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Department of Neurosciences, McMaster University, Hamilton, Ontario, Canada.

1. The electrical and mechanical activities of different regions of the canine lower oesophageal sphincter were measured using the single sucrose gap technique. 2. Spontaneous electrical activity was found in the region 0-6 mm oral to the squamocolumnar border. 3. The electrical activity consisted of bursts of spikes superimposed on slow waves. The slow-wave frequency ranged from 0.6 to 5 min-1 in different muscle strips. 4. The slow wave-spike complex and associated contraction were insensitive to tetrodotoxin and atropine. 5. In the pacemaker region, electrical stimulation of intrinsic nerves evoked excitatory junction potentials (atropine sensitive), inhibitory junction potentials (non-adrenergic) and post-stimulus excitation. 6. Increase in the frequency of the slow waves was obtained by muscarinic receptor stimulation (carbachol 10(-7) M) and 10 mM-KCl. 7. The distal lower oesophageal sphincter exhibited a high basal tension but did not show spontaneous electrical activity and stimulation of intrinsic nerves revealed only non-cholinergic, non-adrenergic inhibition. 8. The electrical slow-wave activity observed in the proximal sphincter may constitute the control mechanism for the phasic nature of the contractile activity seen during both the postprandial period and phase III of the interdigestive migrating myoelectric complex. 9. The neural cholinergic activity present in the proximal lower oesophageal sphincter suggests the possibility of neural modulation of the myogenic control activity.