[Postsynaptic ionic endplate currents of fast and slow chick muscle fibers. Effect of cholinesterase inhibition].

The mean values of the rise time and half-time decay of miniature end-plate currents (MEPC) recorded extracellularly or by the voltage clamp technique in the synapses of slow muscle fibres were 2.5 times higher than in the fast ones. Inhibition of AChE prolonged the time course of MEPC in slow and fast fibres 1.5 and 3.5 times, respectively. As a result, the difference between the time courses of fast and slow MEPC completely disappeared. Voltage dependence of the MEPC decay rate is found to be smaller in slow synapses than in fast ones, especially in the range between -80 mV and -140 mV. This difference between fast and slow synapses was more pronounced after AChE-inhibition or after ethanol treatment. The nature of the difference in MEPC time course in fast and slow synapses is discussed.