α-Bungarotoxin, κ-bungarotoxin, α-cobratoxin and erabutoxin-b do not affect [3H]acetylcholine release from the rat isolated left hemidiaphragm |
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Authors: | C Apel J ?í?ný G Wagner I Wessler |
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Institution: | (1) Department of Pharmacology, University of Mainz, Obere Zahlbacher Strasse 67, D-55101 Mainz, Germany;(2) Present address: Institute of Physiology, Academy of Sciences, CZ-14200 Praque, Czech Republic |
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Abstract: | Endplate preparations of the rat left hemidiaphragm were incubated with 3H]choline to label neuronal transmitter stores. Nerve evoked release of newly-synthesized 3H]acetylcholine was measured in the absence of cholinesterase inhibitors to investigate whether snake venom neurotoxins by blocking presynaptic nicotinic autoreceptors affect evoked transmitter release. Contractions of the indirectly stimulated hemidiaphragm were recorded to characterize the blocking effect of -neurotoxins at the postsynaptic nicotinic receptors.Neither the long chain neurotoxins -cobratoxin (1 g ml–1) and -bungarotoxin (5 g ml–1) nor the short chain neurotoxin erabutoxin-b (0.1, 1 and 10 gml–1) affected the nerve-evoked release of 3H]acetylcholine. -Bungarotoxin (1 and 5 g ml–1), a toxin preferentially blocking neuronal nicotinic receptors, did also not affect evoked 3H]acetylcholine release, whereas (+)-tubocurarine (1 M) under identical conditions reduced the release by about 50%. -Bungarotoxin, -cobratoxin and erabutoxin-b concentration-dependently (0.01–0.6 g ml–1)inhibited nerve-evoked contractions of the hemidiaphragm. All neurotoxins except erabutoxin-b enhanced the basal tritium efflux immediately when applied to the endplate preparation or to a non-innervated muscle strip labelled with 3H]choline. This effect was attributed to an enhanced efflux of 3H]phosphorylcholine, whereas the efflux of 3H]choline and 3H]acetylcholine was not affected.It is concluded that the -neurotoxins and -bungarotoxin do not block presynaptic nicotinic receptors of motor nerves. These nicotinic autoreceptors differ from nicotinic receptors localized at the muscle membrane and at autonomic ganglia. |
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Keywords: | Rat phrenic nerve -Neurotoxins" target="_blank">gif" alt="agr" align="BASELINE" BORDER="0">-Neurotoxins |
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