• crotamine;
  • myasthenia gravis;
  • myasthenic rats;
  • neostigmine;
  • skeletal muscle

Introduction: Crotamine is a basic, low-molecular-weight peptide that, at low concentrations, improves neurotransmission in isolated neuromuscular preparations by modulating sodium channels. In this study, we compared the effects of crotamine and neostigmine on neuromuscular transmission in myasthenic rats. Methods: We used a conventional electromyographic technique in in-situ neuromuscular preparations and a 4-week treadmill program. Results: During the in-situ electromyographic recording, neostigmine (17 μg/kg) caused short-term facilitation, whereas crotamine induced progressive and sustained twitch-tension enhancement during 140 min of recording (50 ± 5%, P < 0.05). On the treadmill evaluation, rats showed significant improvement in exercise tolerance, characterized by a decrease in the number of fatigue episodes after 2 weeks of a single-dose treatment with crotamine. Conclusions: These results indicate that crotamine is more efficient than neostigmine for enhancing muscular performance in myasthenic rats, possibly by improving the safety factor of neuromuscular transmission. Muscle Nerve, 2013