EFFECTS OF MUSCLE ELECTRICAL-ACTIVITY ON THE TRANSMISSION OF DEVELOPING NEUROMUSCULAR-JUNCTION

Miniature endplate potentials (MEPPS) caused by the spontaneous releas e of ACh from the growth cone of cholinergic neurons, are recorded by the whole-cell patch-clamp technique on a large number of 1-day cultur ed myoballs which have contact neurites of co-cultured neurons. Both m uscle cell and neuron are dissociated from the 1-day-old (about stage 20) Xenopus embryo. Frequency and/or amplitude of MEPPs can obviously increase after the repetitive high-level depolarization caused by the stimuli on muscle cells. No detectable changes of single ACh receptor channel property are observed by using the single-channel recording te chnique. These results suggest that the mechanism of the increase of M EPPs after electrical activity of postsynaptic muscle cells probably i nvolve some alteration of presynaptic membrane.