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Two classes of channel-specific toxin from funnel web spider venom

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Michael E Adams at University of California, Riverside
Michael E Adams
Edward E. Herold
Edward E. Herold
Edward E. Herold
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Virginia J. Venema
Virginia J. Venema
Virginia J. Venema
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1. The paralytic effects and neuromuscular actions ofAgelenopsis aperta venom on insects were analyzed biochemically and electrophysiologically. 2. Paralysis caused byAgelenopsis venom is correlated with two effects on neuromuscular transmission: postsynaptic inhibition and presynaptic excitation. These effects are explained by the actions of two classes of toxins purified by RPLC, theα- and μ-agatoxins. 3. Theα-agatoxins are low molecular weight, acylpolyamines which cause rapid, reversible paralysis correlated with use-dependent postsynaptic block of EPSPs and ionophoretic glutamate potentials. The μ-agatoxins are cysteine-rich polypeptides which cause irreversible paralysis and repetitive action potentials originating in presynaptic axons or nerve terminals. 4. The joint actions of theα- and μ-agatoxins lead to significantly higher rates of paralysis than are obtained by either toxin class alone, and this may relate to enhancement by excitatory μ-agatoxins of use-dependent block caused byα-agatoxins.
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Ionic differences in ‘fast’ and ‘slow’ neuromuscular transmission in body wall muscles of Musca domestica larvae
Article
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1. The reversal potential of the fast and slow excitatory postsynaptic potential (EPSP) of longitudinal body wall muscles 6A and 7A ofMusca domestica larvae were studied in various saline solutions. 2. The reversal potentials of both fast and slow EPSPs are made more negative by decreasing the sodium ion concentration and made more positive by increasing the potassium ion concentration. The reversal potential of the slow EPSP becomes more negative with increasing bicarbonate ion concentration, whereas the reversal potential of the fast EPSP is unaffected by changes in bicarbonate ions. 3. If both axons are stimulated to give a composite response, the slight difference in the reversal potentials of the fast and slow EPSPs gives a biphasic wave form at membrane potentials near reversal. The size of this biphasic wave increases with increasing bicarbonate ion concentration. 4. Analysis of the haemolymph ofMusca larvae revealed a bicarbonate ion concentration of 10.32 mM (S.D.1.3) and a pH of 7.1 (S.D.0.05). 5. It is concluded that fast and slow responses use different ionic channels. It is tentatively suggested that bicarbonate ions affect the reversal potential of the slow EPSP by increasing the intracellular potassium concentration. The fast and slow EPSP may therefore utilise channels whose conductances are differentially sensitive to intracellular potassium concentration.
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