NEUROMUSCULAR MECHANISMS OF ESOPHAGEAL RESPONSES AT AND PROXIMAL TO A DISTENDING BALLOON

To determine the neuromuscular mechanisms involved in esophageal responses at and proximal to a distending stimulus, a manometric catheter incorporating a latex balloon at its distal end was positioned in the smooth muscle esophagus of alpha-chloralose-anesthetized opossums and used to record intraluminal pressures over the balloon and at several sites proximal to the balloon. Air inflation of the balloon evoked simultaneous phasic contractions at several sites proximal to the balloon that were abolished by bilateral cervical vagotomy. With the balloon located in the midesophagus, these proximal contractions were also abolished by atropine, and simultaneous suction electrode recordings indicated that they were associated with smooth muscle membrane depolarization and spike burst without preceding hyperpolarization. With the balloon located in the distal esophagus, the evoked proximal contractions were less atropine sensitive. Phasic pressure fluctuations recorded by the balloon itself were not affected by atropine or bilateral cervical vagotomy but were increased in amplitude by tetrodotoxin. These opossum studies suggest that unlike responses below a distending balloon, which have been shown to be noncholinergic and mediated by intramural neuromuscular mechanisms, proximal contractions depend on vagal pathways and, depending on esophageal location, muscarinic-cholinergic transmission. Contractions at the level of the distending balloon appear to be myogenic in origin.