ABSTRACT
A variety of bacterial exotoxins interfere with signal transduction through type-II receptors by adenosine diphosphate-ribosylating G-proteins. Tetrodotoxin and saxitoxin act on the sodium channel by binding to its “target site 1”. Toxic diterpenoids named grayanotoxins have been isolated from leaves of various Rhododendron, Kalmia, Leucothoe and Ericaceae plant species. Grayanotoxins depolarize nerve and muscle membranes by increasing sodium permeability. This effect is reversible by washing and it can be abolished by tetrodotoxin in a noncompetitive manner. Dendrotoxins are a group of single chain neurotoxins devoid of enzymatic activity and were identified as facilitating neurotransmitter release at peripheral and central synapses. The postsynaptically acting toxins are low molecular weight, basic proteins. Elctrophysiological studies confirmed that the toxin blocks neuromuscular transmission by a postjunctional action. A large number of toxins acting on nervous structures, synapses or ion-channels have been discovered during the last decades.
