RESUMO
Here, we report the neurotoxic effects aroused by the intracerebral injection (in rats) of Tb1, which is a neurotoxin isolated from Tityus bahiensis scorpion venom. Biochemical analyses have demonstrated that this toxin is similar to the gamma toxin from T. serrulatus, which is a ß-scorpion toxin that acts on sodium channels, causing the activation process to occur at more hyperpolarized membrane voltages. Male Wistar rats were stereotaxically implanted with intrahippocampal electrodes and cannulas for electroencephalographic recording and the evaluation of amino acid neurotransmitters levels. Treated animals displayed behavioral and electroencephalographic alterations similar to epileptiform activities, such as myoclonus, wet dog shakes, convulsion, strong discharges, neuronal loss, and increased intracerebral levels of glutamate. Scorpion toxins are important pharmacological tools that are widely employed in ion channel dysregulation studies. The current work contributes to the understanding of channelopathies, particularly epilepsy, which may originate, among other events, from dysfunctional sodium channels, which are the main target of the Tb1 toxin.
Assuntos
Ácido Glutâmico/metabolismo , Neurotoxinas/toxicidade , Venenos de Escorpião/toxicidade , Convulsões/induzido quimicamente , Animais , Comportamento Animal/efeitos dos fármacos , Eletroencefalografia , Hipocampo/efeitos dos fármacos , Hipocampo/patologia , Hipocampo/fisiologia , Masculino , Neurotoxinas/química , Ratos Wistar , Venenos de Escorpião/química , Escorpiões , Convulsões/metabolismo , Convulsões/patologia , Convulsões/fisiopatologia , Canais de Sódio/fisiologiaRESUMO
Transcranial random noise electrical stimulation (tRNS) of the human brain is a non-invasive technique that can be employed to increase the excitability of the cerebral cortex; however, the physiological mechanisms remain unclear. Here we report for the first time the effects of short-term (250â¯ms) random noise electrical stimulation (RNS) on in-vitro acutely-isolated brain pyramidal neurons from the somatosensory and auditory cerebral cortex. We analyzed the correlation between the peak amplitude of the Na+ current and its latency for different levels of RNS. We found three groups of neurons. The first group exhibited a positive correlation, the second, a negative correlation, and the third group of neurons did not exhibit correlation. In the first group, both the peak amplitude of a TTX-sensitive Na+ current and its inverse of latency followed similar inverted U-like functions relative to the electrical RNS level. In this group, the RNS levels in which the maximal values of the inverted U-like functions occurred were the same. In the second group, the maximal values of the inverted U-like functions occurred at different levels. In the third group, only the peak amplitude of the Na+ current exhibited a clear inverted U-like function, but the inverse of the latency versus the electrical RNS, did not exhibit a clear inverted U-like function. A Hodgkin-Huxley neuron model reproduces our experimental results and shows that the observed behavior in the Na+ current could be due to the impact of RNS on the kinetics of activation and inactivation of the Na+ channels.
Assuntos
Córtex Cerebral/citologia , Córtex Cerebral/fisiologia , Ruído , Células Piramidais/fisiologia , Animais , Estimulação Elétrica/métodos , Distribuição Aleatória , Ratos , Ratos Wistar , Canais de Sódio/fisiologia , Fatores de TempoRESUMO
Reptiles are the first amniotes to develop an intromitent penis, however until now the mechanisms involved in the electrical field stimulation-induced contraction on corpora cavernosa isolated from Crotalus durissus terrificus were not investigated. Crotalus and rabbit corpora cavernosa were mounted in 10 mL organ baths for isometric tension recording. Electrical field stimulation (EFS)-induced contractions were performed in presence/absence of phentolamine (10 µM), guanethidine (30 µM), tetrodotoxin (1 µM and 1mM), A-803467 (10 µM), 3-iodo-L-Tyrosine (1 mM), salsolinol (3 µM) and a modified Krebs solution (equimolar substitution of NaCl by N-methyl-D-glucamine). Immuno-histochemistry for tyrosine hydroxylase was also performed. Electrical field stimulation (EFS; 8 Hz and 16 Hz) caused contractions in both Crotalus and rabbit corpora cavernosa. The contractions were abolished by previous incubation with either phentolamine or guanethidine. Tetrodotoxin (1 µM) also abolished the EFS-induced contractions of rabbit CC, but did not affect EFS-induced contractions of Crotalus CC. Addition of A-803467 (10 µM) did not change the EFS-induced contractions of Crotalus CC but abolished rabbit CC contractions. 3-iodo-L-Tyrosine and salsolinol had no effect on EFS-induced contractions of Crotalus CC and Rabbit CC. Replacement of NaCl by N- Methyl-D-glucamine (NMDG) abolished EFS-induced contractions of rabbit CC, but did not affect Crotalus CC. The presence of tyrosine hydroxylase was identified in endothelial cells only of Crotalus CC. Since the EFS-induced contractions of Crotalus CC is dependent on catecholamine release, insensitive to TTX, insensitive to A803467 and to NaCl replacement, it indicates that the source of cathecolamine is unlikely to be from adrenergic terminals. The finding that tyrosine hydroxylase is present in endothelial cells suggests that these cells can modulate Crotalus CC tone.
