A regenerating release of acetylcholine from mouse motor nerve terminals treated with anticholinesterase agents.

It was found by intracellular recording with glass microelectrodes that train stimulation (50-200 Hz) of the phrenic nerve of intact or cut mouse diaphragm induced an accumulative depolarization of the endplate and triggered after a few pulses an 'all-or-none' regenerative depolarization lasting for 300-900 ms when acetylcholinesterase was inhibited by neostigmine or diisopropylfluorophosphate. This depolarization was associated with a noise of the membrane potential and a failure of the end plate potential. Low Ca2+ prolonged whereas high Ca2+ shortened the duration of regenerative depolarization which needed no further stimulation once triggered. d-Tubocurarine abolished the depolarization while restoring the end plate potential. A regenerative release of acetylcholine due to an activation of presynaptic cholinoceptors is speculated.