Elucidation of the mechanism and site of action of quinuclidinyl benzilate (QNB) on the electrical excitability and chemosensitivity of the frog sartorius muscle.

The effects of the muscarinic antagonist quinuclidinyl benzilate (QNB) on transmission at the frog sartorius neuromuscular junction have been examined. QNB decreases endplate potential (EPP) amplitude without affecting miniature endplate (MEPP) frequency or resting potential. QNB also increased the latency of the EPP and the nerve terminal spike in a frequency dependent fashion, suggesting the site of action is the unmyelinated nerve terminal. Since the rate and amplitude of muscle action are potentials decreased it is likely that QNB causes a blockade of electrically excitable sodium channels; the agent also blocks ionic channels associated with nicotinic acetylcholine receptors. It is possible that these effects of QNB may explain some of the behavioral disturbances produced by its administration.