title: Etomidate evokes synaptic vesicle exocytosis without increasing miniature endplate potentials frequency at the mice neuromuscular junction.
abstract: Etomidate is an intravenous anesthetic used during anesthesia induction. This agent induces spontaneous movements, especially myoclonus after its administration suggesting a putative primary effect at the central nervous system or the periphery. Therefore, the aim of this study was to investigate the presynaptic and postsynaptic effects of etomidate at the mouse neuromuscular junction (NMJ). Diaphragm nerve muscle preparations were isolated and stained with the styryl dye FM1-43, a fluorescent tool that tracks synaptic vesicles exo-endocytosis that are key steps for neurotransmission. We observed that etomidate induced synaptic vesicle exocytosis in a dose-dependent fashion, an effect that was independent of voltage-gated Na(+) channels. By contrast, etomidate-evoked exocytosis was dependent on extracellular Ca(2+) because its effect was abolished in Ca(2+)-free medium and also inhibited by omega-Agatoxin IVA (30 and 200nM) suggesting the participation of P/Q-subtype Ca(2+) channels. Interestingly, even though etomidate induced synaptic vesicle exocytosis, we did not observe any significant difference in the frequency and amplitude of miniature end-plate potentials (MEPPs) in the presence of the anesthetic. We therefore investigated whether etomidate could act on nicotinic acetylcholine receptors labeled with α-bungarotoxin-Alexa 594 and we observed less fluorescence in preparations exposed to the anesthetic. In conclusion, our results suggest that etomidate exerts a presynaptic effect at the NMJ inducing synaptic vesicle exocytosis, likely through the activation of P-subtype voltage gated Ca(2+) channels without interfering with MEPPs frequency. The present data contribute to a better understanding about the effect of etomidate at the neuromuscular synapse and may help to explain some clinical effects of this agent.
authors.affiliation: Departamento de Morfologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Priscila Aparecida Costa
authors.initials: PA
authors.lastname: Valadão
authors.affiliation: Departamento de Fisiologia e Biofísica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Lígia Araújo
authors.initials: LA
authors.lastname: Naves
authors.affiliation: Departamento de Cirurgia, Faculdade de Medicina, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Renato Santiago
authors.initials: RS
authors.lastname: Gomez
authors.affiliation: Departamento de Morfologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil. Electronic address: cguati@icb.ufmg.br.
authors.forename: Cristina
authors.initials: C
authors.lastname: Guatimosim
mesh_terms: D000818:Animals; D020865:Calcium Channels, P-Type / Q000187:drug effects / Q000378:metabolism; D020907:Calcium Channels, Q-Type / Q000187:drug effects / Q000378:metabolism; D003964:Diaphragm / Q000187:drug effects / Q000294:innervation; D004305:Dose-Response Relationship, Drug; D005045:Etomidate / Q000494:pharmacology*; D005071:Evoked Potentials / Q000187:drug effects*; D005089:Exocytosis / Q000187:drug effects*; D005260:Female; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D051379:Mice; D009045:Motor Endplate / Q000187:drug effects*; D009469:Neuromuscular Junction / Q000187:drug effects*; D011978:Receptors, Nicotinic / Q000187:drug effects; D013572:Synaptic Vesicles / Q000187:drug effects*
chemical_list: D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D006993:Hypnotics and Sedatives; D011978:Receptors, Nicotinic; D005045:Etomidate
keywords: ACh; EGTA; Etomidate; FM1-43; GABA; MEPP; NMJ; Neuromuscular junction; Nicotinic receptors; Synaptic vesicle; TTX; acetylcholine; alpha-bungarotoxin; etilenoglicol-bis-β-aminoetil éster; miniature end plate potential; neuromuscular junction; tetrodotoxin; α-BGT; γ-amino butyric acid