The amino terminal half of the nicotinic β-subunit extracellular domain regulates the kinetics of inhibition by neuronal bungarotoxin

Subtypes of nicotinic receptors previously reported to be unaffected by neuronal bungarotoxin (NBT), including α3β4-containing and muscle type (α1β1γδ) receptors, are shown to be inhibited by this toxin, but with rapid kinetics of onset and recovery. This inhibition is in contrast to the slow and prolonged inhibition of α3β2-containing receptors, suggesting that the beta subunits determine the kinetics of NBT inhibition of α3 receptors. We have coexpressed chimeric beta subunits with α3, and our results show that the first 121 amino acids of the beta subunit extracellular domain are sufficient to regulate the kinetics of NBT inhibition. This domain is also an important determinant of whether cytisine will act as a full agonist or a partial agonist of nictonic receptors formed with α3.