On potassium functional feedback in neuromuscular junction.

The dependence of the reversal potential (Erev) of intracellular end-plate potentials (epp) on activity patterns was studied in frog neuromuscular preparations. A shift of Erev to the positive side was found with change in frequency of stimulation from 1/sec to 50/sec. This shift corresponds to the increase of potassium concentration in the synaptic cleft to 7.0 mM. The effect of potassium concentration [K+]0 in the bath solution on quantal content (m) of epp was studied. The quantity m increased when [K+]0 was varied within the range 4.7-8.7 mM; m decreased when [K+]0 was greater than 8.7 mM. Such a relationship between m and [K+]0 is accounted for by the combined effect of potassium on transmitter secretion and electrogenic processes in motor nerve terminals. The correlation between the change of m with [K+]0 and initial epp amplitudes was found and was attributed to potassium efflux from post-synaptic region in varying quantity depending on the initial epp amplitudes. A scheme of synaptic self-regulation by means of potassium feedback is suggested.