Biogenic antagonists of the nicotinic receptor: their interactions with erabutoxin.

The hypothesis that the sensitivity of the nicotinic ACh-receptor is reduced by some neurotransmitters was evaluated by studying the interaction between these neurotransmitters and erabutoxin-b (ETX-b), known to bind irreversibly with the specific ACh-receptor site. It was found that the blocking action of ETX-b was apparently prevented by previous application of 5-HT, whereas it was not prevented by application of catecholamine (CA). These results indicate that 5-HT blocks the nicotinic ACh-receptor by interacting with the specific ACh binding site, whereas CA blocks it by interacting with an allosteric site of the ACh-receptor ionic channel complex.