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Abstract
Several species of scorpions can cause potentially lethal envenomation, especially in children. Venoms from such scorpions contain protein neurotoxins which can modify Na+- and K+-channel activity to cause considerable enhancement of depolarisation of autonomic nerves with consequent massive release of neurotransmitters producing toxic actions in target organs, especially of the cardiovascular system.
An electrical method for milking venom from a colony of black scorpions (Heterometrus longimanus) maintained in our laboratory is described. The general features and the structure of the venom secreting apparatus of H. longimanus are discussed. Venom from H. longimanus was found to contain relatively high concentrations (mean 1.8 ± 0.3 mM, range 0.4 - 4.5 mM) of noradrenaline (NA)1 which can account for the postjunctional α-agonist activity of the venom; dopamine was present at much (60-fold) lower concentrations (mean 31 ± 4μM) whereas adrenaline was not detected.
Venom from several other species of scorpions (Mesobuthus tamulus, Buthus martensi Karsch, Leiurus quinquestriatus quinquestriatus and Buthus hottentota) was found to mediate adrenergic agonist actions in the rat isolated anococcygeus muscle (Acm)2 via some prejunctional mechanism(s), presumably causing stimulation of adrenergic nerves to release transmitter NA which then acts on the postjunctional α-adrenoceptors. Venom from Leiurus q. quinquestriatus and B. hottentota also produced relaxant responses of the carbachol-precontracted Acm, presumably through stimulation of non-adrenergic non-cholinergic (NANC)3 nerves to release the inhibitory neurotransmitter nitric oxide.