Miniature end plate potentials recorded from mammalian myoneural junction in vivo.

Fibers of the cat soleus muscle had a mean resting potential of 87 millivolts as measured with an intracellular microelectrode. Miniature end plate potentials had a mean amplitude of 0.95 millivolt, a mean frequency of 1.01 per second, a mean duration of 4.44 milliseconds, and a mean rate of rise of 0.99 volt per second. Two populations of response could be discerned on the basis of rate of rise. Neither alpha-chloralose nor nerve section had any significant effect on the response pattern. The in vivo preparation appears to provide a superior representation of the physiology of the myoneural junction.