Patterns and Origin of Some Esophageal Responses to Stretch and Electrical Stimulation

Abstract

The responses of circular muscle of the isolated smooth muscle segment of the opossum esophagus to distension and electrical stimulation were examined. The distal 12 cm of the esophagus were mounted in an isolated organ bath. Six chlorinated silver-wire electrodes, sewn along the length of the organ, recorded bursts of action potentials indicating contractions of the circular muscle. Five- to 10-sec inflations of a 1-ml balloon at various levels of the esophagus caused two kinds of responses. A burst of action potentials occurred rostral to the point of stretch after inflation of the balloon, with a delay of 0.29 to 0.36 sec. It usually occurred just above the point of stretch; it sometimes moved cephalad for a short distance and occasionally appeared below the point of stretch. This is the on response. After deflation of the balloon a brief burst of action potentials occurred caudal to the point of stretch, with a delay of 0.96 to 1.08 sec. This burst of action potentials usually began well below the point of stretch and involved a long segment of distal esophagus. It was commonly propagated caudad. Sometimes it was simultaneous throughout the caudal segment. This was the off response. Electrical stimulation of the serosal surface also produced an off response like that following balloon deflation. The off response to both stimuli was abolished by tetrodotoxin, but not by phenoxybenzamine, tolazoline, hexamethonium, atropine, or methysergide. The on response was not affected by any of these drugs. The off response is a noncholinergic neural excitation; the on response is probably a direct response of the muscle to stretch.