Assuntos
Crotalus/fisiologia , Estimulação Elétrica , Pênis/efeitos dos fármacos , Tetrodotoxina/farmacologia , Compostos de Anilina/farmacologia , Animais , Callithrix , Furanos/farmacologia , Imuno-Histoquímica , Masculino , Contração Muscular/efeitos dos fármacos , Pênis/fisiologia , Coelhos , Receptores Adrenérgicos/fisiologia , Canais de Sódio/fisiologiaRESUMO
Late sodium channel current (late INa) is considered to be an antiarrhythmic target. The prime antiarrhythmic mechanisms of late INa inhibition have been suggested to be (1) suppression of intracellular calcium [Cai]-mediated rhythmic activity (through reduction in Cai secondary to the decrease in intracellular sodium [Nai]) and (2) normalization of repolarization. Endogenous late INa is a small current and acceleration of the heart rate decreases late INa density. Late INa influx may significantly contribute to Nai loading, but it seems to largely occur under the combined conditions of augmented late INa density, bradycardia, and prolonged repolarization. At the same time, the relative contribution of late INa (including endogenous) in any type of prolonged cardiac repolarization is critical. Sodium channel blockers inhibit both late INa and peak INa, and a specific block of late INa might be achieved at slow and normal but seems not at rapid activation rates, at which peak INa, a much greater current, is also likely to be inhibited. The antiarrhythmic potential of a specific inhibition of late INa seems to best fit for, or may be limited to, the prevention of arrhythmias associated with prolonged repolarization, but it seems to be applicable to all types of arrhythmic abnormalities with elongated cardiac repolarization.
Assuntos
Antiarrítmicos/uso terapêutico , Fibrilação Atrial/tratamento farmacológico , Bloqueadores dos Canais de Sódio/uso terapêutico , Canais de Sódio/fisiologia , Animais , Antiarrítmicos/farmacologia , Fibrilação Atrial/fisiopatologia , Humanos , Ranolazina/farmacologia , Ranolazina/uso terapêutico , Bloqueadores dos Canais de Sódio/farmacologiaRESUMO
Scorpion stings on humans are medically relevant because they may contain toxins that specifically target ion channels. During antivenom production, pharmaceutical companies must use a large number of experimental animals to ensure the antivenom's efficacy according to pharmacopeia methods. Here we present an electrophysiological alternative for the evaluation of horse antivenoms produced against two species of Moroccan scorpions: Buthus mardochei and Androctonus mauretanicus. Human sodium and potassium channels and acetylcholine nicotinic receptors were analyzed by standard patch-clamp techniques. The results showed that the antivenom is capable of reversing ion current disruption caused by the venom application. We propose the use of this in vitro technique for antivenom evaluation as an alternative to using a large number of live animals.
Assuntos
Antivenenos/farmacologia , Venenos de Escorpião/toxicidade , Canais de Sódio/fisiologia , Alternativas aos Testes com Animais , Animais , Fenômenos Eletrofisiológicos , Células HEK293 , Humanos , EscorpiõesRESUMO
OBJECTIVE AND DESIGN: Sodium channels are highly expressed in nociceptive sensory neurons during hypernociceptive conditions. Based on the presence of a glycosidic portion in the sodium channel ß subunit associated to the antinociceptive effect of leguminous lectins via lectin domain, this study investigated the antinociceptive activity of the lectin isolated from Lonchocarpus araripensis seeds (LAL) in mice behavioral models and in NaV current in the nociceptor of rat dorsal root ganglion (DRG). MATERIAL/METHODS: LAL antinociceptive activity and the participation of opioid system, lectin domain and sodium channels were evaluated in Swiss mice models of nociception (formalin, capsaicin, hot plate, tail flick, von Frey) and in primary cultures of Wistar rats neurons of DRG (patch clamp). RESULTS: LAL presented inhibitory effects in the nociception induced by chemical and mechanical, but not by thermal stimuli and reduced total Na(+) current. LAL activity was inhibited by the lectin association with its binding sugar N-acethyl-glucosamine. CONCLUSION: LAL inhibits peripheral hypernociception by mechanisms that involve the lectin domain, inflammatory mediators and Na(+) channels. The innovative inhibitory action of leguminous lectins on NaV current brings new insights for the investigation of sodium channels role in nociception.
