Spontaneous release of transmitter substance in multiquantal units

The occurrence of spontaneous miniature potentials at the neuromuscular junction of the rat has been described in a previous paper (Liley, 1956a). In that paper reference was made to the frequent observation of spontaneous large 'miniature' potentials with amplitudes several times the modal value of a series of potentials and, at one junction, calculations showed that more of these large potentials occurred than could be accounted for by the random coincidence of the 'unitary' miniature potentials. The present paper deals with a further investigation of this phenomenon. It would seem paradoxical to designate potentials whose amplitudes may reach 12 mV as 'miniature' potentials; hence, in this paper, such potentials will be referred to as 'giant potentials'. In distinction, 'miniature potentials' will refer to the 'unitary' spontaneous potentials.