Presynaptic and postsynaptic effects of the venom of the Australian tiger snake at the neuromuscular junction

• Published in: British journal of pharmacology 1973-10, Vol.49 (2), p.340-354
• Main Authors: DATYNER, M. E., GAGE, P. W.
• Format: Article
• Language: English
• Subjects: Acetylcholine - pharmacology; Action Potentials - drug effects; Animals; Antivenins - pharmacology; Bufo marinus; Calcium; Carbachol - antagonists & inhibitors; Chemoreceptor Cells - drug effects; Computers; Electric Stimulation; Electrophysiology; In Vitro Techniques; Magnesium; Membrane Potentials - drug effects; Microelectrodes; Muscle Contraction - drug effects; Neuromuscular Junction - drug effects; Neuromuscular Nondepolarizing Agents - pharmacology; Receptors, Neurotransmitter - drug effects; Snakes; Toxicology; Tubocurarine - pharmacology; Venoms - administration & dosage; Venoms - pharmacology
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1973.tb08381.x

Summary 1 Crude venom (TSV) from the Australian tiger snake (Notechis scutatus scutatus) has both presynaptic and postsynaptic effects at the neuromuscular junctions of toads. 2 TSV (50 μg/ml) rapidly blocked indirectly elicited muscle twitches without affecting the compound action potential in the sciatic nerve or twitches elicited by direct stimulation. 3 Low concentrations of the venom (1–10 μg/ml) reduced the amplitude of miniature endplate potentials (m.e.p.ps) and inhibited the depolarization of muscle fibres normally caused by carbachol. It was concluded that a fraction of the venom binds to acetylcholine receptors. 4 The frequency of m.e.p.ps was at first increased by TSV at a concentration of 1 μg/ml. Occasional, high frequency ‘bursts’ of m.e.p.ps were recorded in some preparations. The mean frequency of m.e.p.ps appeared to fall after several hours in the venom. 5 The quantal content of endplate potentials (e.p.ps) was reduced by the venom. With low concentrations (1 μg/ml), an initial increase in quantal content was often seen. When the quantal content was markedly depressed there was no parallel reduction in the amplitude of nerve terminal spikes recorded extracellularly, though a later fall in size and slowing of time course was often seen. 6 There was evidence that TSV eventually changed the normal Poisson characteristics of the spontaneous release of quanta and this may be correlated with electronmicroscopic changes in nerve terminals. 7 Tiger snake antivenene counteracted the postsynaptic, but not the presynaptic effects of TSV when they had developed.