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Presynaptic and postsynaptic effects of the venom of the Australian tiger snake at the neuromuscular junction
Author(s) -
DATYNER M. E.,
GAGE P. W.
Publication year - 1973
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1973.tb08381.x
Subject(s) - postsynaptic potential , neuromuscular junction , venom , carbachol , stimulation , biophysics , chemistry , anatomy , acetylcholine , biology , neuroscience , pharmacology , receptor , biochemistry
Summary1 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.