The effects of antivenom on the in vitro neurotoxicity of venoms from the taipans Oxyuranus scutellatus, Oxyuranus microlepidotus and Oxyuranus scutellatus canni

The venoms of the inland (Oxyuranus microlepidotus), coastal (O. scutellatu s) and Paguan (O. s. canni) taipans are among the most potent in the world. The present study compared the in vitro neurotoxic effects of these venoms and the protective effects of taipan antivenom. Venom (10 mu g/ml) from al l three snakes abolished nerve-mediated twitches of the chick biventer cerv icis muscle preparation with the following rank order of potency (based on the time taken to inhibit 90% of the twitch response; t(90)): O. microlepid otus (27 +/- 3 min) > O. scutellatus (42 +/- 3 min) = O. S. canni (48 +/- 5 min). This inhibitory effect of all three venoms was primarily postsynapti c in origin as evidenced by the inhibition of responses to exogenous acetyl choline (ACh; 1 mM) and carbachol (CCh; 20 mu M); but not potassium chlorid e (40 mM). In contrast, the presynaptic neurotoxins taipoxin (3 mu g/ml) an d paradoxin (3 mu g/ml) abolished nerve-mediated twitches without producing a significant effect on contractile responses to exogenous agonists. Prior incubation of the tissue with taipan antivenom (1 unit/ml for 10 min) mark edly attenuated the inhibitory effects of taipoxin (3 mu g/ml) and paradoxi n (3 mu g/ml), as well as O. scutellatus (10 mu g/ml) and O. s. canni (10 m u g/ml) venom. However, in the presence of antivenom, O. microlepidotus ven om (10 mu g/ml) still abolished nerve-mediated twitches and responses to AC h and CCh. The results of the current study indicate that taipan antivenom, raised against O. scutellatus venom, is effective, in vitro, against the n eurotoxic effects of venom from the Papuan and coastal taipans, as well as the presynaptic effects of venom from the inland taipan. However, the antiv enom appears less effective against the postsynaptic effects of the latter. It is possible that inland taipan venom contains a component not neutralis ed by the antivenom which may contribute to the extreme potency of this ven om. (C) 1999 Elsevier Science Ltd. All rights reserved.