Oxygen uptake and mechanical tension in esophageal smooth muscle from opossums and cats

In 44 opossums and 4 cats weighing 1.5-2.5 kg, measurements of O2 consumption were made on esophageal muscle strips using a modified Clark-type polarograph. All strips were cut in the transverse axis of the esophagus and comprised the circular and longitudinal muscle layers and intrinsic nerves. Strips were 20 mm long, 2 mm wide, and less than 0.5 mm thick. The average uptake by all strips was less than 5 microliters O2 . mg dry muscle-1.h-1 at 37 degrees C and was temperature dependent (Q10, 2.2). There was no difference in base-line O2 consumption between strips coming from the proximal, middle, or distal third of the esophageal body and strips coming from the lower esophageal sphincter. Increases in length or tension increased the O2 consumption by sphincter strips but had no effect on body strips. Carbachol (10(-5) M) led to increases of base-line muscle tension and O2 consumption in both sphincter and body strips. Isoproterenol (10(-6) M) decreased the baseline tension and O2 consumption in sphincter strips only. The maintenance of a high basal tension by the lower esophageal sphincter is oxygen dependent and therefore an active muscular process. Also, no gradient of metabolic activity can be demonstrated along the smooth muscle segment of the esophagus.