Inhibition of L-glutamate and GABA synaptosome uptake by crotoxin, the major neurotoxin from Crotalus durissus terrificus venom

This paper describes a brief study on the crotoxin mechanism of action, regarding the transport of GABA and L-glutamate in rats cortico-cerebral synaptosomes and in heterologous systems, such as COS-7 cells expressing gabaergic transporters, and C6 glioma cells and Xenopus oocytes expressing glutamatergic transporters. Crotoxin concentrations over 1 µM caused an inhibitory effect of ³H-L-glutamate and ³H-GABA, and reversibly inhibited L-glutamate uptake by C6 glioma cells. When COS-7 cells were assayed, no inhibition of the ³H-GABA transport could be evidenced. Crotoxin kept its inhibitory effect on neurotransmitters uptake even when Ca2+ ions were removed from the medium, therefore, independently of its PLA2 activity. In addition, high concentrations (2 mM) of BPB did not avoid the action of crotoxin on the neurotransmitters uptake. Crotoxin also inhibited ³H-L-glutamate, independently on Na+ channel blockade by TTX. In addition, an evaluation of the lactic dehydrogenase activity indicated that uptake inhibition does not involve a hydrolytic action of crotoxin upon the membrane. We may also suggest that crotoxin acts, at least partially, altering the electrogenic equilibrium, as evidenced by confocal microscopy, when a fluorescent probe was used to verify cell permeability on C6 glioma cells in presence of crotoxin

Effects of β-adrenoceptor antagonists in the neural nitric oxide release induced by electrical field stimulation and sodium channel activators in the rabbit corpus cavernosum

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOβ-Adrenoceptor antagonists may present receptor-independent mechanisms, such as blockade of voltage-gated sodium channels. This study aimed to investigate the effects of non-selective (propranolol), and selective β1- (atenolol, metoprolol and betaxolol) and β2-adrenoceptor (ICI 118,551) antagonists in the nitric oxide (NO)-mediated rabbit corpus cavernosum relaxations induced by either electrical field stimulation (EFS) or activators of voltage-gated sodium channels. The sodium channel blockers tetrodotoxin and saxitoxin abolished the relaxations induced by EFS or sodium channel activators of binding site-2 (aconitine and veratridine), site-3 (Ts3 toxin), site-4 (Ts1 toxin) and site-5 (brevetoxin-3). The β-adrenoceptor antagonists failed to affect the relaxations induced by EFS, aconitine and veratridine. Relaxations induced by Ts3 and Ts1 toxins, as well as brevetoxin-3, were markedly reduced by prior addition of propranolol, betaxolol and ICI 118,551. During the established relaxation induced by Ts3 toxin, propranolol failed to restore the basal tone. In conclusion, β-adrenoceptor antagonists may cause an allosteric inhibition at the binding site-3, -4 and -5 of voltage-gated sodium channels, leading to blockade of neural NO release. © 2005 Elsevier B.V.β-Adrenoceptor antagonists may present receptor-independent mechanisms, such as blockade of voltage-gated sodium channels. This study aimed to investigate the effects of non-selective (propranolol), and selective β1- (atenolol, metoprolol and betaxolol) and β2-adrenoceptor (ICI 118,551) antagonists in the nitric oxide (NO)-mediated rabbit corpus cavernosum relaxations induced by either electrical field stimulation (EFS) or activators of voltage-gated sodium channels. The sodium channel blockers tetrodotoxin and saxitoxin abolished the relaxations induced by EFS or sodium channel activators of binding site-2 (aconitine and veratridine), site-3 (Ts3 toxin), site-4 (Ts1 toxin) and site-5 (brevetoxin-3). The β-adrenoceptor antagonists failed to affect the relaxations induced by EFS, aconitine and veratridine. Relaxations induced by Ts3 and Ts1 toxins, as well as brevetoxin-3, were markedly reduced by prior addition of propranolol, betaxolol and ICI 118,551. During the established relaxation induced by Ts3 toxin, propranolol failed to restore the basal tone. In conclusion, β-adrenoceptor antagonists may cause an allosteric inhibition at the binding site-3, -4 and -5 of voltage-gated sodium channels, leading to blockade of neural NO release5191-2146153FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOsem informaçã

