Ceruleotoxin: a possible marker of the cholinergic ionophore

Ceruleotoxin, a toxin component of Bungarus caeuleus venom, blocks in vivo the depolarisation caused by carbamylcholine on the isolated electroplaque from Electrophorus electricus and in vitro in increase of 22Na+ and 42K+ efflux caused by cholinergie agonists on excitable receptor-rich microsacs prepared from Torpedo marmorata electric organ. However, at variance with the typical alpha-toxins, ceruleotoxin does not interfere with the binding of [3H]acetylcholine and of alpha-[3H]toxin to the cholinergic receptor site. Ceruleotoxin also slightly modifies 35SO 2 4-and [14C]glucose efflux. Some of its effects on the postsynaptic membrane may be related to the presence of a phospholipase activity present in the preparation and are discussed in those terms. It is proposed that ceruleotoxin selectively blocks the electrogenic action of acetylcholine on the postsynaptic membrane without binding to the cholinergic receptor site, and might serve as an useful tool to characterise the ion translocating device, the ionophore, associated with the cholinergic receptor site.