Assuntos
Analgésicos , Fabaceae , Lectinas , Dor/tratamento farmacológico , Canais de Sódio/fisiologia , Analgésicos/farmacologia , Analgésicos/uso terapêutico , Animais , Capsaicina , Formaldeído , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/fisiologia , Temperatura Alta , Lectinas/farmacologia , Lectinas/uso terapêutico , Masculino , Camundongos , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Nociceptividade/efeitos dos fármacos , Estimulação Física , Ratos Wistar , SementesRESUMO
1,8-Cineole is a terpenoid present in many essential oil of plants with several pharmacological and biological effects, including antinociceptive, smooth muscle relaxant and ion channel activation. Also, 1,8-cineole blocked action potentials, reducing excitability of peripheral neurons. The objective of this work was to investigate effects of 1,8-cineole on Na(+) currents (INa(+)) in dissociated superior cervical ganglion neurons (SCG). Wistar rats of both sexes were used (10-12 weeks old, 200-300g). SCG's were dissected and neurons were enzymatically treated. To study 1,8-cineole effect on INa(+), the patch-clamp technique in whole-cell mode was employed. 1,8-Cineole (6.0mM) partially blocked INa(+) in SCG neurons. The effect stabilized within â¼150s and there was a partial recovery of INa(+) after washout. Current density was reduced from -105.8 to -83.7pA/pF, corresponding to a decrease to â¼20% of control. 1,8-Cineole also reduced the time-to-peak of INa(+) activation and the amplitude and decay time constants of INa(+) inactivation. Current-voltage plots revealed that 1,8-cineole left-shifted the V1/2 of both activation and inactivation curves by â¼10 and â¼20mV, respectively. In conclusion, we demonstrate that 1,8-cineole directly affects Na(+) channels of the SCG by modifying several gating parameters that are likely to be the major cause of excitability blockade.
Assuntos
Cicloexanóis/farmacologia , Monoterpenos/farmacologia , Neurônios/efeitos dos fármacos , Bloqueadores dos Canais de Sódio/farmacologia , Canais de Sódio/fisiologia , Gânglio Cervical Superior/efeitos dos fármacos , Animais , Eucaliptol , Feminino , Ativação do Canal Iônico/efeitos dos fármacos , Masculino , Neurônios/fisiologia , Ratos Wistar , Gânglio Cervical Superior/citologia , Gânglio Cervical Superior/fisiologiaRESUMO
The respiratory pattern generator modulates the sympathetic outflow, the strength of which is enhanced by challenges produced by hypoxia. This coupling is due to the respiratory-modulated presympathetic neurons in the rostral ventrolateral medulla (RVLM), but the underlining electrophysiological mechanisms remain unclear. For a better understanding of the neural substrates responsible for generation of this respiratory-sympathetic coupling, we combined immunofluorescence, single cell qRT-pCR, and electrophysiological recordings of the RVLM presympathetic neurons in in situ preparations from normal rats and rats submitted to a metabolic challenge produced by chronic intermittent hypoxia (CIH). Our results show that the spinally projected cathecholaminergic C1 and non-C1 respiratory-modulated RVLM presympathetic neurons constitute a heterogeneous neuronal population regarding the intrinsic electrophysiological properties, respiratory synaptic inputs, and expression of ionic currents, albeit all neurons presented persistent sodium current-dependent intrinsic pacemaker properties after synaptic blockade. A specific subpopulation of non-C1 respiratory-modulated RVLM presympathetic neurons presented enhanced excitatory synaptic inputs from the respiratory network after CIH. This phenomenon may contribute to the increased sympathetic activity observed in CIH rats. We conclude that the different respiratory-modulated RVLM presympathetic neurons contribute to the central generation of respiratory-sympathetic coupling as part of a complex neuronal network, which in response to the challenges produced by CIH contribute to respiratory-related increase in the sympathetic activity.
Assuntos
Fenômenos Eletrofisiológicos/fisiologia , Bulbo/fisiologia , Neurônios/fisiologia , Fenômenos Fisiológicos Respiratórios , Sistema Respiratório/inervação , Sistema Nervoso Simpático/fisiologia , Animais , Tronco Encefálico/fisiologia , Canais de Cálcio Tipo T/fisiologia , Eletromiografia , Coração/inervação , Coração/fisiologia , Hemodinâmica/fisiologia , Hipóxia/fisiopatologia , Masculino , Bulbo/citologia , Técnicas de Patch-Clamp , Ratos , Ratos Wistar , Músculos Respiratórios/inervação , Músculos Respiratórios/fisiologia , Canais de Sódio/fisiologia , Sistema Nervoso Simpático/citologia , Canais de Ânion Dependentes de Voltagem/fisiologiaRESUMO
The number of Caesarean births has increased worldwide. Respiratory distress syndrome is associated with caesarean delivery, especially in the absence of labor. During the latter stages of pregnancy physiologic changes occur that are accelerated with the onset of labor, which is accompanied by changes in hormones and mediators in the mother and fetus. An acceleration in the evacuation of lung liquid is held in this period, largely dependent sodium channels sensitive to amiloride than are found in the alveolar epithelium. The failure of these mechanisms can lead to newborn severe respiratory difficulty and require intensive care, mechanical ventilation and surfactant. We need to develop preventive and therapeutic strategies to improve outcomes in this vulnerable population.
