ACTIVE PHASE OF FROG'S END-PLATE POTENTIAL

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Abstract
The period during which the end pLate membrane is actively depolarized during neuromuscular transmission is short compared with the end plate potential (e.p.p.) and the later part of the e.p.p. is a passive dissipation of the charge. The actively depolarizing phase was investigated by clamping the membrane potential at constant value and by measuring the current flowing through the end plate membrane during neuromuscular transmission (end plate current) by use of negative feed-back. Total duration of the active phase was 4-5 msec at 17[degree] C. The time course was lengthened by lowering the temperature, eserinizing (physostigmine) and sinomenine. Analysis of the relationship between the muscle membrane potential and the magnitude of the end plate current showed that the e.p.p. was produced by a constant e.m.f. (10-20 mv) and a variable resistance at the end plate membrane. The peak value of the resistance at normal end plate membrane was 60-100 K[OMEGA].