SUMMARY1. An attempt was made to analyse further the factors which might determine the time course of the falling phase of the end-plate current.2. The end-plate current was measured by 'clamping' the membrane potential during neuromuscular transmission. The falling phase of the endplate current had an exponential and a non-exponential portion.3. The exponential portion of the falling phase of the end-plate current was found to be strongly affected by changes in the membrane potential and by relatively small changes in temperature.4. It is suggested that the two rate constants which determine the dissociation of the receptor-mediator complex are affected by both temperature and the membrane potential. Under certain experimental conditions these two rate constants alone seem to determine the time course of the exponential portion of the falling phase of the end-plate current.

SUMMARY1. Intracellular recordings of the end-plate current at different membrane potentials were made, using a voltage-clamp technique.2. When the membrane potential is varied between about +40 and -120 mV, the half-decline time of the end-plate current increases from about 0-6 msec to about 1*6 msec.3. It is suggested that the stability of receptor-mediator complex is affected by the membrane potential.

Rat pars intermedia cells secrete a number of peptides mechanisms controlling this event are still poorly derived from the post-translational processing of understood. pro-opiomelanocortin (POMC), including ,-endorphin,

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SUMMARY1. The mechanism of procaine action on post-synaptic receptors for acetylcholine was studied by recording the end-plate current at membrane potentials ranging from about + 30 to about -140 mV.2. It has been found that at resting membrane potential of about -60 to -80 mV the end-plate current has a fast initial and a slow late component. During hyperpolarization of the muscle fibre the amplitude of the slow component is depressed and its half-time lengthened. When the membrane potential is inverted the difference in the time course of both components is much less pronounced or absent.3. It is suggested that procaine modifies the receptor response induced by acetylcholine, and that this modification is dependent on membrane potential.