Abstract
The venom of the Sydney funnel web spider, Atrax robustus, produced marked contractions of isolated human intercostal muscles. In the presence of either d-tubocurarine or manganese ions these contractions were abolished, as were the contractions produced by stimulation of nerve fibres within the preparations. From these results it is concluded that the venom evokes the release of acetylcholine from motor nerve endings. In preparations exposed to the venom for periods in excess of 1 hr, however, the contractions produced by both the venom and nervous stimulation gradually became reduced in size and eventually both were abolished. At this time the muscle still responded to direct electrical stimulation and it was possible, by increasing the stimulus parameters, to restore some nerve-induced contractions. From these results it is concluded that, after initially evoking the release of acetylcholine, the venom subsequently blocks the release of this compound.
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