Does α-Bungarotoxin Inhibit Motor Endplate Acetylcholinesterase?

α-BUNGAROTOXIN, a specific and irreversible binding agent of acetylcholine receptors of the motor endplate1,2 and of other nicotinic cholinergic receptors3, has no inhibitory effect upon acetylcholinesterase preparation from electroplax of electric eel3. Stale and Župancic4 have, however, reported that, when a minced preparation of mouse diaphragm was used, α-bungarotoxin as well as d-tubocurarine markedly inhibited the membrane acetylcholinesterase when acetylcholine concentrations lower than 12 µM were used. They took this result as evidence to support their hypothesis that the anionic centre of the enzyme in the motor endplate is the acetylcholine receptor5. We attempted, therefore, to re-examine the effect of α-bungarotoxin by using intact acetylcholinesterase in the motor endplate in order to test the hypothesis and to establish the specificity of binding of the toxin.