Sub-miniature end-plate potentials at untreated frog neuromuscular junctions.

1. Some properties of unusually small spontaneous miniature end-plate potentials (sub-min.e.p.p.s) at untreated end-plates of adult frogs have been examined. 2. These small potentials, which show a fast time course, add a highly skewed component to the normal Gaussian distribution of min.e.p.p. amplitudes. 3. Sub-min.e.p.p.s were not evoked by single nerve stimuli, though their frequency could be raised by tetanic nerve stimulation. 4. When min.e.p.p. rate was raised by addition of lanthanum, submin.e.p.p. frequency was also increased, though by a smaller factor than normal min.e.p.p.s. In contrast, sub-min.e.p.p. frequency was unchanged when min.e.p.p. rates were raised by either ethanol or hypertonic solutions.