Relaxation of rabbit corpus cavernosum by selective activators of voltage-gated sodium channels: Role of nitric oxide-cyclic guanosine monophosphate pathway

To investigate the capacity of voltage-gated Na+ channel activators such as batrachotoxin, aconitine, veratridine, Ts 1 (formerly Tityus gamma-toxin), and brevetoxin-3 to induce relaxation of rabbit isolated corpus cavernosum (RbCC) and the pharmacologic mechanisms underlying this phenomenon. The voltage-gated Na+ channels of the corpus cavernosum are essential for erectile function. A number of biologic toxins exert their effects by modifying the properties of these channels. Methods. Male New Zealand white rabbits were anesthetized with pentobarbital sodium. Strips of RbCC were transferred to 10-mL organ baths containing oxygenated and warmed Krebs solution. The RbCC strips were connected to force-displacement transducers, and changes in isometric force were recorded using a PowerLab 400 data acquisition system. Corporeal smooth muscle was precontracted submaximally with phenylephrine (10 mumol/L). Results. The binding site-2 (batrachotoxin, aconitine, and veratridine) and binding site-5 (brevetoxin-3) voltage-gated Na+ channel activators caused slow-onset RbCC relaxations, and the binding site-4 activator Ts I produced transitory relaxations followed by a return to baseline. The Na(+)channel blockers tetrodotoxin and saxitoxin (0.1 mumol/L each) abolished the relaxations induced by these agonists. Similarly, the nitric oxide synthase inhibitor N-omega-nitro-L-arginine methyl ester (100 mumol/L) markedly reduced the relaxations and L-arginine (1 mmol/L) restored the relaxations. The soluble guanylyl cyclase inhibitor 1H-[1 2,4] oxidiazolo[4,3-alpha] quinoxalin-1-one (10 mumol/L) reduced the relaxations, and the phosphodiesterase type 5 inhibitor sildenafil (100 nmol/L) significantly potentiated the relaxations by all activators. Conclusions. Our results indicate that the relaxations evoked by selective activators of voltage-gated Na+ channels are mediated by the release of nitric oxide from nitrergic nerves and the activation of the nitric oxide-cyclic guanosine monophosphate pathway in the smooth muscle cells of erectile tissue62358158

The Complete Amino Acid Sequence Of Toxin Tstx-vi Isolated From The Venom Of The Scorpion Tityus Serrulatus

[No abstract available]9559560

Data from: Relationships between forest cover and fish diversity in the Amazon River floodplain

1.Habitat degradation leads to biodiversity loss and concomitant changes in ecosystem processes. Tropical river floodplains are highly threatened by land cover changes and support high biodiversity and important ecosystems services, but the extent to which changes in floodplain land cover affect fish biodiversity remains unknown. 2.We combined fish and environmental data collected in situ and satellite-mapped landscape features to evaluate how fish species with different ecological strategies and assemblage structures respond to deforestation in floodplains of the Amazon River. We surveyed 462 floodplain habitats distributed along a gradient of land cover, from largely forested to severely deforested. Rather than analyze only taxonomic metrics, we employed an integrative approach that simultaneously considers different aspects of fish biodiversity (i.e., beta diversity and taxonomic and functional assemblage structure) to facilitate mechanistic interpretations of the influence of land cover. 3.Spatial patterns of fish biodiversity in tropical floodplain rivers were strongly associated with forest cover as well as local environmental conditions linked to landscape gradients. Several species and functional groups defined by life history, feeding, swimming/microhabitat-use strategies were positively associated with forest cover. Other species, including some that would usually be considered habitat generalists and species directly dependent on autochthonous resources (e.g., planktivores), were most common in areas dominated by herbaceous vegetation or open-water habitats associated with the opposite extreme of the forest cover gradient. Beta-diversity and the degree of uniqueness of species combinations within habitats were also positively associated with forest cover. 4.Synthesis and applications. Our results, demonstrating that spatial patterns of fish biodiversity are associated with forest cover, indicate that deforestation of floodplains of the Amazon River results in spatial homogenization of fish assemblages and reduced functional diversity at both local and regional scales. Floodplains worldwide have undergone major land cover changes, with forest loss projected to increase during the next decades. Conserving fish diversity in these ecosystems requires protecting mosaics of both aquatic habitats and floodplain vegetation, with sufficient forest cover being critically important

