, had and increase in the locomotor activity and producedsmaller number of eggs, compared to Rock. Population-cages assays showed that the mutant allele frequency considerably diminished over 15 generations under an environmental free of insecticide, corroborating the hypothesis of side effects hitchhiked by the resistance. Finally, we presented a series of evidence that the occurrence of gene duplication in Ae. aegypti NaV. The presence of the mutationIle1011Met always in heterozygosis was the first suggestion for the phenomena. Sequencing of the IIS6NaV region of individual mosquitoes showed the presence of three haplotypes, of which suggested theconfiguration of one duplicated allele. Crosses experiments with parental with known genotypes for the1011 site corroborated the hypothesis of gene duplication. Molecularly, copy number variation assays based on real-time PCR suggested the amplification of five times more copies of the evaluated NaV fragment in the laboratory lineage than in Rock...

A Case of Sudden Cardiac Death due to Pilsicainide-Induced Torsades de Pointes

An 84-year-old male received oral pilsicainide, a pure sodium channel blocker with slow recovery kinetics, to convert his paroxysmal atrial fibrillation to a sinus rhythm; the patient developed sudden cardiac death two days later. The Holter electrocardiogram, which was worn by chance, revealed torsade de pointes with gradually prolonged QT intervals. This drug is rapidly absorbed from the gastrointestinal tract, and most of it is excreted from the kidney. Although the patient's renal function was not highly impaired and the dose of pilsicainide was low, the plasma concentration of pilsicainide may have been high, which can produce torsades de pointes in the octogenarian. Although the oral administration of class IC drugs, including pilsicainide, is effective to terminate atrial fibrillation, careful consideration must be taken before giving these drugs to octogenarians.

Development of cardioplegic solution without potassium: experimental study in rat / Desenvolvimento de solução cardioplégica sem potássio: estudo experimental em ratos

INTRODUCTION: Myocardial preservation during open heart surgeries and harvesting for transplant are of great importance. The heart at the end of procedure has to resume its functions as soon as possible. All cardioplegic solutions are based on potassium for induction of cardioplegic arrest. OBJECTIVE: To assess a cardioplegic solution with no potassium addition to the formula with two other commercially available cardioplegic solutions. The comparative assessment was based on cytotoxicity, adenosine triphosphate myocardial preservation, and caspase 3 activity. The tested solution (LIRM) uses low doses of sodium channel blocker (lidocaine), potassium channel opener (cromakalin), and actin/myosin cross bridge inhibitor (2,3-butanedione monoxime). METHODS: Wistar rats underwent thoracotomy under mechanical ventilation and three different solutions were used for "in situ" perfusion for cardioplegic arrest induction: Custodiol (HTK), Braile (G/A), and LIRM solutions. After cardiac arrest, the hearts were excised and kept in cold storage for 4 hours. After this period, the hearts were assessed with optical light microscopy, myocardial ATP content and caspase 3 activity. All three solutions were evaluated for direct cytotoxicity with L929 and WEHI-164 cells. RESULTS: The ATP content was higher in the Custodiol group compared to two other solutions (P<0.05). The caspase activity was lower in the HTK group compared to LIRM and G/A solutions (P<0.01). The LIRM solution showed lower caspase activity compared to Braile solution (P<0.01). All solutions showed no cytotoxicity effect after 24 hours of cells exposure to cardioplegic solutions. CONCLUSION: Cardioplegia solutions without potassium are promised and aminoacid addition might be an interesting strategy. More evaluation is necessary for an optimal cardioplegic solution development.

