Binding of anti-acetylcholine receptor antibodies inhibits the acetylcholine receptor mediated cation flux.

A fast kinetics, spectroscopic technique has been applied to the study of the transient cation flux associated to the binding of cholinergic agonist to native acetylcholine receptor (AcChR)-rich membrane vesicles in presence of anti-AcChR antibodies. The technique is based on the collisional quenching of an intravesicularly trapped fluorophore by externally added T1+ which substitutes for physiologically occurring cations. Presence of polyclonal Fab fragments from goat anti-AcChR antibodies bound to the membrane AcChR promotes a 80-90% inhibition on the observed rate constants of T1+ influx. The observed inhibition process appears to follow a non-competitive pattern between antibody and cholinergic ligand binding, suggesting that in the AcChR protein the antigenic sites responsible for ion translocation may be other than those involved in ligand binding.