Reversible Neuromuscular Blockade by Modified Neurotoxin from Naja naja siamensis 1

Summary

The objective of this study was to determine whether modified neurotoxins (7) from Naja naja siamensis produced competitive neuromuscular blockade. Each modified toxin as well as native neurotoxin from N.n. siamensis was tested at several concentrations for its inhibitory effects upon acetylcholine-induced contractures in frog rectus abdominus muscles in vitro. Whereas native neurotoxin induced irreversible blockade, neuromuscular blockade with either the carbamylated or acetylated derivatives was deemed to be truly competitive because: (i) Inhibition of acetylcholine contractures was readily reversible upon washing with toxin-free solution; (ii) dose-response curves for acetylcholine were shifted parallel to the right without depression of maxima; (iii) slopes of regression line for pA₂ determination were not different from unity.