INTRODUÇÃO: Preservação do miocárdio durante cirurgias cardíacas abertas e de colheita para transplante são de grande importância. O coração ao final do processo tem de retomar as suas funções, logo que possível. Todas as soluções cardioplégicas são baseadas em potássio, para indução de parada cardioplégica. OBJETIVO: Comparar a uma solução cardioplégica sem adição de potássio à sua fórmula com duas outras soluções cardioplégicas disponíveis comercialmente. A avaliação comparativa foi baseada na citotoxicidade, preservação miocárdica (adenosina trifosfato, ATP) e atividade da caspase 3. A solução testada (LIRM) utiliza baixas doses de bloqueador de canal de sódio (lidocaína), abridor do canal de potássio (cromacalina) e inibidor da ponte actina/miosina (2,3-butanodiona monoxima). MÉTODOS: Ratos Wistar foram submetidos à toracotomia sob ventilação mecânica e três soluções diferentes foram utilizadas para perfusão in situ para a indução de parada cardioplégica: soluções Custodiol (HTK) Braile (G/A) e LIRM. Após parada cardíaca, os corações foram retirados e mantidos em câmara fria por 4 horas. Após esse período, o coração foi avaliado com microscopia de luz ótica, o conteúdo de ATP miocárdico e atividade da caspase 3. Todas as três soluções foram avaliadas quanto à citotoxicidade direta com células L929 e WEHI-164. RESULTADOS: A quantidade de ATP foi maior no grupo Custodiol em comparação às com outras duas soluções (P<0,05). A atividade de caspase foi menor no grupo HTK quando comparado às soluções LIRM e G/A (P<0,01). A solução LIRM demonstrou menor atividade da caspase em comparação à solução Braile (P<0,01). Todas as soluções não mostraram qualquer efeito de citotoxicidade após 24 horas de exposição das células às soluções cardioplégicas. CONCLUSÃO: Soluções cardioplégicas sem potássio são uma perspectiva e a adição de aminoácido pode ser uma estratégia interessante. Mais avaliações são necessárias para o desenvolvimento ideal da solução cardioplégica.

Effect of cAMP on short-circuit current in isolated human ciliary body / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Cyclic adenosine monophosphate (cAMP) could activate chloride channels in bovine ciliary body and trigger an increase in the ionic current (short-circuit current, Isc) across the ciliary processes in pigs. The purpose of this study was to investigate how cAMP modulates Isc in isolated human ciliary processes and the possible involvement of chloride transport across the tissue in cAMP-induced Isc change.</p><p><b>METHODS</b>In an Ussing-type chamber system, the Isc changes induced by the cAMP analogue 8-bromo-cAMP and an adenylyl cyclase activator forskolin in isolated human ciliary processes were assessed. The involvement of Cl(-) component in the bath solution was investigated. The effect of Cl(-) channel (10 µmol/L niflumic acid and 1 mmol/L 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS)), K(+) channel (10 mmol/L tetraethylammonium chloride (TEA)), or Na(+) channel blockers (1 mmol/L amiloride) on 8-bromo-cAMP-induced Isc change was also studied.</p><p><b>RESULTS</b>Dose-dependently, 8-bromo-cAMP (10 nmol/L-30 µmol/L) or forskolin (10 nmol/L-3 µmol/L) increased Isc across the ciliary processes with an increase in negative potential difference on the non-pigmented epithelium (NPE) side of the tissue. Isc increase induced by 8-bromo-cAMP was more pronounced when the drug was applied on the NPE side than on the pigmented epithelium side. When the tissue was bathed in low Cl(-) solutions, the Isc increase was significantly inhibited. Finally, niflumic acid and DIDS, but not TEA or amiloride, significantly prevented the Isc increase induced by 8-bromo-cAMP.</p><p><b>CONCLUSIONS</b>cAMP stimulates stroma-to-aqueous anionic transport in isolated human ciliary processes. Chloride is likely to be among the ions, the transportation of which across the tissue is triggered by cAMP, suggesting the potential role of cAMP in the process of aqueous humor formation in human eyes.</p>

Inhibitory effects of propofol on supraoptic nucleus neurons of rat hypothalamus in vitro / 生理学报

To investigate the effects of novel intravenous general anesthetic propofol on membrane electrophysiological characteristics and action potential (AP) of the supraoptic nucleus (SON) neurons and possible ionic mechanisms, intracellular recordings were conducted in SON neurons from the coronal hypothalamic slice preparation of adult male Sprague Dawley (SD) rats. The results showed that bath application of 0.1 mmol/L propofol induced a significant decline in resting potential (P < 0.01), and higher concentrations of propofol (0.3 and 1.0 mmol/L) decreased time constant and slope resistance of cell membrane (P < 0.01). Under the hyperpolarizing current pulses exceeding 0.5 nA, an anomalous rectification was induced by hyperpolarization-activated cation channel (I(h) channel) in 11 out of 18 tested SON neurons. Bath of propofol reversibly decreased the anomalous rectification. Moreover, 0.1 mmol/L propofol elevated threshold level (P < 0.01) and decreased Max L. slope (P < 0.05) of the spike potential in SON neurons. Interestingly, 0.3 and 1.0 mmol/L propofol nullified APs in 6% (1/18) and 71% (12/17) tested SON neurons, respectively. In the SON neurons where APs were not nullified, propofol (0.3 mmol/L) decreased the amplitude of spike potential (P < 0.05). The higher concentrations of propofol (0.3 and 1.0 mmol/L) decreased firing frequencies evoked by depolarizing current pulses (0.1-0.7 nA), and shifted the current intensity-firing frequency relation curves downward and to the right. These results suggest that propofol decreases the excitability of SON neurons by inhibiting I(h) and sodium channels.