Assuntos
Cesárea/efeitos adversos , Procedimentos Cirúrgicos Eletivos/efeitos adversos , Síndrome do Desconforto Respiratório do Recém-Nascido/etiologia , Adulto , Células Epiteliais Alveolares/metabolismo , Líquidos Corporais/fisiologia , Cesárea/estatística & dados numéricos , Terapia Combinada , Procedimentos Cirúrgicos Eletivos/psicologia , Procedimentos Cirúrgicos Eletivos/estatística & dados numéricos , Feminino , Hormônios/metabolismo , Humanos , Recém-Nascido , Trabalho de Parto/fisiologia , Pulmão/embriologia , Pulmão/fisiologia , Gravidez , Alvéolos Pulmonares/metabolismo , Síndrome do Desconforto Respiratório do Recém-Nascido/epidemiologia , Síndrome do Desconforto Respiratório do Recém-Nascido/fisiopatologia , Síndrome do Desconforto Respiratório do Recém-Nascido/terapia , Canais de Sódio/fisiologia , Procedimentos DesnecessáriosRESUMO
Integrative and firing properties are important characteristics of neuronal circuits and these responses are determined in large part by the repertoire of ion channels they express, which can vary considerably between cell types. Recently, a new mode of operation of voltage dependent sodium channels has been described that generates a so-called resurgent Na+ current. Accumulating evidence suggests resurgent Na current participates in the generation of sub-threshold inward Na+ current causing membrane depolarization which provides the necessary drive to fire high-frequency action potentials. Recent studies indicate that resurgent Na+ current could be a more widespread feature than previously thought.
Assuntos
Neurônios/fisiologia , Canais de Sódio/fisiologia , Animais , Fenômenos Eletrofisiológicos , Humanos , Ativação do Canal Iônico/fisiologia , Canal de Sódio Disparado por Voltagem NAV1.6 , Proteínas do Tecido Nervoso/fisiologia , Técnicas de Patch-ClampRESUMO
INTRODUCTION: Coitus in snakes may last up to 28 hours; however, the mechanisms involved are unknown. AIM: To evaluate the relevance of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP)-phosphodiesterase type 5 (PDE5) system in snake corpus cavernosum reactivity. METHODS: Hemipenes were removed from anesthetized South American rattlesnakes (Crotalus durissus terrificus) and studied by light and scanning electronic microscopy. Isolated Crotalus corpora cavernosa (CCC) were dissected from the non-spiny region of the hemipenises, and tissue reactivity was assessed in organ baths. MAIN OUTCOME MEASURES: Cumulative concentration-response curves were constructed for acetylcholine (ACh), sodium nitroprusside (SNP), 5-cyclopropyl-2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyrimidin-4-ylamine (BAY 41-2272), and tadalafil in CCC precontracted with phenylephrine. Relaxation induced by electrical field stimulation (EFS) was also done in the absence and presence of N(ω) nitro-L-arginine methyl ester (L-NAME; 100 µM), 1H-[1, 2, 4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 µM) and tetrodotoxin (TTX; 1 µM). RESULTS: The hemipenes consisted of two functionally concentric corpora cavernosa, one of them containing radiating bundles of smooth muscle fibers (confirmed by α-actin immunostaining). Endothelial and neural nitric oxide synthases were present in the endothelium and neural structures, respectively; whereas soluble guanylate cyclase and PDE5 were expressed in trabecular smooth muscle. ACh and SNP relaxed isolated CCC, with the relaxations being markedly reduced by L-NAME and ODQ, respectively. BAY 41-2272 and tadalafil caused sustained relaxations with potency (pEC(50) ) values of 5.84 ± 0.17 and 5.10 ± 0.08 (N=3-4), respectively. In precontracted CCC, EFS caused frequency-dependent relaxations that lasted three times longer than those in mammalian CC. Although these relaxations were almost abolished by either L-NAME or ODQ, they were unaffected by TTX. In contrast, EFS-induced relaxations in marmoset CC were abolished by TTX. CONCLUSIONS: Rattlesnake CC relaxation is mediated by the NO-cGMP-PDE5 pathway in a manner similar to mammals. The novel TTX-resistant Na channel identified here may be responsible for the slow response of smooth muscle following nerve stimulation and could explain the extraordinary duration of snake coitus.
