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Excitatory and inhibitory junction potentials in canine antral circular muscle

Abstract The possibility was investigated that canine antral circular muscle received a direct innervation from intrinsic motor nerves to initiate electrical slow waves. Thin slices of antral muscle were used for intra‐cellular recordings in vitro. Single electrical shocks evoked slow waves identical to spontaneous slow waves, at all sites across the entire thickness of the circular muscle. Excitation was mediated by non‐cholinergic (atropine‐resistant) excitatory junction potentials that gave rise either to attenuated or to full slow waves, depending on the refractory period of the smooth muscle cells. Short bursts of electrical shocks evoked non‐cholinergic (atropine‐resistant) inhibitory junction potentials which were followed by a rebound slow wave. Prolonged stimulation (at 1 Hz) evoked slow waves at a rate of 3–4 cycles per minute; stimulation at greater frequencies (2–10 Hz) evoked a hyperpolarization that gave way to breakthrough slow waves at a rate of 5–6 cycles per minute. Long periods of hyperpolarization were followed by an ‘off‐response’ involving a burst of slow waves that slowly decreased in frequency. In summary, canine antral circular muscle possesses a complex motor innervation involving excitatory and inhibitory neurostransmitters (of unknown type), similar to the motor innervation of the adjacent pyloric circular muscle and nearby duodenal circular muscle.