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. Erev of epc was estimated by two methods--extrapolation and interpolation. In K+-enriched solution Erev obtained by linear extrapolation from high-mp region changed according to the Takeuchi equation. The behavior of Erev 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 Erev 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.