Assuntos
GMP Cíclico/metabolismo , Neurônios Nitrérgicos/efeitos dos fármacos , Óxido Nítrico Sintase/metabolismo , Pênis/irrigação sanguínea , Pênis/inervação , Bloqueadores dos Canais de Sódio/farmacologia , Canais de Sódio/efeitos dos fármacos , Canais de Sódio/fisiologia , Tetrodotoxina/farmacologia , Acetilcolina/farmacologia , Animais , Callithrix , Carbolinas/farmacologia , Crotalus , Nucleotídeo Cíclico Fosfodiesterase do Tipo 5/metabolismo , Relação Dose-Resposta a Droga , Endotélio Vascular/anatomia & histologia , Endotélio Vascular/efeitos dos fármacos , Técnicas In Vitro , Masculino , Microscopia Eletrônica de Varredura , NG-Nitroarginina Metil Éster/farmacologia , Nitroprussiato/farmacologia , Oxidiazóis/farmacologia , Pênis/anatomia & histologia , Pirazóis/farmacologia , Piridinas/farmacologia , Quinoxalinas/farmacologia , Tadalafila , Vasodilatadores/farmacologiaRESUMO
Previous work shows that transforming growth factor-ß1 (TGF-ß1) promotes several heart alterations, including atrial fibrillation (AF). In this work, we hypothesized that these effects might be associated with a potential modulation of Na(+) and K(+) channels. Atrial myocytes were cultured 1-2 days under either control conditions, or the presence of TGF-ß1. Subsequently, Na(+) (I(Na)) and K(+) (I(K)) currents were investigated under whole-cell patch-clamp conditions. Three K(+) currents were isolated: inward rectifier (I(Kin)), outward transitory (I(to)), and outward sustained (I(Ksus)). Interestingly, TGF-ß1 decreased (50%) the densities of I(Kin) and I(Ksus) but not of I(to). In addition, the growth factor reduced by 80% the amount of I(Na) available at -80 mV. This effect was due to a significant reduction (30%) in the maximum I(Na) recruited at very negative potentials or I(max), as well as to an increased fraction of inactivated Na(+) channels. The latter effect was, in turn, associated to a -7 mV shift in V(1/2) of inactivation. TGF-ß1 also reduced by 60% the maximum amount of intramembrane charge movement of Na(+) channels or Q(max), but did not affect the corresponding voltage dependence of activation. This suggests that TGF-ß1 promotes loss of Na(+) channels from the plasma membrane. Moreover, TGF-ß1 also reduced (50%) the expression of the principal subunit of Na(+) channels, as indicated by western blot analysis. Thus, TGF-ß1 inhibits the expression of Na(+) channels, as well as the activity of K(+) channels that give rise to I(Ksus) and I(Kin). These results may contribute to explaining the previously observed proarrhythmic effects of TGF-ß1.
Assuntos
Miócitos Cardíacos/fisiologia , Canais de Potássio/fisiologia , Canais de Sódio/fisiologia , Fator de Crescimento Transformador beta1/farmacologia , Animais , Células Cultivadas , Ativação do Canal Iônico/efeitos dos fármacos , Miócitos Cardíacos/efeitos dos fármacos , Canal de Sódio Disparado por Voltagem NAV1.5 , Técnicas de Patch-Clamp , Canais de Potássio/efeitos dos fármacos , Ratos , Ratos Wistar , Canais de Sódio/efeitos dos fármacosRESUMO
We examined modification of sodium channel gating by Tityus bahiensis scorpion venom (TbScV), and compared effects on native tetrodotoxin-sensitive and tetrodotoxin-resistant sodium currents from rat dorsal root ganglion neurons and cardiac myocytes. In neurons, TbScV dramatically reduced the rate of sodium current inactivation, increased current amplitude, and caused a negative shift in the voltage-dependence of activation and inactivation of tetrodotoxin-sensitive channels. Enhanced activation of modified sodium channels was independent of a depolarizing prepulse. We identified two components of neuronal tetrodotoxin-resistant current with biophysical properties similar to those described for NaV1.8 and NaV1.9. In contrast to its effects on neuronal tetrodotoxin-sensitive current, TbScV caused a small decrease in neuronal tetrodotoxin-resistant sodium current amplitude and the gating modifications described above were absent. A third tetrodotoxin-resistant current, NaV1.5 recorded in rat cardiac ventricular myocytes, was inhibited approximately 50% by TbScV, and the remaining current exhibited markedly slowed activation and inactivation. In conclusion, TbScV has very different effects on different sodium channel isoforms. Among the neuronal types, currents resistant to tetrodotoxin are also resistant to gating modification by TbScV. The cardiac tetrodotoxin-resistant current has complex sensitivity that includes both inhibition of current amplitude and slowing of activation and inactivation.
