O anestésico intravenoso etomidato estimula a exocitosse de vesículas sinápticas em junção neuromuscular de camundongos

Abstract

The general anesthetics are used in clinical practice in order to induce analgesia, unconsciousness, amnesia and muscle relaxation. For decades efforts have been made to elucidate the possible molecular mechanisms of action of these agents. Etomidate is used in clinical practice as one of the main agents to induce anesthesia. It can cause some spontaneous movements, especially myoclonus in approximately 50-80% of patients after administration, thus suggesting a possible effect of these agents in the peripheral nervous system. Furthermore, some studies suggest that anesthetics may act on ion channels located on presynaptic terminal by changing the release of neurotransmitters, changing the organization of nicotinic receptors of the muscle cells as well changing its membrane potentials. Thus, the aim of this study was to investigate the presynaptic and postsynaptic effects of etomidate at the mouse neuromuscular junction. Nerve-muscle preparations were isolated and labeled with the fluorescent probe FM1-43 (4 M), a powerful tool to monitor exocytosis and endocytosis of synaptic vesicles. The nerve-muscle preparations were then exposed to different concentrations of etomidate (0.1, 1,2,8,10, and 40 M) and were subsequently visualized using a fluorescence optical microscope. We found that clinically relevant concentrations of etomidate stimulates exocytosis of synaptic vesicles. This effect was not inhibited by tetrodotoxin (1M), a channel blocker for voltage-sensitive Na +, demonstrating that etomidate may act by stimulating exocytosis of vesicle by a mechanism independent of Na+. However, exocytosis was inhibited by -conotoxin MVIIC (50 M) a blocking nonspecific channels for Ca2 + and voltage sensitive channels by blocking voltage-sensitive Ca2 +-type P / Q -AGA-IVA (200nM).Using electrophysiology, we searched for putative alterations in the frequency and amplitude of MEEPs in the presence of etomidate. Concerning frequency and amplitude of MEEPs, we demonstrated that etomidate did not change these parameters. We also investigated whether this drug could act in some way to nicotinic acetylcholine receptors labeled with -bungarotoxin-Alexa 594 (12 M) and we observed that etomidate, can act in any way on the postsynaptic nicotinic receptors. In conclusion, the results presented here show that etomidate exerts a presynaptic at the neuromuscular junction, likely through activation channels for Ca2 + voltage dependent on the type P / Q, and that this drug can also act at the postsynaptic membrane interfering with the nicotinic acetylcholine receptors. These results may help to understand some of the clinical effects of this agent on neuromuscular function.