Abolishment of non-quantal release of acetylcholine from the mouse phrenic nerve endings by toosendanin.

The hyperpolarizing effect (H-effect) of d-tubocurarine on the end-plate of the isolated diaphragm pretreated with an anticholinesterase was irreversibly abolished by toosendanin (1 X 10(-5) g/ml), indicating the blockade of spontaneous non-quantal release of acetylcholine (ACh). The H-effect was also inhibited, but temporarily, when toosendanin (a dose of 0.6 LD50) was subcutaneously injected into the mouse and the diaphragm was isolated 40-120 min after injection. During such an inhibitory period, however, spontaneous release of ACh remained facilitated. It is concluded that the effect of toosendanin on non-quantal release of ACh was different from its effect on quantal release not only at the direction but also at the time course.