Excitatory effects of Buthus C56 toxin on Drosophila larval neuromuscular junction

Abstract

Buthus C56 toxin from venom of the Indian red scorpion Mesobuthus tamulus was studied for its effects on spontaneous miniature excitatory junctional potentials (MEJP) on Drosophila larval neuromuscular junctions. C56 toxin was isolated on CM-Cellulose with linear gradient of ammonium acetate buffer, pH 6.0. Toxin purity was determined on SDS slab gel electrophoresis. Effective concentration of C56 toxin was based on contraction paralysis units (CPU) in Drosophila 3rd instar larvae by microinjection (0.1 CPU/ml = 2 x 10-6 g/ml). The toxin-induced excitatory junctional potentials were studied for calcium dependency (0.2 mM to 1.2 mM Ca2+) in Drosophila Ringer. Excitatory junctional potential amplitude was increased with increasing calcium concentration; maximum increase in the frequency at 0.4 mM Ca2+/4 mM Mg2+ Drosophila Ringer. It was suggested that while amplitude of excitatory junctional potentials was increased with concentration, maximum frequency increase at 0.4 mMCa2+/4 mM Mg2+ Drosophila Ringer may be due to augmented Ca2+ influx in 0.4 mM Ca2+, when NMDA receptors were maximally activated in C56 toxin-treated Drosophila larval neuromuscular junction