Venom of Collett's snake (Pseudechis colletti) blocks the binding of α-bungarotoxin to acetylcholine receptors at chick but not human neuromuscular junctions: A histochemical study

Transverse cryosections, 6–8 μm thick, were cut from unfixed biventer cervicis muscles of chicks and quadriceps muscles of humans, mounted on glass slides and incubated for 1 h in either isotonic phosphate buffered saline, pH 7.3 (PBS), or crude venom of venom of Pseudechis colletti at concentrations between 2.1 and 210 μg ml−1 in PBS. They were then exposed to a fluoresceine-conjugated α-bungarotoxin to label ACh receptor sites. Exposure to the crude venom of P. colletti prevented the labelling of acetylcholine (ACh) receptors in chick muscle in a dose-dependant manner; at a concentration of 2.1 μg ml−1 labelling fell by 20% and at a concentration of 21 μg ml−1 by more than 90%. In contrast, exposure to the venom at concentrations as high as 210 μg ml−1 had no effect on receptor labelling in human skeletal muscle. The results suggest that ACh receptors in human skeletal muscle are relatively resistant to the postsynaptically active neurotoxins in the venom of P. colletti. The data explain the apparent anomaly that the venom blocks neuromuscular transmission in isolated nerve-muscle preparations of the chick whilst human subjects of envenoming bites by P. colletti exhibit no overt signs of neurotoxicity.