Assuntos
Venenos de Escorpião/farmacologia , Bloqueadores dos Canais de Sódio/farmacologia , Canais de Sódio/metabolismo , Tetrodotoxina/farmacologia , Animais , Células Cultivadas , Resistência a Medicamentos , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/fisiologia , Ativação do Canal Iônico/efeitos dos fármacos , Ativação do Canal Iônico/fisiologia , Masculino , Canal de Sódio Disparado por Voltagem NAV1.5 , Canal de Sódio Disparado por Voltagem NAV1.8 , Canal de Sódio Disparado por Voltagem NAV1.9 , Ratos , Ratos Wistar , Agonistas de Canais de Sódio , Canais de Sódio/fisiologiaRESUMO
Linalool is a terpene that occurs as a major constituent of essential oils of many plants of widespread distribution. It possesses several biological and pharmacological activities, including depressant effects on the central nervous system and olfactory receptors. The present study investigated whether linalool affects the excitability of peripheral components of the somatic sensory system. We used sciatic nerve and preparations of intact and dissociated neurons of dorsal root ganglion for extracellular, intracellular and patch-clamp recordings. Linalool concentration-dependently (0.3-2.0mM) and reversibly blocked the excitability of the sciatic nerve. It inhibited peak-to-peak amplitude of the compound action potential (IC(50) was 0.78+/-0.04 mM). At 0.8mM, it reversibly increased rheobase and chronaxy (from 3.2+/-0.1 V and 52.4+/-4.1 micros to 4.2+/-0.3 V and 71.2+/-5.5 micros (n=5), respectively) and inhibited with greater pharmacological potency the amplitude of the compound action potential components corresponding to axons with slower velocity of conduction. In a similar concentration range (0.1-6mM), linalool concentration-dependently and reversibly blocked the generation of action potentials of intact dorsal root ganglion neurons without alteration of resting membrane potential and input resistance, and inhibited the voltage-gated Na(+) current of dissociated dorsal root ganglion neurons. In conclusion, we demonstrated that linalool acts on the somatic sensory system with local anesthetic properties, since it blocked the action potential by acting on voltage-dependent Na(+) channels. This finding is important in showing the potential usefulness of linalool as a pharmacotherapeutic agent.
Assuntos
Gânglios Espinais/efeitos dos fármacos , Monoterpenos/farmacologia , Neurônios/efeitos dos fármacos , Nervo Isquiático/efeitos dos fármacos , Canais de Sódio/fisiologia , Potenciais de Ação/efeitos dos fármacos , Monoterpenos Acíclicos , Animais , Relação Dose-Resposta a Droga , Feminino , Gânglios Espinais/fisiologia , Técnicas In Vitro , Ativação do Canal Iônico , Masculino , Inibição Neural/efeitos dos fármacos , Neurônios/fisiologia , Técnicas de Patch-Clamp , Ratos , Ratos Wistar , Nervo Isquiático/fisiologiaRESUMO
Eugenol is a phenylpropene obtained from the essential oils of plants such as clove and basil which has ample use in dentistry. Eugenol possesses analgesic effects that may be related to the inhibition of voltage-dependent Na+ channels and/or to the activation of TRPV1 receptors or both. In the present study, electrophysiological parameters were taken from the compound action potentials of the isolated rat sciatic nerve and from neurons of the superior cervical ganglion (SCG) impaled with sharp microelectrodes under current-clamp conditions. In the isolated rat sciatic nerve, eugenol inhibited the compound action potential in a concentration-dependent manner. Action potentials recorded from SCG neurons were inhibited by eugenol with an IC(50) of 0.31 mM. At high concentrations (2 mM), during brief applications, eugenol caused significant action potential blockade while it did not interfere with the resting membrane potential or the membrane input resistance. Surprisingly, however, at low eugenol concentrations (0.6 mM), during long time applications, a reversible reduction (by about 50%) in the input membrane resistance was observed, suggesting the possible involvement of a secondary delayed effect of eugenol to reduce neuronal excitability.
