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 μmol/L, enhanced spontaneous vesicle exocytosis monitored by FM1-43 in a Ca2+-dependent and Na+-independent fashion. Higher concentrations of propofol (50, 100, and 200 μmol/L) had no effect on spontaneous exocytosis. By contrast, higher concentrations of propofol inhibited the Na+-dependent exocytosis evoked by 4-aminopyridine but did not affect the Na+-independent exocytosis evoked by KCl. 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