Synthesis, refolding and identification of pharmacological activities of neurotoxin JZTX-XI and R3A-JZTX-XI / 生物工程学报

Kv2.1 channel currents in pancreatic beta-cells are thought to contribute to action potential repolarization and thereby modulate insulin secretion. Because of its central role in this important physiological process, Kv2.1 channel is a promising target for the treatment of type 2 diabetes. Jingzhaotoxin-XI (JZTX-XI) is a novel peptide neurotoxin isolated from the venom of the spider Chilobrachys jingzhao. Two-microelectrode voltage clamp experiments had showed that the toxin inhibited Kv2.1 potassium currents expressed in Xenopus Laevis oocytes. In order to investigate the structure-function relationship of JZTX-XI, the natural toxin and a mutant of JZTX-XI in which Arg3 was replaced by Ala, were synthesized by solid-phase chemistry method with Fmoc-protected amino acids on the PS3 automated peptide synthesizer. Reverse-phase high performance liquid chromatography (RP-HPLC) and matrix assisted laser desorption/ ionization time-of-flight mass spectrometry (MALDI-TOF/TOF MS) were used to monitor the oxidative refolding process of synthetic linear peptides to find the optimal renaturation conditions of these toxins. The experiments also proved that the relative molecular masses of refolded peptides were in accordance with their theoretical molecular masses. RP-HPLC chromatogram of co-injected native and refolded JZTX-XI was a single peak. Under the whole-cell patch-clamp mode, JZTX-XI could completely inhibit hKv2.1 and hNav1.5 channels currents expressed in HEK293T cells with IC50 values of 95.8 nmol/L and 437.1 nmol/L respectively. The mutant R3A-JZTX-XI could also inhibit hKv2.1 and hNav1.5 channel currents expressed in HEK293T cells with IC50 values of 1.22 micromol/L and 1.96 micromol/L respectively. However, the prohibitive levels of R3A-JZTX-XI on hKv2.1 and hNav1.5 channels were reduced by about 12.7 times and 4.5 times respectively, indicating that Arg3 was a key amino acid residue relative to the hKv2.1 channel activity of JZTX-XI, but it is also an amino acid residue correlated with the binding activity of JZTX-XI to hNav1.5 channel. Our findings should be helpful to develop JZTX-XI into a molecular probe and drug candidate targeting to Kv2.1 potassium channel in the pancreas.

Exploring the obscure profiles of pharmacological binding sites on voltage-gated sodium channels by BmK neurotoxins

Diverse subtypes of voltage-gated sodium channels (VGSCs) have been found throughout tissues of the brain, muscles and the heart. Neurotoxins extracted from the venom of the Asian scorpion Buthus martensi Karsch (BmK) act as sodium channel-specific modulators and have therefore been widely used to study VGSCs. α-type neurotoxins, named BmK I, BmK αIV and BmK abT, bind to receptor site-3 on VGSCs and can strongly prolong the inactivation phase of VGSCs. In contrast, β-type neurotoxins, named BmK AS, BmK AS-1, BmK IT and BmK IT2, occupy receptor site-4 on VGSCs and can suppress peak currents and hyperpolarize the activation kinetics of sodium channels. Accumulating evidence from binding assays of scorpion neurotoxins on VGSCs, however, indicate that pharmacological sensitivity of VGSC subtypes to different modulators is much more complex than that suggested by the simple α-type and β-type neurotoxin distinction. Exploring the mechanisms of possible dynamic interactions between site 3-/4-specific modulators and region- and/or species-specific subtypes of VGSCs would therefore greatly expand our understanding of the physiological and pharmacological properties of diverse VGSCs. In this review, we discuss the pharmacological and structural diversity of VGSCs as revealed by studies exploring the binding properties and cross-competitive binding of site 3- or site 4-specific modulators in VGSC subtypes in synaptosomes from distinct tissues of diverse species.

