Mechanical and electrical activity of esophageal smooth muscle during peristalsis

Mechanical events and membrane potential changes in response to evoked swallows and cervical vagal stimulation (10 and 40 Hz) were recorded in anesthetized opossums. Miniature strain-gauge transducers monitored the mechanical activity of the two layers. A suction electrode recorded from the intact esophagus, from a proximally based pedicle flap of longitudinal muscle (LM), and from circular muscle (CM). The onset of swallowing was marked by the onset of mylohyoid activity. During swallows LM contraction preceded CM contraction and was of longer duration. The latencies of LM and CM contraction were 1,980 +/- 38 and 2,250 +/- 101 ms, respectively. The durations of contraction of LM and CM were 5,590 +/- 260 and 3,330 +/- 67 ms, respectively. LM showed no hyperpolarization but showed depolarization and spike burst. The CM showed prompt hyperpolarization followed by depolarization and spike burst. Responses to vagal stimulation were qualitatively similar to swallows. The different components of the responses were quantitatively modified by changes in stimulus frequency. These studies show that, during peristalsis in response to swallows and vagal stimulation, 1) LM contraction occurs before CM and is of longer duration, and 2) unlike CM, LM does not hyperpolarize prior to depolarization.