Depression of mechanical and electrical activity in muscle strips of opossum stomach and esophagus by acidosis

We studied the effect of acidosis on nerve-muscle preparations from the opossum stomach and esophagus. All muscle strips were mounted in superfusion chambers and spontaneous contractile activity was recorded from longitudinal and transverse gastric muscle strips. Mechanical activity in esophageal and oblique gastric muscle strips was elicited by electrical stimulation of intrinsic nerves. The contractile activity of all types of strips changed when the pH of the superfusate was lowered for 30 min from 7.4 to 7.0. The baseline tension rose in strips from the lower esophageal sphincter and in oblique gastric muscle strips, and a baseline tension occurred de novo in longitudinal esophageal strips. Muscle relaxation was also impaired in these three types of strips. The amplitude of contractions declined in transverse strips from the esophageal body and in transverse and longitudinal strips from the stomach. The frequency of spontaneous contractions and of the pacesetter potential as recorded by extracellular electrodes was also reduced by acidosis in muscle strips from the stomach. Similar but less marked changes occurred when the pH was lowered from 7.4 to 7.2 for 30 min. Most changes related to a pH of 7.0 became irreversible after superfusion periods of more than 2 h. These findings indicate that acidosis alters a variety of neuromuscular functions and that its effects are determined by the electrical and contractile characteristics and the intrinsic innervation of individual segments and layers of the gut muscle coat.