[Effects of maitotoxin on the transmission of neuromuscular junction in rats].

AIM AND METHODS

The effects of maitotoxin (MTX) on neuromuscular junction transmission in isolated non-uniformed stretched muscle preparation of rat diaphragms were studied using intracellular recording with microelectrodes.

RESULTS

(1) End-plate potentials (EPPs) were not induced abruptly after 18.0 min 10 microg/L MTX added to the chamber. Hereafter postsynaptic membrane potential was depolarized gradually, and the maximum depolarization value was 27.0 mV. The frequency of mEPP increased markedly after 70.3 min MTX administered, 32 folds compared with control. (2) 20 micromol/L verapamil was added to the chamber 20 min prior to 10 microg/L MTX. No evident effects of verapamil on the above parameters elicited by MTX was produced, except that it was 78.5 min when EPPs were not induced by train stimulation, which was longer than that was induced by MTX alone (P < 0.001).

CONCLUSION

The predominant effect of MTX on the neuromuscular junction transmission was that EPPs couldn't be elicited by indirect stimulation, and which could be inhibited partly by verapamil, a L-type calcium ion channel blocker. Postsynaptic membrane potential depolarization and mEPP frequency increasing induced by MTX couldn't be inhibited by verapamil.