Inhibition of the acetylcholine receptor by histrionicotoxin

1 The action of C5-decahydrohistrionicotoxin (C5-HTX) has been investigated on the extrajunctional acetylcholine (ACh) receptors of denervated rat muscle. 2 C5-HTX causes both a rapid and slow reduction in amplitude of iontophoretic ACh potentials evoked at all frequencies from the extrajunctional receptors. 3 C5-HTX also causes a time-dependent inhibition of the iontophoretic potentials evoked at frequencies greater than 0.02 Hz. This inhibition was observed either alone or superimposed upon desensitization, and may be caused by a similar mechanism to desensitization.