Assuntos
Analgésicos/farmacologia , Eugenol/farmacologia , Neurônios/efeitos dos fármacos , Nervo Isquiático/efeitos dos fármacos , Gânglio Cervical Superior/efeitos dos fármacos , Potenciais de Ação , Animais , Feminino , Técnicas In Vitro , Masculino , Neurônios/fisiologia , Técnicas de Patch-Clamp , Ratos , Ratos Wistar , Nervo Isquiático/citologia , Nervo Isquiático/fisiologia , Canais de Sódio/fisiologia , Gânglio Cervical Superior/citologia , Gânglio Cervical Superior/fisiologia , Fatores de TempoRESUMO
In the vestibular system, the electrical discharge of the afferent neurons has been found to be highly sensitive to external pH changes, and acid-sensing ionic-channels (ASIC) have been found to be functionally expressed in afferent neurons. No previous attempt to assay the ASIC function in vestibular afferent neurons has been done. In our work we studied the electrical discharge of the afferent neuron of the isolated inner ear of the axolotl (Ambystoma tigrinum) to determine the participation of proton-gated currents in the postransductional information processing in the vestibular system. Microperfusion of FMRF-amide significantly increased the resting activity of the afferent neurons of the semicircular canal indicating that ASIC currents are tonically active in the resting condition. The use of ASIC antagonists, amiloride and acetylsalicylic acid (ASA), significantly reduced the vestibular-nerve discharge, corroborating the idea that the afferent neurons of the vestibular system express ASICs that are sensitive to amiloride, ASA, and to FMRF-amide. The sensitivity of the vestibular afferent-resting discharge to the microperfusion of ASIC acting agents indicates the participation of these currents in the establishment of the afferent-resting discharge.
Assuntos
Proteínas do Tecido Nervoso/biossíntese , Neurônios Aferentes/metabolismo , Canais de Sódio/biossíntese , Vestíbulo do Labirinto/metabolismo , Canais Iônicos Sensíveis a Ácido , Ambystoma , Amilorida/farmacologia , Animais , Aspirina/farmacologia , Eletrofisiologia , FMRFamida/farmacologia , Gadolínio/farmacologia , Concentração de Íons de Hidrogênio , Técnicas In Vitro , Ativação do Canal Iônico , Proteínas do Tecido Nervoso/fisiologia , Canais de Sódio/fisiologia , Vestíbulo do Labirinto/citologiaRESUMO
In the present study, the participation of the Na(V)1.8 sodium channel was investigated in the development of the peripheral pro-nociceptive state induced by daily intraplantar injections of PGE(2) in rats and its regulation in vivo by protein kinase A (PKA) and protein kinase C epsilon (PKCvarepsilon) as well. In the prostaglandin E(2) (PGE(2))-induced persistent hypernociception, the Na(V)1.8 mRNA in the dorsal root ganglia (DRG) was up-regulated. The local treatment with dipyrone abolished this persistent hypernociception but did not alter the Na(V)1.8 mRNA level in the DRG. Daily intrathecal administrations of antisense Na(V)1.8 decreased the Na(V)1.8 mRNA in the DRG and reduced ongoing persistent hypernociception. Once the persistent hypernociception had been abolished by dipyrone, but not by Na(V)1.8 antisense treatment, a small dose of PGE(2) restored the hypernociceptive plateau. These data show that, after a period of recurring inflammatory stimuli, an intense and prolonged nociceptive response is elicited by a minimum inflammatory stimulus and that this pro-nociceptive state depends on Na(V)1.8 mRNA up-regulation in the DRG. In addition, during the persistent hypernociceptive state, the PKA and PKCvarepsilon expression and activity in the DRG are up-regulated and the administration of the PKA and PKCvarepsilon inhibitors reduce the hypernociception as well as the Na(V)1.8 mRNA level. In the present study, we demonstrated that the functional regulation of the Na(V)1.8 mRNA by PKA and PKCvarepsilon in the primary sensory neuron is important for the development of the peripheral pro-nociceptive state induced by repetitive inflammatory stimuli and for the maintenance of the behavioral persistent hypernociception.
