Pharmacological characterization of mikatoxin, an α-neurotoxin isolated from the venom of the New-Guinean small-eyed snake Micropechis ikaheka

• Published in: Toxicon (Oxford) Vol. 40; no. 7; pp. 863 - 871
• Main Authors: NIRTHANAN, S, GAO, R, GOPALAKRISHNAKONE, P, GWEE, M. C. E, KHOO, H. E, CHEAH, L. S, MANJUNATHA KINI, R
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Science 01-07-2002
• Subjects: Acetylcholine - pharmacology; Animal poisons toxicology. Antivenoms; Animals; Biological and medical sciences; Carbachol - pharmacology; Chickens; Chromatography, High Pressure Liquid; Diaphragm - drug effects; Dose-Response Relationship, Drug; Elapid Venoms - pharmacology; Elapidae; Guinea Pigs; Medical sciences; Mice; Muscle, Skeletal - drug effects; Neuromuscular Blocking Agents - pharmacology; Neuromuscular Junction - drug effects; Neurotoxins - pharmacology; Nicotinic Antagonists - pharmacology; Rats; Receptors, Nicotinic - drug effects; Receptors, Nicotinic - metabolism; Snake Venoms - isolation & purification; Snake Venoms - pharmacology; Spectrometry, Mass, Electrospray Ionization; Toxicology; New Guinea; Melanesia; Oceania; Peripheral nervous system; Nervous system diseases; Envenomation; Peptides; Rat; Toxicity; Rodentia; Animal origin; Striated muscle; Neuromuscular junction; Ophidia; Characterization; Toxin; Cholinergic receptor; Vertebrata; Mammalia; Guinea pig; Mouse; Animal; Venom; Neurotoxin; Isolation; Reptilia; Nicotinic receptor
• ISSN: 0041-0101; 1879-3150
• DOI: 10.1016/S0041-0101(01)00268-9

Symptoms of envenomation by the New-Guinean small-eyed snake Micropechis ikaheka (Elapidae) include peripheral neurotoxicity and myotoxicity. We have now purified to homogeneity a long-chain neurotoxin, mikatoxin, from M. ikaheka venom by successive gel filtration and reverse-phase chromatography. Electrospray ionization mass spectrometry showed mikatoxin to be a homogenous peptide of MW 7775.6. Mikatoxin was devoid of any phospholipase A(2) activity associated with the crude venom and did not exhibit any intrinsic anticholinesterase activity. In the chick biventer cervicis muscle, it produced an irreversible, concentration-dependent block of responses to exogenously applied acetylcholine and carbachol as well as twitches evoked by nerve, but not by direct muscle stimulation. Moreover, mikatoxin, like alpha-bungarotoxin and erabutoxin-b, did not show significant fade response to train-of-four stimulation of the mouse phrenic nerve-hemi diaphragm muscle. It also failed to block ganglionic transmission in the guinea pig ileum and muscarinic responses in the rat anococcygeus muscle. Our study provides strong evidence for the presence of a neurotoxin (mikatoxin) in M. ikaheka venom that produces neuromuscular blockade in skeletal muscle attributable to selective and irreversible antagonism of postsynaptic nicotinic acetylcholine receptors of the neuromuscular junction and likely contributes to the peripheral neurotoxicity observed in M. ikaheka envenomation.