Síndrome de brugada en un paciente con síncope: presentación de un caso y revisión de la literatura / Brugada syndrome in a patient with syncope: a case report and literature review

El síndrome de Brugada es una enfermedad autosómica dominante esporádica que afecta los canales de sodio de los miocardiocitos. Clínicamente se caracteriza por síncopes recurrentes y/o muerte súbita, que en el electrocardiograma simula un bloqueo de rama derecha, acompañado de elevación peculiar del segmento ST en las derivaciones precordiales derechas (V1, V2 y V3) sin alteración cardiaca estructural. Afecta principalmente a hombres en la cuarta década de la vida y tiene mayor prevalencia en el suroeste asiático. El caso que se describe corresponde a un paciente con antecedentes personales de síncopes, a quien se le encuentra un patrón electrocardiográfico tipo-2 de Brugada y quien además tiene un hermano con historia de síncopes. Con una prueba de mesa basculantes positivo para síncope mediado neuralmente se deja este diagnóstico, pero no se descarta la sospecha inicial de síndrome de Brugada.

Brugada syndrome is a sporadic autosomal dominant genetic disease that affects cardiac sodium channels. It is clinically characterized by recurrent syncope and/or sudden death with electrocardiographic manifestations that simulate a right bundle branch block accompanied by ST-segment elevation in the right precordial leads (V1, V2 and V3) without structural cardiac changes. It mainly affects men in their fourth decade and is most prevalent in southwestern Asia. We present the case of a patient with history of syncope, type-2 Brugada electrocardiographic pattern and who has a brother also with history of syncope. The patient had a positive tilt test for neurocardiogenic syncope. He was diagnosed as neurocardiogenic syndrome, without discarding the initial suspicion of Brugada syndrome.

Interações e associações de medicamentos no tratamento anti-hipertensivo – Antagonistas dos canais de cálcio / Interactions and associations of drugs in antihypertensive treatment – Calcium channel blockers

Os antagonistas dos canais de cálcio (ACC) são agentes anti-hipertensivos particularmente efetivos em idosos e naqueles com atividade da renina plasmática baixa. São também úteis em angina pectoris, taquicardia supraventricular recorrente, fenômeno de Raynaud, enxaqueca, insuficiência cardíaca diastólica e espasmo esofagiano. As principais contra indicações para o uso de ACC são bloqueio atrioventricular de segundo ou terceiro grau (verapamil e diltiazem) e insuficiência cardíaca diastólica com moderada a importante disfunção sistólica. Embora sejam usualmente bem tolerados, uma variedade de efeitos adversos pode ocorrer. Tonturas, cefaleia, rubor facial eedema periférico são os mais comuns.

The calcium channel blockers (CCB) are antihypertensive agents particularly effective in elderly patients and those with low plasma renin activity. They are also useful inangina pectoris, recurrent supraventricular tachycardia, Raynaud’s phenomenon, migraine, diastolic heart failure and esophageal spasm. The main contraindications for the use of CCB are atrioventricularblocks (verapamil and diltiazen) and heart failure with moderate to marked systolic dysfunction. Although they are usually well tolerated, a variety of adverse effects may occur. Dizziness, headache, flushing and peripheral edema are the most common.

Effects of cardioplegia with tetrodotoxin on intracellular sodium overload of ischemia/reperfusion cardiomyocytes / 中国应用生理学杂志

<p><b>AIM</b>To investigate the effects of polarizing cardioplegia solution with sodium channel inhibitor tetrodotoxin (TTX) on intracellular free Na+ concentration ([Na+]i) in isolated cardiomyocytes of rat.</p><p><b>METHODS</b>Ventricular myocytes with beating were isolated from adult rat hearts by enzymatic dissociation, randomly created in group base, group STH2 (contrast group of ischemia/reperfusion) and group TFX (treated group). Both Group STH2 and group TTX were arrested by St. Thomas No. 2 cardioplegia solution and TTX cardioplegia solution respectively, the arrest/re-beating cell model imitating MIRI being established, and imaged by laser scanning confocal microscopy (LSCM) for measuring [Na+]i of cardiomyocytes in different period. The morphology of cardiomyocytes was observed under the inverted microscope.</p><p><b>RESULTS</b>[Na+]i of cardiomyocytes in both group TTX and group STH2 after re-beating was higher than that in group base (P < 0.01), and [Na+]i in group TTX was lower than that in group STH2 (P < 0.01). During arrest, the elevation of [Na+]i in group TTX was lower than that in group STH2. During arrest, the elevation of [Na+]i in group TTX was lower than that in group STH2. Morphologically, after re-beating, the ratio of active cardiomyocytes with normal form in group TTX was higher than that in group STH2 (P < 0.01).</p><p><b>CONCLUSION</b>Contrast depolarized cardioplegia solution, TTX cardioplegia solution could alleviate ischemia reperfusion injury and intracellular Na+ overload of cardiomyocytes.</p>

