Depolarizing neuromuscular blocking action of coryneine derived from aconite root in isolated mouse phrenic nerve-diaphragm muscles.

The mode of the neuromuscular blocking action of coryneine (a quaternary ammonium derivative of dopamine) derived from aconite root was investigated in isolated phrenic nerve-diaphragm muscles and denervated diaphragm muscles of mice. Coryneine (20-150 microM) blocked the nerve-evoked twitch response without affecting the contraction evoked by electrical stimulation of the muscle. The blocking effect was reversed by neostigmine, a cholinesterase inhibitor. The electrical charge-response curve on depolarization produced by iontophoretically applied acetylcholine (ACh) at the endplate regions in normal muscles was shifted to the right on decreasing the maximal response by 40 microM coryneine. The double-reciprocal plot revealed that coryneine reduced the apparent affinity of ACh for its receptor on decreasing the maximal response. Coryneine (20 microM-2mM) itself depolarized the endplate membrane and this effect was reversibly suppressed by 1 and 5 microM pancuronium. Coryneine 30 microM-10mM) produced contractions of denervated muscles in a concentration-dependent manner and the effects were reduced by 70nM pancuronium. These results indicate that coryneine is a depolarizing agent and a mixed-type competitive and noncompetitive neuromuscular blocker.