Reversal potential of the end‐plate currents and potassium feedback at the neuromuscular synapse

The experiments were carried out at the neuromuscular junction of the frog. E rev of epc was estimated by two methods—extrapolation and interpolation. In K + ‐ enriched solution E rev obtained by linear extrapolation from high‐mp region changed according to the Takeuchi equation. The behavior of E rev obtained by interpolation was better described by the Goldman‐Hodgkin‐Katz equation. Under the change of the nerve stimulation frequency from 0.5 to 50/sec, the positive shift of E rev estimated by both methods was observed. This indicates K + accumulation in active synaptic segments during activity. The elimination of the potassium current of epc by clamping of mp at the − 130 mV level resulted in the lowering of facilitation under paired nerve stimulation (20 msec interval) and in the decrease of the rate of facilitation under 50/sec frequency stimulation. The data support the presence of antidromic K + action in the neuromuscular synapse.