Effect of intravenous anesthetic propofol on synaptic vesicle exocytosis at the frog neuromuscular junction

Aim： To investigate the presynaptic effects of propofol, a short-acting intravenous anesthetic, in the frog neuromuscular junction. Methods： Frog cutaneous pectoris nerve muscle preparations were prepared. A fluorescent tool （FM1-43） was used to visualize the effect of propofol on synaptic vesicle exocytosos in the frog neuromuscular junction. Results： Low concentrations of propofol, ranging from 10 to 25 pmol/L, enhanced spontaneous vesicle exocytosis monitored by FM1- 43 in a Ca^2＋dependent and Na＋-independent fashion. Higher concentrations of propofol （50, 100, and 200 pmol/L） had no effect on spontaneous exocytosis. By contrast, higher concentrations of propofol inhibited the Na^＋-dependent exocytosis evoked by 4-aminopyri- dine but did not affect the Na^＋-independent exocytosis evoked by KCI. This action was similar and non-additive with that observed by tetrodotoxin, a Na^＋ channel blocker. Conclusion： Our data suggest that propofol has a dose-dependent presynaptic effect at the neuromuscular transmission which may help to understand some of the clinical effects of this agent on neuromuscular function.