[Variation of the time constant (tau) of the decay of end-plate current during focalized transmitter release].

The variations of the time constant tau of the end-plate current (epc) have been studied at the clamped neuromuscular junction of the frog while transmitter release was focalised by local iontophoretic application of Ca++. In the absence of any anticholinesterasic drug, tau varies according to the variations of the intensity of epc (Iepc) due to pre or postsynaptic experimental procedure. It is suggested that focalisation of transmitter release induces local acetylcholinesterase inhibition by an excess of substrate; then the transmitter life time in the synaptic cleft is momentarily increased, allowing repeated binding of Ach to postsynaptic receptors.