Relation between electrical and mechanical activity in esophageal smooth muscle.

Experiments were performed in anesthetized opossums. Electrical and mechanical activity was recorded simultaneously from the esophageal body at 5, 3, and 1 cm above the lower esophageal sphincter (LES). Esophageal responses were evoked by electrical stimulation of vagal efferents or by induced swallowing. Electrical and mechanical activity was associated in 86% and dissociated in 14% of the 1,200 responses examined. The frequency of dissociation was dependent on the site in the esophagus and the frequency of vagal efferent stimulation (P less than 0.05). The interval between the onset of electrical and mechanical events, called electromechanical delay, had a regional gradient: 5 cm above LES greater than 3 cm greater than 1 cm (P less than 0.01). This delay was also dependent on the frequency of stimulation. The amplitude of spike burst and the number of spikes in a burst closely correlated with the amplitude of contraction. These studies show that electromechanical responses and dissociations are dependent on the regional level in the esophagus and the frequency of vagal stimulation.