Gradients of Contractions in the Opossum Esophagus

Abstract

Contractions of longitudinal and circular smooth muscle strips from the opossum esophagus were monitored in vitro. Three types of experiments were performed. (1) KC1-induced contractions were recorded isometrically, and the time intervals between rhythmic contractions were measured by computer. In longitudinal muscle strips, the interval between contractions increased progressively from 1.95 sec for strips taken 6 cm from the gastroesophageal junction (GES) to 3.15 sec for strips taken 1 cm from the GES. There was no gradient in circular muscle strips. (2) Contractions were induced by transmural electrical stimulation. The ability of strips to follow stimuli at progressively shorter interstimulus intervals was determined. Circular muscle strips, but not longitudinal muscle strips, showed a gradient in the ability to follow high frequency stimulation. (3) The stimulus-response delay was determined with transmural electrical stimulation. For circular muscle strips, the delay increased from 0.8 sec for strips taken 12 cm from the GES to 2.2 sec for strips taken 1 cm from the GES. No gradient existed for longitudinal muscle strips. Thus, differences exist over very short segments of the esophagus, in the nerves, muscle, or both, which may partially account for peristaltic movements. A hypothesis is proposed about the nature of peristalsis in the smooth muscle of the esophagus.