The sensitivity of nicotinic synapses in bullfrog sympathetic ganglia to α‐bungarotoxin and neuronal‐bungarotoxin

The sensitivity of nicotinic synapses to α‐bungarotoxin (α‐Bgt) and neuronal‐bungarotoxin (n‐Bgt) was measured in the B and C cell systems of bullfrog paravertebral sympathetic ganglia 9 and 10 by recording extracellular compound postganglionic action potentials from the rami communicantes. High concentrations (10 μm) of α‐Bgt applied for up to 8 h had no effect upon synaptic transmission in either the B or C cell system. Ganglia pretreated with collagenase were also insensitive to α‐Bgt. In control experiments on isolated sartorius muscle preparations, nerve‐evoked twitches were fully blocked by 30‐100nM α‐Bgt. Nicotinic transmission in the B and C cell systems was reversibly blocked by 30–300 nm n‐Bgt. Block appeared within 25–45 min of exposure to toxin and reversed fully with a half‐time of 40‐80min. This was indistinguishable from washout times after block by 100 μm (+)‐tubocurarine. The results demonstrate close parallels between the bungarotoxin sensitivity of neuronal nicotinic receptors mediating ganglionic transmission in functional subclasses of bullfrog sympathetic neurones and the bungarotoxin sensitivity which has been reported for autonomic neurones in avian and mammalian preparations. 1994 British Pharmacological Society