Identification of phospholipase A 2 and neurotoxic activities in the venom of the New Guinean small-eyed snake ( Micropechis ikaheka)

Abstract

The Papua New Guinean small-eyed snake ( Micropechis ikaheka) is recognised as a cause of life-threatening envenoming in certain parts of New Guinea. The clinical features suggest the presence of toxins acting at the neuromuscular junction and on muscle. We have used the mouse phrenic nerve-hemidiaphragm preparation, a phospholipase A 2 assay, and 125I-neurotoxin-binding radioimmunoassays to look for toxic activities in the crude venom and in preliminary high-performance liquid chromatography (HPLC) fractions. Micropechis ikaheka venom at 1 and 3 μg/ml completely abolished nerve-evoked muscle twitch within 70 min at 37 °C. There was also a sustained contracture of the muscle and some reduction in twitch tension evoked by direct stimulation; these were explained by the presence of phospholipase A 2 activity. The venom inhibited the binding of 125I-α-bungarotoxin to detergent-extracted human muscle acetylcholine receptor (AChR), and inhibited acetylcholine receptor function in a muscle cell line. It also inhibited binding of 125I-ω-conotoxin GVIA to detergent-extracted human frontal cortex voltage-gated calcium channels, but this appeared to be dependent on the phospholipase A 2 activity. Identification of the main neurotoxic fractions following HPLC are shown.