The effects of α- and β-neurotoxins from the venoms of various snakes on transmission in autonomic ganglia

Abstract

We have previously shown that certain commercially available lots of α-bungarotoxin block transmission in ciliary and choroid neurons of both pigeon and chicken ciliary ganglia at a concentration of 10 μg/ml (1.2 μM). The blockade is antagonized by pre-incubation with 100 μM tubocurarine. Further evidence that this blockade is produced by a postsynaptic action, as one would expect of an α-neurotoxin, are our findings that: (a) exposure to the toxin prevents the depolarization of ganglion cells normally seen in response to the cholinergic agonist, carbachol; and (b) the blocking activity of the toxin is removed by treatment with membranes purified from Torpedo electric organ containing an excess of α-neurotoxin binding sites. A high affinity binding site for [ 125I]α-bungarotoxin was characterized in the chicken ciliary ganglion. However, since it is labelled equally well by lots of α-bungarotoxin which block transmission and those that do not, this site does not appear to be involved in the blockade of transmission. α-Cobratoxin (from Naja naja siamensis), the α-neurotoxin L.s. III (from Laticauda semifasciata) and certain lots of α-bungarotoxin produce a partial blockade of transmission in ciliary neurons of the pigeon ciliary ganglion at a concentration of 10 μg/ml (1.2 μM), but have no effect on transmission in choroid neurons. Two other α-neurotoxins from Laticauda semifasciata, erabutoxin a and erabutoxin b, have no effect on transmission in either cell population at this concentration. None of the α-neurotoxins tested had any effect on transmission in either the rat superior cervical ganglion or the rat pelvic ganglion at concentrations up to 100 μg/ml (12 μM). Collagenase treatment of these ganglia, in an attempt to increase access of the toxins to ganglion cells, did not alter these negative results. β-Bungarotoxin (0.5 μg/ml, 0.02 μM) produces a complex blockade of transmission in both avian ciliary ganglia and rat superior cervical ganglia. Unlike the action of α-bungarotoxin, the blockade of ciliary ganglion transmission by β-bungarotoxin is irreversible and is not prevented by pretreatment with tubocurarine.