Some properties of spontaneous excitatory junction potentials recorded from arterioles of guinea-pigs.

1. Spontaneous excitatory junction potentials were recorded from electrically short segments of arterioles taken from the intestinal submucosa of guinea-pigs. 2. Histograms of the amplitudes of these spontaneous potentials were unimodal; their amplitudes often corresponded with the amplitudes of the smallest evoked potentials recorded from the same preparation. 3. The time courses of both spontaneous and evoked potentials were very similar and it is suggested that evoked potentials are made up by the simultaneous occurrence of several spontaneous potentials. 4. The mean quantal content of evoked potentials was always far fewer than the number of varicosities present in the preparations. 5. It is suggested that during neuromuscular transmission, transmitter is released at relatively few sites throughout the ground plexus for each nerve impulse.