Recent advances in the structure-activity relationship study of small-molecule sodium channel blockers with analgesic effects / 药学学报

Pain is one of the common clinical symptom, previous studies have implicated sodium channels as a key constituent in pain signaling. Sodium channel blockers with efficient sodium channel blockade effect play an important role in analgesic treatment. However, most drugs used in clinic have many drawbacks and can not meet the demand of the clinical use. Therefore, for the development of new generation of sodium channel blockers, it is of great significance to find small molecule sodium channel blocking lead compounds with novel chemical scaffolds and new structures, sodium channel blocking activity and structure-activity relationship are discussed in detail, and current problems and trends in future research are also emphasized.

The inhibition of tamoxifen on sodium channel in SHG-44 glioma cell-line / 中国应用生理学杂志

<p><b>AIM</b>To explore the effect of tamoxifen on voltage-dependent sodium channels in SHG-44 glioma cell line.</p><p><b>METHODS</b>Whole-cell patch clamp technique was used to record the Na currents in SHG-44 cell line and to investigate the effect of tamoxifen of different concentration on this channel currents.</p><p><b>RESULTS</b>This channel activated and inactivated quickly. Tamoxifen could significantly decrease the amplitude of Na currents of SHG-44 cell line. This block effect was dose dependent and voltage dependent. When the holding potential was 0 mV, 8 micromol/L tamoxifen could block this currents 69%. The half inhibition concentration (IC50) was 5.54 micromol/L.</p><p><b>CONCLUSION</b>Tamoxifen could significantly block the voltage dependent sodium channel in malignant glioma cell line SHG-44. It might be one of the mechanisms that tamoxifen inhibit glioma proliferation. clamp technique was used to record the Na currents in SHG-44 cell line and to investigate the effect of tamoxifen of different concentration on this channel currents.</p><p><b>RESULTS</b>This channel activated and inactivated quickly. Tamoxifen could significantly decrease the amplitude of Na currents of SHG-44 cell line. This block effect was dose dependent and voltage dependent. When the holding potential was 0 mV, 8 micromol/L tamoxifen could block this currents 69%. The half inhibition concentration (IC50) was 5.54 micromol/L.</p><p><b>CONCLUSION</b>Tamoxifen could signifi-cantly block the voltage dependent sodium channel in malignant glioma cell line SHG-44. It might be one of the mechanisms that tamoxifen inhibit glioma proliferation.</p>

Effects of Arg20 mutation on sodium channels activity of JZTX-V / 生物工程学报

Jingzhaotoxin-V(JZTX-V) isolated from the venom of the spider Chilobrachys jingzhao is a novel potent inhibitor that acts on tetrodotoxin-resistant and tetrodotoxin-sensitive sodium channels in adult rat dorsal root ganglion(DRG) neurons. It is a 29-residue polypeptide toxin including three disulfide bridges. To investigate the structure-function relationship of the toxin, a mutant of JZTX-V in which Arg20 was substituted by Ala, was synthesized by solid-phase chemistry method with Fmoc-protected amino acids on the PS3 automated peptide synthesizer. The synthetic linear peptide was then purified by reversed-phase high performance liquid chromatography and oxidatively refolded under the optimal conditions. The refolded product was analyzed by matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry(MALDI-TOF MS) and electrophysiological experiments for its relative molecular weight and prohibitive activity of sodium channels respectively. The present findings show that the prohibitive effect of R20A-JZTX-V on TTX-S sodium channels in DRG neurons is almost the same as that of native JZTX-V, suggesting that Arg20 does not play any important role in inhibiting TTX-S sodium currents in DRG neurons. In contrast, the prohibitive level of R20A-JZTX-V on TTX-R sodium channels is reduced by at last 18.3 times, indicating that Arg20 is a key amino acid residue relative to the bioactivity of JZTX-V. It is presumed that the decrease in activity of R20A-JZTX-V is due to the changes of the property in the binding site in TTX-R sodium channels.