Assuntos
Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Inflamação/fisiopatologia , Proteínas do Tecido Nervoso/fisiologia , Dor/fisiopatologia , Proteína Quinase C-épsilon/metabolismo , Canais de Sódio/fisiologia , Animais , Sequência de Bases , Primers do DNA , Dinoprostona/administração & dosagem , Ativação Enzimática , Inflamação/induzido quimicamente , Masculino , Canal de Sódio Disparado por Voltagem NAV1.8 , Dor/enzimologia , Reação em Cadeia da Polimerase , Ratos , Ratos WistarRESUMO
Fibromyalgia (FM) is the most frequent cause of generalized pain in the community. Trauma and infection are frequent FM triggering events. A consistent line of investigation suggests that autonomic dysfunction may explain the multi-system features of FM, and that FM is a sympathetically maintained neuropathic pain syndrome. Dorsal root ganglia (DRG) are potential sympathetic-nociceptive short-circuit sites. Sodium channels located in DRG (particularly Nav1.7) act as molecular gatekeepers of pain detection at peripheral nociceptors. Different infecting agents may lie dormant in DGR. Trauma or infection can induce neuroplasticity with an over-expression of sympathetic fibers and sodium channels in DRG. Nerve growth factor (NGF) mediates these phenotypic changes, which enable catecholamines and/or sympathetic impulses to activate nociceptors. Several DRG sodium "channelopathies" have been recently associated to rare painful-dysautonomic syndromes, such as primary erythermalgia and paroxysmal extreme pain disorder (formerly familial rectal pain syndrome). We propose that enhanced DRG excitability may play a key role in FM pain. Individuals at risk would be those with genetically determined sympathetic hyperactivity, or those with inherent sodium channelopathies. Today's stressful environment may contribute to permanent sympathetic hyperactivity. Trauma or infection would induce sodium channels up-regulation and sympathetic sprouting in DRG through NGF over-expression. High levels of NGF have been reported in the cerebro-spinal fluid of FM patients. These post-traumatic (or post-infective) phenotypic changes would induce a sympathetically maintained neuropathic pain syndrome resulting in widespread pain, allodynia and paresthesias - precisely, the key clinical features of FM. If this hypothesis proves to be true, then sodium channel blockers could become therapeutic options for FM pain.
Assuntos
Fibromialgia/fisiopatologia , Gânglios Espinais/fisiopatologia , Canais de Sódio/fisiologia , Sistema Nervoso Simpático/fisiopatologia , Canalopatias/fisiopatologia , Fibromialgia/complicações , Fibromialgia/genética , Humanos , Modelos Neurológicos , Dor/etiologia , Dor/fisiopatologia , Canais de Sódio/genética , SíndromeRESUMO
The effect of carbamazepine, phenytoin, valproate, oxcarbazepine, lamotrigine and topiramate, that are among the most widely used antiepileptic drugs (AEDs), and of the new putative AED vinpocetine on the Ca(2+) channel-mediated release of [(3)H]Glu evoked by high K(+) in hippocampal isolated nerve endings was investigated. Results show that carbamazepine, oxcarbazepine and phenytoin reduced [(3)H]Glu release to high K(+) to about 30% and 55% at concentrations of 500 microM and 1500 microM, respectively; lamotrigine and topiramate to about 27% at 1500 microM; while valproate failed to modify it. Vinpocetine was the most potent and effective; 50 microM vinpocetine practically abolished the high K(+) evoked release of [(3)H]Glu. Comparison of the inhibition exerted by the AEDs on [(3)H]Glu release evoked by high K(+) with the inhibition exerted by the AEDs on [(3)H]Glu release evoked by the Na(+) channel opener, veratridine, shows that all the AEDs are in general more effective blockers of the presynaptic Na(+) than of the presynaptic Ca(2+) channel-mediated response. The high doses of AEDs required to control seizures are frequently accompanied by adverse secondary effects. Therefore, the higher potency and efficacy of vinpocetine to reduce the permeability of presynaptic ionic channels controlling the release of the most important excitatory neurotransmitter in the brain must be advantageous in the treatment of epilepsy.
Assuntos
Anticonvulsivantes/farmacologia , Canais de Cálcio/fisiologia , Ácido Glutâmico/metabolismo , Canais de Sódio/fisiologia , Sinaptossomos/efeitos dos fármacos , Sinaptossomos/metabolismo , Animais , Bloqueadores dos Canais de Cálcio/farmacologia , Relação Dose-Resposta a Droga , Interações Medicamentosas , Hipocampo/ultraestrutura , Masculino , Potássio/farmacologia , Ratos , Ratos Wistar , Bloqueadores dos Canais de Sódio/farmacologia , Tetrodotoxina/farmacologia , Trítio/metabolismo , ômega-Agatoxina IVA/farmacologiaRESUMO
BACKGROUND: Acid sensing ion channels (ASIC) are ionic channels activated by transient pH reductions in the ext raceilularenvi ronment. Although the activation mechanism is not fully elucidated, it is clear that the channel is activated by proton binding to its extraceilular domain, a process that is modulated by calcium and zinc. OBJECTIVE: The fact that divalent cations are able to modify ASIC operation, lead us to consider if lead, anotherdivalent cation and widely distributed neurotoxicant, is also capable to affect ASIC function. METHODS: For this purpose, we recordedASiC currents in rat dorsal root ganglion neurons using the whole cell patch-clamp technique. RESULTS: The results indicated that lead inhibits ASIC currents in a concentration -dependent fashion. CONCLUSIONS: These results contribute to the understanding of the activation mechanism of ASIC and to explain some of the toxic mechanisms of lead in the organism.