Bothropstoxin-I reduces evoked acetylcholine release from rat motor nerve terminals: Radiochemical and real-time video-microscopy studies
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Data
2013-01-01
Autores
Correia-de-Sá, Paulo
Noronha-Matos, José B.
Timóteo, Maria A.
Ferreirinha, Fátima
Marques, Patrícia
Soares, Andreimar M.
Carvalho, Cicilia [UNESP]
Cavalcante, Walter L.G. [UNESP]
Gallacci, Márcia [UNESP]
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Resumo
Understanding the biological activity profile of the snake venom components is fundamental for improving the treatment of snakebite envenomings and may also contribute for the development of new potential therapeutic agents. In this work, we tested the effects of BthTX-I, a Lys49 PLA2 homologue from the Bothrops jararacussu snake venom. While this toxin induces conspicuous myonecrosis by a catalytically independent mechanism, a series of in vitro studies support the hypothesis that BthTX-I might also exert a neuromuscular blocking activity due to its ability to alter the integrity of muscle cell membranes. To gain insight into the mechanisms of this inhibitory neuromuscular effect, for the first time, the influence of BthTX-I on nerve-evoked ACh release was directly quantified by radiochemical and real-time video-microscopy methods. Our results show that the neuromuscular blockade produced by in vitro exposure to BthTX-I (1 μM) results from the summation of both pre- and postsynaptic effects. Modifications affecting the presynaptic apparatus were revealed by the significant reduction of nerve-evoked [3H]-ACh release; real-time measurements of transmitter exocytosis using the FM4-64 fluorescent dye fully supported radiochemical data. The postsynaptic effect of BthTX-I was characterized by typical histological alterations in the architecture of skeletal muscle fibers, increase in the outflow of the intracellular lactate dehydrogenase enzyme and progressive depolarization of the muscle resting membrane potential. In conclusion, these findings suggest that the neuromuscular blockade produced by BthTX-I results from transient depolarization of skeletal muscle fibers, consequent to its general membrane-destabilizing effect, and subsequent decrease of evoked ACh release from motor nerve terminals. © 2012 Elsevier Ltd.
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[3H]-Acetylcholine release, Bothropstoxin-I, Neuromuscular transmission, Phospholipase A2, Real-time transmitter exocytosis, Snake venom, Bothropstoxin I, calcium independent phospholipase A2, lactate dehydrogenase, snake venom, unclassified drug, acetylcholine release, animal cell, animal experiment, animal model, animal tissue, Bothrops, bothrops jararacussu, catalysis, controlled study, evoked response, exocytosis, female, fluorescence analysis, histopathology, in vitro study, intracellular space, male, muscle necrosis, nerve cell membrane steady potential, nerve ending, neuromuscular blocking, nonhuman, postsynaptic potential, presynaptic potential, priority journal, quantitative analysis, radioassay, rat, skeletal muscle, toxin analysis, video microscopy, Acetylcholine, Animals, Crotalid Venoms, Diaphragm, Exocytosis, Female, Fluorescent Dyes, L-Lactate Dehydrogenase, Male, Microelectrodes, Microscopy, Video, Motor Neurons, Muscle Contraction, Myography, Phospholipases A2, Phrenic Nerve, Presynaptic Terminals, Pyridinium Compounds, Quaternary Ammonium Compounds, Rats, Rats, Wistar, Bothrops jararacussu, Rattus
Como citar
Toxicon, v. 61, n. 1, p. 16-25, 2013.