Intracellular recordings were made from neurones in the submucous plexus of guinea-pig small intestine. Approximately 20% of all neurones studied appeared to lack synaptic input; two types of neurones without synaptic input were identified. The action potential recorded from one of these types of ganglion cells was followed by a prolonged after-hyperpolarization. The after-hyperpolarization was abolished by Co2+ or Mn2+. A Ca2+ component of the evoked action potential was demonstrated after the Na+ component had been abolished by tetrodotoxin (TTX). The other type of neurone was characterized by a high input resistance (220-320 M omega) and spontaneous action potentials which were unaffected by hexamethonium, curare, atropine or TTX. The ionic basis of the action potentials evoked from spontaneously active cells differed from other enteric neurones. These action potentials exhibited a TTX-insensitive Na+ component as well as a Ca2+ component. It is suggested the spontaneously active neurones may be responsible for the ongoing synaptic activity recorded from many submucous plexus neurones in the absence of stimulation.
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