Participation Of Na+ Channels In The Potentiation By Tityus Serrulatus α-toxin Tstx-v Of Glucose-induced Electrical Activity And Insulin Secretion In Rodent Islet β-cells

The effects of TsTx-V, an α-toxin isolated from Tityus serrulatus venom, on electrical activity and insulin secretion by rodent pancreatic islet cells were studied. TsTx-V (5.6 μg/ml) depolarized mouse pancreatic β-cells, diminished the membrane input resistance and increased the duration of the active phase of glucose-induced electrical activity. Similar results were observed with the Na+ channel agonist veratridine (110 μM). Both agents potentiated glucose (8.3 mM)-induced insulin secretion in rat islet. In the presence of TsTx-V or veratridine, insulin secretion increased 2- and 1.4-fold over basal values, respectively (P<0.001). The Na+ channel antagonist tetrodotoxin (6 μM) significantly decreased glucose- and TsTx-V-induced insulin secretion (P<0.001). TsTx-V also stimulated insulin secretion at low glucose concentrations (2.8 mM) whereas the β-toxin, Ts-γ (gamma toxin), also obtained from Tityus serrulatus venom, significantly reduced TsTx-V-induced secretion at sub- and suprathreshold concentrations of glucose. These results are consistent with a model whereby Na+ channels participate in glucose-induced electrical activity. Alteration in the activity of these channels changes the length of time during which the β-cell depolarizes, thereby altering the secretory behavior of the cell. The construction of a three-dimensional model for TsTx-V revealed a conserved core containing an α-helix and three β-strands, with minor differences when compared with toxins from other scorpion venoms. © 2003 Elsevier Science Ltd. All rights reserved.41810391045Arantes, E.C., Sampaio, S.V., Vieira, C.A., Gliglio, J.R., What is tityustoxin? (1992) Toxicon, 30, pp. 786-789Arantes, E.C., Ricioppo Neto, F., Sampaio, S.V., Vieira, C.A., Giglio, J.R., Isolation and characterization of TsTx-V, a new neurotoxin from T. serrulatus scorpion venom which delays the inactivation of Na+ channels (1994) Biochim. Biophys. Acta, 1199, pp. 69-75Ashcroft, F.M., Adenosine 5′-triphosphate-sensitive potassium channels (1988) Ann. Rev. Neurosci., 11, pp. 97-118Atwater, I., Mears, D., Rojas, E., Electrophysiology of the pancreatic β-cell (1996) Diabetes Mellitus: A Fundamental and Clinical Text, pp. 78-102. , D. LeRoith, S.I. Taylor, & J.M. Olefsky. Philadelphia, PA: Lippincott-RavenBarhanin, J., Giglio, J.R., Liopold, L., Schmid, A., Sampaio, S.V., Lazdunski, M., Tityus serrulatus venom contains two classes of toxins: Tityus δ toxin is a new tool with a very high affinity for studying the Na channel (1982) J. Biol. Chem., 257, pp. 12553-15558Barnes, S., Hille, B., Veratridine modifies open sodium channels (1988) J. Gen. 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Acta, 1243, pp. 309-314Misler, S., Barnett, D.W., Gillis, K.D., Pressel, D.M., Electrophysiology of stimulus-secretion coupling in human β-cell (1992) Diabetes, 41, pp. 1221-1228Novaes, G., Chetto-De-Queiroz, A., Carvalho-Cardoso, C., Burllachani-De- Carvalho, M.H., Ribeiro-Filho, L.A., Oliveira-Gonçalves, A., Nesibioblastosis associated with chronic experimental pancreatitis produced by a scorpion toxin, tityustoxin, in rats (1990) Braz. J. Med. Biol. Res., 23, pp. 1149-1151Novello, J.C., Arantes, E.C., Varanda, W.A., Oliveira, B., Giglio, J.R., Marangoni, S., TsTx-IV, a short chain four-disulfide-bridge neurotoxin from Tityus serrulatus venom, which acts on Ca2+-activated K+ channels (1999) Toxicon, 37, pp. 651-660Pinheiro, C.B., Marangoni, S., Toyama, M.H., Polikarpov, I., Structural analysis of Tityus serrulatus Ts1 neurotoxin at atomic resolution: Insights into interactions with Na+ channels (2003) Acta Crystallogr. D Biol. 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