An optimized recording method to characterize biophysical and pharmacological properties of acid-sensing ion channel / 神经科学通报·英文版

<p><b>OBJECTIVE</b>To re-confirm and characterize the biophysical and pharmacological properties of endogenously expressed human acid-sensing ion channel 1a (hASIC1a) current in HEK293 cells with a modified perfusion methods.</p><p><b>METHODS</b>With cell floating method, which is separating the cultured cell from coverslip and putting the cell in front of perfusion tubing, whole cell patch clamp technique was used to record hASIC1a currents evoked by low pH external solution.</p><p><b>RESULTS</b>Using cell floating method, the amplitude of hASIC1a currents activated by pH 5.0 in HEK293 cells is twice as large as that by the conventional method where the cells remain attached to coverslip. The time to reach peak at two different recording conditions is (21+/-5) ms and (270+/-25) ms, respectively. Inactivation time constants are (496+/-23) ms and (2284+/-120) ms, respectively. The cell floating method significantly increases the amiloride potency of block on hASIC1a [IC50 is (3.4+/-1.1) micromol/L and (2.4+/- 0.9) micromol/L, respectively]. Both recording methods have similar pH activation EC50 (6.6+/-0.6, 6.6+/-0.7, respectively).</p><p><b>CONCLUSION</b>ASICs channel activation requires fast exchange of extracellular solution with the different pH values. With cell floating method, the presence of hASIC1a current was re-confirmed and the biophysical and pharmacological properties of hASIC1a channel in HEK293 cells were precisely characterized. This method could be used to study all ASICs and other ligand-gated channels that require fast extracellular solution exchange.</p>

Mechanisms underlying low Ca(2+)(o)-induced increased excitability of hippocampal neurons / 神经科学通报·英文版

<p><b>OBJECTIVE</b>Concentration of extracellular calcium ([Ca(2+)](o)) in the central nervous system decreases substantially in different conditions. It results in facilitating neuronal excitability. The goal of this study is to examine the mechanisms of enhanced neuronal excitation in low [Ca(2+)](o) in order to provide new clues to treat the hyperexcitability diseases in clinic.</p><p><b>METHODS</b>Whole-cell patch-clamp technique and neuron culture were used in the study.</p><p><b>RESULTS</b>The firing threshold of cultured hippocampal neurons decreased markedly in low [Ca(2+)](o) saline. Unexpectedly, apamine and isoprenaline, antagonists of medium afterhyperpolarization (mAHP) and slow AHP (sAHP) respectively, had no statistic significant effect on excitability of neurons. TTX at a low concentration was sufficient to inhibit I(NaP), which blocked the increase of firing frequency in low [Ca(2+)](o). It also reduced the number of spikes in normal [Ca(2+)](o).</p><p><b>CONCLUSION</b>These results suggest that in cultured hippocampal neurons, modulation of spiking threshold but not AHP may cause the increased excitability in low [Ca(2+)](o).</p>

The study of sodium channels involved in pain responses using specific modulators / 生理学报

Voltage-gated sodium channels (VGSCs) are transmembrane proteins responsible for generation and conduction of action potentials in excitable cells. Physiological and pharmacological studies have demonstrated that VGSCs play a critical role in chronic pain associated with tissue or nerve injury. Many long-chain peptide toxins (60-76 amino acid residues) purified from the venom of Asian scorpion Buthus martensii Karsch (BmK) are investigated to be sodium channel-specific modulators. The alpha-like neurotoxins that can bind to receptor site 3 of sodium channels, named as BmK I and BmK abT, could induce nociceptive effects in rats. On the contrast, the beta-like neurotoxins that can bind to receptor site 4 of sodium channels, named as BmK AS, BmK AS-1 and BmK IT2, could produce potent anti-nociceptive effects in animal pain models. BmK I could strongly prolong the fast inactivation of tetrodotoxin (TTX)-sensitive Na(+) currents on the rat dorsal root ganglia (DRG) neurons together with the augmentation of peak current amplitude. However, BmK IT2 and BmK ASs, potently suppressed both the peak TTX-resistant and TTX-sensitive Na(+) currents on rat small DRG neurons. Moreover, BmK ASs could decrease the excitability of small DRG neurons. Thus, the nociception/anti-nociception induced by scorpion neurotoxins may attribute to their distinct modulation on sodium channels in primary afferent sensory neurons. Therefore, the sodium channel-specific modulators from BmK venom could be used as not only pharmacological tools for better understanding the roles of VGSCs in pain signal conduction, but also lead molecules in the development of ideal analgesics targeting VGSCs.