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Non-technical summary What is known about gastric electrophysiology and used in motility clinics throughout the world is mostly deduced from animal studies and extracellular recordings from human patients. Extracellular recording from gastrointestinal muscles, however, is prone to extensive motion artifact, and it is not clear that animal models can be translated directly to human physiology. Therefore, we have performed a detailed analysis of electrical activity from carefully mapped specimens of gastric muscle removed from humans during surgery for gastric cancers. Our data show several important differences in electrical activity recorded with intracellular microelectrodes and accepted gastric electrophysiological dogma. We observed ongoing electrical slow wave activity in the gastric fundus; we also found no evidence for a slow wave frequency gradient. Muscles from all regions through the thickness of the muscularis demonstrated intrinsic pacemaker activity, and this corresponded with the widespread distribution of pacemaker cells.

1. Intracellular microelectrodes were used to identify three major electrophysiological categories of neurone in both the internal and external submucous plexuses of the porcine small intestine. 2. Two classes of neurone with a long-lasting after-hyperpolarization following their action potential were differentiated by the presence or absence of fast excitatory synaptic inputs (EPSPs) and were termed AH neurones. S neurones received fast EPSPs but did not display after-hyperpolarizations. 3. The mean resting membrane potentials of the three groups of neurones showed a similar trend in both plexuses, with significantly higher values for the two populations of AH neurone than for S neurones. No significant variation of input resistance with cell type was detected. Neuronal input resistance was significantly greater in the internal submucous plexus than in the external submucous plexus. 4. Over 80% of AH neurones in the internal submucous plexus displayed fast EPSPs but a similar percentage of AH neurones in the external submucous plexus did not show fast EPSPs. S neurones constituted 60% of cells studied in the internal submucous plexus but less than 30% of the cell population in the external submucous plexus. 5. This study of porcine submucous neurones has revealed both similarities and differences to previous work in the guinea-pig small intestine. The most contrasting features are the relative abundance and subclassification of AH neurones in the pig in addition to the apparent paucity of slow synaptic potentials. The differences in the neuronal profiles of the internal and external submucous plexuses may reflect a differentiation of function between the two enteric nerve networks.

1. E.p.s.p.s and terminal potentials (t.p.s) produced by the action of single medial gastrocnemius Ia afferent fibres were examined with intracellular microelectrodes in cat triceps surae motoneurones. 2. Simple terminal potentials (t.p.s) appeared as positive-negative diphasic waves with a single positive peak. Shape indices of excitatory post-synaptic potentials (e.p.s.p.s) recorded in conjunction with simple t.p.s indicate that these e.p.s.p.s were generated at an electrotonically confined compartment on the motoneurone somadendritic membrane. 3. Compound t.p.s. were similar ones, except that they had two or more positive peaks. Shape indices of e.p.s.p.s recorded in conjunction with compound t.p.s indicate that these e.p.s.p.s were generated at two or more electrotonically separate compartments. 4. E.p.s.p. latency and post-synaptic electrotonic delay were determined for a group of single fibre e.p.s.p.s with simple t.p.s. The shortest recorded latency was 0.26 msec. By subtracting estimated electrotonic delay, the shortest synaptic delay obtained for a medial gastrocnemius Ia single fibre e.p.s.p. was 0.17 msec. 5. The finding of a significant synaptic delay supports the hypothesis that the Ia-motoneurone synapse is a chemically mediated synapse.