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Abstract
The counter effects of higenamine and coryneine, components of aconite root, on acetylcholine (ACh) release from motor nerve terminals in the mouse phrenic nerve–diaphragm muscle preparation were studied by a radioisotope method. Both nerve-evoked release and spontaneous release of [3H]-ACh from the preparation preloaded with [3H]-choline were measured. The change in the tetanic tension of muscle was simultaneously recorded in the same preparation. Higenamine (10 μM) augmented both the nerve-evoked and spontaneous ACh releases, and the muscle tension. The effects were inhibited by pretreatment with propranolol (10 μM), a β-adrenoceptor antagonist. Coryneine reduced the nerve-evoked release of ACh, accelerated the decay of tetanic tension (tetanic fade) at 30 μM, and it depressed the peak amplitude of tetanic tension at a higher concentration of 100 μM. These results suggest that of the two components contained in aconite root, higenamine increases ACh release via activation of β-adrenoceptor, and conversely coryneine depresses ACh release by preferentially acting at motor nerve terminal.