Methyllycaconitine: a selective probe for neuronal α-bungarotoxin binding sites

The ability of methyllycaconitine (MLA) to inhibit the binding of [¹²⁵I]α-bungarotoxin to rat brain membranes, frog and human muscle extracts and the human muscle cell line TE671 has been measured. MLA showed a markedly higher affinity for the rat brain site (K_i 1.4 × 10⁻⁹ M) than for the muscle receptors (K_i; 10⁻⁵-10⁻⁶ M). Structure modelling techniques were used to fit the structure of MLA to a nicotinic pharmacophore model. MLA is the first low molecular weight ligand to be shown to discriminate between muscle nicotinic receptors and their α-bungarotoxinbinding counterpart in the brain, and as such may be a useful structural probe for pursuing the structural and functional properties of the neuronal protein.