Effect of Vipoxin (V. amm. meridionalis) and its components on neuromuscular transmission

Vipoxin is the main toxic component isolated from the venom of long-nosed viper Vipera ammodytes meridionalis, which population is widely distributed on the Bulgarian area. The neurotoxin consists of two subunits – unstable and toxic phospholipase A₂ (PLA2) and non-toxic acidic component without enzymatic activity (Vipoxin’s acidic components, VAC). In the current study, the action of neurotoxic complex was examined by neurophysiological in vivo experimental model on anaesthetized rats. Vipoxin produces neuromuscular blockade in a dose-dependent manner with non-depolarizing post-junctional site of action. It was found that isolated PLA₂ displays significantly lower blocking activity in comparison with Vipoxin when both have been applied in equimolar concentration. That implies the stabilizing role of VAC and its significance for the toxicity of the whole complex. The Vipoxin-induced neuromuscular blockade is completely reversed when antivenom is administrated.