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      Electrical field stimulation-induced contractions on Pantherophis guttatus corpora cavernosa and aortae

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          Abstract

          A tetrodotoxin (TTX)-resistant mechanism is responsible for the electrical field stimulation (EFS)-induced contractions and relaxations of Crotalus durissus terrificus corpora cavernosa. Here it was investigated whether this mechanism also occurs in corpora cavernosa and aortae of the non-venomous snake Pantherophis guttatus corpora cavernosa and aortae. Corpora cavernosa and aortic rings isolated from Pantherophis guttatus snake were mounted in organ bath system for isometric tension recording. EFS-induced contractions in both tissues were performed in the presence and absence of guanethidine (30 μM), phentolamine (10 μM) and tetrodotoxin (1 μM). In another set of experiments, the endothelium was removed from aortic rings and EFS-induced contractions were performed in the denuded rings. Electrical field stimulation-induced contractions were frequency-dependent in Pantherophis guttatus corpora cavernosa and aortic rings. The contractions were significantly reduced in the presence of guanethidine (30 μM) or phentolamine (10 μM). Pre-treatment with tetrodotoxin had no effect on the EFS-induced contractions of either corpora cavernosa or aortic rings. Surprisingly, the EFS-induced contractions of aortic rings denuded of endothelium were almost abolished. These results indicate that the TTX-resistant mechanism is present in EFS-induced contractions of Pantherophis guttatus corpora cavernosa and aortae. The experiments performed in the aorta indicate that the endothelium is the main source for the release of catecholamines induced by EFS.

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          Most cited references26

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          Characterization of three inhibitors of endothelial nitric oxide synthase in vitro and in vivo.

          1. Three analogues of L-arginine were characterized as inhibitors of endothelial nitric oxide (NO) synthase by measuring their effect on the endothelial NO synthase from porcine aortae, on the vascular tone of rings of rat aorta and on the blood pressure of the anaesthetized rat. 2. NG-monomethyl-L-arginine (L-NMMA), N-iminoethyl-L-ornithine (L-NIO) and NG-nitro-L-arginine methyl ester (L-NAME; all at 0.1-100 microM) caused concentration-dependent inhibition of the Ca2(+)-dependent endothelial NO synthase from porcine aortae. 3. L-NMMA, L-NIO and L-NAME caused an endothelium-dependent contraction and an inhibition of the endothelium-dependent relaxation induced by acetylcholine (ACh) in aortic rings. 4. L-NMMA, L-NIO and L-NAME (0.03-300 mg kg-1, i.v.) induced a dose-dependent increase in mean systemic arterial blood pressure accompanied by bradycardia. 5. L-NMMA, L-NIO and L-NAME (100 mg kg-1, i.v.) inhibited significantly the hypotensive responses to ACh and bradykinin. 6. The increase in blood pressure and bradycardia produced by these compounds were reversed by L-arginine (30-100 mg kg-1, i.v.) in a dose-dependent manner. 7. All of these effects were enantiomer specific. 8. These results indicate that L-NMMA, L-NIO and L-NAME are inhibitors of NO synthase in the vascular endothelium and confirm the important role of NO synthesis in the maintenance of vascular tone and blood pressure.
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            Tetrodotoxin Blockage of Sodium Conductance Increase in Lobster Giant Axons

            Previous studies suggested that tetrodotoxin, a poison from the puffer fish, blocks conduction of nerve and muscle through its rather selective inhibition of the sodium-carrying mechanism. In order to verify this hypothesis, observations have been made of sodium and potassium currents in the lobster giant axons treated with tetrodotoxin by means of the sucrose-gap voltage-clamp technique. Tetrodotoxin at concentrations of 1 x 10-7 to 5 x 10-9 gm/ml blocked the action potential but had no effect on the resting potential. Partial or complete recovery might have occurred on washing with normal medium. The increase in sodium conductance normally occurring upon depolarization was very effectively suppressed when the action potential was blocked after tetrodotoxin, while the delayed increase in potassium conductance underwent no change. It is concluded that tetrodotoxin, at very low concentrations, blocks the action potential production through its selective inhibition of the sodium-carrying mechanism while keeping the potassium-carrying mechanism intact.
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              Evolutionary diversification of TTX-resistant sodium channels in a predator-prey interaction.

              Understanding the molecular genetic basis of adaptations provides incomparable insight into the genetic mechanisms by which evolutionary diversification takes place. Whether the evolution of common traits in different lineages proceeds by similar or unique mutations, and the degree to which phenotypic evolution is controlled by changes in gene regulation as opposed to gene function, are fundamental questions in evolutionary biology that require such an understanding of genetic mechanisms. Here we identify novel changes in the molecular structure of a sodium channel expressed in snake skeletal muscle, tsNa(V)1.4, that are responsible for differences in tetrodotoxin (TTX) resistance among garter snake populations coevolving with toxic newts. By the functional expression of tsNa(V)1.4, we show how differences in the amino-acid sequence of the channel affect TTX binding and impart different levels of resistance in four snake populations. These results indicate that the evolution of a physiological trait has occurred through a series of unique functional changes in a gene that is otherwise highly conserved among vertebrates.
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                Author and article information

                Contributors
                Role: ConceptualizationRole: Data curationRole: Formal analysisRole: InvestigationRole: MethodologyRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: InvestigationRole: Project administrationRole: Writing – review & editing
                Role: Data curationRole: Formal analysis
                Role: Data curationRole: Resources
                Role: Resources
                Role: Project administrationRole: Resources
                Role: ConceptualizationRole: Funding acquisitionRole: InvestigationRole: ResourcesRole: SupervisionRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: ConceptualizationRole: Data curationRole: Funding acquisitionRole: InvestigationRole: MethodologyRole: Project administrationRole: ResourcesRole: SupervisionRole: VisualizationRole: Writing – original draftRole: Writing – review & editing
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                19 April 2018
                2018
                : 13
                : 4
                : e0196123
                Affiliations
                [1 ] Faculty of Medical Sciences, Department of Pharmacology, University of Campinas, (UNICAMP), Campinas, Brazil
                [2 ] Faculty of Biomedical Engineering, Brazil University, Itaquera—São Paulo, Brazil
                [3 ] University of Vale do Paraiba (UNIVAP), São José dos Campos, Brazil
                [4 ] Institute of Biomedical Sciences, University of Sao Paulo (USP), Sao Paulo, Brazil
                University of Calgary, CANADA
                Author notes

                Competing Interests: The authors have declared that no competing interests exist.

                Author information
                http://orcid.org/0000-0002-9816-2061
                Article
                PONE-D-18-05652
                10.1371/journal.pone.0196123
                5908133
                29672643
                0dce65f0-770a-4a9a-96e9-7f88c6a33bb5
                © 2018 Campos et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 20 February 2018
                : 6 April 2018
                Page count
                Figures: 6, Tables: 0, Pages: 9
                Funding
                Funded by: funder-id http://dx.doi.org/10.13039/501100001807, Fundação de Amparo à Pesquisa do Estado de São Paulo;
                Award ID: FAPESP; 2011/11828-4
                Award Recipient :
                Funded by: funder-id http://dx.doi.org/10.13039/501100003593, Conselho Nacional de Desenvolvimento Científico e Tecnológico;
                Award ID: CNPq; 140731/2013-0
                Award Recipient :
                This study was supported by Fundação de Amparo a Pesquisa do Estado de São Paulo (Fapesp: 2011/11828-4) (GDN) ( http://www.fapesp.br/) and by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq: 140731/2013-0) (RC) ( http://cnpq.br/). The funders had no role in study design and data collection.
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